TECHNICAL FIELD
The present invention relates generally to coating compositions for coating paper. The
present invention also relates to paper coated with said coating compositions and to
methods of making said coating compositions and said coated paper. The present
invention further relates to a method of printing comprising applying ink to said coated
paper.
BACKGROUND OF THE INVENTION
Paper may be coated with various coating compositions to provide the paper with certain
properties that make it suitable for particular uses. In certain applications, for example, it
may be desirable for paper to be suitable for ink jet printing. An ink jet printer operates
by ejecting droplets of dye or pigment suspended in aqueous or solvent-based medium
from a nozzle onto a substrate such as paper. Each droplet adheres to the paper as a
dot and a collection of dots form a printed image. Preferably, when the ink is applied to
the paper, it will remain in a well focussed symmetrical dot. The ink should not be
absorbed too deeply by the paper or optical density will be lost at the paper surface and
the dot of ink may be spread out in an irregular manner to cover a larger area than
intended and appear rough at the edges. It is also desirable for the ink to dry quickly to
avoid smudging. An acceptable combination of properties (e.g. print density, print index,
line and edge quality, smudge index) is not straight-forward to achieve for good quality
ink jet paper.
As such, there is a continued need for alternative and/or improved paper coating
compositions, particularly those suitable for coating paper which is intended for use in
ink jet printing.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a coating
composition comprising a binder, an alkali earth metal compound and an anionic
dispersant.
In certain embodiments, the coating composition optionally comprises a cationic polymer
and the coating composition has a solids content of at least about 45 wt% and a
Brookfield viscosity equal to or less than about 1500 mPa.s. Thus, in accordance with a
further aspect of the present invention, there is provided a coating composition
comprising a binder, an alkali earth metal compound, an anionic dispersant and
optionally a cationic polymer, wherein the coating composition has a solids content of at
least about 45 wt% and a Brookfield viscosity equal to or less than about 1500 mPa.s.
In certain embodiments, the coating composition comprises 0 wt% cationic polymer.
Thus, in accordance with a further aspect of the present invention, there is provided a
coating composition comprising a binder, an alkali earth metal compound and an anionic
dispersant, wherein the coating composition comprises 0 wt% cationic polymer.
In certain embodiments, the coating composition consists essentially of or consists of
the binder, the alkali earth metal compound and the anionic dispersant.
In certain embodiments, the alkali earth metal compound has a dso equal to or greater
than about 0.4 m and/or a BET specific surface area of less than about 40 m2/g. Thus,
in accordance with a further aspect of the present invention, there is provided a coating
composition comprising a binder, an alkali earth metal compound and an anionic
dispersant, wherein the alkali earth metal compound has a dso equal to or greater than
about 0.4 pm and/or a BET specific surface area of less than about 40 m2/g.
In accordance with a second aspect of the present invention, there is provided a paper
comprising a fibrous substrate coated with a coating composition, wherein the coating
composition comprises a binder, an alkali earth metal compound and an anionic
dispersant. The coating composition may, for example, be in accordance with any of the
aspects or embodiments described herein.
In accordance with a third aspect of the present invention, there is provided a method of
making a coating composition comprising combining a binder, an alkali earth metal
compound and an anionic dispersant. The coating composition may, for example, be in
accordance with any of the aspects or embodiments described herein.
In certain embodiments, the alkali earth metal compound, the anionic polymer, any
optional additional inorganic particulate material and any optional cationic polymer may
be combined into a first composition (e.g. aqueous slurry) before this first composition is
combined with the binder to make the coating compositions described herein. The
optional additional inorganic particulate material may, for example, be combined with the
first composition to form a second composition before the second composition is
combined with binder to make the coating compositions described herein. Thus, in
accordance with a further aspect of the present invention, there is provided a composition
comprising an alkali earth metal compound, an anionic polymer, optionally a cationic
polymer and optionally a further inorganic particulate material.
In accordance with a fourth aspect of the present invention, there is provided a method
of making a coated paper comprising coating a fibrous substrate with a coating
composition, wherein the coating composition comprises a binder, an alkali earth metal
compound and an anionic dispersant. The coating composition may, for example, be in
accordance with any of the aspects or embodiments described herein.
In accordance with a fifth aspect of the present invention, there is provided a method of
printing comprising applying ink to a coated paper, wherein the coated paper comprises
a fibrous substrate coated with a coating composition, wherein the coating composition
comprises a binder, an alkali earth metal compound and an anionic dispersant. The
coating composition may, for example, be in accordance with any of the aspects or
embodiments described herein.
In accordance with certain embodiments of any aspect of the present invention, the alkali
earth metal compound is an alkali earth metal carbonate. In certain embodiments, the
alkali earth metal compound is calcium carbonate. In certain embodiments, the alkali
earth metal carbonate is precipitated calcium carbonate (PCC).
In certain embodiments of any aspect of the present invention, the cationic polymer is
present in the coating composition in an amount equal to or less than about 2 wt%
relative to the total weight of inorganic particulate material in the composition. In certain
embodiments, the cationic polymer is present in the coating composition in an amount
equal to or less than about 1 wt% relative to the total weight of inorganic particulate
material in the composition. In certain embodiments, there is no cationic polymer present
in the coating composition, i.e. the cationic polymer is present in the composition in an
amount of 0 wt%.
In certain embodiments of any aspect of the present invention, the alkali earth metal
compound (e.g. calcium carbonate such as PCC) has a dso equal to or greater than about
0.4 m. In certain embodiments, the alkali earth metal carbonate (e.g. calcium carbonate
such as PCC) has a dso equal to or greater than about 0.6 pm. In certain embodiments,
the alkali earth metal carbonate (e.g. calcium carbonate such as PCC) has a dso equal
to or greater than about 0.8 pm. In certain embodiments, the alkali earth metal carbonate
(e.g. calcium carbonate such as PCC) has a dso equal to or greater than about 1.0 pm.
In certain embodiments of any aspect of the present invention, the alkali earth metal
compound (e.g. calcium carbonate such as PCC) has a BET specific surface area less
than about 40 m2/g. In certain embodiments, the alkali earth metal compound (e.g.
calcium carbonate such as PCC) has a BET specific surface area equal to or less than
about 30 m2/g. In certain embodiments, the alkali earth metal compound (e.g. calcium
carbonate such as PCC) has a BET specific surface area equal to or less than about 20
m /g. In certain embodiments, the alkali earth metal compound (e.g. calcium carbonate
such as PCC) has a BET specific surface area equal to or less than about 10 m2/g.
In certain embodiments of any aspect of the present invention, the coating composition
further comprises an aluminosilicate. In certain embodiments, the aluminosilicate is
kaolin. In certain embodiments, the aluminosilicate is calcined kaolin. In certain
embodiments, the aluminosilicate is hydrous kaolin.
In certain embodiments of any aspect of the present invention, the weight ratio of alkali
earth metal compound to aluminosilicate ranges from about 60:40 to about 95:5. In
certain embodiments, the weight ratio of alkali earth metal compound to aluminosilicate
ranges from about 70:30 to about 90:10. In certain embodiments, the weight ratio of alkali
earth metal compound to aluminosilicate is about 85:15.
In certain embodiments of any aspect of the present invention, the binder is a cationic
binder. In certain embodiments, the binder is starch. In certain embodiments, the binder
is cationic starch.
In certain embodiments of any aspect of the present invention, the anionic dispersant is
a homopolymer and/or a copolymer of (meth)acrylic acid. In certain embodiments, the
anionic dispersant is a homopolymer of acrylic acid.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a black print density equal to or greater than about 1.0. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a black print density equal to or greater than about 1.1 . In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a black print density equal to or greater than about 1.2.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a magenta print density equal to or greater than about 0.7. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a magenta print density equal to or greater than about 0.8. In
certain embodiments, ink printed on paper coated with the coating composition or ink
printed on the coated paper has a magenta print density equal to or greater than about
0.9.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a cyan print density equal to or greater than about 0.7. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a cyan print density equal to or greater than about 0.8. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a cyan print density equal to or greater than about 0.9.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a yellow print density equal to or greater than about 0.7. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a yellow print density equal to or greater than about 0.8. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a yellow print density equal to or greater than about 0.9.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a print index equal to or greater than about 400. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a print index equal to or greater than about 420. In certain
embodiments, ink printed on paper coated with the coating composition or ink printed on
the coated paper has a print index equal to or greater than about 440.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a line quality equal to or greater than about 0.8. In certain
embodiments of any aspect of the present invention, ink printed on paper coated with
the coating composition or ink printed on the coated paper has a line quality equal to or
greater than about 0.85. In certain embodiments of any aspect of the present invention,
ink printed on paper coated with the coating composition or ink printed on the coated
paper has a line quality equal to or greater than about 0.9.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has an edge quality equal to or less than about 15. In certain
embodiments of any aspect of the present invention, ink printed on paper coated with
the coating composition or ink printed on the coated paper has an edge quality equal to
or less than about 14. In certain embodiments of any aspect of the present invention, ink
printed on paper coated with the coating composition or ink printed on the coated paper
has an edge quality equal to or less than about 13.
In certain embodiments of any aspect of the present invention, ink printed on paper
coated with the coating composition of the invention or ink printed on the coated paper
of the invention has a smudge index after 5 seconds equal to or greater than about 9 .
In certain embodiments, ink printed on paper coated with the coating composition or ink
printed on the coated paper has a smudge index after 15 seconds equal to or greater
than about 9.5. In certain embodiments, ink printed on paper coated with the coating
composition or ink printed on the coated paper has a smudge index after 15 seconds
equal to about 10.
In certain embodiments of any aspect of the present invention, the ink is a pigment-based
ink or a dye-based ink. In certain embodiments, the coated paper is adapted to be used
for printing with pigment-based inks and/or dye-based inks.
In certain embodiments of any aspect of the present invention, the coating composition
has a Brookfield viscosity equal to or less than about 1500 mPa.s. In certain
embodiments, the coating composition has a Brookfield viscosity equal to or less than
about 1000 mPa.s. In certain embodiments, the coating composition has a Brookfield
viscosity equal to or less than about 800 mPa.s.
