Note: Descriptions are shown in the official language in which they were submitted.
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COATED SUBSTRATE
TECHNICAL FIELD
The present invention relates generally to coated substrates which have been
coated
with two different coating compositions. The present invention further relates
to the use
of two different coating compositions to coat a substrate and a method of
making a
coated substrate.
BACKGROUND OF THE INVENTION
Coating compositions are used widely to coat numerous types of substrates
(e.g.
different materials) which are used for numerous applications. In particular,
coating
compositions may be used to coat substrates which are used to package goods
such
as food and beverage products, electronic products, automotive products,
medical/pharmaceutical products and cosmetic products. The coated substrate
may,
for example, be paper or the like.
It is often desirable or necessary that the coating composition reduces or
prevents the
permeation of gases, vapours and liquids through the substrate. For example,
it is often
desirable or necessary to reduce or prevent the permeation of water and/or
organic
substances such as oils (e.g. mineral oils) through the substrate. This may,
for
example, prevent contamination and/or spoilage of the packaged products (e.g.
food/beverage) by the transmitted substances.
In some situations it is desirable or necessary to prevent the permeation of
both water
and oils through a substrate. However, many coated substrates are not able to
effectively reduce or prevent the permeation of both water and oil through the
substrate. It is therefore desirable to provide improved or at least
alternative coated
substrates that can reduce or prevent the permeation of both water and oil
through a
substrate. For example, it may be desirable to provide a coated substrate
which
demonstrates improved water barrier properties and/or improved oil barrier
properties.
This may, for example, allow a reduced coat weight to be used. It may also be
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desirable to provide a coated substrate that has been coated with water-based
coating
compositions and may, for example, be easily recyclable.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided
a substrate
coated with a first coating comprising an alcohol-based binder and an
inorganic
particulate material, and a second coating comprising a latex binder and a
phyllosilicate.
In accordance with a second aspect of the present invention, there is provided
a use of
a first coating composition comprising an alcohol-based binder and an
inorganic
particulate material and a second coating composition comprising a latex
binder and a
phyllosilicate to coat a substrate (e.g. to make a substrate in accordance
with the first
aspect of the present invention).
In accordance with a third aspect of the present invention, there is provided
a method
of coating a substrate (e.g. to make a substrate in accordance with the first
aspect of
the present invention) comprising coating the substrate with a first coating
composition
comprising an alcohol-based binder and an inorganic particulate material and a
second
coating composition comprising a latex binder and a phyllosilicate.
In accordance with further aspects of the present invention, there is provided
a coating
composition comprising an alcohol-based binder and an inorganic particulate
material
and a coating composition comprising a latex binder and a phyllosilicate.
In certain embodiments of any aspect of the present invention, the substrate
is paper.
In certain embodiments of any aspect of the present invention, the alcohol-
based
binder is polyvinyl alcohol.
In certain embodiments of any aspect of the present invention, the inorganic
particulate
material is selected from an alkaline earth metal carbonate or sulphate (e.g.
calcium
carbonate, magnesium carbonate, dolomite, gypsum), a phyllosilicate, an
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aluminosilicate (e.g. hydrous kandite clay including kaolin, halloysite clay,
ball clay,
anhydrous (calcined) kandite clay including metakaolin, fully calcined kaolin
and mica),
talc, chlorite, pyrophyllite, serpentine, perlite, diatomaceous earth,
magnesium
hydroxide, aluminium trihydrate and combinations thereof. In certain
embodiments, the
inorganic particulate material is an aluminosilicate. In certain embodiments,
the
inorganic particulate material is kaolin.
In certain embodiments of any aspect of the present invention, the inorganic
particulate
material has a shape factor equal to or greater than about 10. In certain
embodiments,
the inorganic particulate material has a shape factor equal to or greater than
about 30.
In certain embodiments, the inorganic particulate material has a shape factor
equal to
or greater than about 90.
In certain embodiments of any aspect of the present invention, the inorganic
particulate
material and alcohol-based binder are present in the first coating in a weight
ratio of
from about 5:1 to about 1:5. In certain embodiments, the inorganic particulate
material
and alcohol-based binder are present in the first coating in a weight ratio of
from about
2:1 to about 1:1.
In certain embodiments of any aspect of the present invention, the latex
binder is a
styrene butadiene binder.
In certain embodiments of any aspect of the present invention, the
phyllosilicate is
selected from clays (e.g. kaolin), talc, mica, chlorite, pyrophyllite,
serpentine and
combinations thereof. In certain embodiments, the phyllosilicate is talc.
In certain embodiments of any aspect of the present invention, the
phyllosilicate has a
shape factor equal to or greater than about 10. In certain embodiments, the
phyllosilicate has a shape factor equal to or greater than about 30. In
certain
embodiments, the phyllosilicate has a shape factor equal to or greater than
about 90.
In certain embodiments of any aspect of the present invention, the
phyllosilicate and
latex binder are present in the second coating in a weight ratio of from about
5:1 to
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about 1:10. In certain embodiments, the phyllosilicate and latex binder are
present in
the second coating in a weight ratio of from about 2:1 to about 1:1.
In certain embodiments of any aspect of the present invention, the first
coating has a
coat weight equal to or less than about 30 gsm (g/m2). In certain embodiments,
the first
coating has a coat weight equal to or less than about 15 gsm or equal to or
less than
about 10 gsm. In certain embodiments of any aspect of the present invention,
the
second coating has a coat weight equal to or less than about 30 gsm (g/m2). In
certain
embodiments, the second coating has a coat weight equal to or less than about
15 gsm
or equal to or less than about 10 gsm. In certain embodiments of any aspect of
the
present invention, the first and second coatings have a total coat weight
equal to or
less than about 50 gsm (g/m2). In certain embodiments, the first and second
coatings
have a total coat weight equal to or less than about 30 gsm or equal to or
less than
about 20 gsm.
In accordance with any aspect of the present invention, the first and second
coatings
are layered such that the first coating is closer to the substrate than the
second coating
(e.g. wherein the first coating is directly in contact with the substrate and
the second
coating is directly in contact with the first coating). In certain
embodiments, the first and
second coatings are layered such that the second coating is closer to the
substrate
than the first coating (e.g. wherein the second coating is directly in contact
with the
substrate and the first coating is directly in contact with the second
coating). Thus, in
certain embodiments, the first and second coating compositions are applied
sequentially to the substrate. In certain embodiments, the first coating
composition is
applied to the substrate before the second coating composition is applied to
the
substrate. For example, the first coating composition may be applied directly
to the
substrate and the second coating composition may be applied directly to the
first
coating. In certain embodiments, the second coating composition is applied to
the
substrate before the first coating composition is applied to the substrate.
