Note: Descriptions are shown in the official language in which they were submitted.
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BOARD COMPRISING HYDROTALCITE
Field of the Invention
The present invention generally relates to board containing cellulosic fibres
and
hydrotalcite as well as the production thereof; packaging materials and
packages
comprising the board and the production thereof as well as uses of the
packaging
materials for packaging of foodstuff, beverages, pharmaceuticals, cosmetics
and tobacco.
Backaround of the Invention
Packages are widely used throughout the world, for example to transport goods
and
protect the contents of the packages. It has proven especially difficult to
design packages
for maintaining the original properties of contents, such as foodstuff,
beverages,
pharmaceuticals and cigarettes. The quality of the content may be reduced
either by the
content itself changing over time, or by quality-reducing substances being
supplied from or
through the package. The content can be treated, e.g. pasteurised, as with
milk, or dried,
as with flour. Usually, the packages are designed with several plies or layers
which often
are made of different materials. Thus, each ply and each material has a
specific quality
and purpose in the package, such as preventing the transfer of oxygen, water
or water
vapour to the content of the package.
Packaging materials are frequently used for packaging solid and liquid
foodstuffs and
beverages, e.g. cereals, milk, juice, wine and water. Such packaging materials
are usually
made of board comprising several layers or plies of cellulosic fibres,
combined with one or
more layers of plastic material in direct contact with the foodstuff or
beverage. Despite the
use of packages containing a combination of several materials, the content may
acquire an
undesirable smell and/or taste after some time. The substances causing
undesirable smell
and taste are usually oxidation products formed during production and storage
of the
board. Since the packaging blanks usually are shipped flat and opened when
ready to be
filled, the oxidation products may be transferred to the plastic-coated inside
of the
packaging material.
It would be desirable to be able to provide board and board-containing
packaging materials
and packages having less undesirable or unpleasant smell and/or taste. It
would also be
desirable to be able to provide improved processes for the production of such
products.
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Summary of the Invention
The present invention is generally directed to a process for producing board
comprising
(i) providing an aqueous suspension comprising cellulosic fibres;
(ii) adding hydrotalcite to the suspension;
(iii) dewatering the obtained suspension to provide a single ply board.
The present invention is further generally directed to a process for producing
board which
comprises
(i) providing an aqueous suspension comprising cellulosic fibres;
(ii) adding hydrotalcite to the suspension;
(iii) dewatering the obtained suspension to provide a ply comprising
cellulosic fibres and hydrotalcite; and
(iv) attaching said ply to one or more plies comprising cellulosic fibres to
provide a multi ply board comprising two or more plies.
The present invention is also generally directed to board comprising one or
more plies
containing cellulosic fibres, wherein the board further comprises hydrotalcite
distributed
throughout at least one of said one or more plies.
The present invention is further generally directed to a method for producing
a packaging
material which comprises
(i) providing board comprising one or more plies containing cellulosic fibres
and
hydrotalcite; and
(ii) subjecting the board to one or more converting operations selected from
printing,
varnishing, coating, laminating, metallizing, die cutting, scoring, creasing,
foil
blocking, embossing and folding.
The present invention is also generally directed to a packaging material
comprising board
which comprises one or more plies containing cellulosic fibres and
hydrotalcite, wherein it
further comprises one or more grooves, creases or scores.
The invention is further generally directed to a procedure of making a package
comprising:
(i) providing a blank of packaging material comprising board comprising one or
more
plies containing cellulosic fibres and hydrotalcite;
(ii) filling the packaging blank with a solid or liquid content to form an
unsealed
package; and
(iii) sealing the obtained package.
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The present invention is also generally directed to a package comprising board
containing
cellulosic fibres and hydrotalcite, wherein it further comprises a solid or
liquid content.
The invention is further directed to uses of the packaging material comprising
board, which
comprises one or more plies containing cellulosic fibres and hydrotalcite, for
packaging of
solid or liquid foodstuffs, beverages, pharmaceuticals, cosmetics, chocolates,
cigarettes or
tobacco.
Detailed Description of the Invention
According to the present invention it has been found that the problems caused
by
undesirable and unpleasant smell and/or taste of board and packaging materials
and
packages comprising board can be reduced by using hydrotaicite in the
production thereof
as an additive to aqueous cellulosic suspensions. It has also been found that
the present
invention reduces the negative impact on board making processes by the
presence of
disturbing and detrimental substances present in aqueous cellulosic
suspensions,
specifically problems caused by pitch, stickies and anionic low molecular
weight organics.
It has further been found that the addition of hydrotalcite in conjunction
with additives used
for making board also improves the performance of such additives as compared
to when
hydrotalcite is not added. Examples of such additives for which improved
performance can
be observed include drainage and retention aids, sizing agents, etc.
Preferably, the
hydrotalcite is used together with one or more drainage and retention aids
comprising at
least one cationic polymer. Thus, the present invention makes it possible to
obtain a
reduction of undesirable or unpleasant smell and/or taste of board and
packaging materials
comprising board, improved drainage (dewatering) and retention as well as
improved
sizing in board making processes, while simultaneously reducing the content of
disturbing
and detrimental substances in the cellulosic suspension.
