The invention also concerns a multinip calender according to claim 3.

As is known in the state of the art, for producing matt-coated printing paper the paper web is calendered in calendering nips, wherein two calendering rolls with soft surfaces are located opposite to one another. The soft calender has been the most favored type of calender. Also known in the state of the art is a method for calendering matt-surfaced printing paper, wherein a polymer roll with a soft sur- face and a matt thermo roll are used opposite to one another in a double-nip matt- soft calender. By this known concept a very smooth matt paper with very low gloss has been produced.

Known in the state of the art are multinip calenders, for example, super calenders, multinip calenders of the type marketed by the applicant under the OptiLoad trade name. In multinip calenders there is at least one stack of rolls, in which roll stack there are at least three rolls arranged on top of each other. The superimposed rolls are in nip contact with one another, and the paper web or equivalent web-like ma- terial to be calendered is arranged to travel through the nip between the rolls. In the nips there have been oppositely located a thermo roll, which usually is a heat- ing roll with a metal surface, for example, a chilled roll, and a backing roll formed by fiber rolls or polymer-coated rolls, that is, so-called soft rolls.

As regards the state of the art, reference can be made to Published application EP 1 329 549, wherein a calender is presented, where the stack of rolls is formed by at least five rolls, of which at least two are hard rolls and the other rolls are soft- coated, between which nips are formed and of which nips at least one is inde- pendent of the other nips.

Published application 0 822 289 for its part presents a calender having a stack of rolls comprising two end rolls and at least one idle roll, wherein the end rolls comprise a deflection-compensation device acting in the direction of the idle roll, and wherein at least one of the end rolls comprises additional means for compen- sating deflection, which acts in a direction away from the idle roll, and further an additional roll constructed as a variable crown roll and arranged on the other side of this end roll than the idle roll.

Printedpatent specificationEP 0 890 676 for its part presents a calender having several rolls with their axes arranged in the compression plane, whereby adjacent rolls form a nip between one another, and comprising a control device for opening and closing the nip, wherein the nips can be adjusted in such a way that there are at least two open nips in between two closed nips.

Published application DE 198 32 064 for its part presents a calender, wherein for calendering paper or an equivalent web-like material there are two stacks of rolls, where there are a top roll, a bottom roll and two idle rolls, wherein the top roll and the bottom roll are variable crown rolls intended to run several different grades of paper.

It is an objective of the invention to provide a method for producing matt paper by a multinip calender and to provide a multinip calender for producing matt paper.

The invention also aims at providing such a multinip calender for making paper with a matt surface, wherein the problems caused by partial nip runs are avoided.

As is known in the state of the art, partial nip runs have been used in order to pre- vent the paper from being polished against the bright thermo rolls. In the partial nip run, one or more thermo rolls are typically replaced by a polymer roll, and the run is only from nips between the polymer rolls. The partial nip run causes prob- lems for the reason, among others, that when the nips are closed the rolls may get

soiled and may wear, when they are used without paper, and, on the other hand, the rolls being in contact have rotated during the calendering, whereby static elec- tricity has been formed. In addition, partial nip run in multinip calenders with nips open has caused loading problems, because the loading arms withstand only small linear loads.

One of the problems known from the state of the art is that when different paper grades should be run in a paper machine line, different calenders have to be ac- quired in order to produce different paper grades. In fact, it is an objective of the invention to provide an alternative with advantageous investment costs instead of the acquisition of an entirely separate matt calender, but which multinip calender can nevertheless be quickly used also in the making of glossy paper grades.

To achieve the objectives mentioned above and also those emerging hereinafter, the method according to the invention is characterized by the features presented in the characterizing part of claim 1.

The multinip calender according to the invention for its part is mainly character- ized by the features presented in the characterizing part of claim 3.

According to the invention, a web is calendered in a multinip calender having one or more matt thermo rolls, whereby it can be used for running printing paper hav- ing a matt surface.