In certain embodiments of any aspect of the present invention, the coating composition
has a solids content of at least about 45 wt%. In certain embodiments, the coating
composition has a solids content of at least about 50 wt%.
In certain embodiments of any aspect of the present invention, the coating composition
has a solids content of at least about 45 wt% and a Brookfield viscosity equal to or less
than about 1500 mPa.s.
Certain embodiments of any aspect of the present invention may provide one or more of
the following advantages:
• compositions comprising a reduced amount of cationic polymer (e.g. zero
cationic polymer);
• compositions that provide paper that gives desired print properties (e.g. ink jet
print properties) (e.g. improved print properties) such as print density (black,
magenta, cyan, yellow), print index, line and edge quality and smudge index;
• compositions that provide paper which has suitability for (e.g. improved suitability
for) laser marking;
• compositions that provide paper that is suitable for printing with dye-based and
pigment-based inks;
• compositions with relatively high solids content;
• compositions with suitable viscosity for coating paper.
The details, examples and preferences provided in relation to any particular one or more
of the stated aspects of the present invention apply equally to all aspects of the present
invention. Any combination of the embodiments, examples and preferences described
herein in all possible variations thereof is encompassed by the present invention unless
otherwise indicated herein, or otherwise clearly contradicted by context.
DETAILED DESCRIPTION OF THE INVENTION
Coating Compositions
There is provided herein coating compositions suitable for coating a fibrous substrate to
make coated paper. The coating compositions provided herein comprise a binder, an
alkali earth metal compound (e.g calcium carbonate) and an anionic dispersant. The
coating compositions do not comprise a cationic polymer (i.e. comprise 0 wt% cationic
polymer). The coating compositions may, for example, consist essentially of or consist
of a binder, an alkali earth metal compound (e.g. calcium carbonate) and an anionic
dispersant.
The coating compositions may, for example, be advantageous in that they do not
comprise a cationic polymer. This may, for example, enable the coating compositions to
be made cheaply and easily. The coating compositions may, for example, be
advantageous in that they do not comprise cationic polymer but also provide a
composition having a high solids content and a suitable viscosity for paper coating. The
coating compositions may, for example, be advantageous in that they do not comprise a
cationic polymer but also provide paper having desirable print properties such as ink jet
print properties (e.g. improved print properties or print properties that are approximately
equal to the print properties of a paper coated with a composition comprising a greater
amount of a cationic polymer).
The coating composition may, for example, be an aqueous suspension/dispersion. The
solids content of the coating composition may suitably be as high as possible whilst still
giving a suitably fluid composition which may be used in coating a substrate (e.g. a
fibrous substrate, e.g. paper). In certain embodiments, the solids content and viscosity
of the coating colour when applied to the paper may be significant. For example, if the
solids content of the coating colour is too high, then the viscosity will be too high for easy
metering and runnability problems may result, giving rise to so-called scratching and
splashing. However, if the solids content is too low, the coating will flow too easily in the
basepaper pores and poor coverage will result. In addition, there will be more water to
remove thermally and the basepaper fibres may swell and reduce the quality further. At
the desired levels of solids and viscosity, the coating does not penetrate into the pores,
so it is held out onto the surface of the paper and is able to give a smooth surface.
The solids content of the coating composition may, for example, be at least about 45
wt%. For example, the solids content of the coating composition may be at least about
46 wt%, at least about 47 wt%, at least about 48 wt%, at least about 49 wt%, at least
about 50 wt%, at least about 5 1 wt%, at least about 52 wt%, at least about 53 wt%, at
least about 54 wt%, at least about 55 wt%. For example, the solids content of the coating
composition may range from about 45 wt% to about 80 wt%, for example from about 45
wt% to about 75 wt%, for example from about 45 wt% to about 70 wt%, for example from
about 45 wt% to about 65 wt%, for example from about 50 wt% to about 60 wt%. After
application of the aqueous coating composition to the substrate, the coating composition
may be allowed to dry. Thus, the coating may be in the form of a dry residue comprising
a binder, an alkali earth metal compound, an anionic dispersant and optionally a cationic
polymer.
The coating composition may, for example, have a Brookfield viscosity ranging from
about 10 mPa.s to about 500 mPa.s. For example, the coating composition may have
a Brookfield viscosity equal to or less than about 1400 mPa.s, for example equal to or
less than about 1300 mPa.s, for example equal to or less than about 1200 mPa.s, for
example equal to or less than about 1100 mPa.s, for example equal to or less than about
1000 mPa.s, for example equal to or less than about 900 mPa.s, for example equal to or
less than about 800 mPa.s, for example equal to or less than about 700 mPa.s, for
example equal to or less than about 600 mPa.s, for example equal to or less than about
500 mPa.s. The coating composition may, for example, have a Brookfield viscosity equal
to or greater than about 10 mPa.s, for example equal to or greater than about 50 mPa.s,
for example equal to or greater than about 100 mPa.s, for example equal to or greater
than about 150 mPa.s, for example equal to or greater than about 200 mPa.s.
Brookfield viscosity is measured at ambient temperature (22°C) using a Brookfield
Viscometer set to operate at a spindle speed of 100 rpm. The coating composition is
thoroughly mixed using a Heidolph ST-1 laboratory stirrer. Immediately after mixing, the
coating composition is transferred to the viscometer and the viscometer spindle is
immersed in the composition. The viscometer spindle is activated 30 seconds after
cessation of homogenisation and the Brookfield viscosity is recorded 15 seconds later.
Ink printed on paper coated with the coating composition may, for example, have a black
print density equal to or greater than about 1.0. For example, ink printed on paper coated
with the coating composition may have a black print density equal to or greater than
about 1.05, for example equal to or greater than about 1.1 , for example equal to or
greater than about 1.15, for example equal to or greater than about 1.2, for example
equal to or greater than about 1.25, for example equal to or greater than about 1.3, for
example equal to or greater than about 1.35, for example equal to or greater than about
1.4. For example, ink printed on paper coated with the coating composition may have a
black print density up to about 2.0, for example up to about 1.9, for example up to about
1.8, for example up to about 1.7, for example up to about 1.6, for example up to about
1.5.
Ink printed on paper coated with the coating composition may, for example, have a
magenta print density equal to or greater than about 0.7. For example, ink printed on
paper coated with the coating composition may have a magenta print density equal to or
greater than about 0.75, for example equal to or greater than about 0.8, for example
equal to or greater than about 0.85, for example equal to or greater than about 0.9, for
example equal to or greater than about 0.95, for example equal to or greater than about
1.0, for example equal to or greater than about 1.05, for example equal to or greater than
about 1.1 , for example equal to or greater than about 1.15, for example equal to or
greater than about 1.2. For example, ink printed on paper coated with the coating
composition may have a magenta print density up to about 2.0, for example up to about
1.9, for example up to about 1.8, for example up to about 1.7, for example up to about
1.6, for example up to about 1.5.
Ink printed on paper coated with the coating composition may, for example, have a cyan
print density equal to or greater than about 0.7. For example, ink printed on paper coated
with the coating composition may have a cyan print density equal to or greater than about
0.75, for example equal to or greater than about 0.8, for example equal to or greater than
about 0.85, for example equal to or greater than about 0.9, for example equal to or
greater than about 0.95, for example equal to or greater than about 1.0, for example
equal to or greater than about 1.05, for example equal to or greater than about 1.1, for
example equal to or greater than about 1.15, for example equal to or greater than about
1.2. For example, ink printed on paper coated with the coating composition may have a
cyan print density up to about 2.0, for example up to about 1.9, for example up to about
1.8, for example up to about 1.7, for example up to about 1.6, for example up to about
1.5.
Ink printed on paper coated with the coating composition may, for example, have a yellow
print density equal to or greater than about 0.7. For example, ink printed on paper coated
with the coating composition may have a yellow print density equal to or greater than
about 0.75, for example equal to or greater than about 0.8, for example equal to or
greater than about 0.85, for example equal to or greater than about 0.9, for example
equal to or greater than about 0.95, for example equal to or greater than about 1.0, for
example equal to or greater than about 1.05, for example equal to or greater than about
1.1, for example equal to or greater than about 1.15, for example equal to or greater than
about 1.2. For example, ink printed on paper coated with the coating composition may
have a yellow print density up to about 2.0, for example up to about 1.9, for example up
to about .8, for example up to about 1.7, for example up to about 1.6, for example up to
about 1.5.
Print density (reflection print density) is a ratio of incident light on a sample and reflected
light back given by the formula:
Density = I g —
where lo is the intensity of the light source and IR is the intensity of reflected light. This is
measured using a Gretag SpectroEye Densitometer. The print density values assist in
obtaining a full estimate of the colour intensity of the print.
Ink printed on paper coated with the coating composition may, for example, have a print
index equal to or greater than about 330. For example, ink printed on paper coated with
the coating composition may have a print index equal to or greater than about 335, for
example equal to or greater than about 340, for example equal to or greater than about
345, for example equal to or greater than about 350, for example equal to or greater than
about 355, for example equal to or greater than about 360, for example equal to or
greater than about 365, for example equal to or greater than about 370, for example
equal to or greater than about 375, for example equal to or greater than about 380, for
example equal to or greater than about 385, for example equal to or greater than about
390, for example equal to or greater than about 395, for example equal to or greater than
about 400, for example equal to or greater than about 405, for example equal to or
greater than about 410, for example equal to or greater than about 415, for example
equal to or greater than about 420, for example equal to or greater than about 425, for
example equal to or greater than about 430, for example equal to or greater than about
435, for example equal to or greater than about 440. Ink printed on paper coated with
the coating composition may, for example, have a print index up to about 600, for
example up to about 550, for example up to about 500. For example, ink printed on paper
coated with the coating composition may have a print index up to about 490, for example
up to about 480, for example up to about 460, for example up to about 470, for example
up to about 460, for example up to about 450.