Hydrotalcite belongs to the group of materials referred to as clays. The term
"hydrotalcite",
as used herein, refers to hydrotalcite and hydrotalcite-like clays including
layered double
hydroxide compounds, e.g. manasseite, pyroaurite, sjogrenite, stichtite,
barbertonite,
takovite, reevesite, desautelsite, motukoreaite, wermiandite, meixnerite,
coalingite, chloro-
magalumite, carrboydite, honessite, woodwardite, iowaite, hydrohonessite,
mountkeithite,
etc. The hydrotalcite according to the invention can be derived from naturally
occurring
hydrotalcites, synthetic hydrotalcites and chemically and/or physically
modified naturally
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occurring and synthetic hydrotalcites. Naturally occurring hydrotalcites
normally have an
essentially crystalline structure.
However, synthetically obtained hydrotalcites may also contain amorphous
material having
essentially the same chemical composition as the crystalline structures. The
amount of
amorphous material present in synthetic hydrotalcite clays depends mainly on
the reaction
parameters used. The term "clay", as used herein, refers to clays having
essentially
crystalline structure and also to clays both containing crystalline and
amorphous structures.
Clays are characterised by a layered structure wherein atoms within the layers
(lamellae)
are cross-linked by chemical bonds, while the atoms of adjacent layers
interact mainly by
physical forces. The layers of the clay may be non-charged or charged
depending on the
type of atoms present in the layers. If the layers are charged, then the space
between
these layers, also designated as the interlayer space, contains ions which
have the
opposite charge with respect to the charge of the layers. The term "cationic
clay", as used
herein, refers to clays having positively charged layers and anions present in
the interlayer
space. The term "anionic clay", as used herein, refers to clays having
negatively charged
layers and cations present in the interlayer space. Usually the ions in the
interlayer space
are exchangeable. Preferably, the hydrotalcite of the invention is cationic,
i.e. a cationic
clay.
The hydrotalcite of the invention can virtually have any anion, optionally
also water
molecules, present in the interlayer space. Examples of common anions that can
be
present in the interlayer space include N03 , OH", CI", Br, 1", C032", SO42",
Si032, Cr042",
B032" , Mn04 , HGaO32", HV04 , and CI04 , as well as pillaring or
intercalating anions such as
V1oO2$6" and M070246", mono-carboxylates like acetate, dicarboxylates such as
oxalate, and
alkyl sulphonates such as lauryl sulphonate; usually hydroxide and carbonate.
Naturally
occurring hydrotalcites of the invention commonly have carbonate anions in the
interlayer
space.
The layer or lamella of the hydrotalcite suitably comprises at least two
different metal
atoms having different valences. Suitably, one metal atom is divalent and the
other metal
atom is suitably trivalent. However, the layer may also comprise more than two
metal
atoms. The charge of the layer is governed by the ratio of metal atoms having
different
valences. For instance, a higher amount of trivalent metals will render a
layer having an
increased density of the positive charge. Suitably, the hydrotalcite of the
invention
comprises layers containing divalent and trivalent metals in a ratio so that
the overall
charge of the layers is cationic, and the interlayers comprise anions.
Preferably, the layers
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essentially consist of divalent and trivalent metals in such a ratio that the
overall charge of
the layers is cationic.
Synthetically produced and naturally occurring hydrotalcites according to the
invention can
5 be characterised by the general formula:
[Mm2+ Mn3+ (OH)2m+2n] xn/zZ - bH2O,
wherein m and n , independently of each other, are integers having a value
such that m/n
is in the range of from 1 to 10, preferably 1 to 6, more preferably 2 to 4 and
most
preferably values around 3; b is an integer having a value in the range of
from 0 to 10,
suitably a value from 2 to 6, and often a value about 4; Xn/,Z is an anion
where z is an
integer froni 1 to 10, preferably from 1 to 6, suitable Xn/aZ" including N03,
OH", CI", Br, I",
C032", S042", Si032", Cr042", B03z", Mn04, HGaO32, HV04, CI04 , pillaring and
intercalating
anions such as V100286" and M070246", mono-carboxylates like acetate,
dicarboxylates such
as oxalate, and alkyl sulphonates such as lauryl sulphonate; M2+ is a divalent
metal atom,
suitable divalent metal atoms including Be, Mg, Cu, Ni, Co, Zn, Fe, Mn, Cd,
and Ca,
preferably Mg; M3+ is a trivalent metal atom, suitable trivalent metal atoms
including Al, Ga,
Ni, Co, Fe, Mn, Cr, V, Ti and In, preferably Al.
Preferably, the divalent metal is magnesium and the trivalent metal is
aluminium, rendering
the general formula:
[Mgm2+ /ql n3+ (OH)2m+2n] Xn/zZ . bH2O.
Hydrotalcites according to the invention can be prepared by hydrothermal
treatment (solvo
thermal) of a slurry containing an aluminium source and a magnesium source.
Examples of
suitable hydrotalcites of the invention and methods for their preparation
include those
disclosed in International Patent Application Publication No. WO 01/12550, the
disclosure of
which is hereby incorporated herein by reference.
In a preferred embodiment of the invention, the hydrotalcite has a 3R2
stacking. In another
preferred embodiment of the invention, the hydrotalcite has a stacking other
than the 3R2
stacking, for example a 3R, stacking. Differences between the hydrotalcite 3R,
and 3R2
stackings are disclosed in International Patent Application Publication No. WO
01/12550,
the disclosure of which is incorporated herein by reference.
