Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS FOR THE PRODUCTION OF COATED PAPER
The present invention relates to a process for the production of coated paper
or
paperboard pigment, paper or paper board obtainable by the process, a novel
pigment
composition useful therefore and a process for its production.
B The development of ink-jet printers has led to a demand for paper that is
suitable
for that purpose. Particularly, there is a demand for paper that is simple to
produce but
still enables ink-jet printing of high quality.
It has been disclosed to use various kinds of coatings to produce paper
suitable
for ink-jet printing.
US Patent Application Publication 2002/0039639 discloses incorporating a water
soluble metal salt in an ink receiving layer comprising pigments and a
conventional
binder.
US Patent 4554181 discloses a recording surface including a combination of a
water soluble polyvalent metal and a cationic polymer.
US Patent Application Publication 2004/0255820 discloses a pigment that is
surface treated with a water-soluble polyvalent metal salt.
US Patent Application Publication 200510106317 discloses a method for
preparing an ink-jet recording material comprising the steps of forming at
least one
porous layer containing silica particles with an average secondary particle
size of 500 nm
or less, and coating a coating solution for preparing an inorganic particles-
containing
layer so that a solid content of the coated inorganic particles became 0.33
g/m2 or less on
the porous layer.
US Patent 6797347 discloses an ink-jet paper comprising a base paper and a
coating thereon, wherein said coating contains an inorganic pigment modified
with a
positively charged complex and a binder. The positively charged complex
contains a
polyvalent metal ion and an organic ligand.
US Patent Application Publication 2003/0099816 discloses an ink jet-recording
materiai comprising a substrate and a transparent ink-receiving layer
comprising a binder
and a plurality of particles formed by dispersing amorphous silica particles
and applying a
strong mechanical stress to divide the particles.
Other examples of disclosures relating to coated paper are WO 03/011981,
WO 01/53107, WO 01/45956, EP 947349, EP 1120281 EP 1106373 and US 5551975.
It is an object of the invention to provide a pigment composition suitable for
coating paper or paper board for ink-jet printing and that is simple to
produce.
It is another object of the invention to provide a coating formulation that is
simple
to apply on the surface of paper or paper board to make it suitable for ink-
jet printing.
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It is still another object of the invention to provide a paper or paper board
suitable for ink-jet printing that is simple to produce.
It has been found that the objects can be achieved by the present invention,
one
aspect of which concerns a process for the production of coated paper or
paperboard
comprising a step of applying a pigment composition as a coating to at least
one side of a
paper or paperboard web, said pigment composition being an aqueous dispersion
comprising as pigment particles optionally aggregated colloidal particles of
silica or
aluminosilicate prepared from alkali metal silicate by ion exchange or pH-
reduction and
having a surface area from about 30 m2/g to about 450 m2/g, and at least one
cationic
component selected from the group consisting of water soluble aluminium salts
and
cationic polymers with a molecular weight from about 2000 to about 1000000 and
a
charge density from about 0.2 meq/g to about 12 meq/g, wherein at least about
0.4 g
pigment particles from the pigment composition are applied per m2 coated side
of the
paper or paper board web.
It has surprisingly been found that good results are achieved with no or only
very
small amounts of binders conventionally used in paper coating. It is thus
preferred that
the pigment composition applied to the paper or paper board is substantially
free from or
comprises, based on the total amount of pigment particles, less than about 3
wt%,
preferably less than about 2 wt%, most preferably less than about 1 wt% of
organic
coating binders. Such binders include polyvinyl alcohols, optionally modified
starches,
gums, protein binders (e.g. caseins and soy protein binders), latices and
mixtures thereof.
Latices can, for example, be based on styrene butadien, acrylates, vinyl
acetate, co-
polymers of ethylene and vinyl acetates, styrene acrylic esters etc.
The pigment particles of optionally aggregated colloidal particles of silica
or
aluminosilicate preferably have a mean diameter from about 0.005 pm to about
25 pm,
more preferably from about 0.007 pm to about 15 pm, most preferably from about
0.01
pm to about 10 pm. The particles preferably have a surface area from about 40
m2/g to
about 400 m2/g particularly most preferably from about 50 m2/g to about 300
m2/g. The
net surface charge of the pigment particles in the composition is preferably
positive, the
dispersion thus being regarded as predominantly cationic.
