Note: Descriptions are shown in the official language in which they were submitted.
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Filler for Papermaking Process
The present invention relates to a filler comprising calcium salt and
cellulose derivative.
The invention further relates to a method of making the filler, the use of the
filler in
papermaking, a process for papermaking in which the filler is used as an
additive as well
as paper comprising the filler.
Background of the Invention
Highly filled paper is an established trend in the paper industry not only due
to the
savings in the decreased use of fibre, but also due to improved product
quality, such as
higher opacity and better printability. Calcium carbonate-based fillers are
commonly used,
because of their superior light scattering properties. A major drawback in the
production
of highly filled paper, particularly with fillers having high surface area, is
the high
consumption of sizing agent. Thus, as the content of filler in the paper
increases, a larger
amount of sizing agent is required in order to obtain corresponding sizing
results. Hence,
cellulosic suspensions are more difficult to size when the amount of filler
increases.
Sizing is primarily performed in order to achieve water repellence in paper or
board and
reduce edge wicking. It will also affect mechanical properties of paper and
board, such as
dimensional stability, friction coefficient, pliability and folding endurance.
Additionally,
sizing may improve printability specifically by controlling ink spreading and
adhesion.
The sizing process involves the deposition of hydrophobic substances, commonly
referred to as sizing agents, on the fibre surface. Commonly employed sizing
agents are
non-cellulose-reactive sizing agents, e.g. rosin-based sizing agents, and
cellulose-
reactive sizing agents, e.g. alkyl ketene dimers ("AKD") and acid anhydrides
such as
alkenyl succinic anhydride ("ASA"). It is known, however, that cellulose-
reactive sizing
agents, i.e. AKD and ASA, undergo hydrolysis that competes with the desired
reaction
with the fibres. Moreover, sizing losses in the final product can occur due to
size inversion
or migration, size evaporation, mechanical wear of the product, etc.
Bartz and co-workers have observed that during increased fluidity of AKD wax,
some
AKD could penetrate and thereafter be trapped in the pore structure of the
filler (Bartz,
W.; Darroch, M.E.; Kurrle, F.L., "Alkyl ketene dimer sizing efficiency and
reversion in
calcium carbonate filled papers", Tappi Journal, Vol. 77, No. 12, 1994). This
occurs
particularly with the scalenohedral form of PCC, which has the porous rosette
structure
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and high surface area. Voutilainen has shown that fillers with high surface
area adsorb
AKD even better than fibres (Voutilainen, P., "Competitive Adsorption of Alkyl
Ketene
Dimer on Pulp Fibers and CaCO3 Fillers", Proceedings from International Paper
and
Coating Chemistry Symposium, 1996). The presence of Al- and Si-oxides on the
filler
surface may additionally adsorb cationic starch contained in the AKD
particles. It has also
been proposed that a strong interaction, or perhaps even bonding, exists
between AKD
and calcium carbonate filler. These proposed mechanisms with the filler are
naturally
undesired, and efforts should be made to minimise these interaction.
To improve sizing efficiency, it is suggested in U.S. Patent No. 5,514,212
that the surface
of the pigment can be modified with an anionic starch-soap complex. Cooked
starch from
corn or potato is complexed with fatty acid salts and precipitated onto
pigment surfaces
when mixed with precipitated calcium slurry or papermaking furnish containing
high levels
of calcium ions.
U.S. Patent No. 5,972,100 suggests a system consisting of a cellulose-reactive
size
(such as AKD), a cationic dispersing agent (such as cationic starch or
polyamides) and a
filler. Aside from improved sizing, the invention allows independent control
of both filler
loading and sizing separately.
Furthermore, WO 95/13324 refers to calcium carbonate treated with a cellulose
derivative
such as sodium carboxymethyl cellulose ("CMC") having a degree of substitution
of 0.7.
Said treated calcium carbonate is used as filler in alkaline papermaking
suspensions
whereby the brightness of the paper is increased.
U.S. Patent No. 3,730,830 discloses a process for making paper, specifically
photographic paper, comprising the use of synthetic polymer fibres. Prior to
the addition
of the synthetic fibres to the fibre suspension, inorganic pigment or carbon
is added to a
slurry containing carboxymethyl cellulose and the synthetic fibres thereby
achieving
uniform dispersion of the polymer fibres among the cellulose fibres in the
paper stock.
There is still a need for a filler which provides an improved papermaking
process and
better properties of the paper produced. It would be desirable to provide a
filler which
renders possible production of highly filled paper showing excellent printing
and
mechanical properties. It would also be desirable to provide a filler which
reduces the
sizing demand and hereby results in improved sizing efficiency. It would also
be desirable
to provide a filler that is compatible with drainage and retention aids, and
hereby leads to
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good drainage, retention and paper machine runnability, It would also be
desirable to
provide a simple and efficient process for producing a filler showing the
above
characteristics.
