WO2005071159A1

WO2005071159A1 - Arrangement in a paper or board machine for manufacturing matt-finished grades

Info

Publication number: WO2005071159A1
Application number: PCT/FI2005/050003
Authority: WO
Inventors: Mika Viljanmaa; Henri Vaittinen; Kari Hasanen
Original assignee: Metso Paper, Inc.
Priority date: 2004-01-21
Filing date: 2005-01-05
Publication date: 2005-08-04
Also published as: FI20045013A0

Abstract

The invention relates to an arrangement in a paper or board machine for manufacturing matt-finished grades. The paper or board machine is provided with a metal belt calender (10), comprising a metal belt (12) adapted to be driven around at least one guide element (13), and a counter-element (15) arranged outside the belt circuit, whereby between the metal belt (2) and the counter-element (15) is established a calendering zone (N) within which a fibrous web (W) can be subjected to a desired pressure and thermal treatment. The surface of both the metal belt (2) and the counter-element (15) in the metal belt calender (10) is of such a design that the fibrous web (W) passing through the calendering zone (N) is capable of being formed with a matt finish on both sides of the fibrous web (W) in a single operation.

Description

Arrangement in a paper or board machine for manufacturing matt-finished grades

The present invention has its objective in providing an arrangement in a paper or board machine for manufacturing matt-finished grades. Another objective is to provide an arrangement, allowing for manufacturing not only matt-finished grades but also glossy grades with one and the same machine.

Matt grades refer to paper grades with a high smoothness but a low gloss. Typically, Hunter gloss (ISO/DIS 8254/1) is kept at a level below 35%. Paper is perceived by a human eye as matt when the level of gloss is lower than this figure. The minimization of gloss is not critical; it only needs to be kept sufficiently low. In matt production, the softness of a nip becomes a critical calendering parameter. Since paper is only subjected to mild calendering, it is necessary to have minor nip loads in order to achieve desired qualities. I n the event that e.g. the nip in a soft calender is excessively hard, i.e. the soft coating has a high modulus of elasticity, the inconsistency of gloss (gloss mottling) may occur.

One way of making a matt grade is to pattern a thermal roll in a suitable fashion. When the thermal roll temperature is sufficiently hot, the surface of paper becomes plasticized and the pattern is reproduced onto the surface of paper. Thus, the paper is provided with an appropriate smoothness-to-gloss ratio. However, e.g. soft calendering requires two nips in order to produce a desired pattern on both sides of paper.

Even in a metal belt calender, comprising a smooth thermal roll and a smooth metal belt, a potential problem is gloss mottling of paper and/or board. The perpendicular structure of paper or board is generally inconsistent to such a degree that the calendering pressure is principally applied to regions of the greatest thickness. These regions become also more glossy, i.e. the paper/board shall display gloss mottling. Slight gloss mottling is not a problem in paper/board grades with low levels of gloss (e.g. newsprint). However, gloss mottling may be a problem in glossy grades (SC, all coated grades). In the process of calendering glossy grades, at least one of the calendering surfaces (belt or roll) must be elastic for a sufficiently consistent gloss.

It is an objective of the present invention to provide a solution, whereby the manufacture of matt grades is feasible with a relatively simple arrangement, allowing both sides of a fibrous web to be patterned for a matt finish in a single operation. I n order to fulfil this objective, the inventive solution is characterized in that the paper or board machine is provided with a metal belt calender, comprising a metal belt adapted to be driven around at least one guide element, and a counter-element arranged outside the belt loop, whereby between the metal belt and the counter-element is established a calendering zone within which a fibrous web can be subjected to a desired pressure and thermal treatment, and that the surface of both the metal belt and the counter- element in the metal belt calender is of such a design that the fibrous web passing through the calendering zone is capable of being formed with a matt finish on both sides of the fibrous web in a single operation. The counter-element comprises preferably a roll or another belt.