For example,
the second coating composition may be applied directly to the substrate and
the first
coating composition may be applied directly to the second coating.
In certain embodiments of any aspect of the present invention, the substrate
has a
moisture vapour transmission rate (MVTR) equal to or less than about 200 gsm
(g/m2)
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per day. In certain embodiments, the substrate has a MVTR equal to or less
than about
gsm (g/m2) per day. In certain embodiments, the substrate has a MVTR equal to
or
less than about 1 gsm (g/m2) per day. In certain embodiments, the substrate
has a
MVTR equal to or less than about 0.2 gsm (g/m2) per day.
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In certain embodiments of any aspect of the present invention, the substrate
has an oil
vapour transmission rate (OVTR) equal to or less than about 200 gsm (g/m2) per
day.
In certain embodiments, the substrate has an OVTR equal to or less than about
8 gsm
(g/m2) per day. In certain embodiments, the substrate has a OVTR equal to or
less
than about 5 gsm (g/m2) per day. In certain embodiments, the substrate has a
OVTR
equal to or less than about 1 gsm (g/m2) per day.
Certain embodiments of any aspect of the present invention may provide one or
more
of the following advantages:
= improved water barrier properties (e.g. improved MVTR);
= improved oil barrier properties (e.g. improved OVTR);
= improved barrier combination for both water and oil, for example that a
single
coat could not provide in the same way;
= protection of the oil barrier (e.g. lower layer) from detrimental influence
of
moisture and/or water (e.g. if the upper layer provides moisture and/or water
protection);
= protection of the water barrier (e.g. lower layer) from detrimental
influence of oil
and/or grease (e.g. if the upper layer provides oil and/or grease protection);
= reduced coat weight of either one or both of the coatings;
= easily recyclable substrate;
= improved application of one coating on another;
= improved interaction between coatings.
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
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invention unless otherwise indicated herein, or otherwise clearly contradicted
by
context.
DETAILED DESCRIPTION OF THE INVENTION
Coating Compositions
There is provided herein a substrate coated with a first coating and a second
coating.
The first coating comprises an alcohol-based binder and an inorganic
particulate
material and the second coating comprises a latex binder and a phyllosilicate.
Thus,
there is provided herein a first coating composition comprising an alcohol-
based binder
and an inorganic particulate material. There is also provided herein a second
coating
composition comprising a latex binder and a phyllosilicate. The first and
second
coatings on the substrate may, for example, be a dry residue of the first and
second
coating compositions respectively.
The inclusion of inorganic particulate material (e.g. phyllosilicate, talc,
kaolin) in the
coating compositions may advantageously provide benefits such as reduced
liquid
phase mineral oil transmission, making the system cheaper, improving water
barrier
properties (i.e., reducing moisture vapour transmission rates through coated
substrates
such as coated paper) and improving the applicability of the barrier coating
composition
to the substrate (e.g. paper substrate). The inclusion of inorganic
particulate material
(e.g. phyllosilicate, talc, kaolin) in the coating compositions may also
reduce the energy
required for drying of the coating compositions.
First Coating Composition
The first coating composition comprises an alcohol-based binder and an
inorganic
particulate material. For example, the first coating composition may consist
essentially
of an alcohol-based binder and an inorganic particulate material, or may
consist of an
alcohol-based binder and an inorganic particulate material.
The first coating composition may, for example, be an aqueous
suspension/dispersion.
The solids content of the first coating composition may suitably be as high as
possible
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whilst still giving a suitably fluid composition which may be used in coating
a substrate.
The solids content of the first coating composition may, for example, range
from about
10% to about 90% by weight of the composition. For example, the solids content
of the
first coating composition may range from about 10% to about 80%, for example
from
about 10% to about 70%, for example from about 10% to about 60% by weight of
the
composition. After application of the aqueous coating composition to the
substrate, the
coating composition may be allowed to dry. Thus, the first coating may be in
the form of
a dry residue comprising an alcohol-based binder and an inorganic particulate
material.
The term "alcohol" is used herein to mean an organic compound in which a
hydroxyl
functional group (-OH) is bonded to a carbon atom. Therefore, an alcohol-based
binder
is a composition or compound which contains a hydroxyl functional group bonded
to a
carbon atom, which is capable of functioning as a binder in a coating
composition, for
example a barrier coating composition, which may be suitable for coating a
paper
product.
The alcohol-based binder may comprise a primary alcohol having the general
formula
RCH2OH, a secondary alcohol having the general formula RR'CHOH, a tertiary
alcohol
having the general formula RR'R"COH, or a combination thereof. R, R' and R"
represent alkyl groups having from one to twenty carbon atoms. For example R,
R' and
R" may represent alkyl groups having from one to ten carbon atoms. The alcohol-
based binder may, for example, comprise primary, secondary and/or tertiary
alcohol
groups, which may be attached to a polymer backbone.
The alcohol-based binder may, for example, be a polymer comprising a
carboniferous
backbone having hydroxyl functional groups appended therefrom. For example,
the
alcohol-based binder may be polyvinyl alcohol. 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
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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. Hereinafter, the
invention may
tend to be discussed in terms of polyvinylalcohol. However, the invention
should not be
construed as being limited to such embodiments.
The alcohol-based binder component of the first coating composition may serve
not
only as binder when applied to the substrate (e.g. a paper substrate), but may
also
enhance the barrier properties of the first coating composition. The moisture
vapour
transmission rate of the coated substrate may, for example, be improved (e.g.
reduced)
in comparison to the moisture vapour transmission rate of a coated substrate
coated
with a first coating that does not comprise an alcohol-based binder.
The first coating composition may, for example, comprise at least about 20 %
by weight
alcohol-based binder, based on the total weight of the barrier coating
composition, for
example, at least about 25 % by weight alcohol-based binder, for example at
least
about 30 % by weight alcohol-based binder, for example at least about 35 % by
weight
.. alcohol-based binder, for example at least about 40% by weight alcohol-
based binder,
for example at least about 45 % by weight alcohol-based binder, for example at
least
about 50 % by weight alcohol-based binder, for example at least about 55 % by
weight
alcohol-based binder, for example at least about 60 % by weight alcohol-based
binder,
for example at least about 65 % by weight alcohol-based binder, for example at
least
about 70 A) by weight alcohol-based binder or, for example at least about 75
% by
weight alcohol-based binder.
The first coating composition may, for example, comprise up to about 99 % by
weight,
for example up to about 98 % by weight, for example up to about 95 % by
weight, for
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example up to about 90 % by weight, for example up to about 85 % by weight,
for
example, up to about 80 % by weight alcohol-based binder.