Summary of the Invention
The present invention generally relates to a filler comprising calcium salt
and cellulose
derivative. The present invention further generally relates to a filler
comprising calcium
salt and carboxyalkyl cellulose derivative. The invention also generally
relates to a
method of making the filler by mixing a calcium salt-containing material with
a cellulose
derivative, the use of the filler as an additive in papermaking as well as
paper comprising
the filler. The invention further generally relates to a papermaking process
in which the
filler is introduced into an aqueous cellulosic suspension.
More specifically, the invention relates to a filler comprising calcium salt
and cellulose
derivative having a degree of substitution of net ionic groups up to about
0.65. The
invention also relates to a filler comprising calcium salt and a cellulose
derivative having a
degree of substitution of carboxyalkyl groups up to about 0.65. The invention
further
relates to a method of producing a filler which comprises mixing a calcium
salt-containing
material with a cellulose derivative having a degree of substitution of net
ionic groups up
to about 0.65. The invention also relates to a method of producing a filler
which
-comprises mixing a calcium salt-containing material with a cellulose
derivative having a
degree of substitution of carboxyalkyl groups up to about 0.65. The invention
further
relates to a filler obtainable by these methods. The invention further relates
to a
papermaking process which comprises providing an aqueous suspension containing
cellulosic fibres, introducing into the suspension a filler comprising calcium
salt and
cellulose derivative having a degree of substitution of net ionic groups up to
about 0.65,
and dewatering the suspension to form a web or sheet of paper. The invention
also
relates to a papermaking process which comprises providing an aqueous
suspension
containing cellulosic fibres, introducing into the suspension a filler
comprising calcium salt
and cellulose derivative having a degree of substitution of carboxyalkyl
groups up to
about 0.65, and dewatering the suspension to form a web or sheet of paper. In
the
papermaking process, the filler can be introduced into the cellulosic
suspension by
adding the calcium salt and cellulose derivative together as a single
composition.
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3a
In accordance with one aspect of the present invention, there is provided a
filler
comprising calcium salt and an anionic cellulose derivative having a degree of
substitution of net anionic groups up to 0.65, wherein the filler is
substantially free from
fibres or fibrils of cellulose or lignocellulose.
In accordance with another aspect of the present invention, there is provided
a method
of making a filler which comprises mixing a calcium salt-containing material
with a
cellulose derivative having a degree of substitution of net ionic groups up to
0.65 in the
substantial absence of fibres or fibrils of cellulose or lignocellulose.
In accordance with yet another aspect of the present invention, there is
provided a filler
comprising calcium salt and cellulose derivative having a degree of
substitution of net
ionic groups up to 0.65, wherein the cellulose derivative contains cationic
groups and
wherein the net ionic degree of substitution is net anionic, net cationic or
net neutral.
In accordance with still another aspect of the present invention, there is
provided a
method of making a filler which comprises mixing a calcium salt-containing
material with
a cellulose derivative having a degree of substitution of net ionic groups up
to 0.65
wherein the cellulosic derivative contains cationic groups and wherein the net
ionic
substitution is net anionic, net cationic or net neutral.
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Detailed Description of the Invention
The present invention provides a new filler that is suitable for use in
papermaking. It has
surprisingly been found that the filler according to the invention makes it
possible to
reduce some of the problems associated with fillers commonly used in
papermaking and
incorporated in paper. More specifically, by employing the filler of this
invention in
papermaking processes it is possible to provide paper with excellent printing
properties,
e.g. high smoothness, high opacity and whiteness, improved mechanical
properties, e.g.
dry strength, tensile strength, Scott bond and bending stiffness, and improved
sizing
effect. Additional advantages shown by the present invention include good
and/or
improved dewatering and fines retention, which lead to benefits in terms of
paper
machine runnability.
When using the filler in conjunction with a sizing agent, it has been observed
that the
present invention makes it possible to reduce the sizing demand and, thus,
generally
improving sizing efficiency. The improved sizing efficiency is exhibited for
different types
of sizing agents, including non-cellulose and cellulose-reactive sizing
agents, specifically
cellulose-reactive sizing agents such as ketene dimers and acid anhydrides. In
particular,
the invention provides improved sizing efficiency and sizing stability of
filled paper,
especially with high filler loading and/or when fillers with high surface
areas are used.
According to the present invention it has also been observed, unexpectedly,
that the
cellulose derivative can be mixed with and more effectively be adsorbed on or
attached to
the calcium salt-containing material during simple processing. The filler of
the invention
can be regarded as a modified filler, or cellulose derivative-treated filler.
According to the present invention it has been found that very good results
can be
obtained by adding the calcium salt-containing material and cellulose
derivative to a
cellulosic suspension together in a pre-mixed or pre-treated form. The pre-
treatment of
the calcium salt-containing material with the cellulose derivative provides a
convenient
way of separately processing only one component of the cellulosic suspension
to produce
a modified filler, which can be used instead of or partly replacing
conventional filler.
Without being bound by any theory, it is believed that the cellulose
derivative is adsorbed
to the calcium salt-containing material when mixing the components.
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The filler according to the invention comprises a calcium salt and a cellulose
derivative.