A metal belt calender can be used for making a matt-finished paper grade in a single nip, provided that the counter-element and the belt are patterned appropriately and that the calendering temperature is sufficiently high, the pattern carried by the counter- element and the belt being reproduced onto paper on both sides.

Optionally, in another conceivable alternative, one of the metal surfaces, the surface of a counter-element or a belt, is patterned while the other surface is formed with a coating of appropriate elasticity, for example with a polymeric, rubber or fibrous coating.

The inventive solution enables the manufacture of all matt grades, for example the following grades:

- matt SC,

- matt LWC and other coated grades containing mechanical pulp

- matt WFC and other coated grades containing chemical pulp

- other matt grades (boards, WF, etc.)

Benefits offered by the inventive solution include e.g. the fact that the arrangement allows for the symmetrical treatment of a fibrous web on both sides in a single nip, while e.g. conventional soft calendering requires two nips in order to perform a symmetrical treatment. In addition, the matt grades can be produced without a soft coating, which is susceptible to damage.

It is another objective of the invention to provide a solution enabling the use of one and the same machine for manufacturing not only matt grades but also glossy grades, said solution being characterized by what is set forth in the characterizing clause of claim 8. Switching from one grade to another can be performed by circumventing certain machine-related operations either by running the web through devices associated with the discussed operations or by running the web past such devices.

The invention will now be described in more detail with reference to the accompanying drawing, in which:

Rg. 1 shows in a schematic view of principle a section of a paper machine embodying the invention. A paper machine of the invention depicted in fig. 1 comprises a metal belt calender 10, located downstream of a dryer section 4 and including a metal belt 12 adapted to be driven around guide rolls 13. Outside the belt 12 is provided at least one roll 15, establishing a contact surface with the belt and functioning as a counter-element so as to establish between the belt 12 and the roll 15 a calendering zone N for a web W, the web to be treated being passed therethrough whereby it is subjected to a desired pressure impulse and thermal effect as a function of time. At least some of the guide rolls 13 are displaceable for adjusting tension of the belt 12 as desired, as well as possibly for adjusting the length of a contact zone or treatment zone between the belt 12 and the roll 15, for example by varying an overlap angle between the roll 15 and the belt 12. In a solution implemented according to the invention, the surface of both the metal belt and the roll 15 in a metal belt calender is patterned in such a way that, during the passage of a fibrous web through the treatment zone N, the web develops a matt finish on both sides in a single operation. In the solution of fig. 1 , downstream of the metal belt calender 10 is provided a finishing calender 5, designed in the present embodiment as a soft calender. Instead of a soft calender, the finishing calender may comprise also some other soft-nip establishing calender, such as e.g. a shoe calender, a supercalender or a multi-roll calender. A reeling section is designated by reference numeral 6. Various solutions generally related to the operation and design of a metal belt calender have been more fully described e.g. in the present Applicant's earlier international application WO 03/064761 A1 , and thus shall not be described here in detail.

The solution of fig. 1 enables making both glossy and matt-finished grades with one and the same machine. In the process of running glossy grades, the metal belt calender shall be maintained at a minor load or the web shall be run past it directly to the finishing calender 5 for a desired polish. I n the process of running matt grades, the web is passed through the treatment zone N of the metal belt calender for patterning its surfaces for a matt finish, the web being then run past the finishing calender 5 or through the finishing calender while the calendering nips are open.

For coated grades, the paper machine of the invention shall be fitted with a coater upstream and/or downstream of the metal belt calender. When the coater is located upstream of the metal belt calender, glossy grades are made as in the solution of fig. 1 , i.e. by circumventing the metal belt calender or by running the web therethrough with minor loads. Matt grades are also made as shown in the solution of fig. 1 , i.e. matt patterning is performed by the metal belt calender and the finishing calender 5 is bypassed completely or its nips are kept open as the web travels through.