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Preferably, the hydrotalcite is used according to the invention either as a
slurry (suspension)
or powder, which can be easily dispersed in water. The suspension or powder of
hydrotalcite
may further also contain other components such as, for example, dispersing
and/or
protecting agents, which can contribute to the overall effect of the
hydrotalcite. Such agents
can have non-ionic, anionic or cationic character. Examples of suitable
protective agents or
colloids include water-soluble cellulose derivatives, e.g. hydroxyethyl- and
hydroxypropyl-,
methylhydroxypropyl- and ethylhydroxyethyl-cellulose, methyl- and
carboxymethylcellulose,
gelatine, starch, guar gum, xanthan gum, polyvinyl alcohol, etc. Examples of
suitable
dispersing agents include non-ionic agents, e.g. ethoxylated fatty acids,
fatty acids, alkyl
phenois or fatty acid amides, ethoxylated and non-ethoxylated glycerol esters,
sorbitan esters
of fatty acids, non-ionic surfactants, polyols and/or their derivatives;
anionic agents, e.g. as
alkyl or alkylaryl sulphates, sulphonates, ethersulphonates, polyacrylic acid;
and cationic
agent, e.g. esterquats obtained by reacting alkanolamines with mixtures of
fatty acids and
dicarboxylic acids, optionally alkoxylating the resulting esters and
quaternising the products,
quaternised fatty acid amides, betaines, dimethyl dialkyl or dialkylaryl
ammonium salts, and
cationic gemini dispersing agents.
According to the present invention, board is produced by a process which
comprises
adding hydrotalcite to an aqueous cellulosic suspension and then dewatering
the obtained
suspension to form the board. In a preferred embodiment of the invention, the
process
produces a single ply board comprising hydrotalcite which preferably is
distributed
throughout the board, more preferably substantially uniformly distributed
throughout the
board. Single ply board contains just one ply or layer comprising cellulosic
fibres.
In another preferred embodiment of the invention, the process produces a multi
ply board
comprising two or more plies or layers containing cellulosic fibres wherein at
least one of
said two or more plies or layers comprises hydrotalcite. Preferably, the
hydrotalcite is
distributed throughout at least one of said two or more plies, more preferably
substantially
uniformly distributed throughout at least one of said two or more plies, most
preferably in at
least one of the outer plies. Multi ply board according to the invention can
be produced by
forming at least one ply comprising cellulosic fibres and hydrotalcite and
attaching said at
least one ply to one or more plies comprising cellulosic fibres to form the
multi ply board.
For example, multi ply board can be produced by forming the individual plies
or layers
separately in one or several web-forming units and then couching them together
in the wet
state. Examples of suitable grades of multi ply board of the invention include
those
comprising from three to seven plies or layers comprising cellulosic fibres
and at least one
of said plies or layers comprising hydrotalcite.
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In the process of the invention, the board, e.g. single and multi ply board
grades, can be
subjected to further process steps. Examples of suitable process steps include
coating,
e.g. starch coating and pigment coating, printing and cutting. Accordingly,
examples of
suitable boards of the invention include coated board, e.g. starch and/or
pigment coated,
and printed board.
The hydrotalcite can be added at any point in the board production process
starting from the ~
point where wood chips are disintegrated up to the point in the process where
dewatering of
the cellulosic suspension takes place.
According to a preferred embodiment of the invention, the hydrotalcite is
added to a cellulosic
suspension of a pulp making process. The hydrotalcite can be added prior to or
after the
pulping process which can be kraft, mechanical, thermo-mechanical,
chemomechanical,
chemo-thermo-mechanical pulping processes. The hydrotalcite can be added just
before the
pulping process or directly to the pulping process, such as to the digester.
However, it is
preferred that the hydrotalcite is added to the cellulosic suspension
subsequent to chemical
digestion such as after the brown stock washer, or after refining of (chemo-
)mechanical pulp.
Usually, the cellulosic pulp is bleached in a multi stage bleaching process
comprising
different bleaching stages and the hydrotalcite can be added to any bleaching
sequence.
Examples of suitable bleaching stages include chlorine bleaching stages, e.g.
elementary
chlorine and chlorine dioxide bleaching stages, non-chlorine bleaching stages,
e.g. peroxide
stages like ozone, hydrogen peroxide and peracetic acid, and combinations- of
chlorine and
non-chlorine bleaching and oxidizing stages, optionally in combination with
reducing stages
like treatment with dithionite. The hydrotalcite can be added to the
cellulosic suspension
directly to a bleaching stage, preferably to the mixer prior to the bleaching
tower, at any point
between the bleaching and washing stages, and also to a washing stage where
the
hydrotalcite may be partly removed, e.g. in the displacement section.
Preferably, when
adding the hydrotalcite to a cellulosic suspension of a pulp making process,
the pulp obtained
is subsequently used in a board making process.
According to another preferred embodiment of the invention, the hydrotalcite
is added to a
cellulosic suspension of a board making process. The hydrotalcite can be added
to the
cellulosic suspension at any point of the board making process such as to the
thick stock,
thin stock, or to the white water before it is recycled, e.g. prior to the
thin stock feed box.
Preferably, the hydrotalcite is added to the thick stock. The hydrotalcite can
also be added at
more than one point of the pulp and/or board making processes. For instance,
in integrated
pulp and board mills, the hydrotaicite can be added in the process for pulp
production, and
optionally also in the process for board production, and one or more drainage
and retention
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aids can be added in the process for board production. Such processes can
include
dewatering the cellulosic suspension containing hydrotalcite, diluting the
suspension
obtained, adding to the diluted suspension one or more drainage and retention
aids and
dewatering the suspension containing the drainage and retention aids.