Examples of suitable calcium salts include calcium carbonate, calcium sulphate
and
calcium oxalate, preferably calcium carbonate, and mixtures thereof. Calcium
carbonate
is the main constituent in limestone, marble, chalk and dolomite. Calcium
carbonate can
5 be obtained directly from the above mentioned naturally occurring species of
stone and is
then referred to as ground. calcium carbonate ("GCC"). Calcium carbonate can
also be
synthetically produced, commonly referred to as precipitated calcium carbonate
("PCC).
The calcium carbonate is preferably obtained from calcium hydroxide and a
material
which produces carbonate ions in the aqueous phase, such as an alkali metal
carbonate
or carbon dioxide. Both GCC and PCC can be used in the present invention,
preferably
PCC, including any of the various crystalline forms or morphologies that
exist, e.g. calcite
of rhombohedral, prismatic, tabular, cuboid and scalenohedral forms and
aragonite of
acicular form. The PCC usually has a specific area of from about 2 to about 20
m2/g,
suitably from about 7 to about 12 m2/g.
The calcium salt can be present as essentially pure calcium salt, including
mixtures of
one or more calcium salts. It can also be present in the form of a mixture
together with
one or more other components. The term "calcium salt-containing material", as
used
herein, refers to a material comprising calcium salt, and optionally one or
more other
components. Examples of suitable other components of this type include fibres
or fibrils
of cellulose, lignocellulose or similar vegetable materials, inorganic clays,
kaolin, talc,
titanium dioxide, hydrogenated aluminium oxides, barium sulphate, etc.
Preferably, when
used, the other components are suited for use in papermaking.
In calcium salt-containing materials comprising fibres or fibrils of
cellulose, lignocellulose
or similar vegetable materials, at least part of the calcium salt can be
deposited on the
fibres or fibrils. The average thickness of the fibrils can be from about 0.01
up to about 10
pm, suitably up to about 5 pm and preferably up to about 1 pm. The average
length of the
fibrils can be from about 10,pm up to about 1500 gm. Examples of suitable
calcium salt-
containing materials include the composite materials disclosed in U.S. Patent
Nos.
5,731,080; 5,824,364; 6,251,222; 6,375,794; and 6,599,391.
Commercially available composite materials of
this type include SuperFill of M-Real Oy.
The filler according to the invention further comprises a cellulose
derivative. It is preferred
that the cellulose derivative is water-soluble.or at least partly water-
soluble or water-
dispersible., preferably water-soluble or at least partly water-soluble.
Preferably, the
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cellulose derivative is ionic. The cellulose derivative can be anionic,
cationic or
amphoteric, preferably anionic or amphoteric. Examples of suitable cellulose
derivatives
include cellulose ethers, e.g. anionic and amphoteric cellulose ethers,
preferably anionic
cellulose ethers. The cellulose derivative preferably has ionic or charged
groups, or
substituents. Examples of suitable ionic groups include anionic and cationic
groups.
Examples of suitable anionic groups include carboxylate, e.g. carboxyalkyl,
sulphonate,
e.g. sulphoalkyl, phosphate and phosphonate groups in which the alkyl group
can be
methyl, ethyl propyl and mixtures thereof, suitably methyl; suitably the
cellulose derivative
contains an anionic group comprising a carboxylate group, e.g. a carboxyalkyl
group. The
counter-ion of the anionic group is usually an alkali metal or alkaline earth
metal, suitably
sodium.
Examples of suitable cationic groups of cellulose derivatives according to the
invention
include salts of amines, suitably salts of tertiary amines, and quaternary
ammonium
groups, preferably quaternary ammonium groups. The substituents attached to
the
nitrogen atom of amines and quaternary ammonium groups can be same or
different and
can be selected from alkyl, cycloalkyl, and alkoxyalkyl, groups, and one, two
or more of
the substituents together with the nitrogen atom can form a heterocyclic ring.
The
substituents independently of each other usually comprise from I to about 24
carbon
atoms, preferably from I to about 8 carbon atoms. The nitrogen of the cationic
group can
be attached to the cellulose or derivative thereof by means of a chain of
atoms which
suitably comprises carbon and hydrogen atoms, and optionally 0 and/or N atoms.
Usually the chain of atoms is an alkylene group with from 2 to 18 and suitably
2 to 8
carbon atoms, optionally interrupted or substituted by one or more
heteroatoms, e.g. 0 or
N such as alkyleneoxy group or hydroxy propylene group. Preferred cellulose
derivatives
containing cationic groups include those obtained by reacting cellulose or
derivative
thereof with a quaternization agent selected from 2, 3-epoxypropyl trimethyl
ammonium
chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride and mixtures
thereof.
The cellulose derivatives of this invention can contain non-ionic groups such
as alkyl or
hydroxy alkyl groups, e.g. hydroxymethyl, hydroxyethyl, hydroxypropyl,
hydroxylbutyl and
mixtures thereof, e.g. hydroxyethyl methyl, hydroxypropyl methyl, hydroxybutyl
methyl,
hydroxyethyl ethyl, hydroxypropoyl and the like. In a preferred embodiment of
the
invention, the cellulose derivative contains both ionic groups and non-ionic
groups.
