The invention also relates to an arrangement for moistening a fibrous web, for ex- ample, according to the preamble of claim 6.

A fibrous web, such as a paper or cardboard web arriving at a calender has to have a certain moisture level and a uniform moisture profile in the transverse direction of the line so that the fibrous web would be profiled in a sufficiently repeatable and de- sired way in the roll nips of the calender.

Nowadays, water is applied to a fibrous web principally by two different methods ; either as fine water mist before the calender, or as vapour before the roll nip equipped with a thermo roll in a multi-nip calender. Each method has its own drawbacks: applying fine water mist to the surface of a fibrous web, especially a cardboard web, requires specially designed, complex nozzles from the wetting de- vice and very pure clean water (often distilled water) in order to keep the nozzles from becoming blocked. The positioning of the nozzles of the wetting device in the transverse direction of the fibrous web is also precise so that no stripes would be formed to the moisture profile of paper in the longitudinal direction of the line. The absorption of a fine water mist into the fibrous web is poor (only about 50% of the water mist penetrates into the web) so that it is necessary to collect away the excess water remaining on the web in order to keep it from disturbing the moisture balance of the calender and thus causing a variation in the profiling grade in the fibrous web travelling through the calender. The removal of excess water accumulated to the web requires powerful blowers and water extractors.

Controlling the moisture level of the fibrous web on the steam box located before the roll nip of the calender is not without problems, either, as the absorption grade of vapour to the surface of the hot web is poor, and the generation of vapour and its transfer to the site increases the calendering costs.

The purpose of the invention is to eliminate the drawbacks present in the state of the art. Thus, it is an object of the invention to achieve a method for moistening a fi- brous web, in which water or aqueous wetting liquid can be dosed onto the fibrous web as aqueous phase. It also is an object of the invention to achieve a method for

moistening a fibrous web and a moistening arrangement used in it, by means of whch the major part of the wetting liquid can be made to penetrate into the fibrous web. It is an further object of the invention to achieve a moistening method and an arrangement used in it, by means of which the wetting liquid can be made to be ab- sorbed into the fibrous web homogeneously in the transverse direction of the fibrous web. It is a further object of the invention to achieve a moistening arrangement, in which the wetting liquid can be dosed onto the fibrous web by using a moistening tool for the fibrous web so that the liquid will be distributed homogeneously in the transverse direction of the fibrous web. It also is an object of the invention to achieve a moistening arrangement and method, the moistening tool used in which does not require complex nozzles and by means of which it is possible to dose the wetting liquid without the danger of the nozzles becoming blocked, and which, however, does not require the use of highly purified wetting liquid, such as water.

The above mentioned objects are achieved by the method according to claim 1 and the arrangement according to claim 6.

In the method, the fibrous web arrives at the forming zone, which has one or several nips. Such an amount of a wetting liquid with a certain surface tension is applied to the fibrous web before a roll nip in the forming zone, counter-clockwise to the di- rection of propagation of the fibrous web seen from the forming zone that the said wetting liquid forms an essentially uniform liquid film with the thickness S onto the surface of the fibrous web.

In the arrangement of the invention, such an amount of a wetting liquid with a cer- tain surface tension is applied to the fibrous web by a moistening tool before the nip in the forming zone that the said wetting liquid forms an essentially uniform liquid film with the thickness S onto the surface of the fibrous web. The moistening tool is located in the vicinity of the surface of the fibrous web, at such a distance from the said roll nip of the forming zone, counter-clockwise to the direction of travel of the fibrous web, that the wetting agent applied to a place on the surface of the fibrous web by the moistening tool has time to be sufficiently absorbed into the fibrous web before the said nip but, however, so that no considerable amount of the wetting agent evaporates from the surface of the fibrous web before the fibrous web is trans- ferred to the nip/nips in the forming zone.

