U.S. patent application number 10/496123 was filed with the patent office on 2004-12-23 for filler for the manufacture of base paper and method for the manufacture of base paper.
Invention is credited to Anas, Eeva, Leskela, Markku, Nygard, Stina, Pauler-Johansson, Gudrun, Pitakanen, Maija.
Application Number | 20040256067 10/496123 |
Document ID | / |
Family ID | 8562359 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040256067 |
Kind Code |
A1 |
Leskela, Markku ; et
al. |
December 23, 2004 |
Filler for the manufacture of base paper and method for the
manufacture of base paper
Abstract
The invention relates to the use of precipitated calcium
carbonates (PCC) as fillers for the manufacture of base paper
together with mechanical hardwood pulp and chemical softwood pulp,
and to a method for the manufacture of base paper, in which method
pulp produced from hard woods, in particular from the wood of the
genus Populus, and chemical softwood pulp are used together with a
PCC filler. The use of precipitated calcium carbonate (PCC) for the
manufacture of base paper together with mechanical hardwood pulp
and chemical softwood pulp is characterized in that .gtoreq.20 wt-%
of the fibres of the mechanical hardwood pulp is included in the
fibre size fraction of <200 mesh and 10-40 wt-% of them is
included in the fibre size fraction of {fraction (28/48)} mesh, the
brightness of the mechanical hardwood pulp is .gtoreq.75, the
particle size distribution of the precipitated calcium carbonate is
90%.ltoreq.9 .mu.m, 50%.ltoreq.5 .mu.m and 20%.ltoreq.1.5 .mu.m,
and the basis weight of the base paper is 25-150 g/m.sup.2.
Inventors: |
Leskela, Markku; (Lohja,
FI) ; Nygard, Stina; (Lohja, FI) ;
Pauler-Johansson, Gudrun; (Sjaleva, SE) ; Pitakanen,
Maija; (Jyvaskyla, FI) ; Anas, Eeva;
(Aanekoski, FI) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
8562359 |
Appl. No.: |
10/496123 |
Filed: |
May 20, 2004 |
PCT Filed: |
November 21, 2002 |
PCT NO: |
PCT/FI02/00939 |
Current U.S.
Class: |
162/142 ;
162/149; 162/181.2 |
Current CPC
Class: |
D21H 21/52 20130101;
D21H 11/02 20130101; D21H 17/675 20130101 |
Class at
Publication: |
162/142 ;
162/181.2; 162/149 |
International
Class: |
D21H 017/67; D21H
011/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2001 |
FI |
20012328 |
Claims
1. The use of precipitated calcium carbonate (PCC) for the
manufacture of thin base paper together with mechanical hardwood
pulp and chemical softwood pulp, characterized in that .gtoreq.20
wt-% of the fibres of the mechanical hardwood pulp is included in
the fibre size fraction of <200 mesh and 10-40 wt-% of them is
included in the fibre size fraction of {fraction (28/48)} mesh, the
brightness of the mechanical hardwood pulp is .gtoreq.75, the
particle size distribution of the precipitated calcium carbonate is
90%.ltoreq.9 .mu.m, 50%.ltoreq.5 .mu.m and 20%.ltoreq.1.5 .mu.m,
and the basis weight of the base paper is 25-150 g/m.sup.2.
2. The use as claimed in claim 1, characterized in that the
brightness of the mechanical hardwood pulp is .gtoreq.77, the
particle size distribution of the precipitated calcium carbonate is
90%.ltoreq.6.3 .mu.m, 50%.ltoreq.2.7 .mu.m and 20%.ltoreq.0.8
.mu.m, and the basis weight of the base paper is 25-80
g/m.sup.2.
3. The use as claimed in claim 1 or 2, characterized in that the
mechanical hardwood pulp has been manufactured from aspen and/or
from wood species of the genus Populus.