Examples of suitable cellulose derivatives according to the invention include
carboxyalkyl
celluloses, e.g. carboxymethyl cellulose, carboxyethyl cellulose,
carboxypropyl cellulose,
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7
suiphoethyl carboxymethyl cellulose, carboxymethyi hydroxyethyl cellulose ("CM-
HEC"),
carboxymethyl cellulose wherein the cellulose is substituted with one or more
non-ionic
substituents, preferably carboxymethyl cellulose ("CMC"). Examples of suitable
cellulose
derivatives and methods for their preparation include those disclosed in U.S.
Pat. No.
4,940,785,
According to a preferred embodiment of the invention the filler comprises a
calcium salt
containing fibres or fibrils of cellulose or lignocellulose and a cellulosic
derivative
containing cationic groups. The cationic groups can be any one of those listed
in this
application.
In another preferred embodiment of the invention the filler comprises a
calcium salt which*
is substantially free from fibres or fibrils of cellulose or lignocellulose
and a cellulosic
derivative which can be either anionic, cationic or amphoteric.
The terms "degree of substitution" or "DS", as used herein, mean the number of
substituted ring sites of the beta-anhydroglucose rings of the cellulose
derivative. Since
there are three hydroxyl groups on each anhydroglucose ring of the cellulose
that are
available for substitution, the maximum value of DS is 3Ø According to one
preferred
embodiment of the invention, the cellulose derivative has a degree of
substitution of net
ionic groups ("DSM") up to about 0.65, i.e. the cellulose derivative has an
average degree
of net ionic substitution per glucose unit up to about 0.65. The net ionic
substitution can
be net anionic, net cationic or net neutral. When the net ionic substitution
is net anionic,
there is a net excess of anionic groups (net anionic groups = the average
number of
anionic groups minus the average number of cationic-groups, if any, per
glucose unit) and
DSNi is the same as the degree of substitution of net anionic groups ("DSNA").
When the
net ionic substitution is net cationic, there is a net excess of cationic
groups (net cationic
groups = the average number of cationic groups minus the average number of
anionic
groups, if any, per glucose unit) and DSNi is the same as the degree of
substitution of net
cationic groups ("DSNC"). -When the net ionic substitution is net neutral, the
average
number of anionic and cationic groups, if any, per glucose unit is the same,
and DSNi as
well as DSNA and DSNc are 0. According to another preferred embodiment of the
invention, the cellulose derivative has a. degree of substitution of
carboxyalkyl groups
("DScA") up to about 0.65, i.e. the cellulose derivative has an average degree
of
carboxyalkyl substitution per glucose unit up to about 0.65. The carboxyalkyl
groups are
suitably carboxymethyl groups and then DSCA referred to herein is the same as
the
degree of substitution of carboxymethyl groups ("DSCM"). According- to these
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embodiments of the invention, DSNi, DSNA, DSNC and DSCA independently of each
other
are usually up to about 0.60, suitably up to about 0.50, preferably up to
about 0.45 and
more preferably up to 0.40, whereas DSNI, DSNA, DSNC and DSCA independently of
each
other are usually at least 0.01, suitably at least about 0.05, preferably at
least about 0.10
and more preferably at least about 0.15. The ranges of DSNI, DSNA, DSNC and
DSCA
independently of each other are usually from about 0.01 to about 0.60,
suitably from
about 0.05 to about 0.50, preferably from about 0.10 to about 0.45 and more
preferably
from about 0.15 to about 0.40.
Cellulose derivatives that are anionic or amphoteric usually have a degree of
anionic
substitution ("DSA") in the range of from 0.01 to about 1.0 as long as DSNI
and DSNA are
as defined herein; suitably from about 0.05, preferably from about 0.10, and
more
preferably from about 0.15 and suitably up to about 0.75, preferably up to
about 0.5, and
more preferably up to about 0.4. Cellulose derivatives that are cationic or
amphoteric can
have a degree of cationic substitution ("DSc") in the range of from 0.01 to
about 1.0 as
long as DSNI and DSNC are as defined herein; suitably from about 0.02,
preferably from
about 0.03, and more preferably from about 0.05 and suitably up to about 0.75,
preferably
up to about 0.5, and more preferably up to about 0.4. The cationic groups are
suitably
quaternary ammonium groups and then DSc referred to herein is the same as the
degree
of substitution of quaternary ammonium groups ("DSQN"). For amphoteric
cellulose
derivatives of this invention DSA or DSc can of course be higher than 0.65 as
long as
DSNA and DSNC, respectively, are as defined herein. For example, if DSA is
0.75 and DSc
is 0.15, then DSNA is 0.60.
Examples of suitable cellulose derivatives having degrees of substitution as
defined
above include the water-soluble low DS carboxyalkyl cellulose derivatives
disclosed in, co-
pending patent applications filed in the name of Akzo Nobel N.V. of even date.
