Note: Descriptions are shown in the official language in which they were submitted.
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PIGMENT COMPOSITION
The present invention relates to a slurry or dispersion of pigment particles
comprising as dispersant an amphiphilic polymer and the preparation thereof.
The
invention further relates to a coating colour composition, a process for its
preparation, a
process for preparing coated paper or board, and paper or board obtainable by
the
process.
Paper is frequently coated in order to impart certain desired properties to
the
paper. For example, a surface suitable for printing or having improved gloss
characteristics is often desirable.
It is often desired that the paper surface should exhibit a certain degree of
gloss
in order to be aesthetically pleasing, and also from a printing point of view.
Gloss can be
imparted mechanically by calendering of the paper. However, during calendering
the bulk
of the paper will be reduced, which leads to a less rigid paper structure that
is more pliant
and flexible. This secondary effect of extensive calendering in order to
obtain gloss is
however not always desired.
Conventional coating colour compositions for paper usually comprise a slurry
or
dispersion of pigment particles together with various additives. The coating
colour
composition is usually prepared by first providing a dispersion or slurry of
pigment
particles together with one or more dispersants, and then mixing this
dispersion or slurry
with additives such as a binder (e.g. latex or starch) and rheological agents
such as co-
binders or thickening agents (e.g. CMC). Additionally, optical brightening
agents can be
included, and other conventionally used additives such as, pH adjusting
agents, foam
depressants, lubricants, preservatives, insolubilisers, etc.
The use of a high solid substance content coating colour normally leads to
less
energy being required for the drying of the coated paper and possibly less
tendency of
migration of water and binder into the paper web. The total coating operation
will thereby
be faster.
The pigment particles are generally small, weakly charged particles, e.g. with
an
average diameter from about 0.2 to about 1 pm. When suspended in water, the
particles
will have a tendency to aggregate due to the attractive forces if these are
stronger than
the repulsion forces. Thus, when the solid substance level increases in the
pigment
slurry, agglomeration or other problems of dispersing the pigments are likely
to occur.
The addition of one or more dispersants is therefore necessary. Commonly used
dispersants are predominantly anionic, charged polymers, such as polyacrylic
acids
(PAA) and polyphosphates. Typically, the addition of dispersant will lower the
viscosity to
a certain point, after which any further addition of dispersant, due to the
inherent viscosity
of the dispersant, will lead to a significantly increased viscosity. Thus,
there will generally
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be an optimum concentration of the dispersant, corresponding to the minimum
viscosity
of the pigment slurry for a given solid substance level thereof. For a given
dispersant, this
concentration will be mostly dependent on the type of pigment used.
Furthermore, if, for example, a highly charged dispersant (e.g. PAA) is used
in
large amounts, any coated broke obtained will consequently contain high levels
of heavily
charged species, which, when re-introduced at the wet end of the paper
machine, will
interfere with the function of flocculants, and other agents used therein.
Many polymers in solution, especially electrically non-charged ones, exhibit a
temperature dependent viscosity in such a way that the viscosity of the
solution increases
significantly above a certain temperature and the polymer finally starts
gelling or
precipitating due to associations of the polymer chains. The significantly
increased
viscosity is explained by hydrophobic interaction between the polymer chains
caused by
gradual destruction of the water shell around the polymers. As the temperature
is
elevated further, the hydrogen bonds are successively eliminated, and water
molecules
are thereby released. Larger aggregates of associated polymer chains are also
formed,
minimising the total area of the polymer chains exposed to water. In the case
of non-
charged polymers, the temperature at which the significant viscosity increase
starts, can
be raised by the addition of surfactants so the non-charged polymer molecules
will
behave as charged molecules by virtue of the surfactants ions attracted
thereto and no
significant viscosity increase will occur below, for example, 100 C.
It has been disclosed in US 6117491 and US 6123996 to use polymers, whose
viscosity increase at heating, as a thickening agent in paper coating
compositions. Similar
compositions are also disclosed in EP-A-359349.
It is an object of the invention to provide a dispersion or slurry of pigment
particles that has low viscosity but high solids content.
It is another object of the invention to provide a coating colour compositions
based on such a dispersion or slurry, that immobilises rapidly on a paper or
paperboard
surface.
It is still another object of the invention to provide a process of preparing
coated
paper or paperboard having a surface suitable for printing or high gloss
characteristics,
without, for example, extensive calendering.