4. The use as claimed in claim 1 or 2, characterized in that the
mechanical hardwood pulp contains CTMP pulp or pressure groundwood
(PGW) or a combination of them, and the hardwood pulp has been
manufactured from wood species of the genus Populus selected from
the group of the following species: P. tremula, P. tremuloides, P.
balsamea, P. balsamifera, P. trichocarpa, P. heterophylla, aspen
species crossbred from different mother aspens, such as hybrid
aspen species, species produced by gene technology, and poplar.
5. The use as claimed in claim 1 or 2, characterized in that at
least 30% of the fibres of the mechanical hardwood pulp originates
from aspen and/or from wood species of the genus Populus.
6. The use as claimed in claim 1 or 2, characterized in that the
mechanical hardwood pulp contains at least 50% fibres that
originate from aspen and/or wood species of the genus Populus.
7. The use as claimed in claim 1 or 2, characterized in that the
mechanical hardwood pulp contains 70-100% fibres that originate
from aspen and/or trees of the genus Populus and 0-30% fibres that
originate from soft woods and/or other hard woods.
8. A method for the manufacture of thin base paper, in which method
a paper web is formed from a fibre raw material for a paper
machine, characterized in that the fibre raw material is formed by
combining precipitated calcium carbonate (PCC) with mechanical
hardwood pulp and chemical softwood pulp, and .gtoreq.20 wt-% of
the fibres of the mechanical hardwood pulp is included in the fibre
size fraction of <200 mesh and 10-40 wt-% of them is included in
the fibre size fraction of {fraction (28/48)} mesh, the brightness
of the mechanical hardwood pulp is .gtoreq.75, the particle size
distribution of the precipitated calcium carbonate is 90%.ltoreq.9
.mu.m, 50%.ltoreq.5 .mu.m and 20%.ltoreq.1.5 .mu.m, and the basis
weight of the base paper is 25-150 g/m.sup.2.
9. A method as claimed in claim 8, characterized in that the
brightness of the mechanical hardwood pulp is .gtoreq.77, the
particle size distribution of the precipitated calcium carbonate is
90%.ltoreq.6.3 .mu.m, 50%.ltoreq.2.7 .mu.m and 20%.ltoreq.0.8
.mu.m, and the basis weight of the base paper is 25-80
g/m.sup.2.
10. A method as claimed in claim 8 or 9, characterized in that the
mechanical hardwood pulp has been manufactured from aspen and/or
from wood species of the genus Populus.
11. A method as claimed in claim 8 or 9, characterized in that the
mechanical hardwood pulp contains CTMP pulp or pressure groundwood
(PGW) or a combination of them, and the hardwood pulp has been
manufactured from wood species of the genus Populus selected from
the group of the following species: P. tremula, P. tremuloides, P.
balsamea, P. balsamifera, P. trichocarpa, P. heterophylla, aspen
species crossbred from different mother aspens, such as hybrid
aspen species, species produced by gene technology, and poplar.
12. A method as claimed in claim 8 or 9, characterized in that at
least 30% of the fibres of the mechanical hardwood pulp originates
from aspen and/or wood species of the genus Populus.
13. A method as claimed in claim 8 or 9, characterized in that the
mechanical hardwood pulp contains at least 50% fibres that
originate from aspen and/or wood species of the genus Populus.
14. A method as claimed in claim 8 or 9, characterized in that the
mechanical hardwood pulp contains 70-100% fibres that originate
from aspen and/or wood species of the genus Populus and 0-30%
fibres that originate from soft woods and/or other hard woods.
Description
[0001] The present invention relates to the use of precipitated
calcium carbonates (PCC) as fillers for the manufacture of base
paper together with mechanical hardwood pulp and chemical softwood
pulp, and to a method for the manufacture of base paper, in which
method pulp produced from hard woods, in particular from the wood
of the genus Populus, and chemical softwood pulp are used together
with a PCC filler.
PIOR ART
[0002] In base papers, in particular in thin base papers, kaolins
and ground calcium carbonates (GCC) are used as fillers. Thin base
papers are traditionally manufactured in acidic conditions, wherein
it is not possible to use calcium carbonates but other compounds,
and thus PCC and GCC are used mainly in fine papers.