Print index is calculated using the following formula:
Print Index =
where Bn is the black print density of the sample, Cn is the cyan print density of the
sample etc. and B is the black print density of ink printed on a control sample, Co is the
cyan print density of ink printed on the control sample etc. Print density was measured
as described above. The control paper is a commercially available silica-coated paper.
Ink printed on paper coated with the coating composition may, for example, have a line
quality equal to or greater than about 0.8. For example, ink printed on paper coated with
the coating composition may have a line quality equal to or greater than about 0.85, for
example equal to or greater than about 0.9. Ink printed on paper coated with the coating
composition may, for example, have a line quality up to about 1.0, for example up to
about 0.99, for example up to about 0.98, for example up to about 0.97, for example up
to about 0.96, for example up to about 0.95.
Line quality is determined by comparing the contrast between yellow and black areas
and the evenness of a black band through a yellow background. Image analysis is carried
out by printing ink jet samples and scanning each ink jet printed sample using an Epson
V500 photo scanner at 600 dpi and 24-bit colour and constant settings. All of the
automatic corrections are turned off and the same histogram settings (0, .0, 255:0, 255)
are used for all samples. An image of 500x300 pixels is collected in the area where there
is a black band running across a yellow background. The coloured image is then
converted into a 256 greyscale image for use in the analysis. A line profile is taken
through the black band. For acceptable or good quality prints, the profile is relatively
smooth (low mottle) and angular with steep sides and a flat bottom. Poorer quality prints
have more variation in the line profile and black band. The difference between the black
and yellow intensity is a measure of the print contrast, wherein the black intensity is the
average of all the minimum black points from the profiles taken from the greyscale
images and the yellow intensity is the average of the yellow background from the profiles
taken from the RGB colour images. The line quality is equal to the width at 25% between
the yellow intensity and the black intensity divided by the width at 75% between the
yellow intensity and the black intensity. Similar width values are better, so a perfect line
would have a line quality of 1. This metric gives an indication of the amount of ink spread
and the degree of mottle or unevenness occurring in connection with the printed black
bar.
Ink printed on paper coated with the coating composition may, for example, have an
edge quality equal to or less than about 15. For example, ink printed on paper coated
with the coating composition may have an edge quality equal to or less than about 14,
for example equal to or less than about 13, for example equal to or less than about 12.
Ink printed on paper coated with the coating composition may, for example, have an
edge quality equal to or more than about 0, for example equal to or more than about 1,
for example equal to or more than about 2 , for example equal to or more than about 3 ,
for example equal to or more than about 4 , for example equal to or more than about 5.
Edge quality is measured by obtaining a pixel view of a thresholded black/yellow
interface and counting the number of white pixels next to each interface black pixel. Edge
quality is the % of interface black pixels with 2 or 3 adjacent white pixels. A lower number
indicates better edge quality.
Ink printed on paper coated with the coating composition may, for example, have a
smudge index after 15 seconds equal to or greater than about 9 . For example, ink printed
on paper coated with the coating composition may have a smudge index after 15
seconds equal to or greater than about 9.5, for example equal to or less than about 10.
For example, ink printed on paper coated with the coating composition may have a
smudge index after 15 seconds equal to about 10.
Smudge index is measured by printing a test print using a desktop printer and
commercial pigment-based ink jet inks. The test contains areas of 00% black ink,
printed as approx 1 cm2 blocks. Fifteen seconds after the print has been made, a finger
from a skilled operator, covered with a rubber glove is contacted with the black printed
square and then pulled downwards applying a constant firm pressure. Any nondried/
non-immobilized ink will be dragged onto the unprinted portion of the paper. The
degree of ink transfer to the paper is assessed visually and given a ranking out of 10,
where 10 indicates no transfer of ink - i.e. the print is dried. A score of around 5 or 6
shows considerable transfer of ink. The test gives a reasonable comparison between
different papers when printed using the same printer and the same ink.
Binder
Any binder capable of providing a coating composition having any one or more of the
advantageous properties described herein may suitably be used. Suitable materials for
use as binders and/or cobinding agents are generally known in the art. For example,
suitable materials include latex, starch, starch derivatives, sodium carboxymethyl
cellulose, polyvinyl alcohol, proteins and combinations thereof. The binder may or may
not be a blend and may or may not consist essentially of or consist of polyvinyl alcohol
or starch. The binder may, for example, be a cationic binder. The binder may, for
example, be starch or a starch derivative. The binder may, for example, be a cationic
starch.
A starch binder may, for example, be derived from natural starch obtained from a known
plant source. Other binders that may be used include, for example, adhesives derived
from natural starch obtained from a known plant source, for example, wheat, maize,
potato or tapioca.
Other exemplary binders include, for example, latex binders. The term "latex" is used
herein to mean a dispersion/suspension (e.g. aqueous dispersion/suspension) of one or
more polymer(s). Commercially available latex products are typically sold as aqueous
emulsions containing 50 wt% latex. These products are suitable for use in the present
compositions. The polymers may, for example, be natural or synthetic. The latex binder
may, for example, be natural rubber latex obtained from, for example, rubber trees. The
latex binder may, for example, be a synthetic latex. The latex binder may, for example,
be a styrene polymer, for example copolymers including styrene monomers. For
example, the latex binder may be a copolymer comprising, consisting essentially of or
consisting of alkene monomers (e.g. ethylene, propylene, butylene, butadiene) and
styrene monomers. For example, the latex binder may be styrene butadiene. The latex
binder may, for example, be polyurethane, polyester and/or polyethyleneacrylate
dispersions. The latex binder may, for example, be an acrylic-based latex or an acetatebased
latex (e.g. polyvinyl acetate, vinyl acetate latex or styrene acrylic or acrylic latex).
The binder may, for example, be casein. The binder may, for example, be an alcoholbased
binder, such as polyvinyl alcohol. Blends comprising or consisting of polyvinyl
alcohol and latex may be particularly advantageous in providing a good balance of
properties. Polyvinyl alcohol may assist in lowering the viscosity of the coating
composition and the latex may assist in lowering the set off tendency of the printed ink.
Polyvinyl alcohol may be obtained by conventional methods known in the art, such as,
for example by partial or complete hydrolysis of polyvinyl acetate to remove acetate
groups. Thus, a person of skill in the art will understand that polyvinyl alcohol obtained
by hydrolysis of polyvinyl acetate may contain pendant acetate groups as well as
pendant hydroxy groups. Thus, in embodiments, the polyvinyl alcohol is derived from
partially or fully hydrolysed polyvinyl acetate. The extent of hydrolysis may be such that
at least about 50 mole % of the acetate groups are hydrolysed, for example, at least
about 60 mole % of the acetate groups are hydrolysed, for example, at least about 70
mole % of the acetate groups are hydrolysed, for example, at least about 80 mole % of
the acetate groups are hydrolysed, for example, at least about 85 mole % of the acetate
groups are hydrolysed, for example, at least about 90 mole % of the acetate groups are
hydrolysed, for example, at least about 95 mole % of the acetate groups are hydrolysed
or, for example, at least about 99 mole % of the acetate groups are hydrolysed. The
polymer may, for example, be a copolymer of polyvinyl alcohol and other monomers,
such as, for example, acetate and acrylate.
The amount of binder in the coating composition will depend on the binder used and the
desired end product. The coating composition may comprise any amount of binder
suitable to allow the surfaces of paper, when coated with the coating composition, to
receive ink without disruption. For example, the coating composition may comprise from
about 1 pph to about 50 pph, for example from about 1 pph to about 40 pph, for example
from about 1 pph to about 35 pph, for example from about 1 pph to about 30 pph, for
example from about 1 pph to about 25 pph, for example from about 1 pph to about 20
pph binder. This is the dry weight of the binder based on the dry weight of total inorganic
particulate material in the coating (e.g. 12 pph binder is 12 g of dry binder in 100 g of dry
inorganic particulate material). For example, the coating composition may comprise from
about 3 pph or from about 5 pph or from about 8 pph to about 50 pph or to about 40 pph
or to about 35 pph or to about 30 pph or to about 25 pph or to about 20 pph binder based
on the total dry inorganic particulate material in the composition. For example, the
coating composition may comprise from about 5 pph to about 50 pph, for example from
about 5 pph to about 40 pph, for example from about 5 pph to about 35 pph, for example
from about 5 pph to about 30 pph, for example from about 5 pph to about 25 pph, for
example from about 5 pph to about 20 pph binder based on the total dry inorganic
particulate material in the composition.
Alkali Earth Metal Compound
The coating compositions provided herein comprise an alkali earth metal compound. The
alkali earth metal compound may, for example, be any alkali earth metal salt, for example
any alkali earth metal acetate, carbonate, citrate, cyanide, sulphate, halide (e.g. chloride,
fluoride), nitrate, nitrite, phosphate, hydroxide. The alkali earth metal compound may, for
example, be an alkali earth metal carbonate. The alkali earth metal compound may, for
example be any calcium salt. Hereinafter, the present invention may tend to be discussed
in terms of calcium carbonate. However, the invention should not be construed as being
limited as such.
The coating compositions provided herein may, for example, comprise calcium
carbonate. Examples of calcium carbonate include ground calcium carbonate (GCC),
precipitated calcium carbonate (PCC), dolomite and surface-modified calcium
carbonate.
The particulate calcium carbonate used in embodiments of the present invention may be
obtained from a natural source by grinding or may be prepared synthetically by
precipitation (PCC), or may be a combination of the two, i.e. a mixture of the naturally
derived ground material and the synthetic precipitated material. The PCC may also be
ground.
When the inorganic particulate material used in embodiments of the present invention is
obtained from naturally occurring sources, it may be that some mineral impurities will
inevitably contaminate the ground material. For example, naturally occurring calcium
carbonate occurs in association with other minerals. In general, however, the inorganic
particulate material used in embodiments of the present invention will contain less than
5% by weight, preferably less than 1% by weight of other mineral impurities.