One aspect of the present invention concerns an aqueous slurry or dispersion
of
pigment particles comprising as dispersant an amphiphilic polymer at least
partly
adsorbed to the pigment particles, wherein the slurry or dispersion exhibits a
temperature
dependent viscosity in such way that the viscosity increases at least with a
factor of about
2, preferably at least with a factor of about 5, most preferably at least with
a factor of
about 10 when the temperature is raised from about 20 up to about 100 C,
preferably
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from about 30 up to about 80 C, most preferably from about 40 up to about 70
C.
Continued heating to higher temperatures finally leads to destabilisation and
intense
aggregation of the system.
In accordance with one aspect of the present invention, there is provided an
aqueous slurry or dispersion of pigment particles comprising as dispersant an
amphiphilic polymer at least partly adsorbed to the pigment particles, wherein
the slurry
or dispersion exhibits a temperature dependent viscosity in such way that the
viscosity
increases at least by a factor of 2 when the temperature is raised from 20 up
to 100 C
and wherein the amphiphilic polymer is selected from the group consisting of
acrylic
ester copolymers having pendant hydrophobic chains, hydrophilic chains
comprising
alkylene oxide groups and exhibiting phosphonic acid or carboxylic acid as
anions,
hydrophobically modified carboxymethyl cellulose, and polyurethane copolymers
exhibiting at least one carboxylic acid residue as an anionic moiety.
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The solids content of slurry or dispersion is suitably above about 60 wt%,
preferably above about 70 wt%. The upper limit is only set by the viscosity,
which below
about 20 C, preferably below about 30 C should be sufficiently low for the
slurry or
dispersion to be possible to pump. Below about 20 C the Brookfield viscosity
is preferably
from about 50 to about 1000 mPas, most preferably from about 50 to about 200
mPas. In
practice, it may then be difficult to provide useful slurries or dispersions
with a solids
io content exceeding about 80 wt%.
The pigment particles are suitably weakly charged and preferably inorganic,
such as clay (e.g. kaolin), TiO2, calcium carbonate, or mixtures thereof. By
the use of
clay, gloss can generally more easily be imparted to the paper. Calcium
carbonate, on
the other hand, is less expensive and Inherently often exhibits a brighter
colour. Calcium
carbonate can, for example, be used in the form of precipitated calcium
carbonate (PCC)
or ground calcium carbonate (GCC) e.g. ground lime stone, marble or chalk. The
present
invention has been found to be particularly favourable when PCC is used as
pigment
particles, which particles generally are difficult to disperse due to their
narrow particle size
distribution.
The average particle diameter of the pigment particles is suitably from about
0.1
to about 2 m, preferably from about 0.2 to about I Jim.
The term dispersant as used herein refers to chemicals participating in the
defloccuiation process of the pigment particles. Thus, the dispersant reduce
the energy
necessary to separate the pigment Into discrete particles, provide stability
that prevents
agglomeration upon storage and decrease the.viscosity at high solids content.
In contrast
to chemicals usually classified as surfactants, the dispersants preferably
have only little
effect on surface tension, only little wetting action, low foaming, but high
deflocculation
power. In contrast to thickening agents that normally are totally dissolved in
the water, the
dispersants of this invention are at least partially adsorbed to the pigment
particles.
The amphiphilic polymer used as dispersant preferably has an average
molecular weight from about 2000 to about 200000, more preferably from about
3000 to
about 100000, and most preferably from about 5000 to about 20000.
The dispersants to be used in the invention have different structure from PAA,
and are, as opposed to the hydrophilic PAA, amphiphilic polymers, i.e.,
contain both
hydrophilic and hydrophobic groups. The hydrophilic groups are preferably
selected from
charged anionic moiety, PEOIPPO (polyethylene oxidelpolypropene.o)ide), or
mixtures
there of. In a preferred class of polymers at least some of the hydrophilic
groups are
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charged, which groups most preferably are selected from inorganic or organic
acidic
residues such as sulphonates, phosphonates, carboxylates, or mixtures thereof.
Preferred polymers are copolymers, comprising hydrophilic and hydrophobic
residues,
which residues preferably are alternating along a backbone, while hydrophilic,
preferably
charged, anchoring groups are positioned along the backbone. The hydrophobic
residues
are preferably C4 to C20, most preferably C4 - C18 carbon chains. The
hydrophilic residues
suitably comprise PEO/PPO chains or segments along the polymer backbone. The
hydrophilic residues preferably comprise from about 5 to about 50 EO/PO units,
most
preferably from about 20 to about 50 EO/PO units.