The term "board, as used herein, refers to board comprising cellulosic fibres
including solid
board, e.g. solid bleached sulphate board (SBS) and solid unbleached sulphate
board
(SUS); paper board, carton board, e.g. folding boxboard (FBB), folding carton
board, liquid
packaging board (LPB), including gable-top, aseptic, brick and non-aseptic
packaging
boards; white lined chipboard (WLC), unbleached kraftboard, grey chipboard and
recycled
board; liner board and container board, including white sulphate kraftliner,
fully bleached
kraftliner, testliner, white sulphate testliner, unbleached kraftliner,
unbleached testliner and
recycled liner; fluting and corrugated fluting. Preferably, the board has a
grammage of at
least 130 g/m2, more preferably in the range of from 140 to 600 g/m2 and most
preferably
from 150 to 450 g/ma. Preferably, the board has a bulk density of 120 to 1200
kg/m3, more
preferably from 150 to 800 kg/m3 and most preferably from 200 to 600 kg/m3.
The process
can be used in the production of board from different types of aqueous
suspensions
comprising cellulosic fibres, or aqueous cellulosic suspensions. Preferably,
the suspension
contains at least 25% by weight and more preferably at least 50% by weight of
such fibres,
based on a dry substance. The cellulosic fibres can be based on bleached and
unbleached
pulps, they can be based on virgin and/or recycled fibres, and the suspension
can be
based on fibres from chemical pulp such as sulphate, sulphite and organosolve
pulps,
mechanical pulp such as thermo-mechanical pulp (TMP), chemo-thermo-mechanical
pulp
(CTMP), refiner pulp and ground wood pulp, from both hardwood and softwood,
and can
also be based on recycled fibres, optionally from de-inked pulps (DIP), and
mixtures
thereof. In multi ply board grades the plies can be made of different types of
pulp.
Examples of suitable multi ply combinations with bleached cellulosic fibre
include bleached
chemical pulp top / DIP, CTMP or mechanical pulp middle I bleached chemical
pulp back;
and bleached chemical pulp top / DIP, CTMP or mechanical pulp middle /
mechanical pulp
back; the top side optionally being coated and the back side optionally being
coated.
The cellulosic suspension can also contain mineral fillers of conventional
types such as, for
example, kaolin, china clay, titanium dioxide, gypsum, talc and natural and
synthetic calcium
carbonates such as chalk, ground marble and precipitated calcium carbonate.
Preferably, the hydrotalcite is added to the cellulosic suspension in an
amount of from about
0.01 % by weight to about 10% by weight, more preferably from about 0.05% by
weight up to
about 5% by weight, calculated as dry hydrotalcite on a dry cellulosic
suspension.
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In the process of the invention the hydrotalcite is preferably used in
conjunction with one or
more additional additives by addition to the aqueous cellulosic suspension
prior to
dewatering. Examples of suitable additional additives include drainage and
retention aids,
cationic coagulants, sizing agents like rosin-based sizing agents and
cellulose-reactive
sizing agents, e.g. ketene dimers and succinic anhydrides, dry strength
agents, wet strength
agents like polymers formed by reaction of polyamines or polyamideamine with
epichlorohydrin, optical brightening agents, dyes, etc.
Examples of suitable drainage and retention aids include organic polymers,
which can be
selected from anionic, amphoteric, non-ionic and cationic polymers, siliceous
materials, and
mixtures thereof. The use of siliceous materials and organic polymers as
drainage and
retention aids, or as flocculating agents, is well known in the art. The term
"drainage and
retention aid", as used herein, refers to a component (agent, additive) which,
when being
added to an aqueous cellulosic suspension, give better drainage and/or
retention than is
obtained when not adding said component. Preferably, the hydrotalcite is used
in
conjunction with at least one cationic polymer. The term "cationic polymer",
as used herein,
refers to an organic polymer having one or more cationic groups, preferably an
overall
cationic charge. The cationic polymer may also contain anionic groups, and
such polymers
are commonly also referred to as amphoteric polymers.
Polymers suitable for use in the process can be derived from natural or
synthetic sources,
and they can be linear, branched or cross-linked. Examples of suitable
polymers include
anionic, amphoteric and cationic polysaccharides, preferably starches;
anionic, amphoteric
and chain-growth polymers, preferably cationic acrylamide-based polymers,
including
essentially linear, branched and cross-linked anionic and cationic acrylamide-
based
polymers; as well as cationic poly(diallyldimethyl ammonium chloride);
cationic polyethylene
imines; cationic polyamines; cationic polyamideamines and vinylamide-based
polymers,
anionic step-growth polymers, preferably anionic naphthalene-based
condensation polymers.
Cationic starch and cationic polyacrylamide are particularly preferred
polymers and they can
be used singly, together with each other or together with other polymers, e.g.
other cationic
and/or anionic polymers. The molecular weight of the polymer is suitably above
1,000,000
and preferably above 2,000,000. The upper limit is not critical; it can be
about 50,000,000,
usually 30,000,000 and suitably about 25,000,000. However, the molecular
weight of
polymers derived from natural sources may be higher.