Ground calcium carbonate (GCC) is typically obtained by grinding a mineral source such
as chalk, marble or limestone, which may be followed by a particle size classification
step, in order to obtain a product having the desired degree of fineness. The particulate
solid material may be ground autogenously, i.e. by attrition between the particles of the
solid material themselves, or alternatively, in the presence of a particulate grinding
medium comprising particles of a different material from the calcium carbonate to be
ground.
Wet grinding of calcium carbonate involves the formation of an aqueous suspension of
the calcium carbonate which may then be ground, optionally in the presence of a suitable
dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents
of which are incorporated by reference in their entirety) for more information regarding
the wet grinding of calcium carbonate.
PCC may be used as the source of particulate calcium carbonate in embodiments of the
present invention, and may be produced by any of the known methods available in the
art. TAPPI Monograph Series No 30, "Paper Coating Pigments", pages 34-35 describes
the three main commercial processes for preparing precipitated calcium carbonate which
is suitable for use in preparing products for use in the paper industry, but may also be
used in connection with the embodiments of the present invention. In all three
processes, limestone is first calcined to produce quicklime, and the quicklime is then
slaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of
lime is directly carbonated with carbon dioxide gas. This process has the advantage that
no by-product is formed, and it is relatively easy to control the properties and purity of
the calcium carbonate product. In the second process, the milk of lime is contacted with
soda ash to produce, by double decomposition, a precipitate of calcium carbonate and
a solution of sodium hydroxide. The sodium hydroxide should be substantially completely
separated from the calcium carbonate if this process is to be commercially attractive. In
the third main commercial process, the milk of lime is first contacted with ammonium
chloride to give a calcium chloride solution and ammonia gas. The calcium chloride
solution is then contacted with soda ash to produce, by double decomposition,
precipitated calcium carbonate and a solution of sodium chloride.
The process for making PCC results in very pure calcium carbonate crystals and water.
The crystals can be produced in a variety of different shapes and sizes, depending on
the specific reaction process that is used. The three main forms of PCC crystals are
aragonite, rhombohedral and scalenohedral, all of which are suitable for use in
embodiments of the present invention, including mixtures thereof. The PCC used in the
present invention may, for example, be in scalenohedral form.
Hereinafter, the invention may tend to be discussed in terms of precipitated calcium
carbonate (PCC). However, the invention should not be construed as being limited as
such.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, have a dso equal to or greater than about 0.4 pm. For example, the alkali earth
metal compound such as calcium carbonate (e.g. PCC) may have a dso equal to or
greater than about 0.45 mhh , for example equal to or greater than about 0.5 m h , for
example equal to or greater than about 0.55 pm. For example, the alkali earth metal
compound such as calcium carbonate (e.g. PCC) may have a dso equal to or greater
than about 0.6 pm. For example, the alkali earth metal compound such as calcium
carbonate (e.g. PCC) may have a dso equal to or greater than about 0.65 m, for example
equal to or greater than about 0.7 pm, for example equal to or greater than about 0.75
pm, for example equal to or greater than about 0.8 pm. For example, the alkali earth
metal compound such as calcium carbonate (e.g. PCC) may have a dso equal to or
greater than about 0.85 pm, for example equal to or greater than about 0.9 pm, for
example equal to or greater than about 0.95 pm, for example equal to or greater than
about .0 pm, for example equal to or greater than about 1.05 pm, for example equal to
or greater than about 1.1 pm. The alkali earth metal compound such as calcium
carbonate (e.g. PCC) may, for example have a dso up to about 1.5 pm, for example up
to about 1.45 pm, for example up to about 1.4 pm, for example up to about 1.35 pm, for
example up to about 1.3 pm, for example up to about 1.25 pm, for example up to about
1.2 pm. For example, the alkali earth metal compound such as calcium carbonate (e.g.
PCC) may have a d5o of about 1.1 pm.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise at least about 65 wt% of particles smaller than 2 pm. For example,
the alkali earth metal compound such as calcium carbonate (e.g. PCC) may comprise at
least about 70 wt%, for example at least about 72 wt% of particles smaller than 2 miti .
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise up to about 80 wt% of particles smaller than 2 pm, for example up to
about 75 wt% of particles smaller than 2 pm.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise at least about 35 wt% of particles smaller than 1 pm. For example,
the alkali earth metal compound such as calcium carbonate (e.g. PCC) may comprise at
least about 40 wt%, for example at least about 42 wt% of particles smaller than 1 pm.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise up to about 50 wt% of particles smaller than 1 m, for example up to
about 48 wt%, for example up to about 45 wt% of particles smaller than 1 pm.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise at least about 5 wt% of particles smaller than 0.5 pm. For example,
the alkali earth metal compound such as calcium carbonate (e.g. PCC) may comprise at
least about 10 wt%, for example at least about 12 wt% of particles smaller than 0.5 pm.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, comprise up to about 20 wt% of particles smaller than 0.5 pm, for example up
to about 15 wt%, for example up to about 12 wt% of particles smaller than 0.5 pm.
Unless otherwise stated, the mean (average) equivalent particle diameter (dso value) and
other particle size properties referred to herein for the inorganic particulate materials are
as measured in a well known manner by sedimentation of the particulate material in a
fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as
supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone:
+ 1 770 662 3620; web-site: www.micromeritics.com), referred to herein as a
"Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot
of the cumulative percentage by weight of particles having a size, referred to in the art
as the 'equivalent spherical diameter' (esd), less than given esd values. The mean
particle size dso is the value determined in this way of the particle esd at which there are
50% by weight of the particles which have an equivalent spherical diameter less than
that dso value.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example have a BET specific surface area less than about 40 m2/g. For example, the
alkali earth metal compound such as calcium carbonate (e.g. PCC) may have a BET
specific surface area equal to or less than about 35 m /g, for example equal to or ess
than about 30 m /g, for example equal to or less than about 25 m2/g, for example equal
to or less than about 20 m2/g, for example equal to or less than about 15 m2/g, for
example equal to or less than about 10 m /g. The alkali earth metal compound such as
calcium carbonate (e.g. PCC) may, for example, have a BET specific surface area equal
to or greater than about 1 m /g, for example equal to or greater than about 5 m2/g.
The alkali earth metal compound such as calcium carbonate (e.g. PCC) may, for
example, be present in the coating composition in an amount ranging from about 50 wt%
to about 98 wt% based on the total dry weight of the composition. For example, the
calcium carbonate may be present in the coating composition in an amount ranging from
about 55 wt% to about 95 wt%, for example from about 60 wt% to about 90 wt%, for
example from about 65 wt% to about 85 wt%, for example from about 70 wt% to about
80 wt% based on the total dry weight of the composition.
Anionic Dispersant
Any anionic dispersant suitable for dispersing fine particle solids may be used. The
anionic dispersant may, for example, comprise, consist essentially of or consist of
neutralized salts of polymers or copolymers (e.g. alkali metal salts and ammonium salts).
The salts may, for example, comprise an alkali metal salt (e.g. sodium salt) or an
ammonium salt.
The anionic dispersant may, for example, be one or more polycarboxylates (i.e. a
polymer having at least one monomer containing a carboxylate group), such as a vinyl
or olefinic group substituted with at least one carboxylic acid group or a water soluble
salt. The polycarboxylate may also comprise non-carboxylate containing monomers.
Exemplary monomers for a polycarboxylate anionic dispersant include, for example,
acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid,
maleic anhydride, isocrotonic acid, aconitic acid, mesaconic acid, sinapinic acid,
undecylenic acid, angelic acid, hydroxacrylic acid, and vinyl acetate. Copolymers may
include monomers containing a vinyl or olefinic group such as styrene. The
polycarboxylate may, for example, be partially or wholly neutralized salts of the polymer
or copolymer.
The anionic dispersant may, for example, be a polyacrylate and/or a salt of polyacrylate
(e.g. sodium polyacrylate) or a maleic anhydride copolymer and/or a salt of a maleic
anhydride copolymer. The anionic dispersant may, for example, be a homopolymer
and/or a copolymer of acrylic acid and/or methacrylic acid and/or maleic acid and/or
maleic anhydride. For example, the anionic dispersant may be a water soluble
homopolymer or copolymer of acrylic acid and/or methacrylic acid and/or maleic acid
(e.g. a maleic acrylic copolymer). For example, the anionic dispersant may comprise,
consist essentially of or consist of a homopolymer of acrylic acid. The anionic dispersant
may, for example, be partially or wholly neutralized salts of the polymer or copolymer.
The polymer or copolymer (e.g. maleic acrylic copolymer) may have a molar ratio of
acrylic acid units to maleic acid units ranging from 0.5:1 to 10:1 . The polymer or
copolymer (e.g. maleic acrylic copolymer) may have a mass average molecular mass
ranging from 1,000 to 100,000, for example a molecular mass ranging from 1,000 to 30,
000, from 2,000 to 8,000 or from 1,000 to 10,000.
Any combination of the exemplary anionic dispersants described herein may also be
used. Hereinafter, the invention may tend to be discussed in terms of polyacrylates, in
particular homopolymers of acrylic acid. However, the invention should not be construed
as being limited as such.
The anionic dispersant may, for example, be present in the coating composition in an
amount ranging from about 0.1 pph to about 5 pph. This is the dry weight of the anionic
dispersant based on the dry weight of the total inorganic particulate material in the
coating (e.g. 2 pph anionic dispersant is 2 g of dry anionic dispersant in 100 g of dry
inorganic particulate material). For example, the anionic dispersant may be present in
the coating composition in an amount ranging from about 0.1 pph to about 4 pph, for
example from about 0.1 pph to about 3 pph, for example from about 0.1 pph to about 2
pph, for example from about 0.1 pph to about 1 pph based on the total dry inorganic
particulate material in the composition. For example, the anionic dispersant may be
present in the coating composition in an amount ranging from about 0.5 pph to about 5
pph, for example from about 1 pph to about 5 pph, for example from about 1 pph to about
4 pph, for example from about 1 pph to about 3 pph, for example from about 1 pph to
about 2 pph based on the total dry inorganic particulate material in the composition.
