[0001] In general present invention relates to a method for multiroll calendering according
to preamble part of claim 1.
[0002] Calendering is generally carried out in order to improve the properties, like smoothness
and gloss, of a web-like material such as a paper or board web. In calendering the
web is passed into a nip, i.e. calendering nip, formed between rolls that are pressed
against each other, in which nip the web becomes deformed as by the action of temperature,
moisture and nip pressure. In the calender the nips are formed between a smooth-surfaced
press roll such as metal roll and a roll coated with resilient material such as a
polymer roll. The resilient-surfaced roll adjusts itself to the forms of the web surface
and presses the opposite side of the web evenly against the smooth-surfaced press
roll. Multinip, or multiroll calendering is calendering in a calendering unit, in
which the nips are formed between a smooth-surfaced press roll such as metal roll
and a roll coated with resilient material such as a polymer roll and the linear load
increases in multinip calenders from the upper nip to the lower nip due to gravitation,
unless roll relies systems are used. From prior art multiroll calenders are known,
in which the set of rolls of which is formed of two stacks of rolls, each stack of
rolls comprising at least two calender rolls. Multinip or multiroll calender are known
for example by brand names OptiLoad and TwinLine. In
FI patent 96334 is disclose a method for calendering a paper or an equivalent web material in a calender
in which method the web to be calendered is passed through nips formed by a deflection-compensated
upper roll and a deflection-compensated lower roll, and by two or more intermediate
rolls arranged between the upper and lower roll. The rolls are arranged as a substantially
vertical stack of rolls.
[0003] As fiber web machine running speeds and the need for calendering increases, a possibility
to carry out various types of calendering for calendering different fiber web grades
by means of a calender is also needed, which can be carried out for example by means
of running with fewer nips than all nips, in which the web is passed through a calender
such that during calendering the web being calendered is calendered only in some of
the possible nips of the calender. In prior art this is usually possible only by changing
rolls of a calender for grade change. In
WO publication 2006/051169 a method in a multiroll calender, a multiroll calender and a method for loading a
calender roll of a multiroll calender is disclosed. In the method a fiber web is calendered
in a multi roll calender comprising two stacks of rolls, both stacks comprising at
least two calender rolls. In the multiroll calender at least one intermediate roll
is locked to a lower position whereby loading the rolls above or below the locked
roll, a required number of calendering nips can be provided for use. In this prior
art publication also various ways of guiding the web to be calendered through the
calendering nips of the calender roll stacks is disclosed but the running direction
of the web is always same in each stack of the calender during calendering in each
configuration.
[0004] In
WO 2007/082986 is disclosed a calendering method by which both glossy fiber web grades and high
matte-surface fiber web grades are calendered in the same multiroll calender by using
calendering nips in reverse order for glossy grades and for matte grades.
[0005] The line between paper and board is flexible and paper and board are available in
a wide variety of grades and can be divided according to basis weight in two categories:
papers with a single ply and a basis weight of 25 - 300 g/ m
2 and boards manufactured in multi-ply technology and having a basis weight of 150
- 600 g/ m
2. It should be noted that the borderline between paper and board is flexible since
board grades with lightest basis weights are lighter than the heaviest paper grades.
Generally speaking, paper is used for printing and board for packaging.
[0007] Mechanical-pulp based, i.e. wood-containing printing papers include newsprint, uncoated
magazine and coated magazine paper.
[0008] Newsprint is composed either completely of mechanical pulp or may contain some bleached
softwood pulp (0 - 15 %) and/or recycled fiber to replace some of the mechanical pulp.
General values for newsprint can be regarded as follows: basis weight 40 - 48,8 g/m
2, ash content (SCAN-P 5:63) 0 - 20 %, PPS s10 roughness (SCAN-P 76:95) 3,0 - 4,5 µm,
Bendtsen roughness (SCAN-P 21:67) 100 - 200 ml/min, density 200 - 750 kg/m
3, brightness (ISO 2470:1999) 57 - 63 %, and opacity (ISO 2470:1998) 90 - 96 %.
[0009] Uncoated magazine paper (SC=supercalendered) usually contains mechanical pulp to
50 - 70 %, bleached softwood pulp to 10 - 25 %, and fillers to 15 - 30%. Typical values
for calendered SC paper (containing e.g. SC-C, SC-B. SC-A/A+) include basis weight
40 - 60 g/m
2, ash content (SCAN-P 5:63) 0 - 35 %, Hunter gloss (ISO/DIS 8254/1) < 20 - 50 %, PPS
s10 roughness (SCAN-P 76:95) 1,2 - 2,5 µm, Bendtsen roughness (SCAN-P 21:67) 100 -
200 ml/min, density 700 - 1250 kg/m
3, brightness (ISO 2470:1999) 62 - 70 %, and opacity (ISO 2470:1998) 90-95%.