Examples of suitable siliceous materials include anionic silica-based
particles and anionic
clays of the smectite type. Preferably, the siliceous material has particles
in the colloidal
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range of particle size. Anionic silica-based particles, i.e. particles based
on Si02 or silicic acid,
are preferably used and such particles are usually supplied in the form of
aqueous colloidal
dispersions, so-called sols. Examples of suitable silica-based particles
include colloidal silica
and different types of polysilicic acid, either homopolymerised or co-
polymerised. The silica-
5 based sols can be modified and contain other elements, e.g. aluminium,
boron, nitrogen,
zirconium, gallium, titatnium and the like, which can be present in the
aqueous phase and/or
in the silica-based particles. Examples of suitable silica-based particles of
this type include
colloidal aluminium-modified silica and aluminium silicates. Mixtures of such
suitable silica-
based particles can also be used. Examples of suitable drainage and retention
aids
10 comprising anionic silica-based particles include those disclosed in U.S.
Patent Nos.
4,388,150; 4, 927, 498; 4, 954, 220; 4, 961, 825; 4,980, 025; 5,127, 994;
5,176, 891; 5, 368, 833;
5,447,604; 5,470,435; 5,543,014; 5,571,494; 5,573,674; 5,584,966; 5,603,805;
5,688,482;
and 5,707,493; which are hereby incorporated herein by reference.
Examples of suitable anionic silica-based particles include those having an
average particle
size below about 100 nm, preferably below about 20 nm and more preferably in
the range of
from about 1 to about 10 nm. As conventional in the silica chemistry, the
particle size refers
to the average size of the primary particles, which may be aggregated or non-
aggregated.
The specific surface area of the silica-based particles is suitably above 50
m2/g and prefer-
ably above 100 m2/g. Generally, the specific surface area can be up to about
1700 m2/g and
preferably up to 1000 m2/g. The specific surface area is measured by means of
titration with
NaOH in a well known manner, e.g. as described by G.W. Sears in Analytical
Chemistry
28(1956): 12, 1981-1983 and in the U.S. Patent No. 5,176,891. The given area
thus
represents the average specific surface area of the particles.
Preferably, the anionic silica-based particles have specific surface area
within the range of
from 50 to 1000 m2/g, more preferably from 100 to 950 m2/g. Sols of silica-
based particles of
these types also encompass modifications, for example with any of the elements
mentioned
above. Preferably, the silica-based particles are present in a sol having a S-
value in the
range of from 8 to 50 %, preferably from 10 to 40%, containing silica-based
particles with a
specific surFace area in the range of from 300 to 1000 m2/g, suitably from 500
to 950 m2/g,
and preferably from 750 to 950 m2/g, which sols can be modified as mentioned
above. The
S-value can be measured and calculated as described by Iler & Dalton in J.
Phys. Chem.
60(1956), 955-957. The S-value indicates the degree of aggregation or microgel
formation
and a lower S-value is indicative of a higher degree of aggregation.
In yet another preferred embodiment of the invention, the silica-based
particles are selected
from polysilicic acid, either homopolymerised or co-polymerised, having a high
specific
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surface area, suitably above about 1000 m2/g. The specific surface area can be
within the
range of from 1000 to 1700 m2/g and preferably from 1050 to 1600 m2/g. The
sols of
modified or co-polymerised polysilicic acid can contain other elements as
mentioned above.
In the art, polysilicic acid is also referred to as polymeric silicic acid,
polysilicic acid microgel,
polysilicate and polysilicate microgel, which all are encompassed by the term
polysilicic acid
used herein. Aluminium-containing compounds of this type are commonly also
referred to as
polyaluminosilicate and polyaluminosilicate microgel, which are both,
encompassed by the
terms colloidal aluminium-modified silica and aluminium silicate used herein.
Examples of suitable anionic clays of the smectite type include
montmorillonite/bentonite,
hectorite, beidelite, nontronite, saponite, laponite, preferably bentonite.
Examples of suitable
anionic bentonite clays include those disclosed in U.S. Patent Nos. 4,753,710;
5,071,512;
and 5,607,552, which are hereby incorporated herein by reference.
Examples of suitable cationic coagulants (also referred to as trash catchers
and fixatives)
include water-soluble organic polymeric coagulants and inorganic coagulants.
The cationic
coagulants can be used singly or together, i.e. a polymeric coagulant can be
used in
combination with an inorganic coagulant. Examples of suitable water-soluble
organic
polymeric cationic coagulants include cationic polyamines, polyamideamines,
polyethylene
imines, dicyandiamide condensation polymers and polymers of water soluble
ethylenically
unsaturated monomer or monomer blend which is formed of 50 to 100 mole %
cationic
monomer and 0 to 50 mole % other monomer. The amount of cationic monomer is
usually at
least 80 mole %, suitably 100 %. Examples of suitable ethylenically
unsaturated cationic
monomers include dialkylaminoalkyl (meth)-acrylates and -acrylamides,
preferably in
quaternised form, and diallyl dialkyl ammonium chlorides, e.g. diallyl
dimethyl ammonium
chloride (DADMAC), preferably homopolymers and copolymers of DADMAC. The
organic
polymeric cationic coagulants usually have a molecular weight in the range of
from 1,000 to
700,000, suitably from 10,000 to 500,000. Examples of suitable inorganic
coagulants
include aluminium compounds, e.g. alum and polyaluminium compounds, e.g.
polyalumi-
nium chlorides, polyaluminium sulphates, polyaluminium silicate sulphates and
mixtures
thereof.