The matt-coated thermo rolls are most suitably matt thermo rolls with a ceramic surface and their coating is preferably a ceramic layer, whose thickness is in a range of 300-500 Fm and which comprises AlzOs and Zur02 or Cr203, TiO2 and possibly a third metal oxide or A12TiO5, preferably 50-80 % of A1203 and 20- 50 % of Zr02 or 50-92 % of Cr203, 3-50 % of Ti02 and possibly a third metal oxide or AkTiOs, and the coating roughness is most suitably Ra = 0,2-2, 0, um,

preferably 0,4-1, 0 Rm. When required, the coating is finished to get a suitable surface roughness for the desired matt paper quality.

According to an advantageous embodiment of the invention, all thermo rolls of the multinip calender are matt-coated thermo rolls, whereby matt grades can be run in the multinip calender through all nips, whereby a very smooth matt quality is achieved.

The invention also makes it possible for one and the same multinip calender to have thermo rolls, which are both bright and matt-surfaced thermo rolls, whereby one and the same multinip calender can be used to run both matt grades and glossy grades by changing the running method.

The arrangement according to the invention can be very advantageously applied with a paper machine line already having a multinip calender, whereby its thermo rolls or some of them can be replaced by matt-coated thermo rolls and, on the other hand, the multinip calender can be very quickly restored for making glossy grades by replacing the matt-coated thermo rolls with normal thermo rolls having a bright surface.

In the following, the invention will be described in greater detail referring to the figure in the accompanying drawing, but the intention is not to limit the invention in any narrow way to the details of the figure.

Figure 1 is a schematic view of a multinip calender known as such from the state of the art and which is arranged in accordance with the invention for producing matt paper.

Figures 2A and 2B are schematic views of two different running method applica- tions for running paper in a multinip calender according to one embodiment of the invention.

In Figure 1 a super calender is indicated generally by reference number 10 and it comprises a calender body 11, wherein a stack of rolls 12 formed by several rolls is mounted in the vertical plane. The stack of rolls 12 comprises a top roll 13, a bottom roll 14 and several idle rolls 15-22 arranged on top of one another in be- tween the top roll and the bottom roll, which rolls are arranged in such a way that they are in nip contact with each other. A paper web W is guided by way of a spreader roll 135 and a take-off roll 136 into a top nip Ni and further through the other nips N2-Ng of the calender and finally out of a bottom nip Ng. In the spaces between nips Nl-Ng the paper web W is taken off the roll surface with the aid of take-off rolls 156,167.

In the multinip calender according to Figure 1, the idle rolls in the stack of rolls 12a are formed in turns by thermo rolls with a matt surface and by their backing rolls with a soft surface. However, it is entirely possible for the number of idle rolls to be essentially smaller than shown in the figure, however, more than 4 rolls. It is also fully clear that the number of idle rolls may even be essentially higher than shown in the figure, and the rolls may be located, for example, in two stacks of rolls, each one with more than 4 rolls. Of the thermo rolls 15,17, 20,22 at least one is heating, suitably at least the uppermost ones 15,17 and preferably all thermo rolls are heating rolls.

The calender's 10 top roll 13 is a variable crown roll, the bearing housing 131 of which is attached directly and rigidly to the calender body 11. The shaft of the variable crown top roll 13 is mounted in said bearing housing 131 and in the nor- mal manner the roll is equipped with internal loading devices, which can be used for adjusting the deflection of the shell of the roll in the desired manner.

In a corresponding manner, the calender's bottom roll 14 is a variable crown roll, whose roll shell is mounted to rotate on the roll shaft and which roll 14 is

equipped with internal loading devices, which can be used for adjusting the de- flection of the roll shell in the desired manner. The shaft of bottom roll 14 is mounted in bearing housings 141, which are mounted in loading arms 144, which are attached to the calender body 11 to pivot with the aid of swivels 145. In between the calender body 11 and the loading arms 144 bottom cylinders 143 are mounted, which can be used for moving the bottom roll 14 in the vertical plane.