The term diameter as used herein refers to the equivalent spherical diameter.
Preferred pigment particles are colloidal primary particles of silica,
aluminosilicate or a mixture thereof, or porous aggregates formed by
aggregation of
colloidal primary particles of silica, aluminosilicate or a mixture thereof in
an aqueous sol,
or a mixture of the above kinds of particles.
Colloidal primary particles of silica or aluminosilicate have preferably been
formed from an aqueous solution of alkali metal silicate where alkali metal
ions are
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removed through an ion exchange process or where the pH of the alkali metal
silicate
solution has been reduced by the addition of an acid. A process based on ion
exchange
follows the basic principles described in R.K. Iler, "The Chemistry of Silica"
1979, pages
333-334 and results in an aqueous sol comprising colloidal negatively or
positively
charged particles of silica or aluminosilicate. A process based on pH-
reduction of alkali
metal silicate follows the basic principles described in e.g. US patents
5176891, 5648055,
5853616, 5482693, 6060523 and 6274112.
Particularly preferred sols comprise colloidal primary particles of silica
that may
or may not be surface modified, for example with a metal oxide such as oxide
of
aluminium, titanium, chromium, zirconium, boron or any other suitable metal.
The surface area of the primary particles is from about 30 m2/g to about 450
m2/g, preferably from about 40 m2/g to about 400 m2/g most preferably from
about 50
m2/g to about 300 m2/g. The dry content of the aqueous sol of primary
particles is
preferably from about 0.5 wt% to about 60 wt%, most preferably from about 1
wt% to
about 50 wt%.
Suitable aqueous sols of colloidal primary particles of silica or
aluminosilicate are
commercially available, for example under the trademarks LudoxTM, SnowtexT"'
BindzilT"', NyacolT , VinnsilT"' or FennosilTM.
Unlike a sol formed by dispersing a powder, the colloidal particles in a sol
prepared from alkali metal silicate by ion exchange or pH-reduction have never
been
dried to a powder, such as in the case for e.g. precipitated silica, gel-type
silica or fumed
silica.
In the case the particles in the composition are aggregates of colloidal
primary
particles, the mean particle diameter of these primary particles is preferably
from about 5
nm to about 125 nm, most preferably from about 7 nm to about 100 nm. The
colloidal
primary particles are preferably in the form of an aqueous sol as described
above.
Aggregation of primary particles in a sol to form a dispersion of porous
aggregates may be performed with any suitable method, such as those described
in R.K.
Iler, "The Chemistry of Silica" 1979, pages 364-407. The degree of aggregation
can be
followed by measuring the viscosity and applying the Einstein and Mooney
equations
(see e.g. R.K. Iler, "The Chemistry of Silica" 1979, pages 360-364). The
aggregation may
be performed as a separate step or in a mixture also comprising other pigment
particles.
In one embodiment, an anionic sol (comprising negatively charged colloidal
primary particles) and a cationic sol (comprising positively charged colloidal
primary
particles) are mixed, resulting in the formation of porous aggregates of
primary particles
from both the sols.
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In another embodiment a salt, preferably selected from divalent, multivalent
or
complex salts, is added to an anionic or cationic sol also resulting in the
formation of
porous aggregates. Examples of salts are aluminium chloride, poly aluminium
chloride,
poly aluminium silicate sulfate, aluminium sulfate, zirconium carbonates,
zirconium
acetates, alkali metal borates, and mixtures thereof.
In still another embodiment a bridging substance is used to form the
aggregates
from the primary particles. Examples of suitable bridging substances are
synthetic and
natural polyelectrolytes such as CMC (carboxymethyl celiulose), PAM
(polyacrylamides),
polyDADMAC (poly diallyl dimethyl ammoniumchloride), polyallyl amines,
polyamines,
starch, guar gums, and mixtures thereof.