When the coater is located between a metal belt calender and a finishing calender, the metal belt calender is used in the case of glossy grades for precalendering and drying. Final polishing, after the coating process, is performed by a finishing calender. The coating conceals a matt finish formed on the web by a metal belt calender, so that does not cause trouble in the production of glossy grades. I n the process of manufacturing matt grades, the metal belt calender is used for patterning base stock with a matt pattern and the web is run past the coating station and the finishing calender. If desired, however, a coating can be applied on top of matt-finished base stock.

The coater may also be provided both upstream of a metal belt calender and between a metal belt calender and a finishing calender. The finishing calender may comprise e.g. a soft, shoe, multi-roll or long-nip calender. Making glossy or matt-finished grades can be effected according to the above principles by circumventing, if necessary, one or more of the devices included in line. Coating, for example, can be done by using either just one of the coaters or both.

Claims

1. An arrangement in a paper or board machine for manufacturing matt- finished grades, characterized in that the paper or board machine is provided with a metal belt calender (10), comprising a metal belt (12) adapted to be driven around at least one guide element (13), and a counter- element (15) arranged outside the belt loop, whereby between the metal belt (2) and the counter-element (15) is established a calendering zone (N) within which a fibrous web (W) can be subjected to a desired pressure and thermal treatment, and that the surface of both the metal belt (2) and the counter- element (15) in the metal belt calender (10) is of such a design that the fibrous web (W) passing through the calendering zone (N) is capable of being formed with a matt finish on both sides of the fibrous web (W) in a single operation.

2. An arrangement as set forth in claim 1 , characterized in that the surface of both the metal belt (12) and the counter-element (15) is patterned so as to provide a matt finish on a fibrous web.

3. An arrangement as set forth in claim 1 , characterized in that the metal belt (12) or the counter-element (15) has its surface patterned in such a way that the side of the fibrous web (W) lying against the discussed patterned surface (12 or 15) produces a matt finish, and that the counter-surface (15 or 12) is provided with such a coating that it becomes elastic, thus providing a matt pattern on the surface of the fibrous web lying against it.

4. An arrangement as set forth in any of claims 1-3, characterized in that the counter-element comprises a roll (15) or another belt.

5. An arrangement as set forth in any of claims 1-4, characterized in that the paper or board machine includes a coater and that the metal belt calender is located downstream of the coater.

6. An arrangement as set forth in any of claims 1-4, characterized in that the paper or board machine includes a coater and that the metal belt calender is located upstream of the coater.

7. An arrangement as set forth in any of claims 1-4, characterized in that the paper or board machine includes two coaters and that the metal belt calender is located between the coaters.

8. An arrangement as set forth in any of the preceding claims, characterized in that the paper or board machine further includes a finishing calender (5), located in-line downstream of the metal belt calender, the same machine being capable of running either matt grades or glossy grades.

9. An arrangement as set forth in claim 8, characterized in that the finishing calender (5) comprises a soft-nip establishing calender, selected from the group of: a soft calender, a shoe calender, a supercalender, and a multi-roll calender.

10. An arrangement in a paper or board machine for manufacturing glossy or matt-finished grades in one and the same machine, characterized in that the paper or board machine is provided with a metal belt calender (10), comprising a metal belt (12) adapted to be driven around at least one guide element (13), and a counter-element (15) arranged outside the belt circuit, whereby between the metal belt (2) and the counter-element (15) is established a calendering zone (N) within which a fibrous web (W) can be subjected to a desired pressure and thermal treatment, and that the surface of both the metal belt (2) and the counter-element (15)^' in the metal belt calender (10) is of such a design that the fibrous web (W) passing through the calendering zone (N) is capable of being formed with a matt finish on both sides of the fibrous web (W) in a single operation, and that downstream of the metal belt calender (10) is located a finishing calender (5).

11. An arrangement as set forth in claim 10, characterized in that the machine further includes a coater located upstream of the metal belt calender (10) and/or downstream thereof, yet upstream of the finishing calender (5).