The inorganic particulate material may, for example, be selected from an
alkaline earth
metal carbonate or sulphate (e.g. calcium carbonate, magnesium carbonate,
dolomite
and gypsum); a phyllosilicate, an aluminosilicate (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 inorganic particulate material may, for example, be an aluminosilicate,
for
example, kaolin. The inorganic particulate material may, for example, be
kaolin having
a high shape factor. The inorganic particulate material may, for example, be a
magnesium silicate. Hereinafter, the invention may tend to be discussed in
terms of
kaolin. However, the invention should not be construed as being limited to
such
embodiments.
A kaolin product of high shape factor is considered to be more "platey" than a
kaolin
product of low shape factor. "Shape factor", as used herein, is a measure of
the ratio
of particle diameter to particle thickness for a population of particles of
varying size and
shape as measured using the electrical conductivity methods, apparatuses, and
equations described in U.S. Patent No. 5,576,617. As the technique for
determining
shape factor is further described in the '617 patent, the electrical
conductivity of a
composition of an aqueous suspension of orientated particles under test is
measured
as the composition flows through a vessel. Measurements of the electrical
conductivity
are taken along one direction of the vessel and along another direction of the
vessel
transverse to the first direction. Using the difference between the two
conductivity
measurements, the shape factor of the particulate material under test is
determined.
The shape factor of the inorganic particulate material, for example, kaolin,
may be
equal to or greater than about 10. For example, the shape factor may be equal
to or
greater than about 20, or equal to or greater than about 30, or equal to or
greater than
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about 40, or equal to or greater than about 50, or equal to or greater than
about 60 or
equal to or greater than about 70. The shape factor may be equal to or greater
than
about 80, for example equal to or greater than about 90 or equal to or greater
than
about 100. For example, the shape factor of the inorganic particulate material
may be
.. up to about 95 or up to about 100 or up to about 110 or up to about 150.
For example,
the shape factor may lie in one or more of the following ranges: 20 to 150; 20
to 110;
20 to 100; 30 to 150; 30 to 110; 30 to 100; 40 to 150; 40 to 110; 40 to 100;
50 to 150;
50t0 110; 50 to 100; 60 to 150; 60t0 110; 60t0 100; 70 to 150; 70 to 110; 70
to 100;
80 to 150; 80t0 110; 80 to 100; 90 to 150; 90t0 110; 90 to 100.
Unless otherwise stated, the mean (average) equivalent particle diameter (d50
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 d50 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 d50 value. The term cis() is the particle
size value less
than which there are 90% by weight of the particles.
The inorganic particulate material may, for example, have a mean equivalent
particle
diameter (d50) less than or equal to about 10 microns ( m) (by Sedigraph),
e.g. less
than or equal to about 8 m, or less than or equal to about 6 rn, or less
than or equal
to about 4 m, or less than or equal to about 2 m, or less than or equal to
about 1.5
m, particularly less than or equal to about 1 p.m, e.g. less than or equal to
about 0.5
.. pin, e.g. less than or equal to about 0.4 pm or, e.g., less than or equal
to about 0.3 m.
The value of d50 may, for example, be in the range of about 0.2 pm to about 2
pm, for
example about 0.3 to about 1.5 pm, for example about 0.3 to about 1 pm, or for
example about 1 pm to about 2 pm.
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The inorganic particulate material may, for example, have a d90 of less than
or equal to
about 5 jim, particularly less than or equal to about 3 1.1.m, e.g., less than
or equal to
about 2 1.1.m. The value of d90 may, for example, be in the range of about 0.5
pm to
about 3 pm, for example about 1 pm to about 3 pm or, for example, about 0.5 pm
to 2
pm.
The range of fine content of inorganic particulate, i.e. the wt% less than
0.25 pm may
lie in the range of about 5 wt% to about 95 wt%, for example about 40 wt% to
about 90
wt% or about 5 wt% to about 20 wt%.
The kaolin may, for example, have a shape factor equal to or greater than
about 30
and a d90 of less than about 2 p.m. For example, the kaolin may have a shape
factor
equal to or greater than about 60, or 70, or 90, and a d90 of less than about
2 [trn.
The kaolin may, for example, have a shape factor between about 10 and about 20
and
a d50 of less than about 1 ,m, for example, less than or equal to about 0.5
prrI.
The kaolin may, for example, have a shape factor between about 25 and about 50
and
a d50 of less than about 0.3 lam.
The inorganic particulate material may, for example, be an aluminosilicate
having a
shape factor between about 20 and 40, and a d50 of less than about 0.5 pm.
Kaolin clay used in this invention may be a processed material derived from a
natural
source, namely raw natural kaolin clay mineral. The processed kaolin clay may
typically
contain at least about 50% by weight kaolinite. For example, most commercially
processed kaolin clays contain greater than about 75% by weight kaolinite and
may
contain greater than about 90%, in some cases greater than about 95% by weight
of
kaolinite.
Kaolin clay used in the present invention may be prepared from the raw natural
kaolin
clay mineral by one or more other processes which are well known to those
skilled in
the art, for example by known refining or beneficiation steps.
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For example, the clay mineral may be bleached with a reductive bleaching
agent, such
as sodium hydrosulfite. If sodium hydrosulfite is used, the bleached clay
mineral may
optionally be dewatered, and optionally washed and again optionally dewatered,
after
the sodium hydrosulfite bleaching step.
The clay mineral may be treated to remove impurities, e. g. by flocculation,
flotation, or
magnetic separation techniques well known in the art. Alternatively the clay
mineral
may be untreated in the form of a solid or as an aqueous suspension.
The process for preparing the particulate kaolin clay used in the present
invention may
also include one or more comminution steps, e.g., grinding or milling. Light
comminution of a coarse kaolin is used to give suitable delamination thereof.
The
comminution may be carried out by use of beads or granules of a plastic (e. g.
nylon),
sand or ceramic grinding or milling aid. The coarse kaolin may be refined to
remove
impurities and improve physical properties using well known procedures. The
kaolin
clay may be treated by a known particle size classification procedure, e.g.,
screening
and centrifuging (or both), to obtain particles having a desired d50 value or
particle size
distribution.
When the inorganic particulate material is obtained from naturally occurring
sources, it
may be that some mineral impurities will contaminate the ground material. For
example, naturally occurring kaolin may be present in association with other
minerals.
Thus, the inorganic particulate material may include an amount of impurities.
In
general, however, the inorganic particulate material will contain less than
about 5% by
weight, preferably less than about 1% by weight, of other mineral impurities.