Cationic Polymer
The term cationic polymer may, for example, encompass polymers possessing a net
positive charge. The cationic polymer may, for example, be a cationic dispersant. Thus,
the coating compositions provided herein may not comprise a cationic dispersant. The
cationic polymer may, for example, be a synthetic cationic polymer, thus the coating
compositions provided herein may not comprise a synthetic cationic dispersant. The
cationic polymer may, for example, be a polymeric amine, such as a polymer of
quaternary amines, or a polymer of amines that can be converted to quaternary amines,
and combinations thereof. The cationic polymer may contain two or more different
cationic monomers, or contain a cationic monomer and other non-ionic or anionic
monomers. Suitable monomers in the cationic polymer may include one or more
monomers selected from water soluble polyolefins containing quaternary ammonium
groups which may be in the polymer chain, for example, epichlorohydrin/dimethylamine
copolymers (EPI/DMA), alkyl-or dialkyldiallylammonium halides, such as
dimethyidiallylammonium chloride (DMDAAC), diethyldiallyl ammonium chloride
(DEDAC), dimethyldiallyl ammonium bromide (DMDAAB) and diethyldiallyl ammonium
bromide (DEDAAB), methylacryloyl-oxyethyltrimethyl ammonium chloride (METAC),
acryloy-oxyethyltrimethyl ammonium chloride (AETAC), methacryloyloxyethyltrimethyl
ammonium methosulfate (METAMS), acryloyoxyethyltrimethyl ammonium methosulfate
(AETAMS) or methacrylamido-propyitrimethyl ammonium chloride (MAPTAC). Other
exemplary monomers include dimethylaminoethylacrylate,
dimethylaminoethylmethacrylate, dimethylamino propylmethacrylamide and its methyl
chloride or dimethyl sulfate quaternary ammonium salts, dimethylaminoethylacrylate and
its methyl chloride salt, methacrylamidopropyltrimethylammonium chloride and its
unquaternized amine form, acrylamidopropyltrimethylammonium chloride and its
unquaternized amine form, and dimethylamine and epichlorohydrin.
Exemplary polymers may also include products of copolymerizing epichlorohydrin and
amines, especially secondary amines, alone or in combination, and polymers made by
polymerizing any of the above listed cationic monomers with non-ionic monomers such
as acrylamide, methacrylamide or N, N- dimethylacrylamide.
Exemplary cationic polymers may include polydiallyldimethylammonium chloride
(pDADMAC), copolymers of quaternary dimethylaminoethyl acrylate, and copolymers of
quaternary dimethylaminoethyl methacrylate, and copolymers of
epichlorohydrin/dimethylamine (EPI/DMA). Exemplary suitable polymers are
commercially available as AgeflocB-50LV®, Nalco62060®, Nalco7135, Nalco 7132®,
and Nalco 8850®.
Other exemplary cationic polymers may include condensates of formaldehyde with
melamine, urea, or cyanoguanidine. The cationic polymers may also include copolymers
of the aforementioned cationic monomers with nonionic monomers, such as acrylamide,
methacrylamide, vinyl acetate, vinyl alcohol, N-methylolacrylamide, or diacetone
acrylamide, and/or anionic monomers, such as acrylic acid, methacrylic acid, AMPS, or
maleic acid, such that the net charge of these polymers is cationic.
The cationic polymer may have a weight average molecular weight ranging from about
1,000 daltons to about 5,000, 000 daltons, as determined by gel permeation
chromatography. For example, the cationic polymer may have a molecular weight of at
least about 1,000, such as molecular weights of at least about 2,000, at least about
5,000. at least about 10,000, at least about 25,000, at least about 50,000, at least about
100,000, at least about 250,000, at least about 500,000 or at least about 1,000, 000.
Physical blends of cationic polymers containing different cationic moieties or blends of
cationic polymers possessing different molecular weight averages and distributions may
also be used.
The bulk viscosity of the at least one cationic polymer may also reflect its weight average
molecular weight. For example, the cationic polymer may have a bulk viscosity of at least
about 300 cps, such as a bulk viscosity of at least about 400 cps. For example, the
cationic polymer may have a bulk viscosity ranging from about 300 cps to about 10,000
cps. For example, the cationic polymer has a bulk viscosity of at least about 2,000, such
as a bulk viscosity of at least about 3,000 cps, such as a bulk viscosity of at least about
4,000 cps, or bulk viscosities ranging from about 4,000 cps to about 10,000, or from
about 4,000 cps to about 6,000 cps.
The cationic polymer may, for example, be present in the coating composition in an
amount less than about 2 wt% relative to the total weight of inorganic particulate material
in the composition or relative to the total weight of alkali earth metal compound such as
calcium carbonate in the composition. For example, the cationic polymer may be present
in the coating composition in an amount less than about 1.5 wt%, for example less than
about 1 wt%, for example less than about 0.5 wt%, for example less than about 0.1 wt%,
for example less than about 0.05 wt% relative to the total weight of inorganic particulate
material in the composition or relative to the total weight of alkali earth metal compound
such as calcium carbonate in the composition. The cationic polymer may, for example,
not be present in the coating composition (i.e. present in the coating composition in an
amount of 0 wt%). For example, the coating composition may comprise from 0 wt% to
about 2 wt% cationic polymer. For example, the coating composition may comprise from
about 0.05 wt% or from about 0.1 wt% or from about 0.5 wt% or from about 1 wt% to
about 2 wt% cationic polymer relative to the total weight of inorganic particulate material
in the coating composition or relative to the total weight of alkali earth metal compound
such as calcium carbonate in the composition.
Further Additives
Additional Inorganic Particulate Material
The coating composition may, for example, comprise one or more additional inorganic
particulate materials. For example, the coating composition may consist essentially of or
consist of a binder, an alkali earth metal compound, an anionic dispersant and an
additional inorganic particulate material (e.g. an aluminosilicate). Use of an additional
inorganic particulate material (e.g. an aluminosilicate such as kaolin, for example
hydrous kaolin) may, for example, improve the suitability of the coated paper to be used
for laser marking.
The additional inorganic particulate material may, for example, be selected from an
alkaline earth metal compound (e.g. alkali earth metal carbonate or sulphate (e.g.
magnesium carbonate, dolomite and gypsum)); a phyllosilicate, an aiuminosilicate (e.g.
hydrous kandite clay including kaolin, halloysite clay, ball clay, anhydrous (calcined)
kandite clay such as metakaolin, fully calcined kaolin and mica); talc, chlorite,
pyrophyllite, serpentine, perlite, diatomaceous earth, magnesium hydroxide, aluminium
trihydrate and combinations thereof. The additional inorganic particulate material may,
for example, be an aiuminosilicate, for example, kaolin. For example, the coating
composition may further comprise hydrous kaolin or partially calcined kaolin or fully
calcined kaolin.
For example, the aiuminosilicate may be an anhydrous kaolin clay having at least about
65 wt% of particles smaller than 2 pm, for example at least about 75 wt% of particles
smaller than 2 pm, for example at least about 85 wt% of particles smaller than 2 pm, for
example at least about 90 wt% of particles smaller than 2 pm. The anhydrous kaolin clay
may, for example, have a dso ranging from about 0.4 pm to about 0.8 pm, for example
from about 0.5 pm to about 0.7 pm, for example about 0.65 pm. The anhydrous kaolin
clay may, for example, have a surface area up to about 20 m2/g, for example up to about
15 m2/g, for example ranging from about 10 m2/g to about 15 m2/g.
For example, the aiuminosilicate may be a hydrous clay having at least about 65 wt% of
particles smaller than 2 pm, for example at least about 75 wt% of particles smaller than
2 pm, for example at least about 85 wt% of particles smaller than 2 pm, for example at
least about 90 wt% of particles smaller than 2 pm. The hydrous aiuminosilicate may, for
example, have a least about 50 wt% of particles smaller than 1 pm, for example at least
about 60 wt% of particles smaller than 1 pm, for example at least about 65 wt% of
particles smaller than 1 pm, for example at least about 70 wt% of particles smaller than
1 pm. The hydrous aiuminosilicate may, for example, have at least about 30 wt% of
particles smaller than 0.5 pm, for example at least about 35 wt% of particles smaller than
0.5 pm, for example at least about 40 wt% of particles smaller than 0.5 pm, for example
at least about 45 wt% of particles smaller than 1 pm. The hydrous aiuminosilicate may,
for example, have a dso ranging from about 0.4 pm to about 0.7 pm, for example from
about 0.5 pm to about 0.6 pm. The hydrous aiuminosilicate may, for example, have at
least about 90 wt% of particles smaller than 2 pm, at least about 70 wt% of particles
smaller than 1 pm and at least about 45 w†% of particles smaller than 0.5 pm. The
hydrous aluminosilicate may, for example, have a surface area up to about 20 m2/g, for
example up to about 15 m /g, for example ranging from about 10 m2/g to about 15 m2/g.
The weight ratio of alkali earth metal compound (e.g. calcium carbonate) to additional
inorganic particulate materia! (e.g. aluminosilicate) may range from about 60:40 to about
95:5. For example, the weight ratio of alkali earth metal compound (e.g. calcium
carbonate) to additional inorganic particulate material (e.g. aluminosilicate) may range
from about 65:35 to about 90:10, for example from about 70:30 to about 85:15, for
example from about 75:25 to about 85:15. For example, the weight ratio of alkali earth
metal compound (e.g. calcium carbonate) to additional inorganic particulate material
(e.g. aluminosilicate) may be about 85:15.
