Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
THE USE OF SERPENTINITE AS AN ADDITIVE
The present invention relates to the use of finely powdered
serpentinite as an additive in paper industry, either as an
additive or filler in paper or board, as a remover of pitches,
resins, e~tractives and other so-called stickles, or as a no-
trainer of flour both in paper industry processes-and in payer
industry process waters. Serpentinite can be used for these
purposes either as such or blended with a suitable material,
for instance talcum.
In paper industry fillers are primarily used in order to replace
part of the expensive wood fiber ingredients by cheaper mineral
ingredients, but fillers also affect many properties of paper
and board, either improving or weakening the quality.
Fillers improve several characteristics of paper and board, par-
titularly optical qualities and qualities relating to printabi-
lily. Apart from saving wood fibers, the main purpose for using fillers is to improve opacity, brightness, printing ink adsorb-
lion, the smoothness of the surface, the evenness of the imprint,
porosity and the feel of the paper, as well as the friction,
stiffness and flatness ox paper and board. Other effects are
increased density, improved dimensional stability and smoothing
of the look-through.
Remarkable porosity is generally also required of the filler,
mainly due to printability reasons. Printing ink penetrates
best into porous material with a large specific surface. Fillers
improve the refractory qualities of paper and board. If the
filler-fiber network is as dense and strong as possible, the
refractory properties are good.
Fillers generally weaken the strength qualities and sizing dune-
ability of paper and board. Large filler additions may cause
tinting in the drying section of the paper machine, on the cutter
and in the calenders. The reason for tinting is the weakening
of picking resistance, which is caused by fillers, and it can
be prevented for instance by starch additions or by top sizing.
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The most important paper and board fillers in current use are
bolls, talcum, gypsum, chalk, calcium carbonate, barium sulfate,
siliceous earth, titanium dioxide, zonk sulfide, aluminum
hydroxide, montmorillonite and synthetic silicates.
The greatest disadvantage with fillers is their weak adhesion to
the fiber network. The main reason for this so-called weak no-
tension of the fillers is the fact that the z-potential of most
fillers, as well as that of most fibers, is negative. Therefore
the most important factor affecting the retention is the filter
effect created when the fiber network retains the filler particles.
The filter effect itself is determined by the thickness of the
pulp web conveyed on the wire, the density of the fiber net and
the strength of the suction imposed on the web.
On the other hand, also the physical properties of the filler
particles affect the retention. Large particles are filtered
better than small particles, which easily penetrate the filtering
layer. In this respect an elongate or fiber-shaped particle is
preferable to a ball-shaped particle. Heavy particles are not
filtered as easily as light particles.
A number of problems in paper industry arise when pitch, resin
- and extractives enter the process, and particularly when various
stickles attached to recirculated material, i.e. recirculated
fibers, enter the process. These stickles consist of various
hot-melt glues, waxes, adhesive tapes, bitumic impurities and
pitch. All of these stickles cause several drawbacks both in
the machine and the product. They stick into the pores of the
felt located on the wire and thus gradually prevent the water
from filtering through the felt. As a result too much water
tends to remain in the pulp. During operation the stickles
stick onto the rolls of the machine when the temperature in the
aquaria ~ri~e~s^~ma~x. -130C). The sticking kiwi ye seen as bun
zones in the drying cylinder. As a result both the appearance
and the durability of the final product are disadvantageously
affected.
In order to remove the stickles, several chemicals are used in
the prior art, for instance albumen, sulfuric acid, resin glues,
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slimicides, urea-based substances, substances containing
phosphate or nitrate, ammonia salts, crystal and talcum.
An example of the use of crystal is the SW inventor's
certificate 579,367, which also mentions the use of
serpentinite and breast as additives in crystal in
order to increase the z-potential. At present talcum is
probably the most popular remover chemical for pitch and
stickles. The difficulties in removing the stickles are
caused, among other things, by the fact that the stickles
are often peeled off the surfaces of the recirculated
fibers in comparatively large, plate-like fractions.