The water-
soluble cellulose derivatives suitably has a solubility of at least 85 % by
weight, based on
total weight of dry cellulose derivative, in an aqueous solution, preferably
at least 90 % by
weight, more preferably at least 95 % by weight, and most preferably at least
98 % by
weight.
The cellulose derivative usually has an average molecular weight which is at
least 20,000
Dalton, preferably at least 50,000 Dalton, and the average molecular weight is
usually up
to 1,000,000 Dalton, preferably up to 500,000 Dalton.
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Preferably, in the filler according to the invention, the cellulose derivative
is at least in part
adsorbed on or attached to the calcium salt or other components present in the
calcium
salt-containing material. Suitably, at least about 10 % by weight, preferably
at least about
30 % by weight, more preferably at least about 45 % by weight and most
preferably at
least about 60 % by weight of the cellulose derivate is adsorbed on or
attached to the
calcium salt or other components present in the calcium salt-containing
material.
The filler according to the invention usually has a calcium salt content of at
least 0.0001
% by weight; the calcium salt content can be from about 0.0001 to about 99.5 %
by
weight, suitably from about 0.1 to about 90 % by weight, and preferably from
about 60 to
about 80 % by weight, based on the weight of the solids of the filler, i.e.
based on the dry
weight of the filler. The filler usually has a cellulose derivative content of
at least 0.01 %
by weight; the cellulose derivative content can be from about 0.01 to about 30
% by
weight, suitably from about 0.1 to about 20 % by weight, and preferably from
about 0.3 to
about 10 % by weight, based on the weight of the solids of the filler.
The.filler according to the invention can be supplied as a solid material that
can be
essentially free of water. It can also be supplied as an aqueous composition.
The content
of aqueous phase, or water, can vary within wide limits, depending on the
method of
production and intended use.
The present invention also relates to a method of making a filler which
comprises mixing
a cellulose derivative, e.g. any one of the cellulose derivatives defined
herein, with a
calcium salt-containing material, e.g. any one of the calcium salt-containing
materials
defined herein, which comprises calcium salt, and optionally one or more other
components. The cellulose derivative and calcium salt-containing material are
suitably
used in amounts so as to provide a filler according to the invention having
contents of
cellulose derivative and calcium salt as defined herein.
The cellulose derivative and calcium salt-containing material used can be
present as
solids or in aqueous compositions, and mixtures thereof. The calcium salt-
containing
material is suitably present as a finely divided material. The mixing can be
achieved by
adding the cellulose derivative to the filler, or vice versa, in a batch, semi-
batch or
continuous process. According to a preferred embodiment of the invention, the
cellulose
derivative is added as a solid to an aqueous composition of the calcium salt-
containing
material and the composition obtained is then suitably subjected to effective
dispersing to
dissolve the cellulose derivative. Preferably, the mixing is carried out by
first forming a
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neutral to alkaline aqueous phase, suitably an aqueous solution, of cellulose
derivative
which is then mixed with an aqueous composition of calcium salt-containing
material.
Prior to mixing with the calcium salt-containing material, the aqueous phase
of cellulose
derivative can be subjected to pre-treatment, e.g. homogenisation,
centrifugation and/or
5 filtration, for example for separating undissolved cellulose derivative, if
any, from the
aqueous phase.
Preferably, the cellulose derivative is mixed with the calcium salt-containing
material to
allow at least part of the cellulose derivative to adsorb on or attach to the
calcium salt-
10 containing material, preferably so that it is hardly removed from the
material by dilution
with water. This can be accomplished by carrying out mixing under a period of
time that is
sufficient long to allow the adsorption on attachment. Suitably the mixing
time is at least
about 1 min, preferably at least about 5 min, more preferably at least about
10 min and
most preferably at least about 20 min. Mixing periods of even several hours (1
- 10 h) are
possible if it is desired to reach a high degree of attachment. Suitably, at
least about 10 %
by weight, preferably at least about 30 % by weight, more preferably at least
about 45 %
by weight and most preferably at least about 60 % by weight of the cellulose
derivate is
transferred from the aqueous phase and adsorbed on or attached to the calcium
salt or
other components present in the calcium salt-containing material.
The pH of the aqueous phase of cellulose derivative is usually adjusted for
sorption of the
specific cellulose derivative used at a value from about 4 to about 13,
preferably from
about 6 to about 10, more preferably from about 7 to about 8.5. A suitable
base or acid
can be used for adjusting the pH. Examples of suitable bases include
bicarbonates and
carbonates of alkali metals and alkali metal hydroxides, suitably sodium
bicarbonate,
sodium carbonate and sodium hydroxide. Examples of suitable acids include
mineral
acids, organic acids and acid salts, suitably sulphuric acid and its acid
salts, such as
alum. In general, at a lower pH, i.e. a pH from about 4.0 to neutral,
adsorption of the
cellulose derivative is higher but solubility is decreased, whereas at higher
pH the
adsorption is reduced but solubility is increased.