Thus, the stack of rolls 12 can be loaded by the bottom cylinders 143 and, in addi- tion, said bottom cylinders 143 can be used to open the stack of rolls 12. Owing to the variable crown bottom roll 14 linear pressure profiles can be kept uniform in the nips Nl-Ng of the stack of rolls 12. The bottom roll 14 is also equipped with a flexible polymer coating 142.

According to the invention, the uppermost idle roll 15 is a thermo roll with a matt surface, which at its ends is journalled to rotate in bearing housings 151. The bear- ing housings 15 la are mounted in arms 152, which are pivoted to turn in the cal- ender body 11 with the aid of swivels 153 in the axial direction of roll 15. The arms 152 are provided with relieving devices 154, which are pressure medium- operated piston-cylinder devices, which at their one end are attached to said arms 152 and at their opposite end to the calender body 11. The piston-cylinder devices 154 may be hydraulic or pneumatic cylinders or equivalent ones.

The uppermost but one idle roll 16 is a roll with a soft surface provided with a flexible polymer coating 166. Said roll 16 is journalled to rotate at its ends in bearing housings 161, which are mounted correspondingly in arms 162. The arms 162 are pivoted to turn in the calender body 11 with the aid of the roll's 16 axial swivels 163. The arms 162 are equipped with relieving devices, for example, with pressure medium-operated piston-cylinder devices 164, which at their one end are attached to said arms 162 and at their opposite end to the calender body 11. Fur- thermo, bearing housings of the take-off roll 167 are attached to the bearing housings 161 of the uppermost but one idle roll 16. Although the support for the

other idle rolls is not shown in any greater detail in the figure, it can still be clearly seen in the figure that the support for these rolls 17-22 is of a similar kind.

According to an advantageous application of the invention, the idle rolls 15-22 of the stack of rolls 12 are formed in turns by thermo rolls with a matt surface and by rolls with a soft surface. According to the invention, at least one thermo roll is a thermo roll with a matt surface. It is also possible to equip the thermo rolls with heating, either so that all thermo rolls 15,17, 20,22 in the stack of rolls 12 are heating rolls or so that only the uppermost thermo rolls 15,17 in the stack of rolls 12 are arranged as heating ones. When required, cooling can be arranged in the soft rolls 16,18, 19,21 with a polymer surface.

Thus, according to the invention, in the calender at least one thermo roll has a matt surface, preferably more, most suitably all, whereby it is possible to run matt-coated calendering grades. The thermo roll with a matt surface is preferably a ceramic roll, whose coating is a ceramic layer having a preferable thickness in a range 300-500 hum, which preferably comprises 50-80 % of A1203 and 20-50 % of Zr02 or 50-92 % of Cr203, 3-50 % of Ti02 and possibly a third metal oxide or Al2Ti05, and the roughness of the coating is most suitably Ra = 0,2-2, 0 Rm, preferably 0,4-1, 0 ism. when required, the coating is finished to have a sur- face roughness suitable for the desired matt paper grade.

Figures 2A and 2B show two different running method applications. In Figures 2A and 2B, reference marking p indicates polymer rolls, m indicates matt thermo rolls and k indicates bright thermo rolls. The web is indicated by reference mark- ing W.

Figure 2A shows a running method for running a glossy grade, whereby the matt rolls m make smoothness and rolls k make the gloss. Figure 2B again shows a running method using the same set of rolls for running a matt grade, and as

emerges from Figure 2B, the web W does not meet any bright thermo roll k, whereby its surface will not be polished.

As emerges from the running method applications of a multinip calender accord- ing to one embodiment of the invention shown in Figures 2A and 2B, a consider- able advantage is achieved with the invention, when one and the same multinip calender can be used for running both glossy grades and grades with a matt sur- face by changing the running method and by choosing the nips, through which the web W is run, according to the desired paper grade.

In the foregoing, the invention has been described by referring to one type of mul- tinip calender only, but the idea according to the invention can be fully applied also in multinip calenders of other types, and the intention is not to restrict the invention to concern only the application shown in the figure.