[0003] In coated base papers, the paper must be dense in order that
coating colour shall stay on the surface of the paper forming a
well-covering layer and shall not be able to penetrate into the
base paper during the coating process. In order that coated paper
should have good printability, it is desired that coating layers
cover the base paper completely. Thin coating layers shall provide
good coverage and the gloss of printed paper shall be high without
disturbing variation. Moreover, the bonding strength of the paper,
which is measured, when needed, as a Scott bond value, must be
sufficiently high in order that the paper shall not crack during
printing.
[0004] Papers are printed typically with a heatset offset printing
press, in which connection the surface of finished coated paper may
bubble if the strength of the base paper in the z-direction is not
sufficient. This phenomenon is particularly critical in the case of
double-coated paper when the surface of the paper is dense and the
vapours produced from the paper's own moisture in the dryer section
of the heat offset printing press cannot escape through the
surfaces of the paper. In view of the quality of base paper, the
filler should additionally have a high opacity (light scattering)
and brightness, but at the same time it is also very important that
the filler does not reduce the bonding strength of the paper nor,
on the other hand, increase the porosity of the base paper.
[0005] In sheet-fed offset printing, the strength in the
z-direction is also critical even though printing ink is not dried
in a separate dryer. In sheet-fed offset, the requirement for
strength is caused by the fact that printing inks are very viscous
and, at the outlet side of the printing nip, the paper is subjected
to a force that tends to crack the paper.
[0006] As known, precipitated calcium carbonates (PCC) are good
fillers in particular in uncoated fine papers. They provide high
brightness and opacity and, as compared with other mineral fillers,
bulk is also better. The advantages attained are basically based on
the fact that in the process of manufacturing PCC the shape and
size of particles can be controlled by varying process control
parameters. High brightness is based on the fact that, since the
process is synthetic, by means of pure raw materials it is possible
to obtain an end result that is better than that of ground calcium
carbonates. The manufacture of PCC is also economically competitive
in large plants as compared with other fillers.
[0007] In view of papermaking, the shape and size of the filler
particles can be adjusted within fairly large limits. This has led,
among other things, to the fact that PCC pigments have also become
competitive as coating pigments.
[0008] Calcium carbonate pigments can generally be used only in
papermaking processes that have a neutral or alkaline pH.
Carbonates dissolve under acidic conditions. It has been possible
to avoid this limitation as well by developing PCC pigments that
can be used in slightly acidic conditions.
[0009] PCC pigments have achieved a strong position as fillers of
uncoated fine papers, the particles being typically complex in
shape and fairly large in size, and also in coatings of fine
papers, the particles being typically simpler and smaller in
size.
[0010] Conventionally, PCC fillers are used in uncoated office
papers in proportions of over 15 wt-%, the aim being to increase
brightness and opacity and to reduce costs. The particle morphology
of PCC has been designed so that bulk is also preserved as well as
possible. As a result of this, the particles of PCC are "sea
urchin"-like in morphology, which is again very weak from the
viewpoint of the density and bonding strength of the web. Synthetic
precipitated PCC is either aragonite or calcite depending on the
manufacturing conditions. Typically, aragonite is needle-like in
morphology, which is suitable for the coating of paper. Calcite
precipitates as scalenohedral, i.e. mainly grain-shaped, or
light-scattering rhombohedral, i.e. cubic agglomerates, which
increase the bulk of paper, or as prismatic, i.e. semolina-shaped,
spherical or roundish particles, which are often complex in shape,
relatively large in size and represent, from the viewpoint of
paper, a compromise in respect of their properties. The appended
FIG. 1 illustrates the particles by means of SEM pictures. The
particles used in the coatings of fine papers are simpler in type
and smaller in size.
