Note: Descriptions are shown in the official language in which they were submitted.
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PROCEDURE FOR THE MANUFACTURE OF PAPER
The present invention relates to a procedure
for the manufacture of paper, in which procedure at
least one mechanical pulp component, a binding agent
and other components are mixed to form paper pulp, the
paper pulp is made into a web and the web is dried
and, if desired, finished.
In the present application, 'paper' refers to
web-like products generally produced by means of a pa-
per or cardboard machine and containing cellulose fib-
res and/or lignocellulose fibres, products which are
either coated or uncoated, thinner or thicker, consis-
ting of one or more layers, and which are generally
called paper or cardboard.
The present patent application does not con-
tain a more detailed description of the formation of a
paper web from paper pulp in a paper machine, the dry-
ing of the web or the possible finishing; as for these
matters, reference is made to the methods generally
known in the industry and to relevant literature.
The quality requirements regarding different
paper sorts are continuously growing. In the case of
printing paper, excessively fast drying of the prin-
ting ink may result in a rough paper surface and the
formation of steam bubbles, which may lead to cracking
of the paper while the surface remains undamaged- This
problem is encountered especially when the z-strength
or internal bond strength of the paper is too low. The
problem is particularly difficult in the case of paper
that has been manufactured using a high-intensity for-
mer for web formation.
As for the features characteristic of the in-
vention, reference is made to the claims.
The invention is based on research work in
which it was established that the internal bond
strength of paper can be increased by mixing a mecha-
nical pulp component and a binding agent together and
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adding the other pulp components to this mixture at a
later stage.
Particularly good results have been reached
by postrefining the mechanical pulp component and mi-
xing the binding agent into the postrefined mechanical
pulp component.
Similarly, very good results have been
reached by performing the postrefining of the mechani-
cal pulp component after the binding agent has been
added to it.
The invention allow2 the binding agent to
spread uniformly into the mechanical pulp component
and get bound with it. At the same time, when postre-
fining is employed, there appear in the pulp component
new fibre surfaces, to which the binding agenz can ef-
fectively adhere-
The postrefining is done at a desired pulp
consistency, e.g. over 210, and for high-consistency
pulps up to 45 a; thus, the refining can preferably be
implemented at a consistency of e.g. 3 - 18 %.
The energy consumption in postrefining may
vary within broad limits and is e.g. 10 - 100 kWh/ton,
preferably e.g. of the order of 10 - 20 - 70 kWh/ton.
- In the procedure of the invention, the postrefining
can be performed using any type of pulp refiner, as is
generally known in paper and pulp technology.
The mechanical pulp used is any kind of
mechanical pulp, e.g. groundwood, refiner groundwood
or recycled pulp containing groundwood and/or refiner
groundwood or a mixture of these in arbitrary propor-
tions. The pulp used in making printing paper, to
which the invention appertains in particular, is gene-
rally pulp defibrated, sortad and bleached in a known
manner
The mechanical pulp may be.=produced from any
sort of wood, stalked plants or in general from any
vegetable fibre, e.g. broad-leaved trees, coniferous
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trees, straw, reeds, etc.
Paper produced according to the invention may
contain mechanical pulp in arbitrary proportions as is
generally known in paper industry, e.g. 10 - 80 wt-%,
usually 20 - 60 wt-a.
The proportion of binding agent added into
the mechanical pulp may be as is ganerally known in
paper industry, e.g. 2 - 3 a, even more, e.g. up to 5
a. The binding agent may be any binding agent commonly
used in paper industry. The binding agent may be e.g.
selected from groups starch derivatives, galacto man-
nones, cellulose derivatives, acryl amides, different
types of polymeric dispersions (i.e. latexes), etc.
The binding agents may be non-ionic, anionic or catio-
nic. Accordingly e-g. following binding agents are
mentioned: natural xanthan gums, such as arabic gum,
ghatti gum, pectin, dragacanth, karaya, alagin, gua-
rar, guarin, carubin or other non-modified or modified
anionic or cationic polysaccharide compounds; amylo-
pectines and other starch derivatives and starches;
CMC, ethylcellulose, hydroxyethylcellulose and other
cellulose derivatives; modified cationic or anionic or
non-ionic binding agents, as are generally known in
paper industry (e.g. US patent 5104487).