The temperature is not critical; in operations in non-pressurized conditions
the
temperature is typically from about 10 to about 100 C, preferably from about
20 to about
80 C. However, higher temperatures are more favourable, suitably the
temperature of
the aqueous composition during mixing is from about 30 up to about 70 C, more
preferably from about 40 up to about 60 C.
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When using calcium salt-containing material also containing other components
than
calcium salt, e.g. fibres or fibrils of cellulose or lignocellulose, the
mixing and attaching of
cellulose derivative can be done simultaneously with precipitation of the
calcium salt on
the fibrils or fibres or after the precipitation. It is also possible to add
the cellulose
derivative before the precipitation. In that case the cellulose derivative is
added either
during beating or in a separate sorption after beating. The cellulose
derivative can be
adsorbed on or attached to the calcium salt-containing material or fibre or
fibril surfaces
and/or sorbed into the fibres or fibrils. Methods of adsorbing similar
cellulose derivatives
to similar filler materials are disclosed in U.S. Patent Nos. 5,731,080;
5,824,364;
6,251,222; 6,375,794; and 6,599,391.
The filler obtained by the method of the invention can be used as such, for
example in
papermaking. If present as an aqueous composition, it can be used directly or
it can be
dried, if desired, for example to simplify shipping.
The present invention also relates to a process for the production of paper
which
comprises providing an aqueous suspension containing cellulosic fibres
("cellulosic
suspension"), introducing into the cellulosic suspension a filler, e.g. any
one of the fillers
defined herein, and dewatering the cellulosic suspension to form a web or
sheet of paper.
Preferably, the filler is introduced into the cellulosic suspension by adding
it as a single
composition. Alternatively, the calcium salt, or calcium salt-containing
material (e.g. any
one of the calcium salt-containing materials defined herein), and cellulose
derivative (e.g.
any one of the cellulose derivatives defined herein) can be separately added
to the
cellulosic suspension and the filler is formed in situ in the cellulosic
suspension.
In the process, other components may of course be introduced into the
cellulosic
suspension. Examples of such components include conventional fillers, optical
brightening agents, sizing agents, drainage and retention aids, dry strength
agents, wet
strength agents, etc. Examples of suitable conventional fillers include
kaolin, china clay,
titanium dioxide, gypsum, talc, natural and synthetic calcium carbonates, e.g.
chalk, ground
marble and precipitated calcium carbonate, hydrogenated aluminum oxides
(aluminum
trihydroxides), calcium sulphate, barium sulphate, calcium oxalate, etc. When
using the
filler according to the invention together with conventional filler, the
filler according to the
invention can be present in an amount of at least 1 % by weight, suitably at
least 5 % by
weight, preferably at least 10 % by weight, more preferable at least about 20
% by weight,
and suitably up to about 99 % by weight, based on the dry weight of all
fillers. Examples
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of suitable sizing agents include non-cellulose-reactive sizing agents, e.g.
rosin-based sizing
agents like rosin-based soaps, rosin-based emulsions/dispersions, and
cellulose-reactive
sizing agents, e.g. emulsions/dispersions of acid anhydrides like alkenyl
succinic
anhydrides (ASA), alkenyl and alkyl ketene dimers (AKD) and multimers.
Examples of
suitable drainage and retention aids include organic polymeric products, e.g.
cationic,
anionic and non-ionic polymers including cationic polyethylene imines,
cationic, anionic
and non-ionic polyacrylamides, cationic polyamines, cationic starch, and
cationic guar;
inorganic materials, e.g. aluminium compounds, anionic microparticulate
materials like
colloidal silica-based particles, clays of smectite type, e.g. bentoinite,
montmorillonite;
colloidal alumina, and combinations thereof. Examples of suitable combinations
of
drainage and retention aids include cationic polymers and anionic
microparticulate
materials, e.g. cationic starch and anionic colloidal silica-based particles,
cationic
polyacrylamide and anionic colloidal silica-based particles as well as
cationic
polyacrylamide and bentoinite or montmorillonite. Examples of suitable wet
strength
agents include polyamines and polyaminoamides. Paper containing filler
according to the
invention and cationic starch shows very good strength properties.
According to a preferred embodiment of the invention, at least one sizing
agent is
introduced into the cellulosic suspension to produce sized paper containing
filler.
Preferably, the sizing agents are cellulose-reactive sizing agents of the
types mentioned
herein. Suitable ketene dimers have the general formula (I) below, wherein R1
and R2
represent saturated or unsaturated hydrocarbon groups, usually saturated
hydrocarbons,
the hydrocarbon groups suitably having from 8 to 36 carbon atoms, usually
being straight or
branched chain alkyl groups having 12 to 20 carbon atoms, such as hexadecyl
and
octadecyl groups. The ketene dimers may be liquid at ambient temperature, i.e.
at 25 C,
suitably at 20 C. Commonly, acid anhydrides can be characterized by the
general formula
(II) below, wherein R3 and R4 can be identical or different and represent
saturated or
unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms,
or R3 and
R4 together with the -C-O-C- moiety can form a 5 to 6 membered ring,
optionally being
further substituted with hydrocarbon groups containing up to 30 carbon atoms.