[0011] However, the PCC pigments have not achieved any particular
success as fillers of thin base papers. In these products, it is
desired that, in respect of quality, the filler shall have high
brightness and opacity, i.e. light-scattering, but at the same time
it is very important that the fillers do not lower the bonding
strength of the paper and, on the other hand, do not increase the
porosity of the base paper. In the development of paper, attempts
are generally made to reduce the basis weights of paper, whereby
opacity decreases, which, in turn, must be compensated for by
increasing the light-scattering coefficient. In addition, density
naturally deteriorates, i.e. decreases when the basis weight is
reduced. The continuously increasing running speeds of paper
machines and coating machines further emphasize the criticality of
density. A problem with known PCC fillers is that they do not meet
simultaneously all the requirements associated with the manufacture
of thin base paper. Typically, the brightness and opacity of the
base paper may be high but, at the same time, the bonding strength
of the base paper has decreased to an alarming extent and its
density has deteriorated such that the coating colour has
penetrated into the base paper.
[0012] FI patent 100 729 describes a filler used in paper
manufacture and mainly consisting of calcium carbonate, and a
method for its manufacture. In the method, calcium carbonate is
precipitated onto the surface of noil fibrils produced from
cellulose fibre and/or mechanical pulp fibre by refining. The noil
fibrils, onto whose surface calcium carbonate particles have
precipitated, form fibres that resemble pearl necklaces, and the
thus produced calcium carbonate aggregates resemble mainly clusters
of pearl necklaces. This filler that is based on cellulose fibre or
mechanical pulp fibre and on calcium carbonate imparts good optical
properties and good strength to the paper.
[0013] FI patent 103 417 discloses a method for manufacturing a
base paper suitable for the manufacture of coated fine paper by
combining groundwood pulp made from hardwood and chemical softwood
pulp. In the method, mechanical pulp manufactured from aspen or
from wood of the genus Populus and chemical softwood pulp are used
as a combination, thereby producing a pulp suitable for the
manufacture of base paper in respect of its strength properties.
The advantages of aspen pulp include high brightness and brightness
stability as compared with spruce groundwood. This is due in
particular to the low lignin content of aspen groundwood pulp or
equivalent mechanical pulp and to its low concentration of carbonyl
groups. By this means it is possible to manufacture fine paper with
high brightness with a lower basis weight than usual.
[0014] Based on the foregoing it may be noted that there exists an
obvious need for a PCC type filler which is suitable in particular
for the manufacture of thin base paper together with mechanical
hardwood pulp and chemical softwood pulp and which meets
simultaneously all the requirements placed on the filler of base
paper, as well as for a method for the manufacture of a base paper
in which mechanical pulp based on hard woods, such as aspen or
trees of the genus Populus, and chemical softwood pulp are used
together with a PCC filler.
OBJECT OF THE INVENTION
[0015] An object of the invention is to provide a method for the
manufacture of base paper, in particular for the manufacture of
thin base paper, by means of which a base paper is obtained that
has a low basis weight, a good internal strength and density, as
well as improved light-scattering and opacity.
[0016] An object of the invention is also the use of precipitated
calcium carbonate (PCC) as a filler for the manufacture of base
paper together with mechanical hardwood pulp and chemical softwood
pulp, which filler meets in particular the requirements placed
above on the filler of base paper.
[0017] An object of the invention is further to provide a method
for the manufacture of base paper, in which method mechanical pulp
based on hard woods, such as aspen or trees of the genus Populus,
and chemical softwood pulp are used together with a PCC filler,
whereby all the desired properties of the base paper can be
achieved simultaneously.
FEATURES CHARACTERISTIC OF THE INVENTION
[0018] The features characteristic of the use of a PCC filler in
the manufacture of base paper together with mechanical hardwood
pulp and chemical softwood pulp, as well as of the method for the
manufacture of base paper according to the invention are set forth
in the claims.
DESCRIPTION OF THE INVENTION
[0019] It has been found that when mechanical hardwood pulp and
chemical softwood pulp are used together with a PCC filler for the
manufacture of base paper, unexpectedly all the characteristics
required of base paper can be achieved simultaneously. In the
method in accordance with the invention, mechanical hardwood pulp,
in particular pressure groundwood (Pressure Ground Wood, PGW) or
chemimechanical pulp (CTMP), made from aspen or from wood species
of the genus Populus, is advantageously combined with chemical
softwood pulp and a PCC filler is used which has a particle size
distribution of 90%.ltoreq.9 .mu.m, 50%.ltoreq.5 .mu.m and
20%.ltoreq.1.5 .mu.m and which is semolina-shaped, grain-shaped or
spherical in its morphology.