The invention is based on that a fibrous web, such as a paper or cardboard web, is wetted before the calendering along the width of the web by a spray containing (aqueous) wetting agent. The viscosity of the wetting agent is higher than that of

pure water so that it forms an uniform flat film onto the surface of the fibrous web, in the vicinity of the application point. As the wetting liquid film uniformly covers the surface of the fibrous web after the application point, the benefit is achieved that the fibrous web is moistened uniformly along the whole width of the fibrous web, and no stripes will be formed to the lateral moisture profile of the fibrous web. The application point has been planned so that the film will be transferred almost 100% into the fibrous web before the roll nip of the forming zone, such as a calender; this again provides the benefit that non-absorbed wetting liquid need not be removed from the fibrous web. Of other additional advantages to be achieved by the inven- tion, the following can be said: an aqueous wetting liquid is preferably applied by spraying it onto the surface of the fibrous web as relatively large droplets, as a con- tinuous water wall so that no complex, blocking-sensitive nozzles will be needed to apply the wetting liquid. The wetting liquid is aqueous, but the water in it need not be distilled, because the size of the nozzles is relatively big so that they will not be- come easily blocked. Compared to other known methods, a considerable increase in moistening efficiency can be achieved by the method of the invention; in the inven- tion, the wetting liquid is transferred to the fibrous web with an efficiency of almost 100%, as again in known moistening methods and arrangements based on methods for applying vapour or water disintegrated to fine droplets, the efficiency is only about 50%.

Other benefits to be achieved by means of the invention appear from the enclosed description of an advantageous embodiment of the invention and claims. The inven- tion is next described in more detail by referring to Figure 1.

Figure 1 is a schematic view of the arrangement of the present invention.

The main parts of the moistening arrangement 1 of Figure 1 are the fibrous web W, which travels through the moistening tool 4 used for the application of the wetting liquid and through the calender 2 used as the forming zone. The moistening tool 4 is a spraying apparatus of the width of the fibrous web. The calender 2 has a pair of rolls pair 3, comprising superimposed the thermo roll 3; 31 and its counter roll 3; 32, to the (roll) nip N between which it is possible to achieve the desired nip pressure in a way known as such (the pair of rolls 3 in the forming zone can also be one of the several nips of the calender, such as roll nips).

In the Figure, the fibrous web W, such as a paper or cardboard web travels from left to right in the direction of the solid-pointed arrow, travelling in its way under the spraying apparatus 4 used as the application tool (moistening tool) for the wetting

liquid L at the point W; W1 of the fibrous web and through the roll nip N of the cal- ender 2. The fibrous web W comes from the drying section of the pulp manufacture (not shown in the Figure), and it may, for example, be supported from its underside on the belt. The body 4; 41 of the spraying apparatus 4 is a spraying beam extending from edge to edge of the fibrous web in the transverse direction of the fibrous web W, the underside of the beam extending to the fibrous web containing spraying noz- zles (not shown in the Figure). The nozzle size of the nozzles and the droplet size of the wetting liquid is relatively big. The nozzle may also be a narrow gap. In the Fig- ure, the direction of travel of the wetting liquid L from the nozzles of the spraying apparatus 2 to the fibrous web W, to the point W; Wl of the fibrous web, and fur- ther in the direction of the calender 2, along with the moving fibrous web, is dis- closed as solid-pointed arrows. In the moistening arrangement 1 of the Figure, the structure of the calender 2 as such is conventional, due to which it has been shown schematically. The calender is a one-nip calender, and it consists of the pair of rolls 3, which has the thermo roll 3; 31 and its counter roll 3; 32. The structure of the thermo roll as such is conventional, and it is a roll with a metal surface, which can be heated either by internal or external heating means in a way known as such. Op- posite the thermo roll 3; 31, there is a conventional counter roll, such as the poly- mer-coated roll 3; 32. Between the thermo roll 31 and its counter roll 32 forming the pair of rolls 3 there remains the roll nip N, to which a desired nip pressure and a nip pressure profile extending longitudinally in relation to the roll nip, i. e. transverse to the direction of travel of the fibrous web W and the machine direction can be generated. Concerning the more detailed structure of the thermo roll 3; 31 and its counter roll 3; 32 as well as the structure and operation of the pressurising means of the roll nip N between them, reference is made to the literature known in this field.