It has been found that those amphiphilic polymers of the invention that per se
do
not exhibit a significant viscosity increase between about 20 to about 100 C,
do so when
partially adsorbed to the pigment particles. If the polymer is charged, it is
believed that
some of the charges are neutralised by adsorbing to the surface of the pigment
particles,
while the polymer will retain its dispersing action by virtue of residual
charges. Thus,
adsorption to the surface through partial electrical neutralisation, and
remaining electrical
charges on the pendant chains is a feature of the preferred polymers of the
invention.
However, also amphiphilic polymers that per se exhibit a significant viscosity
increase
between about 20 to about 100 C can be used in the invention provided they are
effective
as dispersants and exhibit such temperature dependent viscosity properties
also when at
least partially adsorbed to the pigment particles.
At temperatures below about 20 C, the hydrophilic and hydrophobic tails of the
polymers are reaching out from the surface of the pigment particle, thereby
creating
electrosteric or steric stabilisation. By virtue of the latter form of
stabilisation, the polymers
of the present invention are believed to be less sensitive to the presence of
salt than
polymers only relying on an action of stabilisation via electrical charges.
According to a preferred embodiment, the dispersing agent is an acrylic ester
copolymer having pendant hydrophobic chains, hydrophilic chains, and
exhibiting
phosphonic acid or carboxylic acid as anions. The pendant hydrophobic chains
are
0 preferably C4 - C20, and most preferably C4 - C18 carbon chains. Said
hydrophilic chains
preferably comprise alkylene oxide groups, preferably EO (ethylene oxide)
and/or PO
(propylene oxide) groups, more preferably 2 to 50, and most preferably 10 - 30
EO and/or
PO groups. It is preferred that the alkylene oxide groups are only EO groups,
or
essentially only EO groups. Phosphonate groups in the polymer will give rise
to a strong
adsorption to calcium carbonate particles.
According to another preferred embodiment, the dispersant is selected from
0 hydrophobically modified carboxymethyl cellulose (HM-CMC). Particularly
preferred HM-
CMC polymers are those obtainable by a process comprising reacting an alkali
metal
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cellulose with at least three alkylating reagents A, B, and C;
- one or more reagents A being selected from the group of haloacetic acids,
alkali metal
haloacetates, alkali metal vinyl sulfonates, and vinyl sulfonic acid;
- one or more reagents B having the formula R'-(OCH2CH(R2))n-P, wherein R1
5 represents a C2-C7 group, R2 is hydrogen or a methyl group, n is'0-2, and P
represents a
glycidyl ether group, a 3-halo-2-hydroxypropyl ether group, a 1,2-epoxy group,
or a
halide;. and
- one or more reagents C having the formula R3-(OCH2CH(R2))m-P wherein R3
represents a C$-C30 group, m is 0-10, and R2 and P have the meaning as
described
to above. Such HM-CMC polymers are described in more detail in WO 98/56825.
Alternatively copolymers based on polyurethane chemistry can be used as
dispersants, such as those described in US 4096127 or US 4777224, i.e.
polyurethane
copolymers exhibiting at least one carboxylic acid residue as an anionic
moiety. As a
further alternative, copolymers based on alfa-olefin/maleic acid anhydride
chemistry can
be used as dispersants, such as those described in US 4931197, and especially
in
Example 1 therein, i.e. alpha olefin/maleic acid copolymer exhibiting at least
one
carboxylic acid residue as an anionic moiety.
The polymers used as dispersant can also be based on any chemistry being
able to create copolymers exhibiting similar hydrophobic and hydrophilic parts
wherein
the anionic anchoring group may comprise any suitable acidic functionality,
e.g. natural
polymers like carbohydrates modified by introducing charged groups along the
backbone
or grafted with hydrophobic and hydrophilic tails, as exemplified by the
earlier mentioned
hydrophobically modified carboxymethyl cellulose.
It is to be understood that the slurry or dispersion may comprise one or more
amphiphilic polymer as described above, optionally in combination with one or
more other
dispersing agents.
The slurry or dispersion suitably has a solids content from about 40 to about
80
wt%, preferably from about 60 to about 75 wt%, of which the main part,
preferably
substantially all, is made up of pigment particles. It- suitably comprises, as
dispersant,
from about 0.1 to about 4 wt% based on dry pigment, preferably from about 0.1
to about
2 wt% based on dry pigment of one or more amphiphilic polymer as described
above.