The first coating composition may, for example, comprise at least about 20 %
by weight
inorganic particulate material, based on the total weight of the barrier
coating
composition, for example, at least about 25 % by weight inorganic particulate
material,
for example at least about 30 % by weight inorganic particulate material, for
example at
least about 35 % by weight inorganic particulate material, for example at
least about
40% by weight inorganic particulate material, for example at least about 45 %
by
weight inorganic particulate material, for example at least about 50 % by
weight
inorganic particulate material, for example at least about 55 % by weight
inorganic
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particulate material, for example at least about 60 % by weight inorganic
particulate
material, for example at least about 65 % by weight inorganic particulate
material, for
example at least about 70 % by weight inorganic particulate material or, for
example at
least about 75 % by weight inorganic particulate material. The first coating
composition
may, for example, comprise no more than about 99% by weight, for example no
more
than about 98 % by weight, for example no more than about 95 % by weight, for
example no more than about 90 % by weight, for example no more than about 80 %
by
weight, for example no more than about 70 % by weight, for example no more
than
about 60 % by weight, for example no more than about 50 % by weight inorganic
particulate material. The first coating composition may, for example, be
applied as a
single layer.
The weight ratio of inorganic particulate material to alcohol-based binder
may, for
example, range from about 5:1 to about 1:10, for example, from about 5:1 to
about 1:9,
for example, from about 5:1 to about 1: 7, for example, from about 5:1 to
about 1:5, for
example, from about 4:1 to about 1:4, for example, from about 3:1 to about
1:3, for
example, from about 2:1 to about 1:2, for example, from about 1.5:1 to about
1:1.5, for
example, from about 1.25:1 to about 1:1.25. The weight ratio of inorganic
particulate
material to alcohol-based binder may, for example, be about 1:1.
Second Coating Composition
The second coating composition comprises a latex binder and a phyllosilicate.
For
example, the second coating composition may consist essentially of or consist
of a
latex binder and a phyllosilicate, or may consist of a latex binder and a
phyllosilicate.
The second coating composition may, for example, be an aqueous
suspension/dispersion. The solids content of the second coating composition
may
suitably be as high as possible whilst still giving a suitably fluid
composition which may
be used in coating a substrate. The solids content of the second coating
composition
may, for example, range from about 10% to about 90% by weight of the
composition.
For example, the solids content of the second coating composition may range
from
about 10% to about 80%, for example from about 10% to about 70%, for example
from
about 10% to about 60% by weight of the composition. After application of the
aqueous
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coating composition to the substrate, the coating composition may be allowed
to dry.
Thus, the second coating may be in the form of a dry residue comprising a
latex binder
and a phyllosilicate.
The term "latex" is used herein to mean a dispersion/suspension (e.g. aqueous
dispersion/suspension) of one or more polymer(s). The polymers may, for
example, be
natural or synthetic. Therefore, the term "latex binder" means any composition
comprising, consisting essentially of or consisting of one or more polymers,
which is
capable of functioning as a binder in a coating composition, for example a
barrier
coating composition, which may be suitable for coating a paper product.
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. Hereinafter, the invention may tend to be
discussed
in terms of styrene butadiene. However, the invention should not be construed
as being
limited to such embodiments.
The second coating composition may, for example, comprise at least about 20 %
by
weight latex binder, based on the total weight of the barrier coating
composition, for
example, at least about 25 % by weight latex binder, for example at least
about 30 %
by weight latex binder, for example at least about 35 % by weight latex
binder, for
example at least about 40% by weight latex binder, for example at least about
45 % by
weight latex binder, for example at least about 50 % by weight latex binder,
for
example at least about 55 % by weight latex binder, for example at least about
60 % by
weight latex binder, for example at least about 65 % by weight latex binder,
for
example at least about 70 % by weight latex binder or, for example at least
about 75 %
by weight latex binder.
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The second coating composition may, for example, comprise up to about 99 % by
weight, for example up to about 98 % by weight, for example up to about 95 %
by
weight, for example up to about 90 % by weight, for example up to about 85 %
by
weight, for example up to about 80 % by weight latex binder.
The phyllosilicate may, for example, be selected from clays (e.g. kaolin),
talc, mica,
chlorite, pyrophyllite, serpentine and combinations thereof. For example, the
phyllosilicate may be talc. For example, the phyllosilicate may be a
combination of two
or more phyllosilicates, for example a combination of talc and another
phyllosilicate, for
example talc and kaolin. Hereinafter, the invention may tend to be discussed
in terms
of talc. However, the invention should not be construed as being limited to
such
embodiments.
Talc may comprise, consist essentially of, or consist of natural talc
particulate or
synthetic talc particulate or a mixture of natural talc particulate and
synthetic talc
particulate.
As used herein, the term "natural talc" means talc derived from a natural
resource, Le.,
natural talc deposits. Natural talc may be either the hydrated magnesium
silicate of
formula Si4Mg3010(OH)2, which is arranged as a stack of laminae, or the
mineral
chlorite (hydrated magnesium aluminium silicate), or a mixture of the two,
optionally
associated with other minerals, for example, dolomite. Natural talc occurs as
rock
composed of talc crystals.
As used herein, the term "synthetic talc" means talc that has been synthesized
using a
man-made synthetic process. The talc used in the present invention may be a
macrocrystalline talc or microcrystalline talc.
The phyllosilicate mineral may, for example, be bleached with a reductive
bleaching
agent, such as sodium hydrosulfite. If sodium hydrosulfite is used, the
bleached
phyllosilicate mineral may optionally be dewatered, and optionally washed and
again
optionally dewatered, after the sodium hydrosulfite bleaching step.
The phyllosilicate mineral may be treated to remove impurities, e.g. by
flocculation,
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flotation, or magnetic separation techniques well known in the art.
Alternatively the
phyllosilicate mineral may be untreated in the form of a solid or as an
aqueous
suspension.
The process for preparing the phyllosilicate may include one or more
comminution
steps, e.g., grinding or milling. Light comminution of a coarse phyllosilicate
is used to
give suitable delamination thereof. The comminution may use beads or granules
of a
plastic (e.g. nylon), sand or ceramic grinding or milling aid. The coarse
phyllosilicate
may be refined to remove impurities and improve physical properties using well
known
procedures. The phyllosilicate may be treated by a known particle size
classification
procedure, e.g., screening and centrifuging (or both), to obtain particles
having a
desired particle size distribution.
The phyllosilicate may be calcined or non-calcined. For example, the
phyllosilicate may
be calcined talc or non-calcined talc.
When the phyllosilicate is obtained from naturally occurring sources, it may
be that
some mineral impurities will inevitably contaminate the ground material. In
general,
however, the phyllosilicate 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.