The wetting liquid L is applied by the moistening tool 4 onto the surface of the mov- ing fibrous web W to the point W; Wl as big droplets, as a continuous wall. The wetting liquid contains 60-99.99 weight per cent water and 0.01-40 weight per cent suitable water-soluble agent, which increases the viscosity and surface tension of water. Suitable thickening agents are water-soluble thickening agents, such as starch, PVAc and, for example, cellulose-based agents, such as carboxy-methyl cel- lulose. The extent of the viscosity and surface tension of the wetting liquid L in rela- tion to pure water depends on the quality and amount of the thickening agent, and they are adjusted so that the fibrous web has the desired moisture as it arrives at the roll nip N of the forming zone, such as the calender 2 for profiling.

Because of the surface tension that is higher than usual, the wetting liquid L applied to the point W ; Wl of the fibrous web forms a uniform homogeneous liquid bed onto the surface of the fibrous web in the vicinity of the application point W; W1, the thickness S of the bed being mainly determined on the basis of the surface ten- sion of the wetting liquid L. The thickness S of the liquid bed refers to the thickness of the liquid layer immediately after the application point W; Wl on the fibrous web; in the vicinity of the application point, the wetting liquid L acting as the liquid bed moves into the fibres of the fibrous web travelling to the direction of the form- ing zone mainly before the roll nip N of the forming zone (here the calender). The moistening tool 4 is located above the fibrous web, at the distance T from the roll nip, upstream in relation to the direction of travel of the fibrous web. The distance T is such that the moistening tool 4 is so far from the roll nip that the wetting liquid has time to be absorbed from the dosing point W; W1 into the fibrous web mainly before the roll nip N. However, the moistening tool 4 may not be located so far from the roll nip N of the forming zone (calender) that the wetting liquid L would evapo- rate from the surface of the fibrous web W in a way impeding the profiling transac- tion.

By means of the said moistening arrangement 1 of the fibrous web the wetting liq- uid L moves into the fibrous web with good efficiency (almost 100%). In a pre- ferred embodiment, the thickness S of the film of the wetting liquid W immediately after the application point W; Wl of the wetting liquid in the direction of travel (machine direction) of the fibrous web is such that the wetting liquid L will be ab- sorbed into the fibrous web W but, however, it will not evaporate from the fibrous web W immediately after having travelled through the roll nip N in the forming zone.

Only one embodiment of the method and arrangement of the invention has been pre- sented above, and it is obvious for one skilled in the art that it is possible to imple- ment the invention also in many other ways within the scope of protection of the en- closed claims and the inventive idea.

Thus, in one preferred embodiment of the invention, there is a doctor blade located above the fibrous web W, near the surface of the fibrous web, immediately after the moistening tool 2; the said doctor blade is used for removing an air layer near the surface of the fibrous web. Thus, an undisturbed and even travel is guaranteed for the wetting liquid applied from the moistening tool to the point W; Wl of the fi- brous web surface without the turbulent air layer in the vicinity of the web surface disturbing the falling of water to the fast moving fibrous web.

In the moistening arrangement of Figure 1, the forming zone 2 contains one calen- dering nip. However, it is fully possible that the arrangement of the invention is used in connection of multi-nip calenders, in which case the forming zone again comprises the whole area of the multi-nip calender, the multi-nip calender often containing, for example, 10-12 roll nips, and the moistening tool being located at a suitable distance before the first roll nip of the multi-nip calender.

The moistening arrangement for the fibrous web arriving at the calender may also be located, for example, before the belt calender operating as the forming zone, in which case the nip N of the moistening arrangement is located between the belt with a metal or a flexible surface and its counter organ, such as a counter roll or some other equivalent surface. Such a belt calender may be, for example, a device accord- ing to the patent application FI 20020159.