Note: Descriptions are shown in the official language in which they were submitted.
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Method for manufacturing filler containing chemical pulp
The invention relates to a method for manufacturing filler containing chemical
pulp, which filler is prepared by precipitating particles comprising an
organic or
inorganic salt onto the surface of noil fibrils. The invention also relates to
a
method by means of which it is possible to manufacture and/or produce said
filler
in a form that can be used directly in paper and board applications. Further,
an
object of the invention is to provide a method for manufacturing paper and/or
board, which method makes use of chemical pulp having said filler incorporated
therein as dried in chemical pulp bales. The invention also relates to a
method for
improving the manufacturing and usage economy of a filler, in particular a
calcium carbonate based filler, used in the manufacture of paper and board.
In recent times, strenuous efforts have been made to develop calcium carbonate
based fillers and their manufacturing methods in order to be able to meet the
ever-
higher quality requirements of high-quality paper, to reduce the loading to
the
environment and the need of energy, and to improve the runnability of the
paper
and board machine. Traditionally, in the manufacture of paper and board, a
stock
is prepared from mechanical pulp or chemical pulp or from a combination of
them, and the necessary fillers and other additives can be added to this
stock, and
further paper or board of desired quality can be manufactured by a suitable
method.
FI patent 100729 discloses a calcium carbonate based filler which gives the
paper
improved strength properties and a lower basis weight, and by means of which
it
is generally possible to reduce the costs of paper manufacture. The calcium
carbonate based filler is manufactured by precipitating calcium carbonate onto
the
surface of noil fibrils produced from cellulose fibre and/or mechanical pulp
fibre
by refining. In that connection, calcium carbonate crystal aggregates are
formed
that resemble pearl necklaces and are held together by noil fibrils, i.e. fine
fibres,
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and in which the calcium carbonate particles have precipitated onto the noil
fibrils, adhering to them. The diameter of the calcium carbonate particles in
the
aggregates is about 0.2-3 ~tm. This filler, also known under the trademark
SuperFill~, is advantageously based on calcium carbonate and it imparts a
clearly
improved combination of light-scattering and strengths to the paper as
compared
with conventional calcium carbonate based fillers. It is particularly
significant that
the SuperFill~ filler is able to impart a very uniform distribution of light-
scattering material to the paper.
The calcium carbonate based SuperFill~ filler can be manufactured on an
industrial scale mainly as dilute suspensions, which considerably limits the
use of
the filler. This also leads to the fact that SuperFill~ filler can be used
only in
localities where a plant manufacturing SuperFill~ filler is located, because
the
transport of the filler becomes very uneconomical and difficult because of its
high
water content. Moreover, if SuperFill~ filler is manufactured only in small
quantities, manufacturing costs are high, which again leads to the fact that
in some
product applications the price of the filler becomes too high. Further, the
manufacturing process of SuperFill~ filler requires special utilities, such
as, for
example, a sufficiently good source of carbon dioxide, which is not always
available in the localities where paper or board is manufactured.
Based on the above, it may be noted that there exists an obvious need for a
method by means of which it is possible to manufacture and/or produce chemical
pulp that contains SuperFill~ filler, advantageously calcium carbonate based
SuperFill~ filler, which pulp can be used directly in paper and board
applications
and by means of which it is possible to avoid or at least substantially reduce
the
above-mentioned problems of the prior art arrangements.
An object of the invention is a method by means of which it is possible to
manufacture chemical pulp which has SuperFill~ filler, advantageously calcium
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carbonate based SuperFill~ filler, incorporated therein in an amount suitable
for
each paper and board application, as dried and mixed with the chemical pulp,
advantageously dried into bales, thereby making it possible to use SuperFill~
filler
also in manufacturing localities where there is no production plant of said
filler.
An object of the invention is also the thus manufactured chemical pulp which
has
SuperFill~ filler incorporated therein in an amount suitable for each paper
and
board application.
An object of the present invention is further a method for improving the
manufacturing and usage economy of SuperFill~ filler, advantageously calcium
carbonate based SuperFill~ filler.
Further, an object of the invention is a method for manufacturing paper and/or
board, which method makes use of chemical pulp having SuperFill~ filler,
advantageously calcium carbonate based SuperFill~ filler, incorporated therein
as
dried in chemical pulp bales.
The features characteristic of the methods and the chemical pulp according to
the
invention are set forth in the claims.
It has been found that the problems associated with the prior art can be
substantially reduced or avoided by means of the arrangement in accordance
with
the invention, wherein SuperFill~ filler, advantageously calcium carbonate
based
SuperFill~ filler, which has been prepared by precipitating an organic or
inorganic
salt, advantageously calcium carbonate, onto the surface of noil fibrils
produced
by refining from cellulose fibres and/or mechanical pulp fibre, is passed in a
dilute
suspension to a chemical pulp dryer to be mixed with chemical pulp. In
addition
to or instead of calcium carbonate, it is also possible to use another light-
scattering component precipitated onto the surface of noil fibrils, such as an
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organic or inorganic salt, of which gypsum, calcium oxalate, barium sulphate,
precipitated silicas and silicates may be mentioned as examples. The filler
can
also contain optionally a dispersing agent, such as, for example, sodium
hexametaphosphate.