The additional inorganic particulate material (e.g. aluminosilicate) may, for example, be
present in the coating composition in an amount ranging from about 0 pph to about 30
pph. This is the dry weight of the additional inorganic particulate material based on the
dry weight of the total inorganic particulate material in the coating composition (e.g. 12
pph kaolin is 12 g of kaolin in 100 g of total dry inorganic particulate material). For
example, if the total weight of inorganic particulate material in the composition is 100 g ,
15 g (15 pph) may be kaolin and 85 g (85 pph) may be alkali earth metal compound. The
additional inorganic particulate material (e.g. aluminosilicate) may, for example, be
present in the coating composition in an amount ranging from about 2 pph to about 25
pph, for example from about 5 pph to about 20 pph, for example from about 10 pph to
about 15 pph, for example about 15 pph based on the total dry inorganic particulate
material in the composition. The additional inorganic particulate material may, for
example, be used in an amount that enables acceptable or good laser marking of a
coated paper.
Other Optional Additives
The coating compositions may, for example, include one or more optional additives, if
desired. For example, the coating compositions may include one or more of the optional
additives listed below. For example, the coating composition may consist essentially of
or consist of a binder, a calcium carbonate, an anionic dispersant, optionally an additional
inorganic particulate material, optionally a cationic polymer and optionally one or more
of the additives listed below. For example, the coating composition may consist
essentially of or consist of a binder, a calcium carbonate, an anionic dispersant,
optionally an additional inorganic particulate material and optionally one or more of the
additives listed below. For example, the coating composition may consist essentially of
or consist of a binder, a calcium carbonate, an anionic dispersant and optionally one or
more of the additives listed below.
Such optional additives, where present, may suitably be selected from known additives
for coating compositions (e.g. paper coating compositions). Some of these optional
additives may provide more than one function in the coating composition. Examples of
known classes of optional additives are as follows:
(a) one or more cross-linkers (e.g. glyoxals, melamine formaldehyde resins,
ammonium zirconium carbonates);
(b) one or more water retention aids (e.g. sodium carboxymethyl cellulose,
hydroxyethyl cellulose, PVA (polyvinyl acetate), starches, proteins, polyacrylates, gums,
alginates, polyacrylamide bentonite and other commercially available products sold for
such applications);
(c) one or more viscosity modifiers or thickeners (e.g. polyacrylates, emulsion
copolymers, dicyanamide, triols, polyoxyethylene ether, urea, sulphated castor oil,
polyvinyl pyrrolidone, montmorillonite, CMC (carboxymethyl celluloses), sodium alginate,
xanthan gum, sodium silicate, acrylic acid copolymers, HMC (hydroxymethyl celluloses,
HEC (hydroxyethyl celluloses));
(d) one or more lubricity or calendering aids (e.g. calcium stearate, ammonium
stearate, zinc stearate, wax emulsions, waxes, alkyl ketene dimer, glycols);
(e) one or more additional dispersants (e.g. polyelectrolytes such as polyacrylates and
copolymers containing polyacrylate species, polyacrylate salts, sodium
hexametaphosphates, non-ionic polyol, polyphosphoric acid, condensed sodium
phosphate, non-ionic surfactants, alkanolamine and other reagents commonly used for
this function);
(f) one or more antifoamers or defoamers (e.g. blends of surfactants, tributyl
phosphate, fatty polyoxyethylene esters plus fatty acid alcohols, fatty acid soaps, silicone
emulsions, silicone-containing compositions, waxes and inorganic particulates in mineral
oil, blends of emulsified hydrocarbons and other compounds sold commercially to carry
out this function);
(g) one or more dry or wet pick improvement additives (e.g. melamine resin,
polyethylene emulsions, urea formaldehyde, melamine formaldehyde, polyamide,
calcium stearate, styrene maleic anhydride and other compounds sold commercially for
this function);
(h) one or more dry or wet rub improvement and abrasion resistance additives (e.g.
glyoxal based resins, oxidized polyethylenes, melamine resins, urea formaldehyde,
melamine formaldehyde, polyethylene wax, calcium stearate and other compounds sold
commercially for this function);
(i) one or more gloss-ink hold-out additives (e.g. oxidized polyethylenes, polyethylene
emulsions, waxes, casein, guar gum, CMC, HMC, calcium stearate, ammonium stearate,
sodium alginate and other compounds sold commercially for this function);
(j) one or more optical brightening agents (OBA) or fluorescent whitening agents
(FWA) (e.g. stilbene derivatives);
(k) one or more dyes;
(I) one or more biocides or spoilage control agents (e.g. metaborate, sodium
dodecylbenene sulphonate, thiocyanate, organosulphur, sodium benzonate and other
compounds sold commercially for this function);
(m) one or more levelling or evening aids (e.g. non-ionic polyol, polyethylene
emulsions, fatty acid esters and alcohol derivatives, alcohol/ethylene oxide, sodium
CMC, HEC, alginates, calcium stearate and other compounds sold commercially for this
function);
(n) one or more grease or oil resistance agents (e.g. oxidized polyethylenes, latex,
SMA (styrene maleic anhydride), polyamide, waxes, alginate, protein, CMC, HMC);
(o) one or more water resistance additives (e.g. oxidized polyethylenes, ketone resin,
anionic latex, polyurethane, SMA, glyoxal, melamine resin, urea formaldehyde,
melamine formaldehyde, polyamide, glyoxals, stea rates and other compounds sold
commercially for this function);
(p) one or more insolubilizers; and
(q) one or more surfactants.
Any of the above additives and additive types may be used alone or in admixture with
each other and with other additives, if desired.
For all of the above additives, the percentages by weight (based on the total solids
content (100%) of the composition) can vary as understood by those skilled in the art.
Where the additive is present in a minimum amount, the minimum amount may be about
0.01% by weight based on the total solids content of the composition. The maximum
amount of any one or more of the above additives may, for example, be about 5.0% by
weight based on the total solids content of the composition. For example, the maximum
amount may be about 3.0% or 2.0% by weight based on the total solids content of the
composition.
The coating composition may, for example, comprise a starch binder (e.g. a cationic
starch binder) and a precipitated calcium carbonate. For example, the coating
composition may comprise a starch binder (e.g. a cationic starch binder), a precipitated
calcium carbonate and an anionic dispersant that is a homopolymer or copolymer of
(meth)acrylic acid. For example, the coating composition may comprise a starch binder
(e.g. a cationic starch binder), a precipitated calcium carbonate, an anionic dispersnt that
is a homopolymer or copolymer of (meth)acrylic acid and an aluminosilicate (e.g. kaolin).
Coated Paper
There is also provided herein coated paper. The coated paper may, for example,
comprise a fibrous substrate coated with a coating composition. The coating composition
may, for example, be in accordance with any aspect or embodiment described herein,
including all possible combinations and variations thereof.
Ink printed on the coated paper may, for example, have a black print density equal to or
greater than about 1.0. For example, ink printed on the coated paper may have a black
print density equal to or greater than about 1.1, for example equal to or greater than
about 1.2, for example equal to or greater than about 1.3, for example equal to or greater
than about 1.4. Ink printed on the coated paper may, for example, have a black print
density up to about 2.0, for example up to about 1.9, for example up to about 1.8, for
example up to about 1.7, for example up to about 1.6, for example up to about 1.5.
Ink printed on the coated paper may, for example, have a magenta print density equal to
or greater than about 0.7. For example, ink printed on the coated paper may have a
magenta print density equal to or greater than about 0.8, for example equal to or greater
than about 0.9, for example equal to or greater than about 1.0, for example equal to or
greater than about 1.1, for example equal to or greater than about 1.2. Ink printed on the
coated paper may, for example, have a magenta print density up to about 2.0, for
example up to about 1.9, for example up to about 1.8, for example up to about 1.7, for
example up to about 1.6, for example up to about 1.5.
Ink printed on the coated paper may, for example, have a cyan print density equal to or
greater than about 0.7. For example, ink printed on the coated may have a cyan print
density equal to or greater than about 0.8, for example equal to or greater than about
0.9, for example equal to or greater than about 1.0, for example equal to or greater than
about 1. , for example equal to or greater than about 1.2. Ink printed on the coated paper
may, for example, have a cyan print density up to about 2.0, for example up to about 1.9,
for example up to about 1.8, for example up to about 1.7, for example up to about 1.6,
for example up to about 1.5.
Ink printed on the coated paper may, for example, have a yellow print density equal to
or greater than about 0.7. For example, ink printed on the coated paper may have a
yellow print density factor equal to or greater than about 0.8, for example equal to or
greater than about 0.9, for example equal to or greater than about .0, for example equal
to or greater than about 1. 1 , for example equal to or greater than about 1.2. Ink printed
on the coated paper may, for example, have a yellow print density up to about 2.0, for
example up to about 1.9, for example up to about 1.8, for example up to about 1.7, for
example up to about 1.6, for example up to about 1.5.
Ink printed on the coated paper may, for example, have a print index equal to or greater
than about 330. For example, ink printed on the coated paper may have a print index
equal to or greater than about 335, for example equal to or greater than about 340, for
example equal to or greater than about 345, for example equal to or greater than about
350, for example equal to or greater than about 355, for example equal to or greater than
about 360, for example equal to or greater than about 365, for example equal to or
greater than about 370, for example equal to or greater than about 375, for example
equal to or greater than about 380, for example equal to or greater than about 385, for
example equal to or greater than about 390, for example equal to or greater than about
395, for example equal to or greater than about 400, for example equal to or greater than
about 405, for example equal to or greater than about 410, for example equal to or
greater than about 415, for example equal to or greater than about 420, for example
equal to or greater than about 425, for example equal to or greater than about 430, for
example equal to or greater than about 435, for example equal to or greater than about
440. Ink printed on the coated paper may, for example, have a print index up to about
600, for example up to about 550 , for example up to about 500. For example, ink printed
on the coated paper may have a print index up to about 490, for example up to about
480, for example up to about 460, for example up to about 470, for example up to about
460, for example up to about 450.
Print density and print index are as defined and measured as described above.
Ink printed on the coated paper may, for example, have a line quality equal to or greater
than about 0.8. For example, ink printed on the coated paper may have a line quality
equal to or greater than about 0.85, for example equal to or greater than about 0.9. Ink
printed on the coated paper may, for example, have a line quality up to about 1.0, for
example up to about 0.99, for example up to about 0.98, for example up to about 0.97,
for example up to about 0.96, for example up to about 0.95.