Moreover, the paper pulp may contain any ot-
her known additives, such as fillers, agents improving
a certain property or certain properties of paper, co-
lorants, pigments, etc., as is known in ihe art.
In the following, the invention is described
in detail by the aid of a few examples of its embodi-
ments, reference being made to Fig. 1, which repre-
sents the Scott-bond strength of paper produced using
different binding agents and different mixing methods.
Example 1
This experiment was carried out to study the
effect of the binding agent on the properties of paper
manufactured from hardwood mechanical pulp when the
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binder was added, to non-postrefined pulp, the binder
and Lhe pulp were postrefined together or when the
binder was added to postrefined pulp. The pulp used
had been bleached with hydrogen peroxide, dosed at 1.0
a.
Postrefining was performed using a EW labora-
tory refiner, SCE 100 kWh/ton. When the binder was ad-
ded before the refining, the chemical was added into
the pulp, the pulp was mixed for 25 min. and analysed,
the pulp was refined, mixed for 25 mi.n. and analysed.
When the chemical was added after the refining, the
pulp was mixed for 25 min., the pulp was refined, the
binding agent was added into the pulp, the pulp was
mixed for 25 min. and then analysed.
The chemicals used were starch, 2 a; CMC, 0.5
a; and modified polysaccharide, 2 a_ The experiment
also included a 50-min. mixing time with modified po-
lysaccharide. In addition, a 0-test without a binder
and postrefining without a binder were carried out.
The results are shown in Table 1.
Table 1
Scott-bond
J/m2
No binder 1 148 Mixing time 25 min_
2 231 "
Starch 1 385
2 2 380
3 482 "
Modified 1 339
Polysaccharide 2 408
2 95 3 470
CMC 1 160
0.5 0 2 216
3 231
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Modified Poly- 1 346
saccharide 2 % 3 417
In the table, denotation 1 means binder ad-
ded, no refining; 2 means binder added and refined to-
gether with the pulp component; and 3 means binder ad-
ded afLer the refining. The reaults are also shown in
a graphic format in Fig. 1.
According to the test results, mixing the
binding agent in postrefined pulp or postrefining the
pulp after the mixing clearly increased the bond
atrength of paper produced from the pulp.
Example 2
This experiment was carried out to study the
effect of the poztrefining power on the properties of
paper produced from the pulp. Pulp prepared in a man-
ner corresponding to Example 1 was used in the experi-
ment, the postrefiriing power levels (PR SCE) were 0,
50 and 75 kWh/ton. The mixing times were 0, 20 min.,
40 min. and 60 min. The additive used was modified po-
lysaccharide, 2 %. The refining was performed using an
industrial-scale refiner.
The bond strength values of paper produced
from the pulp are shown in Table 2-
Table 2
Pulp 1 1 1 2 2 2 2 2 2
Binder None None None None 2% 2% 20 2% 2~
Mixing
time/min 0 0 0 0 20 40 60 60 60
PR SCE/
kWh/ton 0 50 75 0 0 0 0 50 75
Bond
Strength 203 277 305 195 315 301 307 391 506
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Example 3
This experiment was carried out to study as a
laboratory test the effect of binding agent on pulp
when the binding agent was added after the refining
treatment. In addition, the use of starch at two dos-
age levels was tested. The table shows as a reference
the results of a pilot test carried out with the same
pulp; in this test, the chemical was added before the
postrefining. The pulp used had been produced in a
manner corresponding to Examples 1 and 2.
The results are shown in Table 3.
Table 3
Laboratory test Pilot test
Additions of binding agent Refin.+ Refin.
1.5a 2.0'0~- 2.0% chem. ref.
starch starch mod. polys-
Bond J/m2 450 449 489 482 271
Tensile
Index Nm/g 41.3 41.0 43.6 38.3 36.3
According to the test results, adding the
binding agent after the refining increased the bond
strength and tensile index of a paper sheet made from
the pulp even more than adding it in conjunction with
the refining.
The embodiment examples are only intended to
illustrate the invention without limiting it in any
way, and the embodiments may vary within the scope of
the claims presented below.