Examples of preferred drainage and retention systems according to the
invention comprise:
(i) anionic silica-based particles in combination with cationic
polysaccharides;
preferably starch, or cationic chain-growth polymers, preferably cationic
acrylamide-
based polymer, optionally in combination with cationic coagulant;
(ii) anionic silica-based particles in combination with anionic acrylamide-
based polymer,
optionally in combination with cationic organic polymer and/or cationic
coagulant;
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(iii) bentonite in combination with cationic chain-growth polymers, preferably
cationic
acrylamide-based polymer, optionally in combination with cationic coagulant;
(iv) cationic polysaccharide, preferably cationic starch, in combination with
anionic step-
growth polymer, preferably anionic naphthalene-based condensation polymer;
optionally in combination with cationic coagulant;
(v) cationic chain-growth polymer, preferably cationic acrylamide-based
polymer, in
combination with anionic step-growth polymer, preferably anionic naphthalene-
based
condensation polymer, optionally in combination with cationic coagulant;
(vi) cationic chain-growth polymer, preferably cationic acrylamide-based
polymer, in
combination with cationic coagulant; and
(vii) cationic chain-growth polymer, preferably cationic acrylamide-based
polymer, in
combination with cross-linked anionic and cationic acrylamide-based polymers.
The components of drainage and retention aids can be added to the cellulosic
suspension
in conventional manner and in any order. When using a siliceous material, it
is preferred to
add a cationic polymer to the suspension before adding the siliceous material,
even if the
opposite order of addition may also be used. It is further preferred to add a
cationic
polymer before a shear stage, which can be selected from pumping, mixing,
cleaning, etc.,
and to add the siliceous material after that shear stage. When using a
cationic coagulant, it
is preferably introduced into the suspension prior to introducing cationic
polymer and
siliceous material, if used. Alternatively, the cationic coagulant and
cationic polymer can be
introduced into the suspension essentially simultaneously, either separately
or in admixture,
e.g. as disclosed in U.S. Patent No. 5,858,174, which is hereby incorporated
herein by
reference.
If the hydrotalcite according to the invention is used together with a
drainage and retention
aid, the hydrotalcite can be added to the suspension prior to or after the
addition of the
drainage and retention aid. Preferably, the hydrotalcite is added prior to the
addition of
drainage and retention aid(s). Preferably, the hydrotalcite is added to the
thick stock, or to the
thin stock, and the drainage and retention aid is added to the thin stock. The
hydrotalcite can
also be added to the re-cycled white water. If two or more drainage and
retention aids are
used, i.e. a cationic polymer together with siliceous material, e.g. silica-
based particles, and
optionally anionic organic polymer, the hydrotalcite can be added to the
cellulosic suspension
(stock) prior to, after or in between the addition of the drainage and
retention aids, or together
with any of the drainage and retention aids. The hydrotalcite may also be
added at several
locations in the process, e.g. to the thick stock and again to the thin stock
prior to the addition
of drainage and retention aid.
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The drainage and retention aid(s) according to the invention can be added to
the stock to be
dewatered in amounts which can vary within wide limits depending on, inter
alia, type and
number of components, type of cellulosic suspension, salt content, type of
salts, filler content,
type of filler, point of addition, degree of white water closure, etc.
Generally, the retention and
drainage aid(s) are added in amounts that give better drainage and/or
retention than is
obtained when not adding the components. The cationic polymer is usually added
in an
amount of at least about 0.001 % by weight, often at least about 0.005% by
weight, based on
dry cellulosic suspension, and the upper limit is usually about 3% and
suitably about 1.5% by
weight. Commonly applied addition amounts of cationic polymer are from about
0.01% up to
about 0.5% by weight. Anionic materials, e.g. siliceous materials, i.e.
anionic silica-based
particles and anionic clays of the smectite type, and anionic organic
polymers, are usually
added in an amount of at least about 0.001% by weight, often at least about
0.005% by
weight, based on dry cellulosic suspension, and the upper limit is usually
about 1.0% and
suitably about 0.6% by weight.
When using a cationic coagulant in the process, it can be added in an amount
of at least
about 0.001 % by weight, calculated as dry coagulant on dry cellulosic
suspension. Suitably,
the amount is in the range of from about 0.05 up to about 3.0%, preferably in
the range from
about 0.1 up to about 2.0%.
Furthermore, the process can also be useful in the manufacture of board from
cellulosic
suspensions having high conductivity. In such cases, the conductivity of the
suspension that
is dewatered on the wire is usually at least 1.0 mS/cm, suitably at least 2.0
mS/cm, and
preferably at least 3.5 mS/cm. Conductivity can be measured by standard
equipment such
as, for example, a WTW LF 539 instrument supplied by Christian Berner. The
values
referred to above are suitably determined by measuring the conductivity of the
cellulosic
suspension that is fed into or present in the head box of the board machine
or,
alternatively, by measuring the conductivity of white water obtained by
dewatering the
suspension.
The present invention further encompasses board making processes where white
water is
extensively recycled, or recirculated, i.e. with a high degree of white water
closure, for
example where from 0 to 30 tons of fresh water are used per ton of dry board
produced,
usually less than 20, suitably less than 15, preferably less than 10 and
notably less than 5
tons of fresh water per ton of board.