[0020] For the base paper it is possible to use mechanical hardwood
pulp which is advantageously produced from aspen or from hard woods
of the genus Populus, i.e. wood species of the genus Populus, which
are preferably selected from the group of the following species: P.
tremula, P. tremuloides, P. balsamea, P. balsamifera, P.
trichocarpa and P. heterophylla, or aspen species crossbred from
different mother aspens, such as hybrid aspen species, and species
produced by gene technology, or poplar, or from a blend of
mechanical pulps produced from the above-mentioned species.
Particularly preferable wood species are native aspen P. tremula,
Canadian aspen P. tremuloides, poplar and hybrid aspen. Mechanical
hardwood pulp may optionally contain 70 wt-% of spruce or pine at
the maximum.
[0021] Instead of aspen it is also possible to use other hardwood,
such as, birch, eucalyptus or acacia. Such mechanical hardwood
pulps can be prepared as blends that contain, for example, two hard
woods and then, for example, spruce, as softwood. The proportion of
spruce may be 70% at the maximum, preferably 50% at the maximum,
and particularly preferably below 30%.
[0022] Mechanical hardwood pulps have shorter fibres than chemical
birch pulp or mechanical spruce pulps. Therefore the same basis
weight of mechanical hardwood pulp comprises more fibres than
chemical birch pulp or mechanical spruce pulp. This results in a
higher light-scattering ability, a good formation, i.e. a lower
variation of basis weight in a small scale, in a low surface
roughness, and bulk is also good.
[0023] Mechanical hardwood pulp and in particular chemimechanical
pulp (CMTP) and pressure groundwood (PGW) made from aspen or from
other wood species of the genus Populus contain a large quantity of
short fibres, which impart bulk and light-scattering to the pulp.
By combining mechanical pulp made from aspen or from wood species
of the genus Populus with chemical cellulose pulp made from
softwood using a PCC filler it is possible to produce a base paper
that has excellent light-scattering and opacity, a high brightness
and an even surface, a good strength and density.
[0024] 20-70 wt-% of mechanical hardwood pulp, preferably
aspen-CTMP or aspen-PGW or a combination of them, and 80-30 wt-% of
bleached chemical softwood pulp, calculating from the dry solids of
stock, are used, and at least 20% of the fibres of the mechanical
hardwood pulp are included in the fibre size fraction of <200
mesh and preferably 10-40 wt-% of them are included in the fibre
size fraction of {fraction (28/48)} mesh. Preferably, at least 30
wt-% and particularly preferably at least 50 wt-% of the fibres of
the hardwood pulp originate from aspen, hybrid aspen and/or
poplar.
[0025] Hardwood raw material is chipped, after which mechanical
pulp, refiner mechanical pulp (TMP) or chemimechanical pulp (CTMP)
is manufactured from the chips in a manner known in itself When a
groundwood method is used (GW or PGW), raw material is fed into the
process as logs. A stock is prepared from the mechanical pulp
together with chemical pulp, and a PCC filler having a particle
size distribution of 90%.ltoreq.9 .mu.m, 50%.ltoreq.5 .mu.m and
20%.ltoreq.1.5 .mu.m is used as a filler. In addition, the stock
may contain additives, such as different starches, starch
derivatives and retention agents. The dry solids content of the
stock is 0.1-5 wt-%. As the water phase of the stock it is possible
to use, for example, the circulation water of the paper machine.
Bleached chemical softwood pulp is preferably used as the chemical
pulp. The amount of the mechanical pulp is then 20-80 wt-%,
preferably 30-70 wt-% and the amount of the bleached chemical
softwood pulp is 80-20 wt-%, preferably 70-30 wt-%, calculated from
the dry solids of the stock.