In the method in accordance with the invention, the SuperFill~ filler is
passed in
an aqueous suspension, the solids content of which is O.I-35 wt. %,
advantageously 2-6 wt. %, to a chemical pulp dryer and further to be mixed
with
chemical pulp. After that, the drying of the chemical pulp can be carried out
by
any method conventionally used for drying chemical pulp. Advanteously, the
chemical pulp is dried into bales.
Optionally, it is also possible to use a separate filler drying line in which
SuperFill~ filler is dried, recovered and then mixed, at a desired content in
a range
of 1-70 wt. %, advantageously I-SO wt. %, with chemical pulp in connection
with
the manufacture of the chemical pulp before the chemical pulp is dried. After
that,
the chemical pulp is dried in a conventional manner, advantageously into
bales.
Drying the filler several times does not substantially reduce its bond
potential.
As a result, chemical pulp, advantageously chemical pulp bales, containing a
desired amount of SuperFill~ filler uniformly distributed in the chemical
pulp,
is/are obtained. When needed, the chemical pulp can be refined, but it can
also be
unrefined.
Baled chemical pulp containing SuperFill~ filler can be pulped in a
conventional
manner in a paper or board mill, and it can be added to any conventional pulp
blend used in the manufacture of paper and board. Paper and board can be
manufactured from the SuperFill~ filler containing chemical pulp by methods
known in themselves, from which methods the conventional separate filler
addition phase is now omitted. SuperFill~ filler containing chemical pulp can
be
added to pulp 1-100 %.
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In plants manufacturing coating qualities, the differences in the amounts of
pigment coming with broke can be compensated for in an appropriate manner, for
example, by means of a combination of two chemical pulps having different
5 SuperFill~ filler contents.
The method according to the invention and the thus manufactured chemical pulp
have significant advantages over the arrangements of the prior art. The
invention
makes it possible to substantially improve the profit potential of the
technology
associated with SuperFill~ filler, whereby both the manufacturing economy is
improved and the number of application sites is increased. In accordance with
the
invention, it is possible to manufacture chemical pulp that contains a
suitable filler
amount for each paper and board application. The method makes it possible to
avoid transporting large amounts of water, thereby saving energy, costs and
spaces. The thus manufactured SuperFill~ filler containing chemical pulp can
be
transported even long distances and it can also be used in manufacturing
localities
and in product applications which lack the utilities necessary for building a
PCC
plant, such as, for example, a sufficient source of carbon dioxide or suitable
pulp
processing devices. By this means it is also possible to manufacture chemical
pulp
of uniform quality containing a precisely predetermined amount of SuperFill~
filler. It is possible to manufacture paper and board of more uniform quality,
the
properties of which are superior to those of the paper manufactured in a
conventional manner.
The invention makes a centralized SuperFill~ filler production plant possible,
which has a high capacity and which is capable of manufacturing filler at
lower
costs. The production plant may optionally also comprise a separate drying
line
for the filler.
The method in accordance with the invention is illustrated by means of the
following examples, but the invention is not meant to be limited to them.
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Example 1
Manufacture of SuperFill~ filler containing chemical pulp
a) A SuperFill~ filler suspension was prepared by a known method which is
described, among other things, in FI patent 100729.
b) SuperFill~ filler containing chemical pulp was manufactured by passing 625
kg, calculated as solids, of the SuperFill~ filler suspension manufactured in
point a) and containing 500 kg of CaCo3 and 125 kg of noil fibrils, so as to
be
mixed with chemical pulp (375 kg of unrefined or slightly refined birch pulp),
which was then dried in a conventional manner, and 1000 kg of SuperFill~
filler containing chemical pulp was obtained, calculated as solids.
Example 2
Use of SuperFill~ filler containing chemical pulp in the manufacture of paper
Paper was manufactured from the SuperFill~ filler containing chemical pulp
described in Example 1 in a conventional manner on a paper machine such that 1
ton of paper contained:
600 kg SuperFill~ filler containing chemical pulp which contained
300 kg CaCo3
225 kg birch pulp
75 kg noil fibrils
250 kg birch pulp
150 kg softwood pulp
in total 1000 kg
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SuperFill~ filler containing chemical pulp was added to the stock in the
manufacture of paper such that the paper contained 30 wt. % of CaCOs and, of
the
chemical pulp in the paper, 76 wt. % was birch pulp and 24 wt. % was softwood
pulp. The opacity, brightness, smoothness and formation of the thus
manufactured
paper were superior to those of the corresponding paper which was manufactured
in a traditional manner and to which filler was added separately. Moreover,
the
runnability of the paper machine remained unchanged.