The first coating composition may, for example, comprise at least about 20
c1/0 by weight
phyllosilicate, based on the total weight of the barrier coating composition,
for example,
at least about 25 % by weight phyllosilicate, for example at least about 30
'3/0 by weight
phyllosilicate, for example at least about 35 'Yo by weight phyllosilicate,
for example at
least about 40% by weight phyllosilicate, for example at least about 45 % by
weight
phyllosilicate, for example at least about 50 % by weight phyllosilicate, for
example at
least about 55 % by weight phyllosilicate, for example at least about 60 % by
weight
phyllosilicate, for example at least about 65 % by weight phyllosilicate, for
example at
least about 70 % by weight phyllosilicate or, for example at least about 75 %
by weight
phyllosilicate. The first coating composition may, for example, comprise no
more than
about 99 % by weight, for example no more than about 98 % by weight, for
example no
more than about 95 % by weight, for example no more than about 90 % by weight,
for
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example no more than about 80 % by weight, for example no more than about 70
A by
weight, for example no more than about 60 % by weight, for example no more
than
about 50 `)/0 by weight phyllosilicate. The second coating composition may,
for
example, be applied as a single layer.
The weight ratio of the latex binder and phyllosilicate may be chosen so that
the
maximum weight of phyllosilicate particles is obtained in the coating without
creating
pores in the coating. This may, for example, depend on the particle size of
the
phyllosilicate. The weight ratio of phyllosilicate to latex binder may, for
example, range
from about 5:1 to about 1:10, for example, from about 5:1 to about 1:9, for
example,
from about 5:1 to about 1:7, for example, from about 5:1 to about 1:5, for
example,
from about 4:1 to about 1:4, for example, from about 3:1 to about 1:3, for
example,
from about 2:1 to about 1:2. For example, the weight ratio of phyllosilicate
to latex
binder may be from about 2:1 about 1:1.
The phyllosilicate may, for example, have a high shape factor. Thus, the
phyllosilicate
may be considered to be more "platey" than a phyllosilicate product of low
shape
factor. "Shape factor", as used herein, is as described above in relation to
the first
coating composition.
The shape factor of the phyllosilicate (e.g. talc) may suitably be equal to or
greater than
about 10. For example, the shape factor may be equal to or greater than about
20, or
equal to or greater than about 30, or equal to or greater than about 40, or
equal to or
greater than about 50, or equal to or greater than about 60 or equal to or
greater than
about 70. The shape factor may be equal to or greater than about 80, for
example
equal to or greater than about 90 or equal to or greater than about 100. For
example,
the shape factor of the phyllosilicate (e.g. talc) may suitably be up to about
95 or up to
about 100 or up to about 110 or up to about 150. For example, the shape factor
may
lie in one or more of the following ranges: 20 to 150; 20 to 110; 20 to 100;
30 to 150; 30
to 110; 30 to 100; 40 to 150; 40 to 110; 40 to 100; 50 to 150; 50 to 110; 50
to 100; 60 to
150; 60t0 110; 60t0 100; 70t0 150; 70 to 110; 70 to 100; 80 to 150; 80 to 110;
80 to
100; 90 to 150; 90 to 110; 90 to 100.
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The phyllosilicate (e.g. talc) may, for example, have a mean equivalent
particle
diameter (do) less than or equal to about 10 microns (pm) (by Sedigraph), e.g.
less
than or equal to about 8 m, or less than or equal to about 6 pm, or less than
or equal
to about 4 rn. For example, the phyllosilicate may have a do of less than or
equal to
about 2 m, for example equal to or less than about 1.5 pm. The phyllosilicate
may, for
example, have a do ranging from about 0.1 pm to about 10 pm, for example from
about 0.1 pm to about 5 pm, for example from about 0.1 pm to about 2 pm, for
example from about 0.1 pm to about 1.5 pm, for example from about 0.5 pm to
about 2
pm or from about 0.5 pm to about 1.5 pm.
The phyllosilicate may, for example, have a do of less than or equal to about
20 p.m,
for example less than or equal to about 15 p.m, for example less than or equal
to about
10 IAM. For example, the phyllosilicate may have a do of less than or equal to
about 9
pm, for example less than or equal to about 8 pm, for example less than or
equal to
about 7 pm, for example less than or equal to about 6 pm. The value of do may,
for
example, be in the range of about 1 pm to about 10 pm, for example about 1 pm
to
about 8 pm or, for example, about 1 pm to 6 pm.
The range of fine content of phyllosilicate particles, i.e. the wt% less than
0.25 pm may
lie in the range of about 5 wt% to about 95 wt%, for example about 40wt% to
about 90
wt% or about 5 wt% to about 20 wt%.
The phyllosilicate (e.g. talc) may, for example, have a shape factor of
greater than
about 30 and a do equal to or less than about 2 m.
Optional Additional Components of the First and Second Coating Compositions
The first and/or second coating compositions may contain one or more optional
additional components, if desired. The first and/or second coating
compositions may
optionally comprise one or more further additive components, as discussed
below. The
first and/or second coating compositions may be in the form of an aqueous
suspension
of the binder and inorganic particulate material components defined above, and
optionally one or more further additive components, as discussed below.
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Such additional components, 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;
(b) one or more water retention aids;
(c) one or more viscosity modifiers or thickeners;
(d) one or more lubricity or calendering aids;
(e) one or more dispersants;
(f) one or more antifoanners or defoamers;
(g) one or more optical brightening agents (OBA) or fluorescent whitening
agents
(FWA);
(h) one or more dyes;
(i) one or more biocides or spoilage control agents;
(j) one or more levelling or evening aids;
(k) one or more grease or oil resistance agents;
(I) one or more surfactants;
(m) one more binders other than the alcohol-based and latex binders defined
above,
for example, an acrylic polymer latex, a polyvinyl acetate latex, or a styrene
acrylic
copolymer latex, which may be carboxylated, a starch-based binder, cellulose-
based
binder;
(n) one or more mineral fillers other than the inorganic particulate
materials and
phyllosilicates defined above, for example an alkaline earth metal carbonate
or
sulphate, such as calcium carbonate, magnesium carbonate, dolomite, gypsum, a
hydrous kandite clay such as kaolin, halloysite or ball clay, an anhydrous
(calcined)
kandite clay such as metakaolin or fully calcined kaolin, talc, mica, perlite
or
diatomaceous earth, or combinations thereof.
Any of the above additives and additive types may be used alone or in
admixture with
each other and with other additives, if desired.
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For example, the first and/or second coating compositions may further comprise
one or
more crosslinker(s). For example, the first coating composition may further
comprise
one or more crosslinker(s).