[0026] A paper web is formed for a paper machine from the stock of
mechanical hardwood pulp and chemical pulp in accordance with the
prior art, for example, by using a gap former.
[0027] In the laboratory tests carried out it has been found that,
when using mechanical hardwood pulp, preferably aspen-based pulp,
having a low freeness, CFS.ltoreq.150 ml and a high
brightness.gtoreq.75, preferably.gtoreq.77, and chemical softwood
pulp together with a PCC filler having a particle size distribution
of 90%.ltoreq.9 .mu.m, 50%.ltoreq.5 .mu.m and 20%.ltoreq.1.5 .mu.m,
preferably 90%.ltoreq.6.3 .mu.m, 50%.ltoreq.2.7 .mu.m and
20%.ltoreq.0.8 .mu.m, and particularly preferably 90%.ltoreq.4.3
.mu.m, 50%.ltoreq.1.8 .mu.m and 20%.ltoreq.0.5 .mu.m and which is
grain-shaped, semolina-shaped or spherical in its morphology, it is
possible to manufacture a thin base paper which, in respect of its
quality, meets the requirements placed on base paper and the
properties of which are stated below:
[0028] basis weight 25-150 g/m.sup.2, preferably 25-80
g/m.sup.2,
[0029] light-scattering coefficient.gtoreq.45, preferably.gtoreq.50
and very preferably.gtoreq.55,
[0030] bonding strength.gtoreq.200, preferably.gtoreq.250 and very
preferably.gtoreq.300,
[0031] porosity of paper.ltoreq.500 ml/min, preferably.ltoreq.300
ml/min and very preferably.ltoreq.250 ml/min (in basis weight of 50
g/m.sup.2),
[0032] bulk of paper 1.2-1.8 cm.sup.3/g
[0033] brightness.gtoreq.75%.
[0034] The fibre composition of the base paper in accordance with
the invention comprises 20-70 wt-% of mechanical hardwood pulp,
preferably aspen-based pulp, most preferably aspen groundwood or
aspen-CTMP pulp and very preferably aspen-CTMP pulp, and 80-30 wt-%
of chemical softwood pulp, preferably bleached chemical pine
pulp.
[0035] The base paper can be coated by any suitable method known in
the art, whereby a coating layer having a basis weight of 5-50
g/m.sup.2, preferably 5-30 g/m.sup.2, is formed on at least one
surface, preferably on both surfaces of the paper web.
[0036] High-quality fine paper is obtained from the base paper in
accordance with the invention by coating it with a suitable
pigment-containing coating colour. The coating colour can be
applied to the material web in a manner known in itself. The
coating of the paper can be carried out on-line or off-line by
means of a conventional coating device, i.e. by blade coating, or
by means of film coating or surface spraying.
[0037] The base paper manufactured by the method in accordance with
the invention and the coated paper manufactured further from it can
be calendered by any calendering method known in the prior art.
Preferably, calendering is accomplished on-line as soft
calendering, thereby obtaining smooth and glossy or matte-surfaced
products whose bulk, opacity and stiffness meet the
requirements.
EXAMPLES
[0038] The invention is illustrated with the help of the following
examples. However, it is clear to a person skilled in the art that
the invention is not meant to be limited to the embodiments of the
examples only.
Example 1
[0039] Laboratory Tests with Different Fillers
[0040] In a series of tests, laboratory sheets were produced on a
Formette Dynamique sheet mould. The fibre pulps, broke and
different fillers described below were used at test points. A
standard amount of retention agents and starch was also used.