Any combination including one, two or all three of the above aggregation
methods can also be employed.
Each porous aggregate is formed from at least three primary particles, which
inherently gives at least some pores. The mean particle diameter of the
aggregates is
preferably from about 0.03 to about 25 pm, more preferably from about 0.05 to
about 10
pm, most preferably from about 0.1 pm to about 5 pm. It is to be understood
that the
average diameter of the porous aggregates is always larger than the average
diameter of
the primary particles they are formed from. The surface area of the aggregates
is usually
essentially the same as of the primary particles.
A water soluble aluminium salt as cationic component in the pigment
composition can be any aluminium containing salt and is preferably present in
an amount
from about 0.1 wt% to about 30 wt% most preferably from about 0.2 wt% to about
15
wt%, calculated as wt% A1203 on dry pigment particles. Examples of salts
include
aluminium chloride, poly aluminium chloride, poly aluminium silicate sulfate,
aluminium
sulfate, zirconium carbonates, zirconium acetates , and mixtures thereof. The
aluminium
may be present partly or fully on the surface of the particles of silica or
aluminosilicate or
in the aqueous phase.
The entire content of water soluble aluminium salt may originate from what is
present in a cationic aluminium modified silica sol used for preparing the
pigment
composition, it thus being possible to use a pigment composition consisting
essentially of
a cationic silica sol as a coating. However, the pigment composition may also
comprise
additional aluminium salt.
A cationic polymer as cationic component in the pigment composition has a
molecular weight from about 2000 to about 1000000, preferably from about 2000
to about
500000, most preferably from about 5000 to about 200000. The charge density is
from
about 0.2 meq/g to about 12 meq/g, preferably from about 0.3 meq/g to about 10
meq/g,
most preferably from about 0.5 meq/g to about 8 meq/g. The cationic polymer is
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preferably present in the pigment dispersion in an amount from about 0.1 wt%
to about
30 wt%, more preferably from about 0.5 wt% to about 20 wt%, most preferably
from about
1 wt% to about 15 wt%, based on the amount of dry pigment particles. Examples
of
suitable cationic polymers include syntetic and natural polyelectrolytes such
as PAM
5 (polyacrylam ides), polyDADMAC (poly diallyl dimethyl ammoniumchloride),
polyallyl
amines, polyamines, polysaccharides and mixtures thereof, provided that the
molecular
weight and charged density fulfil the above requirements. The cationic polymer
may be
present partly or fully on the surface of the particles of silica or
aluminosilicate or in the
aqueous phase.
A preferred pigment composition comprises both at least one water soluble
aluminium salt as described above and at least one cationic polymer as
described above.
In an embodiment the composition further comprises other kinds of pigment
particles such as kaolinites, smectites, talcites, calcium carbonate minerals,
precipitated
calcium carbonate, precipitated silica, gel-type silica, fumed silica, and
mixtures thereof.
The content of optionally aggregated colloidal particles of silica or
aluminosilicate
prepared from alkali metal silicate by ion exchange or pH-reduction and having
a surface
area from about 30 m2/g to about 450 m2/g is preferable from about 10 wt% to
100 wt%,
most preferable from about 30 wt% to 100 wt% of the total amount of pigment
particles.
The total content of pigment particles of optionally aggregated colloidal
silica or
aluminosilicate as described above and optional other pigment particles in the
composition is preferably from about 1 wt% to about 60 wt%, most preferably
from about
5 wt% to about 50 wt%, particularly most preferably from about 10 wt% to about
50 wt%.
The pigment composition may also comprise other additives commonly used for
paper coating such as stabilisers, rheology modifiers, optical brighteners,
lubricants,
insolubilizers, dyes, sizing agents etc, as well as various impurities from
the raw
materials. The dry content of the pigment composition is preferably from about
2 wt% to
about 75 wt%, most preferably from about 10 wt% to about 70 wt%. The total
amount of
other additives and possible impurities is preferably from 0 to about 50 wt%,
most
preferably from 0 to about 30 wt%, based on the dry content.