Talcum, which is used for removing extractives, is not
as effective in removing large particles of stickles.
Unlike stickles, extractives~are dispersed in small drops-
which can be bound by mineral ingredients. the sticky
particles have a very light specific weight density
0.8-0.9 g/cm3, lighter than the fiber), therefore they
are not removed in top separators. In order to remove
the stickles, the mineral ingredients should cover the
sticky particle on each side so well that its specific
weight would increase. In that case the sticky particle
could be removed from the process in a top separator.
If the sticky particles are only partly covered by the
mineral ingredients, they are more easily melted as the
temperatures rises along with the process.
,,
According to the present invention, serpentinite can be
used successfully in paper industry both as a filler in
paper or board, as a remover of pitch, resin, extractives
and stokes, and as a retainer of flour.
In accordance with the invention, there is provided a
paper making process wherein a paper product is produced
from pulp and in which serpentinite is incorporated in
the pulp in an amount of 0.5 to 50%, by weight, based
on the weight of the pulp, the serpentinite being in
finely divided form.
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In particular the serpentinite is incorporated in an
amount of at least 1.5%.
In the case where the serpentinite is incorporated in
the pulp to remove pitch, resin, extractives and
stickles, it is suitably incorporated in an amount of
1.5 to 20%, by weight, of the pulp.
In the case where the serpentinite is incorporated as
filler it is suitably employed in an amount of 35~40%,
by weight.
At a pure stage serpentinite is in the form of a moo-
clinical, cryptomerous magnesium silicate, serpentine
[(Omegas)]. The lattice often contains iron and
aluminum. The metal- content-and particularly the iron -
content often determines the color of the serpentinite,
and consequently its brightness, too. Serpentine belongs
to the so-called network silicates and is generally
found as an opaque, soft and fine-flaky compound. Some
types of serpentinite are softer than talcum. The
serpentine network is formed of one silicon tetrahedron
layer, the negative charge whereof is neutralized by a
breast layer. Per each magnesium ion, talcum has two
hydroxyl ions less, and thus the breast layer receives
an extra positive charge, which is neutralized
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by means of another hexagonal layer of silicon tetrahedron.
when serpen-tini-te is crushed and ground, positive charges are created
on the serpentine surfaces. On the other hand, talcum stays almost
neutral or looses its charge in the sludge and can easily remain hydra-
phobic. The extremely high slipperiness of talcum is caused by two
possible slip-planes. Serpentine is less slippery because it has only
one slip-plane. Slipperiness is an advantage if the paper is glazed,
but in many cases it can also be a disadvantage, if the paper is used
for manufacturing cc~plicated products, such as various packing pro-
ducts. Due to its softness, serpentinite does not damage or scratch the machines neither during calendering nor in the drying cylinder.
The paper pulp fires have a negative z-potential, whereas the z-
potential of serpentine is positive (> -I 10 my). This feature is very
important as regards the use of fillers, the removal of stokes and
the collection of fines, because serpentine is easily attached to the
fiber network. In this case serpentine also binds the fines. Thus
the filter effect of the fiber network, which retains the filler part-
ales, looses its importance with respect to retention. Serpentine
also has a crystalline fox which is advantageous with respect to
retention. Nina used as a filler, serpentinite does not need
additional chemicals in order to stick onto the fiber surface.
I've sticking of serpentinite on the fiber surface is enhanced by the
exceptionally large specific surface of serpentinite, which varies
between 50,000 - 500,000 crying depending on the case, and by the great
porosity of serpentinite. The high melting point (around 1400C) of
serpentinite, and the fact that it gradually melts into liquid while
the crystal water is evaporated, render good refractory properties
for a paper which is filled or covered with serpentinite. The porosity
of of serpentinite also allows the use of heat-consuming additives.
Among the advantages of serpentinite can be mentioned its hydra-
fullest, which leads to easy disintegrability, which again
helps the treatment of mineral ingredients. Moreover, the
softness of serpentinite makes it possible to use a grain size
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larger than generally with fillers; the large grain size of
serpentinite increases stiffness and thus reduces curling for example
in envelope papers.