Ink printed on the coated paper may, for example, have an edge quality equal to or less
than about 15. For example, ink printed on the coated paper may have an edge quality
equal to or less than about 14, for example equal to or less than about 13, for example
equal to or less than about 12. Ink printed on the coated paper may, for example, have
an edge quality equal to or more than about 0 . For example, ink printed on the coated
paper may have an edge quality equal to or more than about 1, for example equal to or
more than about 2, for example equal to or more than about 3 , for example equal to or
more than about 4 , for example equal to or more than about 5 .
Line and edge quality are as defined and measured as described above.
Ink printed on the coated paper may, for example, have a smudge index after 15 seconds
equal to or greater than about 9 . For example, ink printed on the coated paper may have
a smudge index after 15 seconds equal to or greater than about 9.5, for example equal
to or less than about 10. For example, ink printed on the coated paper may have a
smudge index after 15 seconds equal to about 10. Smudge index is as defined and
measured as described above.
The term paper, as used in connection with the present invention, should be understood
to mean all forms of paper, including board, such as, for example, white-lined board and
linerboard, cardboard, paperboard, coated board, and the like. There are numerous
types of paper, coated or uncoated, which may be coated using the compositions
disclosed herein, including paper suitable for food packaging, perishable goods other
than food, e.g., pharmaceutical products and compositions, books, magazines,
newspapers and the like, and office papers. The paper may be calendered or super
calendared as appropriate; for example super calendered magazine paper for
rotogravure and offset printing may be made according to the present methods. Paper
suitable for light weight coating (LWC), medium weight coating (MWC) or machine
finished pigmentisation (MFP) may also be coated using the present compositions. The
paper may, for example, be particularly suitable for ink jet printing. The substrate can be
of any basis weight, for example from about 20 gsm to about 300 gsm, for example from
about 50 gsm to about 200 gsm, for example from about 60 gsm to about 120 gsm.
Paper generally comprises a fibrous substrate, such as, for example, cellulose fibres
derived from, for example, wood, rags or grasses. The fibrous substrate may, for
example, be derived from recycled pulp or virgin pulp (i.e. pulp which is not derived from
a recycled material). Alternatively, the fibrous substrate may comprise a mixture of
recycled pulp and virgin pulp. The paper may, for example, be a wood-free paper.
The paper substrate may have opposing first and second surfaces. The coating
composition may, for example, be present on the first surface, the second surface, or
both. The coating composition may, for example, be applied directly to the fibrous
substrate. Alternatively, the coating composition may be applied to an intermediate layer
between the fibrous substrate and the coating composition. The coating composition
may, for example, be a continuous coating on one or more surfaces of the paper.
Alternatively, the coating composition may be discontinuous in that it covers only part of
one or more surfaces of the paper.
The coating composition may, for example, have a coating weight between about 1 gsm
and about 20 gsm (grams per m2) , for example between about 2 gsm and about 15 gsm,
for example between about 5 gsm and about 10 gsm, for example about 10 gsm.
Methods of Making Coating Compositions and Coated Paper
There is further provided a method of making the coating composition described herein
and a method of making the coated paper described herein. The coating composition
and coated paper may, for example, be in accordance with any aspect or embodiment
described herein, including all combinations and possible variations thereof.
The method of making the coating composition may, for example, comprise combining
a binder, an alkali earth metal compound such as calcium carbonate, and an anionic
dispersant, optionally a cationic polymer, optionally an additional inorganic particulate
material and optionally a further additive. The combining may be performed by any
suitable mixing techniques as are known in the art.
The components of the coating composition may, for example, be combined in any order.
For example, a first composition (e.g. aqueous slurry) comprising the inorganic
particulate material (such as the alkali earth metal compound (e.g. calcium carbonate)),
anionic dispersant, optional cationic polymer and the optional further additive may first
be made by combining the respective components and then this composition may be
combined with the binder to make the coating composition. The first composition may,
for example, be screened to obtain a desired particle size distribution before coating.
This first composition may, for example, be anionic.
The method of making the coated paper may, for example, comprise coating a fibrous
substrate with a coating composition as described herein. The coating composition may
be in accordance with any aspect or embodiment described herein, including all
combinations and possible variations thereof.
The coating process may be carried out using standard techniques which are known to
the skilled person. The coating process may also involve calendaring or supercalendaring
the coated substrate.
Methods of coating paper and other sheet materials, and apparatus for performing the
methods, are widely published and well known. Such known methods and apparatus
may conveniently be used for preparing coated paper. For example, there is a review of
such methods published in Pulp and Paper International, May 1994, page 8 et seq.
Sheets may be coated on the sheet forming machine, i.e., "on-machine," or "off-machine"
on a coater or coating machine. Use of high solids compositions is desirable in the
coating method because it leaves less water to evaporate subsequently. However, as is
well known in the art, the solids level should not be so high that high viscosity and
levelling problems are introduced. The methods of coating may be performed using an
apparatus comprising (i) an application for applying the coating composition to the
material to be coated and (ii) a metering device for ensuring that a correct level of coating
composition is applied. When an excess of coating composition is applied to the
applicator, the metering device is downstream of it. Alternatively, the correct amount of
coating composition may be applied to the applicator by the metering device, e.g., as a
film press. At the points of coating application and metering, the paper web support
ranges from a backing roll, e.g. via one or two applicators, to nothing (i.e. just tension).
The time the coating is in contact with the paper before the excess is finally removed is
the dwell time - and this may be short, long or variable. The coating may be added by a
coating head at a coating station. According to the quality desired, paper grades are
uncoated, singie-coated, double-coated and even triple-coated. When providing more
than one coat, the initial coat (precoat) may have a cheaper formulation and optionally
coarser pigment in the coating composition. A coater that is applying coating on each
side of the paper will have two or four coating heads, depending on the number of coating
layers applied on each side. Most coating heads coat only one side at a time, but some
roll coaters (e.g., film presses, gate rolls, and size presses) coat both sides in one pass.
Examples of known coaters which may be employed include, without limitation, air knife
coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll o r
blade coaters, cast coaters, laboratory coaters, gravure coaters, kisscoaters, liquid
application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion
coaters.
Water may be added to the solids comprising the coating composition to give a
concentration of solids which is preferably such that, when the composition is coated
onto a sheet to a desired target coating weight, the composition has a rheology which is
suitable to enable the composition to be coated with a pressure (i.e., a blade pressure)
of between 1 and 1.5 bar.
The coating composition may, for example, be printed on the paper product, e.g., printed
on a surface of the fibrous substrate of the paper product. The printing may utilize a
technique selected from offset printing, flexographic printing or rotogravure printing,
thereby allowing the coating composition to be applied to areas where it is required.
Offset printing is a widely used printing technique, as will be well understood by a person
of ordinary skill in the art. The coating composition is transferred (or "offset") from a plate
to a rubber blanket, then to the surface of the substrate (e.g., paper substrate). The
substrate may be sheet-fed or web-fed. The web-fed process may be heatset or coldset.
The coated paper may be formable or formed into a three-dimensional product, which
may be suitable as food grade or pharmaceutical grade packaging. Coated products
(e.g. coated paper products) include brown corrugated boxes, flexible packaging
including retail and shopping bags, food and hygiene bags and sacks, milk and beverage
cartons, boxes suitable for cereals and the like, self-adhesive labels, disposable cups
and containers, envelopes, cigarette paper and bible paper.
Method of Printing
There is further provided herein a method of printing comprising applying ink to the
coated paper described herein or to paper coated with the coating compositions
described herein. The coated paper and coating compositions may be in accordance
with any aspect or embodiment of the present invention, including all combinations and
possible variations thereof.
The method may, for example, comprise ink jet printing. The method may, for example,
comprise offset printing and/or flexographic printing. For example, the method may
comprise ink jet printing and one or more of offset printing and flexographic printing.
The ink may, for example, be an ink jet ink. The ink may, for example, be a pigmentbased
ink. The ink may, for example, be a dye-based ink. The coating compositions
and/or coated paper of the present invention may, for example, be adapted for printing
using an ink jet ink. The coating compositions and/or coated paper of the present
invention may, for example, be adapted for printing using a pigment-based ink and/or a
dye-based ink.
EXAMPLES
Example 1
The coating compositions shown in Table 1 were prepared by first dispersing the
inorganic particulate material with dispersant to obtain minimum Brookfield viscosity and
incorporating the inorganic particulate material into the coating composition. These
compositions were used to coat paper by hand draw down (HDD) technique using a wire
wound bar. The solids content of the compositions were adjusted until the coatings were
obtained with a dry coat weight ranging from about 5 to about 7 gsm.
The binder was a cationic starch binder.
The calcium carbonate was a precipitated calcium carbonate having a dso of about 1.1
m, approximately 74 wt% of particles smaller than 2 pm and a specific surface area of
about 6.6 m2/g.
The anionic dispersant was an anionic homopolymer of acrylic acid. The anionic
dispersant was a dispersion solution with solids content of about 42.6 wt%.
The additional inorganic particulate material used in Composition 2 was an anhydrous
kaolin clay having at least about 90 wt% of particles smaller than 2 pm, a dso of about
0.65 pm and a specific surface area of about 4 m2/g.
The additional inorganic particulate material used in Composition 3 was a hydrous kaolin
clay having a dso of about 0.6 pm, at least about 90 wt% of particles smaller than 2 pm
and a specific surface area of about 11 m /g.
Table 1.
The black, magenta, cyan and yellow print density, the line quality and the edge quality
of ink printed on paper coated with Compositions 1 to 3, an uncoated white top liner
board (Control Paper 1), a 90 gsm uncoated wood-free paper (Control Paper 2) and a
different 90 gsm fine, uncoated wood-free paper (Control Paper 3) was determined by
the methods described above. The ink used in these tests was a commercially available
water based, pigment-based ink designed for large format ink jet press. The print density
test was performed three times for each sample and the average print density noted.
The results are shown in Table 2 .
Table 2.