For example, the first or second coating compositions may further comprise one
or
more surfactant(s). For example, both the first and second coating
compositions may
further comprise one or more surfactant(s). The use of one or more
surfactant(s) in the
first and/or second coating compositions may, for example, improve the
application of
one coating on another (e.g. the recoatability of the coatings). The use of
one or more
surfactant(s) may, for example, improve the interaction between the two
coatings.
Surfactants include, without limitation, ionic (e.g. anionic and/or cationic)
and non-ionic
surfactants. Anionic surfactants include, for example, sulphate, sulphonate
and
phosphate esters (e.g. ammonium lauryl sulphate, sodium lauryl sulphate,
sodium
lauryl ether sulphate) and carboxylates (e.g. alkyl carboxylates such as
sodium
stearate). Cationic surfactants include, for example, primary, secondary,
tertiary and
quaternary amines and quaternary ammonium species. Non-ionic surfactants
include,
for example, fatty alcohols, cetyl alcohol, stearyl alcohol, cetostearyl
alcohol, leyl
alcohol, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl
ethers,
glucoside alkyl ethers, polyoxyethylene glycol octylphenol ethers, polyoxylene
glycol
alkylphenol ethers, glycerol alkyl ethers, sorbitan alkyl esters,
dodecyldimethylamine
oxide and block copolymers of polyethylene glycol and polypropylene glycol.
The total amount of the one or more surfactant(s) in the first or second
coating
composition may, for example, be from about 0.01 wt% to about 5.0 wt%. For
example,
the total amount of surfactant in the first or second coating composition may
range from
about 0.1 wt% to about 3.0 wt% or from about 0.1 wt% to about 2.0 wt% or from
about
0.1 wt% to about 1.0 wt%. For example, the total amount of surfactant in the
first or
second coating composition may range from about 0.5 wt% to about 3.0 wt% or
from
about 0.5 wt% to about 2.0 wt% or from about 0.5 wt% to about 1.0 wt%. For
example,
the total amount of surfactant in the first or second coating composition may
be about
0.5 wt%.
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For all of the above additives, the percentages by weight (based on the dry
weight of
inorganic particulate material (100%) present in 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 dry
weight
of the inorganic particulate material. The maximum amount of any one or more
of the
above additives may, for example, be about 5.0% by weight based on the dry
weight of
the inorganic particulate material. For example, the maximum amount may be
about
3.0% or 2.0% by weight based on the dry weight of the inorganic particulate
material.
Coated Substrate
A substrate may, for example, be coated with the first and second coating
compositions
described above, including all embodiments thereof in all possible
combinations. Thus,
there is provided herein a substrate provided with a first coating comprising
an alcohol-
based binder and an inorganic particulate material, and a second coating
comprising a
latex binder and a phyllosilicate.
The substrate may, for example, be any material, for example selected from
plastics
(e.g. low density polyethylene, polypropylene, polyamides and the like),
metals (e.g
foils such as aluminium foil), textiles and paper. The material may, for
example, be
coloured, treated (e.g. varnished or laminated) or both. The coating of the
substrates
may, for example, comprise a dry residue of the first and/or second coating
compositions described herein. Hereinafter, the invention may be defined in
terms of
paper substrates. However, the invention should not be construed as being
limited to
such embodiments.
The term paper substrate, 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
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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 substrate may have opposing first and second surfaces. The first and
second coatings may, for example, be present on the first surface, the second
surface,
or both. For example, the first surface may be a surface which faces the
interior of the
paper product when it is formed into a three-dimensional product and the
opposing
second surface may face the exterior of the paper product. The first and/or
second
surfaces may or may not have other intermediary coatings or layers between
each
surface and the first and second coatings described herein. The first and
second
coatings may, for example, be applied directly to the paper substrate.
The first and second coating compositions may be applied to the substrate in
any
order. Thus, the first and second coatings may be layered such that the first
coating is
closer to the substrate than the second coating, or such that the second
coating is
closer to the substrate than the first coating. The first and/or second
coating may be
applied to the substrate directly with no other substances or coatings being
applied
before the first and second coatings are applied and no intermediate
substances or
coatings being applied between the first and second coatings. For example, the
first
coating may be in direct contact with the substrate and the second coating may
be in
direct contact with the first coating. For example, the second coating may be
in direct
contact with the substrate and the first coating may be in direct contact with
the second
coating.
The first coating on the substrate may, for example, have a coating weight
between
about 2 gsm and about 30 gsm (grams per m2), for example between about 3 gsm
and
about 28 gsm. The first coating may, for example, have a coating weight of
less than
about 15 gsm. For example, the first coating may have a coating weight of less
than
about 12 gsm, for example less than about 10 gsm. The first coating may, for
example,
have a coating weight of less than about 8 gsm, for example less than about 6
gsm, for
example less than about 5 gsm.
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The second coating on the substrate may, for example, have a coating weight
between
about 3 gsm and about 30 gsm (grams per m2), for example between about 2 gsm
and
about 28 gsm. The second coating may, for example, have a coating weight of
less
than about 15 gsm. For example, the second coating may have a coating weight
of less
than about 12 gsm, for example less than about 10 gsm. The second coating may,
for
example, have a coating weight of less than about 8 gsm, for example less than
about
6 gsm, for example less than about 5 gsm.
The total coating weight of the first and second coatings on the substrate
may, for
example, range between about 2 gsm and about 50 gsm (grams per m2). For
example,
the total coating weight of the first and second coatings may range from about
2 gsm to
about 40 gsm, for example from about 2 gsm to about 30 gsm. For example, the
total
coating weight of the first and second coatings on the substrate may be less
than about
30 gsm, for example less than about 25 gsm, for example less than about 20
gsm. For
example, the total coating weight of the first and second coatings on the
substrate may
be less than about 15 gsm.
The first and second coating compositions used to coat the substrate may be
barrier
coating compositions. For example, the first and second coating compositions
may
reduce or prevent the permeation of gases and/or vapours and/or liquids
through the
coated substrate. For example, the coating compositions may reduce or prevent
the
permeation of water and/or organic oils through the coated product (i.e.
reduce the
moisture vapour and/or oil vapour transmission rate of the coated product).