The water content is suitably from about 20 to about 60 wt% based on dry
pigment,
preferably from about 25 to about 40 wt% based on dry pigment. The content of
other
component is preferably less than about 0.5 wt% based on dry pigment, most
preferably
less than about 0.1 wt%.
The invention further concerns a process for the - preparation of a slurry or
dispersion as described above comprising a step of mixing pigment particles,
water and
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an amphiphilic polymer that becomes at least partly adsorbed to the pigment
particles to
obtain a slurry or dispersion exhibiting a temperature dependent viscosity as
earlier
described.
The invention also concerns a coating colour composition comprising a slurry
or
dispersion as described above and at least one additive selected from the
group
consisting of binders, co-binders, rheology modifiers, foam depressants,
optical
brightening agents, pH adjusting agents, lubricants, preservatives and
insolubilisers,
wherein the coating colour composition exhibits a temperature dependent
viscosity as
defined in the above description of the slurry or dispersion. Thus, the
viscosity increases
to at least by a factor of about 2, preferably at least by a factor of about
5, most
preferably at least with a factor of about 10 when the temperature is raised
from about 20
up to about 100 C, preferably from about 30 up to about 80 C, most preferably
from
about 40 up to about 70 C.
As for the slurry or dispersion per se, as described above, the properties of
exhibiting a significant viscosity increase between about 20 and about 100 C
depends on
the presence of the amphiphilic polymer as dispersant that is at least
partially adsorbed to
the pigment particles.
The solids content of the coating colour composition is suitably above about
50
wt%, preferably above about 60 wt%. The upper limit is only set by the
viscosity, which
below about 20 C, preferably below about 30 C should be sufficiently low for
the
composition to be applied to the surface of paper or paperboard, Below about
20 C the
Brookfield viscosity is preferably from about 50 to about 5000, most
preferably from about
50 to about 3000 mPas. In practice, it may then be difficult to provide useful
slurries or
dispersions with a solids content exceeding about 80 wt%.
The amphiphilic polymer used as dispersant is preferably present in the
coating
colour composition in an amount, based on 100 pph (part per hundred) pigment
particles,
from about 0.05 to about 10 pph, preferably from about 0.1 to about 5 pph,
most
preferably from about 0.1 to about 2 pph. If the solids content is low, for
example below
about 60 wt%, also the amount of dispersant can in some cases be lower than
the above
figures, while higher amounts sometimes may be required for compositions of
high solids
content. A suitable amount of dispersant to be included can in each case be
established
by person skilled in the art merely by routine experimentation.
The compositions preferably, comprise from about 5 to about 25 pph of one or
more binders. Any conventional binder can be used, such as starch, latex,
protein,
polyvinyl alcohol, and mixtures thereof.
The compositions preferably comprise from about 0.1 to about 5 pph of one or
more co-binders or rheology modifiers. Any conventional co-binder can be used,
such as
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carboxy methyl cellulose (CMC), other cellulose derivatives, polyvinyl
alcohol, sodium
alginate, alkali-swelling polyacrylates, and mixtures thereof.
The compositions preferably comprise from about 0.1 to about 5 pph of
other additives. Any conventional additive can be used, such as foam
depressants,
dispersants (in addition to the amphiphilic polymer at least partly adsorbed
to the pigment
particles), optical brightening agents (OBA), lubricants, pH adjusting agents,
insolubilisers, etc. All these additives are conventional and, can easily be
selected by
those skilled in the art.
A particularly preferred composition of the invention comprise, based on 100
io parts of pigment and calculated on a dry solids content on a weight basis:
pigments, 100
pph; amphiphilic polymer as dispersant, from about 0.1 to about 4 wt pph, most
preferably from about 0.1 to about 2 pph; binders, from about 5 to about 25
pph, most
preferably from about 10 to about 15 pph; co-binders or rheology modifiers,
from about
0.1 to about 4 pph, most preferably from about 0.5 to about 2 pph; other
additives, from
about 0.1 to about 5 pph, most preferably from about 0.1 to about 2 pph.
The invention further concerns a process for the preparation of a coating
colour
composition of the invention comprising the step of mixing a slurry or
dispersion of
pigment particles as earlier described with at least one additive selected
from the group
consisting of binders, co-binders, rheology modifiers, foam depressants,
optical
brightening agents, pH adjusting agents, lubricants, preservatives and
insolubilisers.