[0041] The following fibre pulps were used in the tests:
[0042] Nordic bleached chemical softwood pulp, which was refined to
an SR number of 24 on an Escher Wyss laboratory refiner;
[0043] bleached CTMP containing 85% aspen and 15% spruce, which was
refined to a CSF value of 48 ml on a Voith Sulzer laboratory
refiner (consistency 4.2%, specific edge load 0.3 J/m, specific
energy consumption 90 kWh/t). The fibre distribution of the pulp
and its most important paper technical values measured from
laboratory sheet were:
[0044] length-weighted fibre length: 0.69 mm
[0045] McNett classification +28 mesh: 3.3%
[0046] McNett classification {fraction (28/48)} mesh: 39.4%
[0047] McNett classification {fraction (48/100)} mesh: 22.4%
[0048] McNett classification {fraction (100/200)} mesh: 11.0%
[0049] McNett classification -200 mesh: 23.9%
[0050] tensile index 37.8 Nm/g
[0051] tear index 3.4 mNm.sup.2/g
[0052] bulk 1.79 cm.sup.3/g
[0053] Scott bond 152 J/m.sup.2
[0054] scattering coefficient 47.4 m.sup.2/kg
[0055] brightness 80.9
[0056] There was in total 12% of filler at all test points. In a
paper mill manufacturing coated paper, in practical conditions, the
filler of base paper is composed both of so-called fresh filler and
of the filler coming from coated paper broke (the filler containing
the mineral pigments of coating layer). For this reason, the filler
was dosed to some of the test points as coated broke from a paper
mill, in which broke the mineral main component was the ground
carbonate contained in the coating. At these points, fresh filler
constituted 6 percentage units of the filler and the filler coming
from broke constituted 6 percentage units thereof.
[0057] The fillers used are shown in the following Table 1 and the
appended FIG. 2 illustrates the particle size distributions
graphically. The values have been measured on a Malvern Master Size
device.
1 TABLE 1 Particle size Area Filler D50, .mu.m m.sup.2/g GCC1,
ground calcium carbonate 1.67 6.64 GCC2, ground calcium carbonate
1.1 7.77 PCC1, scalenohedral 2.6 4.98 PCC2, rhombohedral 1.4 7.58
PCC3, scalenohedral/prismatic blend 3.6 3.77
[0058] The properties of the sheets are shown in the following
Table 2. The tensile and tear indexes are geometric means from the
machine and cross-direction results.
2 TABLE 2 Filler Property GCC1 GCC1 GCC2 PCC1 PCC1 PCC2 PCC2 PCC3
PCC3 Broke no/yes no yes no no yes no yes no yes Basis weight,
g/m.sup.2 52.2 50.4 51.9 50.9 50.3 51.7 50.8 51.5 50.6 Density,
kg/m.sup.3 567 560 552 530 541 544 546 515 550 Porosity, Bendtsen,
210 170 240 320 300 280 230 480 240 ml/min ISO brightness 82.0 81.6
82.8 83.0 81.8 84.3 82.5 83.6 82.2 Scattering 47.0 44.8 52.2 54.9
48.4 62.4 51.2 58.2 52.6 coefficient, m.sup.2/kg Scott bond
J/m.sup.2 287 306 281 234 308 266 350 240 286 Tensile index Nm/g
61.1 61.8 57.2 58.0 57.6 53.8 57.6 55.1 57.4 Tear index, 7.0 7.2
7.7 8.0 7.8 7.9 7.6 8.3 7.5 mNm.sup.2/g
[0059] It is seen from the results, as expected, that brightness
and the scattering coefficient become higher when PCC is used as
compared with calcium carbonate. Unexpectedly, it is seen, however,
that, in addition to superior optical properties, PCC1 and
particularly PCC2 can additionally even improve the strength
properties. This has occurred at the points comprising broke in
respect of Scott bond bonding strength and tear strength. The
porosity of papers has also remained at a sufficiently low level
and also here attention is drawn to the surprisingly good results
of PCC2.