As regards the removal of stickles and fresh pitch, serpentinite has
many advantageous characteristics: it has a positive z-potential,
which leads to good adhesion on the surface of the sticky particles,
it is easily disintegrable (hydrophilic), and it has a large specific
surface and high porosity.
Consequently serpentinite can be used in paper industry for removing
fresh pitch and extractives from lumber, particularly in the pro-
diction of grounded pulp and thermal mechanical pulp, as well as for
removing stickles attached to recirculated fibers. According to the
conditions in each factory, serpentinite is added for instance in the
slushes, in the refiners, in a suitable pulp chest near the head box
of the machine, in the suction side of the white water pump, or in the
pulper, when recirculated fibers are in question. The sticky particles
can be coated with serpentinite so completely that they can either be
removed from the process before the filter presses and the diver
section cylinders for instance by means of cleansers, or the sticky
particles can be made so completely insert by serpentinite, that they
can pass through the machine without disturbing the process.
Modern paper factories have closed white water systems, and the fresh
pitch and stickles entering the process are concentrated in the white
water. From time to Tory the so-called closing limit becomes acute.
Serpentinite can also be used in these white waters in order to
separate pitch and stickles. When serpentinite is adsorbed on the
surface of the sticky particle, it can easily be removed from the
water for instance by means of flotation or sedimentation.
In the removal of stickles the grain size of serpentinite is
very important, because finely ground serpentinite coats the
sticky particles better than a coarsely ground material, so that
the coated particles in the paper machine remain unmelted longer
than such particles which do not have this protective coating.
It has been empirically proved -that serpentinite increases the
friction of paper but does not wizen its tensile strength like most
other fillers. This is due to the positive potential of serpentinite,
which leads to a solid join-t between the serpentinite particle and the
negatively charged fiber. Serpentinite has good friction and strength
qualities, and therefore it is a preferable filler for example in
building paper, industrial wrapping, test liner, corrugated fiberboard
and paper core board.
The color of serpentini-te sets certain limits to its use in paper
industry as a filler and remover of sticlcies. Generally the color
of serpentinite is grew. If the paper in question has high quality
requirements as regards color, light-coloured serpentinite can be used
as a filler. Another possibility is to blend serpentinite with talcum
in a required proportion, for instance in connection with double-
lamination. If part of the pulp is made of recirculated fiber, the
removal of stickles is essential. In that case talcum can be totally
replaced by serpentinite, which has a larger specific surface and a
better adsorption capacity In those branches of paper industry which
use recirculated fiber, for instance in bag industry, the friction
increase caused by serpentinite is an essential advantage.
Apart from removing sticky particles and making them inert,
serpentinite can be used in removing color particles and printing
ink leftovers in connection with the drinking of the pulp.
Roy filler proportion in paper and board varies remarkably depending
on the type of paper in question. With offset paper the filler pro
portion is 0-10% of the total amount ox pulp, whereas with LWC-paper
the filler proportion is 35-40% and with same wallpaper bases as high
as 50%. As was already mentioned, in same cases the filler can be
pure serpentinite, and in other cases the serpentinite can be blended
with for instance talcum.
Compared to the total volume of pulp, -the proportion of the agent
meant for removing stickles is relatively small, generally between
1.5-20%. On the other hand, serpentinite has better qualities
for removing pitch, extractives and sticks than the convent
tonally used removers. Thus the prior art removers can
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either totally or at least in major part be replace by serpent
finite. The blending agent can be for instance talcum suited
for this purpose.
Example 1 (comparison example)
This comparison example uses ordinary brown pine sulfite pulp
which was prepared for producing raft sack paper. The qualities
of the pulp are described by the following indexes: surface weight
108, porosity Gurney s/100 ml 90, tensile index 75, stretch 6,7%,
tear index 12,0, ashes 0,4, internal bond strength 30Z J/m2,
lo Taber-rub 10,7 mg/1000g/~5 cycles; sheet: density 746 kf/m3,
and friction coefficient on the glossy side 0,39 and on the coarse
side 0,39.