The invention further concerns a process for the preparation coated paper or
paperboard comprising the steps of applying a coating colour composition as
described
above to a paper or paperboard web followed by bringing said coating colour
composition
to a temperature sufficient for increasing the viscosity at least with a
factor of about 2,
preferably at least with a factor of about 5, most preferably at least with a
factor of about
10, which temperature suitably is above about 20 C, preferably above about 30
C, most
preferably above about 40 C. Thereby the coating will be rapidly immobilised
on the
paper or paperboard, inhibiting any flow of the coating ingredients.
The amount applied is not critical and can be any conventionally used amount,
such as for example from about 1 to about 50 g/m2, preferably from about 3 to
about 25
g/m2, calculated as dry solids per side of the paper or paperboard.
Coating can be performed either on machine or off machine. In either case
different types of coating methods can be used, some of which are more
suitable in the
case of off-machine coating, and others in the case of on-machine coating. For
example,
blade coating is conveniently used in both cases, whereas air knife coating,
roll coating,
size press coating and cast coating are normally only used in on machine
coating. The
predominantly used method, however, is blade coating.
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During coating, the colour is normally initially applied to the paper surface
in a
considerable excessive amount, for example by passing the paper web on a roll
into a
tray containing the coating colour, such as by means of a roll applicator.
Alternatively, a
jet applicator can be used. In the case of blade coating, an excessive amount
of coating
colour is removed from the paper by the scraping or wiping action of a blade,
normally of
metal, pressing continuously against the surface of a roll or cylinder. A
number of
different blade coating units have been developed,.the principle underlying
the method of
blade coating, however, remains essentially the same. The coating colour of
the present
invention can be used- in all conventional coating methods, both on and off
machine, of
1o which blade coating and size press coating, especially blade coating, are
preferred.
After coating, the paper is dried, which in the case of on machine coating
normally is accomplished in the drying section of the machine. Conventionally
used
means of drying in the drying section, such as infra red radiation, hot air,
heated cylinders
or any combination thereof, may be used. The means of drying is not critical
to the
invention. The temperature for the viscosity to increase significantly,
resulting in
immobilisation of the coating colour, is preferably reached when the paper is
subjected to
heat for drying thereof, for example by means of infrared radiation.
By using the specified polymers of the invention as dispersant to the pigment
particles, it has unexpectedly been found that the gloss can be markedly
improved. Other
20. qualities are also unexpectedly improved. For example, a more even
distribution of the
binder of the colour throughout the surface of the coated paper is obtained,
leading to a
reduced mottling phenomenon. The colour density obtained when the paper is
printed is
also increased. An improved cohesion within the applied and dried coating has
also been
observed. Thus, reduced cracking of the coating has been observed when the
paper of
the invention is folded or creased.
Many polymers of the invention when adsorbed onto pigment particles (as
opposed when in solution in absence of such particles) may show an increase in
the
storage modulus (G') when heating by a factor of about 100 or 1000 or even
10000 or
more when measured on a rheometer at low oscillatory shear. At that point, the
water
phase is basically expelled from the coating colour creating a gel-like
structure.
Furthermore, by using polymers as dispersants according to the invention, the
coating can be brought to immobilise essentially instantaneously on a paper
surface
when heated. Accordingly, the coating systems of the invention can be designed
to
immobilise at a desired temperature and thereby customised to each individual
paper
machine.
Moreover, the phenomenon of mottling, which is partly due to migration of
binder
and pigments from the coating into the base paper after coating, and any
additional
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migration also in opposite direction during drying of the coated paper, can be
substantially reduced by use of the coating colour of the present invention.
In some cases it might also be possible to prepare coating colour compositions
with a high solids substance level, thus requiring a shorter period of time
for drying the
paper after coating thereof, which in turn would speed up the manufacturing
process and
lead to a reduced energy consumption. However, at such high solids substance
levels, in
combination with high velocity of the paper machine, it must be secured that
shear
thickening of the colour is avoided when high shear forces are experienced.
As mentioned above, it is possible to prepare paper or paperboard with better
1o properties than with prior art method. Thus, the invention also concerns
paper or
paperboard obtainable by the method described above.
The invention will now be further described through the following Examples.
DispexTM, comprising a conventional anionic, sodium polyacrylate, is used as
the
reference dispersant herein. Calculated on a weight basis, higher amounts are
required
of the dispersants of the invention in order to reach the same low viscosity.
Calculated on
a charge basis the dispersants of the invention are more effective. In the
examples
coating was performed both in a pilot-scale coating machine as well as in a
laboratory
coater. If not otherwise stated all percentages and parts refer to percent and
parts by
weight.