[0010] Coated magazine paper (LWC = light weight coated) contains mechanical pulp to 40
- 60 %, bleached softwood pulp to 25 - 40 %, and fillers and coaters to 20 - 35 %.
General values for LWC paper can be regarded as follows: basis weight 40 - 70 g/m
2, Hunter gloss 50 - 65 %, PPS s10 roughness 0,8 - 1,5 µm (offset), 0,6 - 1,0 µm (roto),
density 1100 - 1250 kg/m
3, brightness 70 - 75 %, and opacity 89 - 94 %.
[0011] General values for MFC (machine finished coated) can be regarded as follows: basis
weight 50 - 70 g/m
2, Hunter gloss 25 - 70 %, PPS s10 roughness 2,2 - 2,8 µm, density 900 - 950 kg/m
3, brightness 70 - 75 %, and opacity 91 - 95 %.
[0012] General values for FCO (film coated offset) can be regarded as follows: basis weight
40 - 70 g/m
2, Hunter gloss 45 - 55 %, PPS s10 roughness 1,5 - 2,0 µm, density 1000 - 1050 kg/m
3, brightness 70 - 75 %, and opacity 91 - 95 %.
[0013] General values for MWC (medium weight coated) can be regarded as follows: basis weight
70 - 90 g/m
2, Hunter gloss 65 - 75 %, PPS s10 roughness 0,6 - 1,0 µm, density 1150 - 1250 kg/m
3, brightness 70 - 75 %, and opacity 89 - 94 %.
[0014] HWC (heavy weight coated) has a basis weight of 100 - 135 g/m
2 and can be coated even more than twice.
[0015] Pulp-produced, wood free printing papers or fine papers include uncoated - and coated
- pulp-based printing papers, in which the portion of mechanical pulp is less than
10 %.
[0016] Uncoated pulp-based printing papers (WFU) contain bleached birchwood pulp to 55 -
80 %, bleached softwood pulp 0 - 30 %, and fillers to 10 -30 %. The values with WFU
have a large variation: basis weight 50 - 90 g/m
2, Bendtsen roughness 250 -400 ml/min, brightness 86 - 92 %, and opacity 83 - 98 %.
[0017] In coated pulp-based printing papers (WFC), the amounts of coating vary widely in
accordance with requirements and intended application, the following are typical values
for once- and twice-coated, pulp-based printing paper: once-coated basis weight 90
g/m
2, Hunter gloss 65 - 80 %, PPS s10 roughness 0,75 - 2,2 µm, brightness 80 - 88 %, and
opacity 91 - 94 %, and twice-coated basis weight 130 g/m
2, Hunter gloss 70 - 80 %, PPS s10 roughness 0,65 -0,95 µm, brightness 83 - 90 %, and
opacity 95 - 97 %.
[0018] Release papers have a basis weight within the range of 25 - 150 g/m
2.
[0019] Other papers include e.g. sackkraft papers, tissues, and wallpaper bases.
[0020] Board making makes use of chemical pulp, mechanical pulp and/or recycled pulp. Boards
can be divided e.g. in the following main groups according to applications thereof:
Corrugated board, comprising a liner and fluting; Boxboards, used for making boxes,
cases, which boxboards include e.g. liquid packaging boards (FBB = folding boxboard,
LPB = liquid packaging board, WLC = white-lined chipboard, SBX = solid bleached sulfite,
SUS = solid unbleached sulfite); Graphic boards, used for making e.g. cards, files,
folders, cases, covers, etc. and Wallpaper bases.
[0021] An object of the present invention is to create a method for multiroll calendering
in which grade change of fiber web is easily applicable.
[0022] In fiber web production one aim is to achieve high capacity of the production line
thus it is very important to minimize down times of machinery of the line. One object
of the invention is providing means for minimizing maintenance time of a multiroll
calender.
[0023] Another object of the present invention is to achieve a method in which possible
disadvantages and problems of known methods and calenders are eliminated or at least
minimized.
[0024] To achieve the objects mentioned above and later the method according to the invention
is mainly characterized by the features of the characterizing part of claim 1.
[0025] Further advantageous features of the invention will be disclosed in the dependent
claims.
[0026] According to the invention a method for multiroll calendering is provided wherein
the running direction of the fiber web to be calendered can be changed in at least
one calender roll stack for calendering a different grade of fiber web.
[0027] According to the invention in the method in first running direction of the at least
one stack of calender rolls the upper side of the web to be calendered is in contact
with a thermo roll in the first stack of calender rolls and the lower side of the
web is in contact with a thermo roll in the second stack of calender rolls and in
second running direction of the at least one stack of calender rolls the upper side
of the web to be calendered is in contact with a thermo roll in the first stack of
calender rolls and the upper side of the web is in contact with a thermo roll in the
second stack of calender rolls so that by using the first running direction two-sided
fiber web grade can be produced and by using the second running direction one-sided
fiber web grade can be produced.