Examples of
acid anhydrides which are used commercially include alkyl and alkenyl succinic
anhydrides
and particularly isooctadecenyl succinic anhydride.
(I) R'-CH=C-CH-R2 (II) 0 0
I I II II
O-C=O R3-C-O-C-R4
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Suitable ketene dimers, acid anhydrides and organic isocyanates include the
compounds
disclosed in U.S. Pat. No. 4,522,686..
The filler according to the invention can be added to the cellulosic
suspension in amounts
which can vary within wide limits depending on, inter alia, type of cellulosic
suspension, type
of paper produced, point of addition, etc. The filler is usually added in an
amount within the
range of from 1 to about 50 % by weight, suitably from about 5 to about 40 %
by weight,
and usually from about 10 to about 30 % by weight, based on the weight of dry
fibres.
Accordingly, the paper according to the invention usually has a content of
filler of this
invention within the range of from I to about 50 % by weight, suitably from
about 5 to
about 40 % by weight, and usually from about 10 to about 30 % by weight, based
on the
weight of dry fibres.
When using other components in the process, these components can be added to
the
cellulosic suspension in amounts which can vary within wide limits depending
on, inter alia,
type and number of components, type of cellulosic suspension, filler content,
type of paper
produced, point of addition, etc. Sizing agents are usually introduced into
the cellulosic
suspension in an amount of at least about 0.01 % by weight, suitably at least
about 0.1 %
by weight, based on the weight of dry fibres, and the upper limit is usually
about 2 % by
weight, suitably about 0.5 % by weight. Generally, drainage and retention aids
are
introduced into the cellulosic suspension in amounts that give better drainage
and/or
retention than what is obtained when not using these aids. Drainage and
retention aids,
dry strength agents and wet strength agents, independently of each other, are
usually
introduced in an amount of at least about 0.001 % by weight, often at least
about 0.005% by
weight, based on dry fibres, and the upper limit is usually about 5% and
suitably about 1.5%
by weight.
The term "paper", as used herein, include not only paper and the production
thereof, but
also other cellulosic fibre-containing sheet or web-like products, such as for
example
board and paperboard, and the production thereof. The process can be used in
the
production of paper from different types of aqueous suspensions of cellulosic
(cellulose-
containing) fibres and the suspensions should suitably contain at least 25% by
weight
and preferably at least 50% by weight of such fibres, based on a dry
substance. The
cellulosic fibres can be based on virgin fibres and/or recycled fibres,
including fibres of
wood or annual or perennial plants. The cellulosic suspension can be wood-
containing or
wood-free, and it can be based on fibres from chemical pulp such as sulphate,
sulphite
and organosolve pulps, mechanical pulp such as thermo-mechanical pulp; chemo-
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thermo-mechanical pulp, refiner pulp and ground wood pulp, from both hardwood
and
softwood, and can also be based on recycled fibres, optionally from de-inked
pulps, and
mixtures thereof. The cellulosic suspension suitably has a pH in the neutral
to alkaline
range, e.g. from about 6 to about 10, preferably from about 6.5 to about 8Ø
The paper produced can be dried, coated and calendered. The paper can be
coated with,
for example, calcium carbonate, gypsum, aluminium silicate, kaolin, aluminium
hydroxide,
magnesium silicate, talc, titanium dioxide, barium sulphate, zinc oxide,
synthetic pigment,
and mixtures thereof.
The grammage of the paper produced can vary within wide limits depending on
the type
of paper produced; usually the grammage is within the range from about 20 to
about 500
g/m2, suitably from about 30 to about 450 g/m2, and preferably from 30 to
about 110 g/m2.
Preferably, the invention is used for the production of uncoated and coated
offset paper,
electrophotography paper, uncoated and coated fine paper, optionally
containing
mechanical pulp, as well as writing and printing papers. An especially
preferred product is
coated offset paper in which high gloss and high opacity and bulk are
combined.
The invention is further illustrated in the following Examples which, however,
are not
intended to limit the same. Parts and % relate to parts by weight and % by
weight, respec-
tively, unless otherwise stated.
Example 1
Fillers according to the invention and for comparison were prepared by
treating calcium
salt-containing material with cellulose derivatives. Cellulose derivatives
used were
carboxymethyl celluloses ("CMC") having DSNI (DSCA = DSCM = DSA = DSNA = DSN!)
of
0.3, 0.32 and 0.7, respectively. Another CMC used was quaternary ammonium
carboxymethyl celluloses ("QN-CMC") having DSCA = DSCM = DSA = 0.4; DSc = DSQN
=
0.17; and DSNI = DSNA = 0.4 - 0.17 = 0.23. The average molecular weights of
the
cellulose derivatives used were in the range of from 100,000 to 400,000..
Calcium salt-
containing materials used were different precipitated calcium carbonates
("PCC") having
a surface area of 5.7 and 10.0 m2/g, respectively. Another calcium salt-
containing
material used was SuperFill (PCC on pulp fines).