Example 2
The coating compositions shown in Table 3 were prepared as described above.
The binder was a cationic starch binder.
The calcium carbonate was a precipitated calcium carbonate having a dso of about 1.1
m, approximately 74 wt% of particles smaller than 2 pm and a specific surface area of
about 6.6 m2/g.
The anionic dispersant was an anionic homopolymer of acrylic acid. The anionic
dispersant was a dispersion solution with solids content of about 42.6 wt%.
The additional inorganic particulate material used in Composition 4 was an anhydrous
kaolin clay having at least about 90 wt% of particles smaller than 2 m i i , a dso of about
0.65 and a specific surface area of about 14 m2/g.
Table 3.
The black, magenta, cyan and yellow print density, print index, line quality, edge quality
and smudge index (15 seconds) of a dye-based ink for ink jet printing, printed on paper
coated with Compositions 4 and 5, a copy paper and a commercially available silicacoated
paper, was determined by the methods described above. The print density test
was performed three times for each sample and the average print density noted.
The results are shown in Table 4.
Table 4.
The foregoing broadly describes certain embodiments of the present invention without
limitation. Variations and modifications as will be readily apparent to those skilled in the
art are intended to be within the scope of the present invention as defined in and by the
appended claims.

The following numbered paragraphs define particular embodiments of the present
invention:
1. A coating composition comprising:
a binder;
an alkali earth metal compound;
an anionic dispersant; and
optionally a cationic polymer;
wherein the coating composition has a solids content of at least about 45
wt% and a Brookfield viscosity equal to or less than about 1500 mPa.s.
2. The coating composition of paragraph 1, wherein the alkali earth metal
compound has a dso equal to or greater than about 0.4 m, for example equal to
or greater than about 0.6 pm, for example equal to or greater than about 0.8
pm, for example equal to or greater than about .0 m.
3. The coating composition of paragraph 1 or 2, wherein the alkali earth metal
compound has a BET specific surface area less than about 40 m2/g, for
example equal to or less than about 30 m /g, for example equal to or less than
about 20 m2/g, for example equal to or less than about 10 m /g.
4 . The coating composition of any one of paragraphs 1 to 3 , wherein the cationic
polymer is present in the coating composition in an amount less than about 2
wt%, for example equal to or less than about 1 wt%, for example 0 wt%, relative
to the total weight of inorganic particulate material in the composition.
5. The coating composition of any one of paragraphs 1 to 4 , wherein the alkali
earth metal compound comprises, consists essentially of or consists of an alkali
earth metal carbonate.
6 . The coating composition of any one of paragraphs 1 to 5 , wherein the alkali
earth metal compound comprises, consists essentially of or consists of calcium
carbonate.
The coating composition of any one of paragraphs 1 to 6 , wherein the alkali
earth metal compound comprises, consists essentially of or consists of
precipitated calcium carbonate.
The coating composition of any one of paragraphs 1 to 7 , wherein the coating
composition further comprises an aluminosilicate.
The coating composition of any one of paragraphs 1 to 8, wherein the
aluminosilicate is kaolin (e.g. calcined kaolin or hydrous kaolin).
The coating composition of paragraph 8 or 9 , wherein the weight ratio of alkali
earth metal compound to aluminosilicate ranges from about 60:40 to about
95:5, for example from about 70:30 to about 90:10, for example about 85:15.
The coating composition of any one of paragraphs 1 to 10, wherein the anionic
dispersant comprises, consists essentially of or consists of a homopolymer
and/or a copolymer of (meth)acrylic acid.
The coating composition of any one of paragraphs 1 to 11, wherein ink printed
on paper coated with the coating composition has a black print density equal to
or greater than about 1.0, for example equal to or greater than about 1.1, for
example equal to or greater than about .2.
The coating composition of any one of paragraphs 1 to 12, wherein ink printed
on paper coated with the coating composition has a magenta print density equal
to or greater than about 0.7, for example equal to or greater than about 0.8, for
example equal to or greater than about 0.9.
The coating composition of any one of paragraphs 1 to 13, wherein ink printed
on paper coated with the coating composition has a cyan print density equal to
or greater than about 0.7, for example equal to or greater than about 0.8, for
example equal to or greater than about 0.9.
The coating composition of any one of paragraphs 1 to 14, wherein ink printed
on paper coated with the coating composition has a yellow print density equal to
or greater than about 0.7, for example equal to or greater than about 0.8, for
example equal to or greater than about 0.9.
The coating composition of any one of paragraphs 1 to 15, wherein ink printed
on paper coated with the coating composition has a print index equal to or
greater than about 400, for example equal to or greater than about 420, for
example equal to or greater than about 440.
The coating composition of any one of paragraphs 1 to 16, wherein ink printed
on paper coated with the coating composition has a line quality equal to or
greater than about 0.8, for example equal to or greater than about 0.85, for
example equal to or greater than about 0.9.
The coating composition of any one of paragraphs 1 to 17, wherein ink printed
on paper coated with the coating composition has an edge quality equal to or
less than about 15, for example equal to or less than about 14, for example
equal to or less than about 13.
The coating composition of any one of paragraphs 1 to 18, wherein ink printed
on paper coated with the coating composition has a smudge index after 15
seconds equal to or greater than about 9 , for example equal to or greater than
about 9.5, for example about 10.
The coating composition of any one of paragraphs 12 to 19, wherein the ink is a
pigment-based ink or a dye-based ink.
The coating composition of any one of paragraphs 1 to 20, wherein the coating
composition has a Brookfield viscosity equal to or less than about 1000 mPa.s,
for example equal to or less than about 800 mPa.s.
The coating composition of any one of paragraphs 1 to 2 1, wherein the coating
composition has a solids content of at least about 50 wt%.
Paper comprising a fibrous substrate coated with the coating composition of
any one of paragraphs 1 to 22.
A method of making the coating composition of any one of paragraphs 1 to 22
comprising combining the binder, alkali earth metal compound and anionic
dispersant.
A method of making the coated paper of paragraph 23 comprising coating a
fibrous substrate with a coating composition of any one of paragraphs 1 to 22.
A method of printing comprising applying ink to a paper coated with the coating
composition of any one of paragraphs 1 to 22 or the coated paper of paragraph
A coating composition comprising:
a binder;
an alkali earth metal compound;
an anionic dispersant; and
optionally a cationic polymer;
wherein the coating composition has a solids content of at least about 45
wt% and a Brookfield viscosity equal to or less than about 1500 mPa.s.
The coating composition of claim 1, wherein the alkali earth metal
compound has:
i) a dso equal to or greater than about 0.4 pm, for example equal to or
greater than about 0.6 pm, for example equal to or greater than about 0.8
pm, for example equal to or greater than about .0 pm; and/or
ii) a BET specific surface area less than about 40 m /g, for example equal to
or less than about 30 m2/g, for example equal to or less than about 20 m2/g,
for example equal to or less than about 10 m2/g.
The coating composition of claim 1 or 2 , wherein the cationic polymer is
present in the coating composition in an amount less than about 2 wt%, for
example equal to or less than about 1 wt%, for example 0 wt%, relative to
the total weight of inorganic particulate material in the composition.
The coating composition of any one of claims 1 to 3, wherein the alkali earth
metal compound comprises, consists essentially of or consists of an alkali
earth metal carbonate, for example calcium carbonate, for example
precipitated calcium carbonate (PCC).
The coating composition of any one of claims 1 to 4, wherein the coating
composition further comprises an aluminosilicate, for example kaolin (e.g.
calcined kaolin or hydrous kaolin).
6. The coating composition of claim 5, wherein the weight ratio of alkali earth
metal compound to aluminosi!icate ranges from about 60:40 to about 95:5,
for example from about 70:30 to about 90:10, for example about 85:15.
7 . The coating composition of any one of claims 1 to 6, wherein the anionic
dispersant comprises, consists essentially of or consists of a homopolymer
and/or a copolymer of (meth)acrylic acid.
8. The coating composition of any one of claims 1 to 7 , wherein ink printed on
paper coated with the coating composition has:
i) a black print density equal to or greater than about 1.0, for example
equal to or greater than about 1.1, for example equal to or greater
than about 1.2; and/or
ii) a magenta print density equal to or greater than about 0.7, for
example equal to or greater than about 0.8, for example equal to or
greater than about 0.9; and/or
iii) a cyan print density equal to or greater than about 0.7, for example
equal to or greater than about 0.8, for example equal to or greater
than about 0.9; and/or
iv) a yellow print density equal to or greater than about 0.7, for example
equal to or greater than about 0.8, for example equal to or greater
than about 0.9.
9. The coating composition of any one of claims 1 to 8, wherein ink printed on
paper coated with the coating composition has:
i) a print index equal to or greater than about 400, for example equal to
or greater than about 420, for example equal to or greater than
about 440; and/or
ii) a line quality equal to or greater than about 0.8, for example equal to
or greater than about 0.85, for example equal to or greater than
about 0.9; and/or
iii) an edge quality equal to or less than about 15, for example equal to
or less than about 14, for example equal to or less than about 13;
and/or
iv) a smudge index after 15 seconds equal to or greater than about 9,
for example equal to or greater than about 9.5, for example about
10.
10. The coating composition of claim 8 or 9, wherein the ink is a pigment-based
ink or a dye-based ink.
11. The coating composition of any one of claims 1 to 10, wherein the coating
composition has:
i) a Brookfield viscosity equal to or less than about 1000 mPa.s, for
example equal to or less than about 800 mPa.s; and/or
ii) a solids content of at least about 50 wt%.
12. Paper comprising a fibrous substrate coated with the coating composition of
any one of claims 1 to 11.
13. A method of making the coating composition of any one of claims 1 to 11
comprising combining the binder, alkali earth metal compound and anionic
dispersant.
14. A method of making the coated paper of claim 2 comprising coating a
fibrous substrate with a coating composition of any one of claims 1 to 11.
15. A method of printing comprising applying ink to a paper coated with the
coating composition of any one of claims 1 to 11 or the coated paper of
claim 12.