A pigment composition as described above is preferably storage stable for at
least one week, most preferably at least one month. The composition may be
used
directly for coating paper or paperboard or form an intermediate product for
preparing a
coating composition.
The coating is preferably applied in an amount sufficient to yield from about
0.5
g/m2 to about 40 g/m2, most preferably from about I g/mz to about 20 g/m2 of
optionally
aggregated colloidal particles of silica or aluminosilicate with a surface
area from about
30 g/m2 to about 450 g/m2 and optionally other pigment particles from the
pigment
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composition per coated side of the paper or paper board. In most cases the dry
amount
of coating applied per coated side of the paper or paper board is preferably
from about
0.5 g/m2 to about 50 g/mz, most preferably from about 1 g/m2 to about 25 g/m2.
The coating is preferably applied to a non-coated side of the paper or paper
board but may also be applied on top of a previously applied coating layer
with the same
or another coating composition. It is preferred not to apply any further
coating of other
kind on top of the layer formed from the coating as described herein.
Applying the coating can be performed either on the paper or board machine or
off the paper or board machine. In either case any type of coating methods can
be used.
Examples of coating methods are blade coating, air knife coating, roll
coating, curtain
coating, spray coating, size press coating (e.g. film press coating) and cast
coating.
After applying the coating the paper is dried, which in the case of on machine
coating preferably is accomplished in a drying section of the machine. Any
means of
drying may be used, such as infra red radiation, hot air, heated cylinders or
any
combination thereof.
The term coating as used herein refers to any method in which pigments are
applied to the surface of paper or paper board, thus including not only
conventional
coating but also other methods such as for example pigmenting.
The paper and paper board to be coated can be made from any kind of pulp,
such as chemical pulp like sulfate, sulfite and organosolve pulps, mechanical
pulp like
thermo-mechanical pulp (TMP), chemo-thermo-mechanical pulp (CTMP), refiner
pulp or
ground wood pulp, from both hardwood and softwood bleached or unbleached pulp
that
is based on based on virgin or recycled fibres or any combination thereof.
Paper and
paper board from any other kind of pulp may also be coated in accordance with
the
invention.
The invention further concerns paper or paper board suitable for ink-jet
printing
obtainable by a process as described above. Such paper or paper board
comprises a
substantially transparent or substantially non-transparent layer comprising
pigment
particles of synthetic amorphous silica or aluminosilicate and optionally
other pigment
particles from the coating composition, the pigment particles preferably
forming a nano-
structure. The dry amount of coating is preferably from about 0.5 g/m2 to
about 50 g/mz,
most preferably from about 1.0 g/m2 to about 25 g/m2. The amount of pigment
particles
from the above described pigment composition per coated side of the paper or
paper
board is preferably from about 0.5 g/m2 to about 40 g/mz, most preferably from
about 1
g/m2 to about 20 g/m2. Preferably no other kind of coating has been applied on
top of this
layer.
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It has been found that the paper or paper board of the invention have
particularly
good properties for ink-jet printing, giving low line blurriness and mottling
and high
printing density for colours, but can advantageously also be used for other
kinds of
printing processes like toner, flexography, letter press, gravure, offset
lithography and
screen printing. It is a particular advantage that such good properties can be
obtained in
a simple manner by applying only small amounts of the coating and without the
need to
apply numerous different coating layers on the paper or paper board. This also
enable
the coating to be applied with a size press, such as a film press, which for
practical
reasons is advantageous. Furthermore, the main components of the pigment
composition
can be made from readily available raw materials.
Some pigment compositions useful for the process of the invention are novel.
An
aspect of the invention thus also concerns a pigment composition in the form
of an
aqueous dispersion as pigment particles optionally aggregated colloidal
particles of silica
or aluminosilicate prepared from alkali metal silicate by ion exchange or pH-
reduction and
having a surface area from about 30 m2/g to about 450 m2/g, and at least one
cationic
polymer having a molecular weight from about 2000 to about 1000000 and a
charge
density from about 0.2 meq/g to about 12 meq/g, said composition being
substantially
free from or comprising, based on the total amount of pigment particles, less
than about 3
wt%, preferably less than about 2 wt%, most preferably less than about 1 wt%
of organic
coating binders. Preferably the composition also comprises a water soluble
aluminium
salt. Organic coating binders include polyvinyl alcohols, optionally modified
starches,
gums, protein binders (e.g. caseins and soy protein binders), latices and
mixtures thereof.