The fillers were prepared by dissolving CMC into water to a consistency of 0.5
% by
weight. Thereafter, the obtained CMC composition was added to PCC filler
slurry and
mixed during 25 to 45 minutes at a temperature of about 50 C. The fillers
according to
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I 7 200
the invention ("Invention Product") and for comparison ("Comparison Product")
were the
following:
Invention Product I ("IPI"): CMC (DSNI 0.3)4reated PCC (5.7 m2lg)
5 Invention Product 2 (1P2"): CMC (DSNI 0.3)-treated PCC (10 m21g)
Invention Product 4 ("1P4"): QN-CMG (DSNI 0.23)-treated SuperFill .
Comparison Product I ("CPI"): CMC (DSM 0.7)-treated PCC (5.7 m2Ig)
Comparison Product 2 SuperFill ,
Comparison Product 3 ("CP3"): CMC (DSNI 0.32)-treated SuperFill 0
Example 2
Sizing of paper produced according to the invention was evaluated and compared
to
paper used for comparison purposes. Paper according to the invention was
produced
using IPI according to Example 1. Paper used for comparison was produced using
CPI
according to Example 1 and using filler containing no cellulose derivative.
Paper sheets were produced from pulp consisting of chemical pulp and
containing
untreated PCC in varying amounts (% by weight, based on dry paper), as
indicated in
Table I . To the pulp suspension was added 2.0 kg/tonne dry fibres of filler
according to
Example 1 and filler containing no cellulose derivative; 3.0 kg/tonne dry
fibres of AKD
(aqueous dispersion Eka Keydime 0223), and a retention system comprising
cationic
starch (Eka PL I510) and silica particles (Eka NP 780). Both the cationic
starch and silica
particles were added in an amount of 0.15 kg/tonne dry fibres. The addition
sequence
was as follows:
Addition of CMC-treated PCC: 0 sec
Addition of AKD dispersion: 30 sec.
Addition of cationic starch: 45 sec.
Addition of silica particles: 60 sec.
Sheet formation: 75 sec.
The sheets were made according to a standard method using a Dynamical Sheet
Former
("Formette", CTP Grenoble). The Cobb60 (SCAN-P 12:64) method was used in order
to
establish the sizing results. Table I shows the results obtained.
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Table I
Test No. PCC Content of Paper Filler Cobb60
1 18% CP1 45
2 19% IP1 25
Example 3
In this Example, papermaking processes according to the invention were
evaluated in
which (i) CMC-treated PCC was added to the pulp suspension, and (ii) CMC and
PCC
(untreated) were separately added to the pulp suspension.
Paper sheets were produced from pulp of the same type used in Example 2 and
containing 30 % by weight, based on dry paper, of untreated PCC (surface area
of 10
m2/g) or CMC (DSN, 0.3)-treated FCC (10 m2/g) (IP2 according to Example 1). To
the pulp
suspension was added 4 kg/tonne dry fibre of cationic starch (PB 970), 3.0
kg/tonne dry
fibres of AKD (aqueous sizing dispersion Eka Keydime C223), and a retention
system
comprising cationic polyacrylamide (Eka PL 1310) and silica particles (Eka NP
780). Both
the cationic polyacrylamide and silica particles were added in an amount of
0.20 kg/tonne
dry paper. When untreated PCC was used, 1.0 kg/tonne of CMC having a DSN, of
0.3
was separately added. No separate addition of CMC was made when adding CMC-
treated PCC. The addition sequence was as follows:
Addition of cationic starch: 0 sec
Addition of CMC-treated PCC / untreated PCC: 30 sec
Separate addition of CMC: 35 sec.
Addition of AKD: 45 sec
Addition of cationic polyacrylamide: 60 sec.
Addition of silica particles: 75 sec.
Sheet formation: 90 sec.
The paper sheets were evaluated as in Example 2. The results are shown in
Table 2.
Table I
Test No. Mode of Addition Filler Cobb60
1 Separately Added Untreated PCC + CMC 65
2 CMC-treated PCC Added IP2 35
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Example 4
Products of Example 1 were used and evaluated in papermaking processes. Paper
sheets were manufactured from a fibre furnish containing 70% by weight of
mixed
hardwood pulp and 30% by weight of softwood pulp refined at 22 and 25 SR,
respectively, in a method similar to Example 3 except that no cationic starch
was used
and use was made of untreated SuperFill a filler (CP2) or CMC-treated
SuperFill filler
(CP3 and 1P4), which was added in an amount so as to give a paper sheet
containing
30% by weight of SuperFill filler. The addition sequence was as follows:
Addition of SuperFill U filler: 0 sec,
Addition of cationic polyacrylamide: 45 sec.
Addition of silica particles: 75 sec.
Addition of AKD: 90 sec.
The results are set forth in Table 3.
Table 3
Test No. Filler Cobb66
1 CP2 80
2 CP3 50
3 1P4 21
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