Example 2
[0060] Manufacture of Base Paper on a Pilot Paper Machine as Well
as its Coating and Calendaring
[0061] The following fibre pulps were used in tests:
[0062] mill-ground Nordic bleached chemical softwood pulp,
[0063] bleached CTMP containing 85% aspen and 15% spruce, which was
after-refined on a pilot-scale refiner with a low specific edge
load while the specific energy consumption was 140 kWh/t. Before
the after-refining, the CSF of the pulp was 115 ml. After the
after-refining, the most important properties of the pulp and
laboratory sheets were:
[0064] CSF 59 ml
[0065] length-weighted fibre length 0.73 mm
[0066] McNett classification +16 mesh: 0.0%
[0067] McNett classification {fraction (16/30)} mesh: 5.4%
[0068] McNett classification {fraction (30/50)} mesh: 31.3%
[0069] McNett classification {fraction (50/200)} mesh: 34.1%
[0070] McNett classification -200 mesh: 29.1%
[0071] brightness 78.6
[0072] tensile index 46.7 Nm/g
[0073] tear index 3.9 mNm.sup.2/g
[0074] density 570 kg/m.sup.3 (bulk 1.75 cm.sup.3/g)
[0075] Scott bond 329 J/m.sup.2
[0076] scattering coefficient 51.5 m.sup.2/kg.
[0077] When these results are compared with the properties of the
pulp after-refined in the laboratory in Example 1, it is seen that
the pilot-scale refiner has yielded clearly more 200 mesh fraction,
whereas there is clearly less {fraction (30/50)} mesh fraction
(corresponds to the fraction {fraction (28/48)} mesh in Example 1)
in the pilot test. The result is typical and it has been found in
practice that the refiner used in the pilot test corresponds to the
paper mill conditions very well. The refiner is equivalent to a
mill refiner in its structure, however, so that the size of the
pilot refiner is smaller.
[0078] Based paper was manufactured from the pulps on a pilot-scale
paper machine. The paper machine had a gap former. The same fillers
were added to the paper as in Example 1 as follows:
[0079] PCC1, scalenohedral
[0080] PCC2, rhombohedral.
[0081] A comparison with ground calcium carbonates was not made any
more but two of the best PCCs were included in the test.
[0082] Standard amounts of starch and the same retention agents
were added to the stock at all test points.
[0083] The base papers were made into rolls which were dried and
then analyzed. The measurement results of the following Table 3 are
means from the measurements of four rolls. The tensile and tear
indexes are geometric means in the machine and cross direction.
3 TABLE 3 Filler Property PCC1 PCC2 Basis weight, g/m.sup.2 51.2
52.3 Proportion of filler, % 14.7 13.4 Density, kg/m.sup.3 756 751
Porosity, Bendtsen, ml/min 264 283 Brightness 77.2 78.8 Scattering
coefficient, m.sup.2/kg 49.6 51.6 Scott bond J/m.sup.2 479 377
Tensile index, Nm/g 37.7 35.9 Tear index, mNm.sup.2/g 7.5 7.5
[0084] It is seen from Table 3 that the properties of the base
papers were relatively close to each other. The comparison is made
more difficult by the higher content of PCC1. As in the laboratory
test, better optical properties, i.e. brightness and scattering
coefficient, were achieved with PCC2.
[0085] After that, the base papers were coated with the same
coating colours and supercalendered. The target coating amount was
18 g/m.sup.2 on both sides of paper. The lineal pressure of
calendering was 280 kN/m.
[0086] The most important properties of the finished paper are
shown in the following Table 4 (the properties are the means of the
sides of the paper).
4 TABLE 4 Filler Property PCC1 PCC2 Basis weight, g/m.sup.2 88.4
89.7 Coating amount, g/m.sup.2 36.4 36.6 Bulk, cm.sup.3/g 0.75 0.75
Brightness 92.3 93.4 Opacity 93.4 93.4 Smoothness 0.60 0.59 Gloss
79.0 78.2
[0087] According to Table 4, the only clear difference after
coating is brightness, which is better in the case of PCC2. The
usual expectation is, however, that if brightness is as many as 1.3
units higher in finished paper, the opacity of the paper having
higher brightness is expected to be clearly lower than it is in the
paper having lower brightness. Thus, the optical properties of the
PCC2-containing paper must be considered superior to those of the
PCC1 paper. There is no practical difference in the surface
properties of the paper (smoothness, gloss).
* * * * *