Latices can, for example, be based on styrene butadien, acrylates, vinyl
acetate, co-
polymers of ethylene and vinyl acetates, styrene acrylic esters etc.
Regarding suitable and preferred amounts and kinds of the components, the
above description of the pigment composition in connection with the process
for the
production of coated paper or paperboard is referred to.
The invention further relates to a process for the production of a pigment
composition as described above comprising mixing a sol of optionally
aggregated
colloidal particles of silica or aluminosilicate prepared from alkali metal
silicate by ion
exchange or pH-reduction and having a surface area from about 30 mz/g to about
450
m 2/g with a cationic polymer having a molecular weight from about 2000 to
about
1000000 and a charge density from about 0.2 meq/g to about 12meq/g and
optionally a
water soluble aluminium salt to an aqueous dispersion in a way so substantial
gelling or
precipitation is avoided. This can be achieved by several alternative process
embodiments.
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One alternative process embodiment comprises a step of adding a sol of
colloidal particles of silica or aluminosilicate having a surface area from
about 30 m2/g to
about 450 m2/g to an aqueous solution of a water soluble aluminium salt,
followed by
adding a cationic polymer as described above. Other components such as other
pigment
particles may be added at any stage in the form of solids, liquids or
dispersions. The
silica or aluminium silicate particles are preferably in the form of an
aqueous sol of
colloidal particles, that may be anionic or cationic. Unless a cationic sol is
used, the
aluminium salt is preferably in such an excess that it is sufficient for
rendering the
resulting dispersion predominantly cationic. At least if an anionic sol is
used, there may
be at least some aggregation of the colloidal particles.
Another alternative process comprises a step of adding a sol of colloidal
particles
of silica or aluminosilicate having a surface area from about 30 m2/g to about
450 m2/g to
an aqueous solution of a cationic polymer as described above, optionally
followed by
adding a water soluble aluminium salt. Other components such as other pigment
particles
may be added at any stage in the form of solids, liquids or dispersions. The
silica or
aluminium silicate particles are preferably in the form of an aqueous sol of
colloidal
particles, that may be anionic or cationic. Unless a cationic sol is used, the
cationic
polymer is preferably in such an excess that it is sufficient for rendering
the resulting
dispersion predominantly cationic. At least if an anionic sol is used, there
may be at least
some aggregation of the colloidal particles.
Still another process embodiment comprises a step of mixing a cationic
aluminium modified aqueous sol of colloidal silica or aluminosilicate with a
cationic
polymer. Although possible, it is not necessary to add further water soluble
aluminium salt
apart from what is present in the sol colloidal silica or aluminosilicate.
Other components
such as other pigment particles may be added at any stage in the form of
solids, liquids
or dispersions.
Regarding suitable and preferred amounts and kinds of the components, the
above description of the pigment composition is referred to.
The invention will now be further described in following examples. Unless
otherwise stated all parts and percentages refer to parts and percent by
weight.
Example 1: Three pigment compositions were prepared.
A) BindzilTM CAT from Eka Chemicals, a silica sol cationised by incorporation
of a
polyaluminium salt, having a surface area of about 500 m2/g and a
concentration of
15 wt% Si02, used as is in the coating.
B) BindzilT"" CAT 220 from Eka Chemicals, a silica sol cationised by
incorporation of a
polyaluminium salt, having a surface area of about 220 m2/g and a
concentration of
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30 wt% Si02, was diluted to a concentration of 15 wt% Si02 prior to the
coating
application.
C) BindzilTM CAT 80 from Eka Chemicals, a silica sol cationised by
incorporation of a
polyaluminium salt, having a surface area of about 80 mz/g and a concentration
of
40 wt% Si02, was diluted to a concentration of 15 wt% Si02 prior to the
coating
application.