The invention further relates to a method for producing a packaging material
which
comprises providing board comprising one or more plies containing cellulosic
fibres and
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hydrotalcite, as defined herein, and subjecting the board to one or more
converting
operations selected from printing, varnishing, coating, e.g. plastics coating,
extrusion
coating, barrier coating, laminating, e.g. plastic film laminating and metal
foil laminating,
e.g aluminium foil laminating, metallizing, die cutting, i.e. stamping out
blanks, creasing,
scoring, stripping, i.e. removal or debris, blanking, i.e. separation of
blanks, foil blocking,
embossing and folding. The term "creasing", as used herein, is also referred
to as scoring
and grooving. Preferably, the method includes one or more converting
operations
comprising scoring or creasing, more preferably two or more operations
comprising scoring
or creasing, for example cutting and scoring or creasing.
The invention also relates to a packaging material comprising board which
comprises one
or more plies containing cellulosic fibres and hydrotalcite, as defined
herein, wherein it
further comprises one or more creases. The creases, also referred to as
scores, grooves
or folding lines, make it easier to fold and erect the packaging material
prior to filling. The
packaging materials of the invention can have one or more layers of plastic
film, metal foil,
e.g. aluminium, and/or barrier coating.
The invention further relates to a procedure of making a package which
comprises
providing a blank of packaging material comprising board comprising one or
more plies
containing cellulosic fibres and hydrotalcite, as defined herein; filling the
blank with a solid
or liquid content to obtain an unsealed package; and then sealing the obtained
package.
Preferably the packaging material comprises one or more grooves, creases or
scores. The
term "blank", as used herein, means an unfilled package or packaging material.
Preferably
the blank is folded and erected prior to filling. Examples of suitable methods
for sealing
include gluing and heat sealing.
Examples of suitable solid and liquid contents include solid and liquid
foodstuffs, e.g.
tomato products, soup and cream; beverages, e.g. milk, fruit juice, wine and
water;
pharmaceuticals; cosmetics; chocolates; cigarettes and tobacco. In a preferred
embodiment, the invention further comprises sterilizing the package and/or the
content.
The term "sterilizing", as used herein, means reducing the number of
microorganisms.
Examples of suitable methods and means for sterilization include heat, e.g.
rapid heating
and cooling, chemicals, e.g. hydrogen peroxide, irradiation, e.g. IR and UV
irradiation. The
filling can be made under sterile conditions.
The invention also relates to a package comprising board comprising one or
more plies
containing cellulosic fibres and hydrotalcite, as defined herein, wherein it
further comprises
a solid or liquid content. The invention further relates to uses of the
packaging material
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comprising board, which comprises one or more plies containing cellulosic
fibres and
hydrotalcite, as defined herein, for packaging of solid or liquid foodstuffs,
beverages,
pharmaceuticals, cosmetics, chocolates, cigarettes or tobacco.
5 Examples of suitable packaging of the invention include foodstuff packaging,
beverage
packaging, sterile packaging and aseptic packaging.
The invention is further illustrated in the following example which, however,
is not intended
to limit the same. Parts and % relate to parts by weight and % by weight,
respectively,
10 "unless otherwise stated.
Example 1
15 In this example, the efficiency of the invention to reduce undesirable
and/or unpleasant taste,
smell and/or odour of board was evaluated.
A chemical substance which is present in board and causes undesirable taste,
smell and/or
odour, n-hexanal, was chosen as a smelling model substance, hereinafter
"smelling
substance". The content of the smelling substance was determined by the so-
called hot
method in which a sample consisting of 2.5 g of packaging material was placed
in a vessel
which then was sealed. After shaking for 5 min and subsequent thermostating at
100 C
for 40 min, an amount of gas above the sample was retrieved and immediately
analysed in
a gas chromatograph. The content of the smelling substance in the amount of
gas was
calculated from the top area of the chromatogram. The degree of undesirable
taste, smell
and/or odour was given as the smelling substance residue, which constitutes a
percentage
share of the content of smelling substance transferred from the cellulosic
sheet or pulp
containing hydrotalcite in relation to the corresponding content transferred
from the sheet
or pulp without additives. Thus, the content of smelling substance transferred
from the
sheet or pulp without any addition of hydrotalcite or paper chemicals was
calculated.
Plies of board with and without hydrotalcite were produced on a pilot machine.
A thick
cellulosic suspension (thick stock) was used based on furnish from a liquid
packaging
board mill consisting of 30 % bleached softwood pulp and 70 % bleached
hardwood pulp.
The thick suspension was diluted with press water from bleached hardwood pulp
to provide
a consistency of 15 g/l. The obtained suspension had a pH of 7 and
conductivity of 0.8
mS/cm. The suspension was stirred and heated to 50 C. In one test, 50 kg/t
hydrotalcite
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(CC-22, Akzo Nobel Catalyst B.V.) was added to the suspension. The suspension
was
stirred for 30 minutes.
Prior to sheet formation, the following additives were added to the suspension
in the
following order: 8 % calcinated clay; I kg/t aluminium sulfate; 4 kg/t
cationic starch
(Perlbond 970); 1.6 kg/t rosin-based sizing agent (Eka Composize L44HT); 1.5
kg/t
aluminium sulfate; 1.5 kg/t sizing agent based on alkenyl ketene dimer (Eka
Keydime
28HF); 5 kg/t cationic starch (Perlbond 970); and 2.5 kg/t silica sol (Eka NP
442). The
suspension was dewatered to form a sheet having a basis weight of
approximately 90
g/mZ.
Directly after production, A4 sized sheets were wrapped in aluminium foil and
sealed in air
tight plastic bags. After two weeks, the sheet was analysed with gas
chromatography for
the smelling substance. Table 1 shows the amount of the smelling substance
after storage
for two weeks.