Thus, the coated substrate may, for example, have a moisture vapour
transmission
rate (MVTR) which is equal to or less than about 200 gsm (g/m2) per day. For
example,
the coated substrate may have a MVTR which is equal to or less than about 150
gsm
per day, for example equal to or less than about 100 gsm per day, for example
equal to
or less than about 50 gsm per day, for example equal to or less than about 30
gsm per
day, for example equal to or less than about 20 gsm per day, for example equal
to or
less than about 10 gsm per day. For example, the coated substrate may have a
MVTR
of equal to or less than about 8 gsm per day, for example equal to or less
than about 5
gsm per day, for example equal to or less than about 4 gsm per day, for
example equal
to or less than about 3 gsm per day, for example equal to or less than about 2
gsm per
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day, for example equal to or less than about 1 gsm per day. For example, the
coated
substrate may have a MVTR of equal to or less than about 0.9 gsm per day, for
example equal to or less than about 0.8 gsm per day, for example equal to or
less than
about 0.7 gsm per day, for example equal to or less than about 0.6 gsm per
day, for
example equal to or less than about 0.5 gsm per day, for example equal to or
less than
about 0.4 gsm per day, for example equal to or less than about 0.3 gsm per
day, for
example equal to or less than about 0.2 gsm per day, for example equal to or
less than
about 0.1 gsm per day. For example, the coated substrate may have a MVTR
ranging
from about 0.01 gsm per day to about 200 gsm per day, for example from about
0.1
gsm per day to about 50 gsm per day, for example from about 0.2 gsm per day to
about 5 gsm per day, for example from about 0.5 gsm per day to about 1 gsm per
day.
Unless otherwise stated, the MVTR may be measured according to TAPP! T448. The
opening of a pot containing silica gel or calcium chloride is covered with the
coated
substrate and the pot is weighed periodically over several hours or days
depending on
the expected MVTR level. The amount of water entering the pot is determined by
measuring the change in weight of the silica gel or calcium chloride. The
experiment is
carried out at 23 C and 50% humidity. Each coating composition may be present
at a
coatweight equal to or less than about 10 gsm (e.g. total coatweight equal to
or less
than about 20 gsm). The substrate used may be a woodfree base paper. The base
paper may be pre-coated with a pre-coating composition to improve smoothness
of the
paper.
The coated substrate may, for example, have an oil vapour transmission rate
(OVTR)
which is equal to or less than about 200 gsm (g/m2) per day. For example, the
coated
substrate may have an OVTR which is equal to or less than about 150 gsm per
day, for
example equal to or less than about 100 gsm per day, for example equal to or
less than
about 50 gsm per day, for example equal to or less than about 30 gsm per day,
for
example equal to or less than about 20 gsm per day, for example equal to or
less than
about 20 gsm per day, for example equal to or less than about 10 gsm per day.
For
example, the coated substrate may have a OVTR of equal to or less than about 8
gsm
per day, for example equal to or less than about 5 gsm per day, for example
equal to or
less than about 4 gsm per day, for example equal to or less than about 3 gsm
per day,
for example equal to or less than about 2 gsm per day, for example equal to or
less
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than about 1 gsm per day. For example, the coated substrate may have a OVTR of
equal to or less than about 0.9 gsm per day, for example equal to or less than
about
0.8 gsm per day, for example equal to or less than about 0.7 gsm per day, for
example
equal to or less than about 0.6 gsm per day, for example equal to or less than
about
0.5 gsm per day, for example equal to or less than about 0.4 gsm per day, for
example
equal to or less than about 0.3 gsm per day, for example equal to or less than
about
0.2 gsm per day, for example equal to or less than about 0.1 gsm per day. For
example, the coated substrate may have an OVTR ranging from about 0.01 gsm per
day to about 200 gsm per day, for example from about 0.1 gsm per day to about
50
gsm per day, for example from about 0.2 gsm per day to about 5 gsm per day,
for
example from about 0.5 gsm per day to about 1 gsm per day.
Unless otherwise stated, the OVTR may be measured a method corresponding to
that
used to measure MVTR. The opening of a pot containing decane or heptane is
covered
with the coated substrate and the pot is weighed periodically over several
hours or
days depending on the expected OVTR level. The amount of decane or heptane
leaving the pot is determined by measuring the change in weight of the pot.
The
experiment is carried out at 23 C and 50% humidity. Each coating composition
may be
present at a coatweight equal to or less than about 10 gsm (e.g. total
coatweight equal
to or less than about 20 gsm). The substrate used may be a woodfree base
paper. The
base paper may be pre-coated with a pre-coating composition to improve
smoothness
of the paper
One advantage of using two different coating compositions may be that the
barrier can
be improved for both organic and water transmission. This may not be possible
in the
same way if only one type of coating is used (e.g. the one coating will only
be
optimized for either organic or water transmission but not both). Without
wishing to be
bound by theory, another advantage may be that the lower or inner layer may be
protected from the detrimental influence of the substance which is blocked by
the upper
or outer layer. For example, an inner organic barrier layer may be protected
from the
detrimental effect of water by using an upper water barrier layer. Therefore,
the inner
layer (e.g. organic barrier layer) may perform better over time because it is
not
deteriorated (e.g. by water).
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Method of Making a Coated Substrate
The coating compositions disclosed herein may be used to coat various
materials and
substrates to form coated substrate. Thus, there is provided herein a use of
the first
and second coatings described above to coat a substrate (to make a coated
substrate)
and a method of coating a substrate. The first and second coatings (first and
second
coating compositions) may be as described above, including all embodiments
thereof
and all possible combinations thereof.
The first and second coating compositions may be prepared by combining (e.g.
mixing)
the binder (e.g. alcohol-based binder or latex binder) and inorganic
particulate material
(e.g. kaolin or phyllosilicate such as talc) and other optional additives in
appropriate
amounts into an aqueous liquid to prepare a suspension of said components. The
coating compositions may suitably be prepared by conventional mixing
techniques, as
will be known in the art. The inorganic particulate material may, for example,
be an
aqueous slurry. This may, for example, be prepared using a suitable mixer,
following
which the slurry is blended with a solution of the binder. The resulting
mixture may be
screened prior to coating.
Slurry make-down process may, for example, include the addition of one or more
additives, for example which may be selected from one or more dispersants, one
or
more wetting agents, one or more pH-adjusting agents. The slurry make-down
process
may, for example, involve dispersing the inorganic particulate material in the
aqueous
medium at high shear, for example between 2000 and 3000 rpm. The final
viscosity of
the phyllosilicate slurry may, for example, range from about 200 cP (200
mPa.$) to
about 400 cP (400 mPa.$). For example, the final viscosity of the
phyllosilicate slurry
may range from about 250 cP (250 mPa.$) to about 350 cP (350 mPa.$).
The method of coating a substrate may, for example, comprise coating the
substrate
with a first coating composition comprising an alcohol-based binder and an
inorganic
particulate material and a second coating composition comprising a latex
binder and a
phyllosilicate.
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The first and second coating compositions may be applied in any order. For
example,
the first coating composition may be applied before the second coating
composition or
the second coating composition may be applied before the first coating
composition.