The three pigment compositions were applied on surface of an uncoated copy
paper (A4 sized Data Copy from M-real) by a drawdown method with a wired rod
as
commonly used in laboratory coating tests. No organic coating binder was
added. After
the coating the paper was dried with an IR-dryer (Hedson Technologies AB,
Sweden).
The dried sheets of papers were evaluated on three inkjet printers, HP
DeskjetT " 5850
from Hewlett-Packard, Epson StylusTM C86 from Epson and Canon iP 4000.
The print result was evaluated using a print picture with seven colour blocs,
cyan, magenta, yellow, red, green, blue and black. The printed blocs and the
unprinted
paper were measured with a spectrophotometer (Color Touch 2 from Technidyne)
and
the colour gamut volume was calculated. The gamut volume is approximated with
a
dodecahedral in the CEI L*a*b* colour space and the measurements of the
colours give
the corners in the dodecahedral (see "Rydefalk Staffan, Wedin Michael;
Litterature review
on the colour Gamut in the Printing Process-Fundamentals, PTF-report no 32,
May
1997"). The results are shown in the table below:
Coating Coat weight Gamut Volume Gamut Volume Gamut Volume
Formulation g/m2 HP Epson Canon
No Coating - 166731 180995 148408
A 2.9 167334
A 2.9 231137
A 3.2 119070
B 2.5 231803
B 2.3 239903
B 2.6 189439
C 1.2 216299
C 1.5 241026
C 1.3 210213
It appears that the silica sols B and C with low surface gave a significant
higher print
quality than silica sol A with high surface area. A visual judgement also
revealed that the
prints of papers form experiments gave good line sharpness and no tendency of
colour
mottling.
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Example 2: In this example five pigment composition were evaluated.
D) A 15 wt% pigment slurry was prepared by dispersing a kaolin coating clay
(SPSTM,
Imerys, UK) in water by using intensive mixing in an UltraTurraxTM.
E) A 15 wt% pigment slurry was prepared by dispersing a gel-type silica,
SylojetTM
5 P612 from Grace Davison in water by using intensive mixing in an
UltraTurraxT""
F) 30 g of BindzilT " 50/80 from Eka Chemicals, an anionic silica sol with a
concentration of 50 wt% (Si02) and a surface area of 80 m2/g, was mixed with
15 g
of kaolin coating clay (SPSTM) and 55 g water in an UltraTurraxTM. Before use
the
composition was further diluted to 15 wt% pigment concentration.
10 G) 30 g of BindzilT"' 50/80, 15 g of kaolin coating clay (SPSTM) and 31 g
water were
mixed in an UltraTurraxTM and transferred into a solution containing 6 g of
aluminium chlorohydrate ( LocronTM from Clariant, 25 wt% AI203) and 18 g water
under vigorous stirring (UltraTurraxTM ). The resulting composition had a
pigment
concentration of 30 % and was then further diluted to 15 wt%.
H) 30 g of BindzilT"" 50/80, 15 g of kaolin coating clay (SPSTM) and 31 g
water were
mixed in an UltraTurraxT"'and transferred into a solution containing 3 g of
polyDADMAC ( 40 wt%, average molecular weight of about 20 000 and cationic
charge density of 7.2 meq/g) and 21 g water under vigorous stirring
(UltraTurraxTM). The resulting composition had a pigment concentration of 30
wt%
and was then further diluted to15 wt%.
Following the same procedure as in Example 1, the compositions were applied
to paper without any organic coating binder and dried and evaluated on three
printers.
The results are shown in the table below:
Coating Coat weight Gamut Volume Gamut Volume Gamut Volume
Formulation g/m2 HP Epson Canon
D 1.7 132721
D 2.1 192600
D 2.3 146150
E 1.8 259309
E 1.3 246995
E 2.0 230879
F 2.1 168525
F 1.6 199542
F 1.9 162425
G 1.6 189934
G 1.4 224625
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Coating Coat weight Gamut Volume Gamut Volume Gamut Volume
Formulation g/m2 HP Epson Canon
G 1.8 192598
H 1.4 197839
H 1.3 218972
H 1.7 143918
It can be seen that compositions G and H containing a cationic component gave
an over-
all better print quality compared to F being a sole blend of siiica sol and
clay.