Example 1 (comparative): A coating colour of a total solids content of 60 wt%
was prepared by uniformly blending 3.38 g (0.9 %) of a 40% aqueous solution of
a
sodium polyacrylate dispersing agent (DispexTM N40 manufactured by Ciba
Specialty
Chemicals), 86.32 g of deionized water, 0.1 g of antifoam (CoatosilTM 1378
manufactured
by Witco), 150 g of scalenohedral precipitated calcium carbonate manufactured
by Huber
Engineered Materials, 33.33 g (11 %) of a 50% dispersion of SB latex (Baystal
P7105
manufactured by Eka Polymer Latex) and 8.40 g (0.6 %) of a 10% aqueous
solution of
CMC (FinnfixTM 10 manufactured by Noviant).
Example 2 (comparative): A coating colour of a total solids content of 60 wt%
was prepared by uniformly blending 1.08 g (0.15 %) of a 10% aqueous solution
of a
sodium polyacrylate dispersing agent (DispexTM N40 manufactured by Ciba
Specialty
Chemicals), 48.98 g of deionized water, 0.1 g of antifoam (CoatosilTM 1378
manufactured
by Witco), 72 g of rhombohedral precipitated calcium carbonate manufactured by
Huber
Engineered Materials, 16.06 g (11 %) of a 50% dispersion of SB latex
(BaystalTM P7105
manufactured by Eka Polymer Latex) and 4.02 g (0.6 %) of a 10% aqueous
solution of
CMC (FinnfixTM 10 manufactured by Noviant).
Example 3: A coating colour of a total solids content of 60 wt% was prepared
by
uniformly blending 30.0 g (2 %) of a 10% aqueous solution of a styrene acrylic
butyl ester
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comb copolymer containing both PEO/PPO combs and phosphonic acid as anchoring
group with a molecular weight distribution between 5000 and 30000 g/mol as
dispersing
agent, 62.68 g of deionized water, 0.1 g of antifoam (CoatosilTM 1378
manufactured by
Witco), 150 g of scalenohedral precipitated calcium carbonate manufactured by
Huber
5 Engineered Materials, 33.33 g (11 %) of a 50% dispersion of SB latex
(Baystal P7105
manufactured by Eka Polymer Latex) and 8.48 g (0.6 %) of a 10% aqueous
solution of
CMC (FinnfixTM 10 manufactured by Noviant).
Example 4: A coating colour of a total solids content of 60 wt% was prepared
by
uniformly blending 9.90 g (1.1 %) of a 17% aqueous solution of a polyurethane
based
1o copolymer containing both PEO segments, C16 alkyl groups and carboxylic
acid as
anchoring group (as described in US 4777224) as dispersing agent, 87.30 g of
deionized
water, 0.1 g of antifoam (CoatosilTM 1378 manufactured by Witco), 150 g of
rhombohedral
precipitated calcium carbonate manufactured by Huber Engineered Materials and
33.33 g
(11 %) of a 50% dispersion of SB latex (BaystalTM P7105 manufactured by Eka
Polymer
Latex).
Example 5: A coating colour of a total solids content of 60 wt% was prepared
by
uniformly blending 2.74 g (0.75 %) of a 20% colloidal dispersion of a
polyurethane
copolymer (JetsizeTM API 5 manufactured by Eka Chemicals), 48.03 g of
deionized water,
0.1 g of antifoam (CoatosilTM 1378 manufactured by Witco), 72 g of
rhombohedral
precipitated calcium carbonate manufactured by Huber'Engineered Materials,
16.06 g (11
%) of a 50% dispersion of SB latex (BaystalTM P7105 manufactured by Eka
Polymer
Latex) and 4.04 g (0.6 %) of a 10% aqueous solution of CMC (FinnfixTM 10
manufactured
by Noviant).
Example 6 (comparative): A coating colour of a total solids content of 60 wt%
was prepared by uniformly blending 0.96 g (0.15 %) of a 10% aqueous solution
of a
sodium polyacrylate dispersing agent (DispexTM N40 manufactured by Ciba
Specialty
Chemicals), 2.43 g (0.75 %) of a 20% colloidal dispersion of a polyurethane
copolymer
(JetsizeTM AP15 manufactured by Eka Chemicals), 50.78 g of deionized water,
0.1 g of
antifoam (CoatosilTM 1378 manufactured by Witco), 64 g of rhombohedral
precipitated
calcium carbonate manufactured by Huber Engineered Materials, 14.28 g (11 %)
of a
50% dispersion of SB latex (BaystalTM P7105 manufactured by Eka Polymer Latex)
and
3.60 g (0.6 %) of a 10% aqueous solution of CMC (FinnfixTM 10 manufactured by
Noviant).