Example 2 Paper friction (cf. example 1)
Paper friction increases remarkably when serpentinite is used as
filler. With a 10% serpentinite addition, the friction on the
coarse side of the paper reached the reading 0,50. On the glossy
side the friction reached the reading 0,42. In both cases the
paper friction was undoubtedly increased.
Example 3 Paper stiffness
Paper stiffness was clearly increased after serpentinite add-
lion. The softness, grain shape and adhesion of serpentinite
; to the fibers allowed the use of larger grain sizes, for instance
-10 m 40% and -20 m 100% compared to conventional fillers, for
example talcum and bonus, -10 m OWE.
example 4 Paper strength qualities (cf. example 1)
The following measured indexes prove that the paper strength
qualities remained essentially similar irrespective of the add-
Zion ox s~p-e~tinite, which was used as the filler. Thy specific
surface of serpentinite was very large i.e. 46 mug With a
10% serpentinite addition, paper ashes were increased to OWE.
a) tensile index
When the serpentinite addition was OWE of the fiber amount,
there was no essential change in the tensile index, which no-
mined in 74. With a 10% addition there was a change which
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could be expressed digitally, the reading of the tensile index now be-
in 68. In -the case of grounded pulp containing recirculated fibers,
a 15~ serpen-tinite addition is required before -there is a noticeable
change in -the tensile index.
b) stretch
Helen -the serpentinite addition was 10% of the fiber amount, the stretch
ox -the paper remained the same as with a 5% addition, i.e. 5.8. In
general -the stretch was slightly decreased, and it is obvious that a
-Ire, addition did not ye-t have a negative effect on the starch.
c) -tear strength
When the serpentinite addition was 10% of the fiber amount, the tear
strength of the paper remained the same as with a 5% addition, i.e.,
12.4. Thus -the tear strength remained practically unchanged. The 10
addition did no-t weaken the tear strength.
d) bursting strength
When -the serpentinite addition was 10% of the fiber amount, -the burst-
in strength of the paper remained -the same as with a 5% addition,
i.e. the bursting strength also remained unchanged. The 10% addition
did not weaken the bursting strength.
Example 5 Removal of pitches, resins, extractives and other
stickles (all of which are later referred -to as sticky particles)
I-t was observed that serpentinite was adsorbed on the surfaces
of the sticky particles.
The adsorption was detected by means of a scanning electron
microscope (SUM), and a microanalyser was used in analyzing the
serpentinite adsorbed on the surfaces of the sticky particles,
so that the line analysis of for instance silicon (So) was run
over -the sticky particles. I-t was observed -that the silicon (So)
intensity increased remarkably when meeting the sticky particles.
Serpentine was adsorbed on the surfaces of the sticky particles
owning -to its exceptional surface qualities, i.e. large specific
surface and hydrophilici-ty, and therefore -the adhesion of the
said particles onto -the pressing felts on the paper machine wire
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was reduced. This means an elongation in tile operation age of
the pressing felts, which directly lowers the operation costs.
- Moreover, the adsorption of the sticky particles onto the various
members of the paper machine, for instance onto the drying Solon
dons, was reduced, because the sticky particles were coated by
the adsorbed serpentinite.
Example 6 Removal of pitches, resins, extractives and other
stickles (all of which are later referred to as sticky particles)
by means of floating in the process waters
The ability of serpentinite to be adsorbed on the surfaces of
the sticky particles makes it possible to remove the sticky par-
tides from the process waters by means of floating the serpent
finite which is adsorbed on the surfaces of the said particles.
It is generally known that serpentinite is easily floated in
a wide pharaoh, but even more easily in an almost neutral area
moreover, in order to be floated serpentinite does not need any
special collector but only a slight amount of flotation oil. In
experimental flotations it was observed that the major part of
the sticky particles was removed along with the floated serpent
finite. Those sticky particles that remained in the process waterer attached to the equipment used in the experiment. Experiments
which were cordite by means of sedimentation without flotation
gave similar results.
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