[0028] Or according to the invention in the method in first running direction of the at
least one stack of calender rolls the lower side of the web to be calendered is in
contact with a thermo roll in the first stack of calender rolls and the upper side
of the web is in contact with a thermo roll in the second stack of calender rolls
and in second running direction of the at least one stack of calender rolls the lower
side of the web to be calendered is in contact with a thermo roll in the first stack
of calender rolls and the lower side of the web is in contact with a thermo roll in
the second stack of calender rolls so that by using the first running direction two-sided
fiber web grade can be produced and by using the second running direction one-sided
fiber web grade can be produced.
[0029] The invention also provides for possibility of using one stack of calender rolls
for production while other stack of calender stack is under maintenance.
[0030] In the method a fiber web grade that has basis weight of 40 -150 g/m
2 is calendered and in the method fiber web is calendered to surface roughness of 0,6
- 4,5 µm PPs.
[0031] According to the invention in the method the fiber web is calendered in a multiroll
calender comprising at least two stacks of at least four calender rolls.
[0032] In this connection the calender roll refers to rolls that form the calendering nip,
upper roll refers to the uppermost roll in a stack of rolls, upper nip refers to the
uppermost calendering nip, formed between the upper roll and the calender roll below
the upper roll, lower roll refers to the lowest roll in a stack of rolls and lower
nip refers to the lowest calendering nip in a stack of rolls, which lowest calendering
nip is formed between the lower roll and the calender roll above the lower roll. Intermediate
nips refer to calender nips formed by means of calender rolls between the rolls between
the upper nip and the lower nip of a calender. In case of horizontal calender stack
upper roll / uppermost calendering nip refers to first nip roll / first nip of the
calendering process and the lower roll / lowest calendering nip to the last roll /
last nip of the calendering process. The stack of rolls can be vertical or inclined
or horizontal. The calender can comprise one stack of rolls or more stacks of rolls,
for example two stacks of rolls. The stacks of rolls may or may not have common support
frame. The running direction of the web defines the side of the web to be calendered
in the calendering nips i.e. which side of the web will be in contact with the smooth-surfaced
calender rolls.
[0033] Further advantageous features of the invention will be disclosed in the dependent
claims.
[0034] In the following the invention is discussed in more detail by reference to figures
of accompanying drawings.
[0035] In figure 1 one example of a multiroll calender is schematically shown with one example
of running direction.
[0036] In the schematic example shown in figure 2 fiber web W is guided in the multiroll
calender example of figure 1 with another running direction in second stack of calender
rolls.
[0037] In the schematic example shown in figure 3 a further example of a multiroll calender
is schematically shown.
[0038] In the schematic example shown in figure 4 fiber web W is guided in the multiroll
calender example of figure 3 with another running direction in second stack of calender
rolls.
[0039] In the following description same reference signs designate for respective components
etc. unless otherwise mentioned and it should be understood that the examples are
susceptible of modification in order to adapt to different usages and conditions within
the frames of the multiroll calender.
[0040] Figures 1 - 4 schematically show examples of multiroll calenders with two stacks
of calender rolls. Multiroll calender 10 shown in figures comprises two stacks of
calender rolls 20, 30, in which a fiber web W is calendered in the calendering nips
between the calender rolls of the stacks of calender rolls. Reference numerals 21
- 25 refer to those of first stack of calender rolls and reference numerals 31 - 35
to those of second stack of calender rolls. By reference sign A after the reference
numeral a calender roll that is a resilient-surfaced calender roll is indicated and
by reference sign B after the reference numeral a calender roll that is a smooth-surfaced
calender roll. Resilient-surfaced calender rolls are soft-surfaced, for example polymer-surfaced
deflection, rolls and smooth-surfaced rolls are metal rolls, or thermo rolls either
heatable and/or coolable rolls.
[0041] In figures 1 and 2 a multiroll calender 10 with two stacks of calender rolls 20,
30 is shown. The two stacks 20, 30 are located next to each other and a multiroll
calender corresponding to the brand TwinLine is presented. The uppers rolls 21, 31
of each stack are deflection compensated rolls. Rolls 22B, 32B, 24B, 25B are thermo
rolls and rolls 23A, 33A are resilient-surfaced polymer rolls. Lower roll 25, 35 of
each stack is a deflection compensated roll.
[0042] As shown in the example of figures 1 and 2 the running direction of the web has been
changed for grade change of fiber web. In the figure 1 a two-sided fiber web grade,
for example wood free coated (WFC), is calendered and in the figure 2 a one-sided
fiber web grade, for example release, is calendered. In figure 1 the upper side of
the web W is in contact with thermo rolls 22B, 24B in the first stack of calender
rolls 20 and the lower side of the web is in contact with thermo rolls 32B, 34B in
the second stack of calender rolls 30. In figure 2 the running direction has been
changed for grade change and in the first stack of calender rolls 20 and again the
upper side of the web is in contact with thermo rolls 32B, 34B in the second stack
of calender rolls 30.