Although composition E, being a gel-type silica, gave the highest gamut
volume,
it was, however, noted that the coated layer on this paper as well as the clay
coating +n
from D were very poorly adhered to the paper surface. This resulted in
extensive chalking
when touching the coated surfaces with the finger tips. It was therefore
evident that these
two pigment compositions could not give a paper useful for printing unless
combined with
a coating binder.
A dusting test on the non printed coated papers were also conducted. A strip
of a
low-tack tape, 5 x15 cm was pressed for 1 minute on the coated paper surface
and
thereafter removed from the paper. The tape was weighted before and after the
contact
with the paper surface and the weight difference gives the amount of dust
removed from
the coated layer.
The papers with coating C (from example 1), D, E and G were tested. The
results are shown in the table below:
Paper sample Amount of dust, mg
C 0.5
D 2.0
E 5.5
G 0.7
The results show that paper produced from compositions C and G had much lower
tendency to dust compared to paper with the conventional pigments D and E when
no
organic binder coating binder was used.
Example 3: In the test an anionic silica sol, BindzilT"' 50/80 from Eka
Chemicals
was used as pigment, a 50 wt% sol with a mean particle size of 40 nm. Two
formulations
were prepared without any PVA-binder.
I) BindzilT"' 50/80 diluted to 30 wt%.
J) 6 g LocronTMwas diluted with 20 g water and 60 g of BindzilTM 50/80 was
added
under vigorous mixing (UltraTurraxTM). The mixing continued during the
addition of
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12
3 g polyDADMAC (same as in example 1) and 11 g water. The final concentration
of silica became 30 wt%.
Following the same procedure as in Example 1, the coatings were applied to
paper and dried (coat weight 8-9 g/mZ) and evaluated on the Epson and HP-
printers. The
results are shown in the table below:
Coating Gamut Volume Epson Gamut Volume
Formulation HP
1 262220 229017
J 260601 261672
It appears that although coating formulation I gave a slightly better gamut
volume on
Epson, formulation J was significantly better on HP and therefore can be
considered as
giving best over-all result. A visual judgement also revealed good line
sharpness and no
tendency of colour mottling.
Example 4: Four coating formulations were prepared. A pigment composition of
equal parts (dry/dry) of anionic silica sol, BindzilT" 50/80 and kaolin a
coating clay
(SPSTM, lmerys, UK) were used in all formulations. As in Example 3 no external
binder
such as PVA was used in any of the formulations.
K) BindzilTM 50/80, SPSTM clay and water were mixed in UltraTurraxTM to a
pigment
concentration of 30 wt%.
L) A pigment slurry containing 15 g BindzilTM (as dry) and 15 g SPS clay was
added
to a water solution containing 6 g LocronTM (as is) under UltraTurraxTM mixing
and
the final pigment concentration became 30 wt %.
M) 3 g polyDADMAC (same as in example 1) was diluted with water and added to a
pigment slurry containing 15 g of BindzilT"' (as dry) and 15 g SPSTM clay
under
Ultra- TurraxTM mixing to a pigment solids of 30 wt %.
N) A pigment slurry was mixed with LocronTM solution as in A. The UltraTurrax
mixing continued and 3 g polyDADMAC (same as in Example 1) was diluted with
water and added to a Locron treated pigment slurry to obtain a final pigment
content of 30 wt%.
Following the same procedure as in Example 3, the coatings were applied to
paper and dried (coat weight 8-9 g/m2) and evaluated on two printers. The
results are
shown in the table below:
CA 02586207 2007-05-01
WO 2006/049547 PCT/SE2005/001524
13
Coating Gamut Volume Epson Gamut Volume
Formulation HP
No coating 178288 163247
K 233379 177191
L 253114 201548
M 233987 208773
N 268608 211090
It appears that the over-all best printing results are obtained with the
compositions
containing an aluminium salt or/and a low cationic molecular weight polymer (
L, M and
N).