Table 1
Test No. Hydrotalcite Smelling Substance
[kg/t] [ng/ml]
1 0 168
2 50 110
Example 1 shows that the invention resulted in a 35 % reduction of the content
of the volatile
smelling substance in the gas phase.
Example 2
Board was made as described in Example 1 except that the amount of
hydrotalcite added
was different. The board obtained was analysed for filler content, also
referred to as ash
retention. Table 2 shows the results.
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Table 2
Test No. Hydrotalcite Filler [%]
[kg/t]
1 0 7.6
2 10 8.2
Table 2 shows that the filler level was higher when adding hydrotalcite in the
process.
Example 3
In this example, sizing performance was evaluated. A cellulosic suspension
from a liquid
packaging board mill was treated with hydrotalcite having the 3R2 stacking (CC-
22, Akzo
Nobel Catalyst B.V.) and with talc (Finntalc P05, Omya) respectively. Sizing,
drainage and
retention aids were added and hand sheets were made (SCAN-C 26:76). Sizing of
the
sheets was measured as Cobb 60 values (SCAN-P 12:64).
A thick cellulosic suspension (thick stock) was used based on furnish from a
liquid
packaging board (LPB) mill consisting of bleached softwood and hardwood pulp.
The
suspension was stirred and heated to 50 C. Hydrotalcite or talc was added to
the
suspension which was stirred for 30 minutes. The thick suspension was then
diluted with
tap water to a consistency of 5 g/L. The obtained suspension had a pH of 8 and
conductivity of 0.7 mS/cm. Before sheet making, 0.3 kg/ton of dry pulp of AKD
(Keydime
C223, Eka Chemicals), 8 kg/ton of dry pulp of cationic starch (Perlbond 970)
and 0.5
kg/ton of dry pulp of silica-based particles (Eka NP 590, Eka Chemicals) were
added. The
sheets had a basis weight of approximately 73 g/m2. Table 3 shows the sizing
results
obtained by addition of different amounts of talc and hydrotalcite to the
liquid packaging
board furnish.
Table 3
Test No. Talc [kg/t] CC-22 [kg/t] Cobb 60
1 0 0 40
2 1 44
3 5 60
4 1 35
5 5 34
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The sizing performance was improved when using hydrotalcite over talc. The
cellulosic
sheet containing bleached pulp and hydrotalcite can be used as a ply of single
ply board
and multi ply board, e.g. top and/or back ply.
Example 4
Sizing performance was evaluated with higher additions of hydrotalcite (CC-22,
Akzo Nobel
Catalyst B.V.) and talc (Finntalc P05, Omya), respectively. Hand sheets were
made and
sizing performance was measured as Cobb 60 (SCAN-P 12:64) values.
A thick cellulosic suspension was used based on furnish from a LPB mill
consisting of
hydrogen peroxide bleached softwood and hardwood sulphate pulp at -4%
consistency.
This suspension was stirred and heated to 50 C. Hydrotalcite or talc was added
to the
suspension which was allowed to stand for 20 minutes. The thick suspension was
then
diluted with bleach filtrate to -3.9 g/l consistency. To the furnish AKD, 1.6
kg/t rosin size,
1.6 kg/t alum, 5.0 kg/t cationic starch and 0.35 kg/t silica-based particles
(Eka NP 590, Eka
Chemicals) were added before making hand sheets (Rapid-Kothen former). The
sheets
had a basis weight of approximately 100 g/m2. Table 4 summarized the sizing
results
obtained by sizing the liquid packaging board furnish.
Table 4
Test No. AKD [kg/t] Talc [kg/t] CC-22 [kg/t] COBB 60
1 0 0 0 258
2 0.5 0 0 250
3 0.8 0 0 131
4 1 0 0 59
5 1.4 0 0 39
6 0.5 5 0 211
7 0.8 5 0 115
8 1 5 0 61
9 1.4 5 0 39
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0.5 0 10 198
11 0.8 0 10 87
12 1 0 10 45
13 1.4 0 10 33
Table 4 shows that the sizing perFormance was improved (lower Cobb 60 values)
using
hydrotalcite compared to talc. The cellulosic sheet containing bleached pulp
and
hydrotalcite can be used as a ply of single ply board and multi ply board,
e.g. top and/or
5 back ply.
Example 5
This example was made in a de-inked pulp (DIP) mill. An aqueous pulp
suspension from
10 the DIP mill was treated with hydrotalcite (CC-22, Akzo Nobel Catalyst
B.V.). The turbidity
of the pulp filtrate was then measured.
The pulp suspension used was a taken between the disc filter and the screw
press in the
DIP plant. The pulp suspension had a consistency of -7%, and was diluted with
tap water
to -4.2%. This suspension pulp was stirred and heated at 50 C. The
hydrotalcite was
added to the pulp suspension which was allowed to stand for 30 minutes. The
pulp
suspension was then filtrated through a GF/A glass fibre filter (-2 pm hole
diameters). The
filtrate was analysed for turbidity in a Hach 2100P turbidity meter. Table 5
shows the
results.
Table 5
Test No. CC-22 [kg/t] Turbidity [NTU]
1 0 71.8
2 2 63.5
3 5 42.3
The turbidity of the filtrate improved (decreased) when mixing de-inked pulp
with
hydrotalcite before filtering. A cellulosic sheet containing DIP and
hydrotalcite can be used
as a ply of multi ply board, e.g. undertop and/or middle ply.