[0043] In figures 3 and 4 a multiroll calender 10 with two stacks of calender rolls 20,
30 is shown. The two stacks 20, 30 are located on top of each other and a multiroll
calender corresponding to the brand OptiLoad is presented. The uppers rolls 21, 31
of each stack are deflection compensated rolls. Rolls 22B, 32B, 24B, 25B are thermo
rolls and rolls 23A, 33A are resilient-surfaced polymer rolls. Lower rolls 25, 35
of each stack are deflection compensated rolls.
[0044] As shown in the example of figures 3 and 4 the running direction of the web has been
changed for grade change of fiber web. In the figure 3 a two-sided fiber web grade,
for example wood free coated (WFC), is calendered and in the figure 4 a one-sided
fiber web grade, for example release, is calendered. In figure 3 the web is calendered
from top to bottom via calendering nips of both stacks of calendering rolls 20, 30
and the lower side of the web W is in contact with thermo rolls 22B, 24B in the first
stack of calender rolls 20 and the upper side of the web is in contact with thermo
rolls 32B, 34B in the second stack of calender rolls 30. In figure 4 the running direction
has been changed for grade change, the web is guided from the lower roll 25 of the
first stack of calender rolls 20 directly to the bottom of the calender and the web
is guided through the second stack of calender rolls 30 from bottom to top and in
the first stack of calender rolls 20 and again the lower side of the web is in contact
with thermo rolls 32B, 34B in the second stack of calender rolls 30.
[0045] In the above the invention has been described by way of example with reference to
the figures of the accompanying drawing. However many modifications and variations
are possible within the scope of protection defined by the appended claims.
1. Procédé de calandrage à rouleaux multiples, dans lequel procédé une nappe fibreuse,
en particulier une nappe de papier ou de carton (W), est calandrée dans une calandre
à rouleaux multiples (10) comprenant au moins deux piles de rouleaux de calandre (20,
30), chaque pile comprenant au moins quatre rouleaux de calandre, dans lequel procédé
le sens de circulation de calandrage à rouleaux multiples de la nappe fibreuse (W)
à calandrer peut être modifié dans au moins une pile de rouleaux de calandre (20,
30) pour calandrer une sorte différente de nappe fibreuse, la nappe fibreuse étant
calandrée à une sorte qui a un poids de base de 40 à 150 g/m2 et une rugosité de surface
de 0,6 à 4,5 pm PPs, caractérisé en ce que, dans le premier sens de circulation de l'au moins une pile de rouleaux de calandre
(20), la face supérieure de la nappe (W) à calandrer est en contact avec au moins
un rouleau thermique (22B, 24B) de la première pile de rouleaux de calandre (20) et
que la face inférieure de la nappe (W) est en contact avec au moins un rouleau thermique
(22B, 24B) de la seconde pile de rouleaux de calandre (30) et que, dans le second
sens de circulation de l'au moins une pile de rouleaux de calandre (20), la face supérieure
de la nappe (W) à calandrer est en contact avec au moins un rouleau thermique (22B,
24B) de la première pile de rouleaux de calandres (20) et la face supérieure de la
nappe (W) est en contact avec au moins un rouleau thermique (22B, 24B) de la seconde
pile de rouleaux de calandre (30), de sorte que, en utilisant le premier sens de circulation,
une sorte de nappe fibreuse à deux faces peut être produite et, en utilisant le second
sens de circulation, une sorte de nappe fibreuse à une face peut être produite ou
que, dans le premier sens de circulation de l'au moins une pile de rouleaux de calandre
(20), la face inférieure de la nappe (W) à calandrer est en contact avec au moins
un rouleau thermique (22B, 24B) de la première pile de rouleaux de calandre (20) et
la face supérieure de la nappe est en contact avec au moins un rouleau thermique (22b,
24B) de la seconde pile de rouleaux de calandre (30) et que, dans le second sens de
circulation de l'au moins une pile de rouleaux de calandre (20), la face inférieure
de la nappe à calandrer est en contact avec au moins un rouleau thermique (22B, 24B)
de la première pile de rouleaux de calandre (20) et la face inférieure de la nappe
(W) est en contact avec au moins un rouleau thermique (22B, 24B) de la seconde pile
de rouleaux de calandre (30), de sorte que, en utilisant le premier sens de circulation,
de la sorte de nappe fibreuse à deux faces peut être produite et, en utilisant le
second sens de circulation, de la sorte de nappe fibreuse à une face peut être produite.