Example 7 (comparative): A coating colour of a total solids content of 60 wt%
was prepared by uniformly blending 0.56 g (0.3 %) of a 40% aqueous solution of
a
sodium polyacrylate dispersing agent (DispexTM N40 manufactured by Ciba
Specialty
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Chemicals), 43.46 g of deionized water, 0.1 g of antifoam (CoatosilTM 1378
manufactured
by Witco), 75 g of kaolin clay (SpeswhiteTM manufactured by Imerys), 16.67 g
(11 %) of a
50% dispersion of SB latex (BaystalTM P7105 manufactured by Eka Polymer Latex)
and
4.18 g (0.6 %) of a 10% aqueous solution of CMC (FinnfixTM 10 manufactured by
Noviant).
Example 8: In this example, the temperature dependent behaviour of the PCC
colour from Example 3 and a conventional PCC colour (Comp. Example 1), were
examined using a rheometer model UDS200 from PAAR Physica. The temperature
tests
were performed between 25 and 85 C within the linear viscoelastic region.
io Table 1. The storage modulus at various temperatures for coatings from
Comparative
Example 1 and Example 3.
Coating of Comp. Example I Coating of Example 3
Temperature ( C) Storage modulus, Temperature ( C) Storage modulus,
G' (Pa) G' (Pa)
25 155 25 11
35 47 35 13
45 47 45 22
55 64 55 171
65 68 65 2110
75 64 75 4820
85 81 85 9010
An aqueous solution of I wt% of the polymer used as dispersing agent in
Example 3, on
the other hand, did not show any visual precipitation during a temperature
increase from
20 - 95 C, i.e. no clouding was observed.
Example 9: In this example, a PCC colour containing a polymer of the invention
from Example 3 and a conventional PCC colour (Comp. Example 1) were each
applied to
a sheet of paper according to the conditions shown in table 2 and the physical
properties
of the coated paper sheets were measured after drying.
Table 2. Application conditions.
Application Helicoater, 1000 rpm
Drying IR- heating and hot air
Coating amount 14 g/m
Calendering Kleinenefers-calendar, 200 m/min, 80 C, 200 kN/m
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The surface roughness (PPS-10) was measured according to SCAN-P 21. The
gloss was measured using a micro-gloss 75 meter from BYK-Gardner. The colour
density is a mean value of yellow, cyan, magenta and black measured on ink jet
print
using a GRETAG D19C densitometer from GretagMacbeth. The contact angle was
measured after 10 seconds using a DAT 1100 from Fibro. The variation of latex
on the
surface has been analysed using a Chromatoscanner from Shimadzu, Japan. High
value
represents unevenly latex distribution. Mottling, uneven ink absorption at
offset print, was
also measured. A high value represents uneven ink absorption. The results of
testing are
shown in table 3.
1o Table 3. Physical properties of coated paper sheets.
None Calendered
calendered
PPS-10 Gloss Colour Contact Standard Mottling
Dispersant o density angle after deviation in
(pm) unit (/o) 10 sec ( ) amount of latex 1-8 mm
Comp. 4.62 38.7 0.85 64 4853 5.09
Example 1
Example 3 3.76 42.0 0.90 81 2875 4.66
Example 10: In this example, the temperature dependent behaviour of PCC colour
of Example 4 and a conventional PCC colour (Comp. Example 1) were examined
using a
rheometer model UDS200 from PAAR Physica. The temperature tests were performed
between 25 and 85 C within the linear viscoelastic region.
Table 4. The storage modulus at various temperatures for Comp. Example 9 and
Example 4.
Comp. Example 1 Example 4
Storage modulus, Temperature ( Storage modulus,
Temperature ( C) G, (Pa) C) G' (Pa)
155 25 81
47 35 246
47 45 1060
64 55 2740
68 65 6320
64 75 9700
81 85 15000
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Example 11: In this example, the PCC colour of Example 5, the PCC colour of
Comp. Example 6, containing a combination of the polymer of the invention and
a
conventional dispersing agent, and a conventional PCC colour from Comp.
Example 2,
were compared. The colours were each applied to a sheet of paper using a draw-
down
coating applicator and the gloss value of the coated paper sheets were
measured after
drying and soft calendering. The results of the testing are shown in table 5.
The gloss was measured using a micro-gloss 75 meter from BYK-Gardner: The
contact angle was measured after.l0 seconds using a DAT 1100 from Fibro. The
colour
density is a mean value of yellow, cyan, magenta and black measured on ink jet
print
using a GRETAG DI9C densitometer from GretagMacbeth.
Table 5. The gloss value of coated paper.
Designation Gloss value for soft Colour Contact angle at
calendered paper density 10 sec ( )
Comp. Example 2 34 1.13 91
Example 5 39 1.14 95
Comp. Example 6 35 1.10 84
As can be seen from Table 5, although a polymer of the invention was used in
Comp.
Example 6, (a colloidal dispersion of a polyurethane copolymer (JetsizeTM AP15
manufactured by Eka Chemicals)), a coating having the desired properties was
not
obtained. This is assumed to be due to that the desired action of the polymer
used in the
invention is prevented by the presence of a species interfering with the
mechanisms
underlying the achievement of such action. As mentioned above, said action is
presently
believed to be based on the association of the polymer of the invention with
the pigment
particles, and thus, the desired result is likely to be prevented from being
obtained by the
presence of the conventional.polyacrylate dispersing agent in the colour.
Accordingly, it is
preferred to only use polymers of the invention as dispersing agent in the
coating colour
of the invention.
Example 12: In this example, a PCC colour of the invention (Example 3) and a
conventional PCC colour (Comp. Example 1) were each applied to a plastic film.
The
coating layer could be separated from the film, the mechanical properties was
measured
using an Alwetron TH1 from Lorentzon & Wettre. The elongation and the tensile
energy
absorption were measured.
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Table 6. The elongation of coated layer.
Designation Elongation (%) Tensile energy absorption (J/m )
Comp. Example 1 0.6 0.6
Example 3 2.9 1.8
Example 13: In this example, the PCC colour of Example 3 of the invention and
the conventional PCC colour of Comp. Example 1, were each applied to a sheet
of paper
as in Example 9. After drying and calendering, the coated paper sheets were
folded and
the foldings examined. The coating of the invention exhibited a markedly
reduced number
of cracks, as compared to the conventional coating.
Example 14: In this example, paper was coated using a draw-down coating
applicator, and the gloss obtained with the coating colour of Example 3 of the
invention
1o was compared to that of a conventional kaolin clay colour (Comp. Example
7), using
Dispex as the dispersant, in which colour the PCC had been replaced with clay
in order to
improve the gloss. After light calendering, the coated paper using the PCC
containing
colour exhibited higher gloss compared to the coated paper using the clay
containing
colour.
Table 7. Gloss value of coated paper
Designation Gloss unit
Example 3 44.3
Comp. Example 7 40.7
Example 15: A coating colour of a total solids content of 60 wt% was prepared
by uniformly blending 0.42 g (0.30 %) of a hydrophobically modified
carboxymethyl
cellulose (HM-CMC) as described in WO 98/56825, having a degree of
substitution of
carboxy methyl groups around 0.95, a degree of substitution of C4 alkyl groups
around
0.1 a degree of substitution of C14 alkyl groups around 0.006, a molecular
weight
distribution between 20000 and 70000 g/mol, and a solids content of 86.3 %,
46.96 g of
deionized water, 150 g of rhombohedral precipitated calcium carbonate with a
solids
content of 80.5 % manufactured by Huber Engineered Materials, 26.83 g (11 %)
of a 50 %
dispersion of SB latex (BaystalTM P7105 manufactured by Eka Polymer Latex) and
1.13 g
(0.75 %) of CMC with a solids content of 89.4 % (FinnfixTM 10 manufactured by
Noviant).
The temperature dependent behaviour of the PCC colour containing HM-CMC,
were examined using a rheometer model UDS200 from PAAR Physica. The
temperature
tests were performed between 25 and 85 C within the linear viscoelastic
region.
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Table 8. The storage modulus at various temperatures for coating with HM-CMC.
Temperature ( C) Storage modulus, G' (Pa)
100
187
254
421
573
726
1180
The PCC colour with HM-CMC and a conventional PCC colour from Comp.
Example 2, were also compared. The colours were each applied to a sheet of
paper
5 using a draw-down coating applicator and the gloss value of the coated paper
sheets
were measured after drying and soft calendering
Table 8. The gloss value of coated paper.
Designation Gloss value for soft calendered paper
Comp. Example 2 34
Example with HM-CMC 43
It appears that a higher gloss can be achieved using a HM-CMC as dispersing
agent
1o compared to the conventional coating colour of Example 2.