The first or second coating composition may be applied directly to the
substrate. This
coating composition may then be allowed to dry and/or crosslink before the
other of the
first and second coating composition is applied. The other of the first and
second
coating composition may then be applied directly to the coating composition
already
present on the substrate.
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 super-
calendaring 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 18
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 added by a coating head at a coating station. According to the
quality
desired, paper grades are uncoated, single-coated, double-coated and even
triple-
coated. When providing more than one coat, the initial coat (precoat) may have
a
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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 or 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.
In one embodiment, the barrier coating is 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. Flexographic printing is a widely used printing technique,
as will be
well understood by a person of ordinary skill in the art. Using this
technique, the coating
.. composition is transferred from a first roll which is partially immersed in
a tank
comprising the coating composition. The coating composition is then
transferred to the
anilox roll (or meter roll) whose texture holds a specific amount of the
coating
composition since it is covered with thousands of small wells or cups that
enable it to
meter the coating composition to the printing plate in a uniform thickness
evenly and
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quickly. The substrate is finally sandwiched between the plate and the
impression
cylinder to transfer the barrier coating. The coated substrate is then fed
through a
dryer, which allows the coating to dry. Advantageously, flexographic printing
enables
the coating composition to be applied in a series of thin layers (e.g., a
series of fiver
layers with a total coat weight of about 5 gsm) which has sufficient hold out
to maintain
good barrier properties (to liquid and/or vapour mineral oil transmission) for
coating
compositions comprising greater than about 60 % by weight, for example,
greater than
about 65 % by weight of inorganic particulate, based on the total dry weight
of the
composition. Rotogravure printing is a widely used printing technique, as will
be well
understood by a person of ordinary skill in the art.
The substrate (e.g. paper) may be formable or formed into a three-dimensional
product, which may be suitable as food grade or pharmaceutical grade
packaging, at
least a portion of a first interior facing surface of the paper substrate is
coated with the
first and second coatings, and a second exterior facing surface of the paper
substrate
may be coated or printed with an ink-based product. The substrate (e.g. paper)
may
be derived from recycled pulp containing mineral oil and/or the ink-based
product may
comprise mineral oil.
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.
The fibrous substrate may comprise 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.
A further aspect of the present invention is directed to packaged foodstuffs,
pharmaceutical products or other perishable goods which are formed from the
coated
substrates (e.g. coated paper substrates) of the present invention. Foodstuffs
are
many and various and include, for example, grain based products such as
breakfast
cereals (e.g., oats, cornflakes and the like), flours (e.g., wheat flour and
the like) and
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bakery products (e.g., breads, pastries and the like). Pharmaceutical products
include,
for example, tablets, powders suspensions and liquid-based products.
There is further provided a non-porous substrate coated with the first and
second
coating compositions described herein. The non-porous substrate may be a
transparent paper, a translucent paper, a plastic film, such as polyethylene,
polypropylene and the like, or a metal foil, such as aluminium foil. The
substrate may
be coloured, treated (e.g., varnished or laminated), or both. There is further
provided a
porous polyolefin substrate (e.g., polyethylene or polypropylene) coated with
the
coating compositions described herein.
EXAMPLES
Example 1
Two different base papers (herein referred to as base paper 1 and base paper
2) were
coated as shown in Table 1 below.
The first and second coating compositions were prepared by high shear mixing
of the
components.
The first and second coatings were applied to the base papers a hand draw down
rod
coater. The first and second coatings, where present, were each applied at a
coat
weight of 10 gsm.
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Table 1.
Coating First Coating Second Coating
1 None None
100 parts kaolin 100 parts kaolin
2 100 parts polyvinyl alcohol 100 parts polyvinyl
alcohol
binder (88% hydrolysis) binder (88% hydrolysis)
65 parts talc 100 parts kaolin
3 35 parts styrene butadiene 100 parts polyvinyl
alcohol
binder binder (88% hydrolysis)
100 parts kaolin
65 parts talc
100 parts polyvinyl alcohol
4 35 parts styrene butadiene
binder (98% hydrolysis)
binder
14 parts crosslinker
100 parts kaolin 65 parts talc
100 parts polyvinyl alcohol 35 parts styrene butadiene
binder (88% hydrolysis) binder
65 parts talc 65 parts talc
6 35 parts styrene butadiene 35 parts styrene
butadiene
binder binder
100 parts kaolin 65 parts talc
7 100 parts polyvinyl alcohol 35 parts styrene
butadiene
binder (98% hydrolysis) binder
Base paper 1 is a wood free paper, pre-coated on its back side on a paper
machine
online using a filmpress (Speedcoater).
5
Base paper 2 is a wood free paper, pre-coated on both sides on a paper machine
online using a filmpress (Speedcoater).
The pre-coat is not considered as a barrier coating but only smoothens the
paper
surface for the following barrier coatings.
The kaolin used in the first and second coatings had a shape factor of 100, a
GE
brightness of 86 and an average particle size, d50 of 1.535 pm.
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The talc used in the first and second coatings had a shape factor of 100, a
talc/chlorite
content of 98% and a d50 of 2 pm.
The polyvinyl alcohol used in the first and second coatings was either:
- a polyvinyl alcohol having a viscosity of 5.5 0.5 mPa.s, 87.7 1.0 mol%
degree of hydrolysis, 10.8 0.8 wt% residual acetyl content and an ester
value of 140 10 mg KOH/g; or
- a polyvinyl alcohol having a viscosity of 6 1.0 mPa.s, 98.4 0.4 mol%
degree of hydrolysis, 1.5 0.4 wt% residual acetyl content and an ester value
of 20 5 mg KOH/g.
The term ester value referred to above denotes the number of mg of KOH needed
to
neutralize the acid released from the ester by saponification in 1 g of
substance. The
residual acetyl content is calculated from the ester value as follows: EV x
0.0767. The
degree of hydrolysis (saponification), H, indicated what percentage of the
basic
polyvinyl acetate molecule is saponified to polyvinyl alcohol. This is
calculated as
follows:
H mol% 1T3 ¨0.1535 EV .1013
100-0.11V49 - EV
The styrene butadiene used was Styron DL1066.
The moisture vapour transmission rate and oil vapour transmission rate of
these
papers coated with the coatings described in Table 1 were measured according
to the
methods described above but at 38 C and 90% humidity (e.g. according to TAPPI
T464). The results are shown in Table 2 below.
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Table 2.
Coating Base Paper 1 Base Paper 2
MVTR OVTR MVTR OVTR
(gsm/day) (gsm/day) (gsm/day) (gsm/day)
1 1807 201 1945 205
2 1107 3 1749 7
3 350 6 662 9
4 470 4 313 4
263 2 263 7
6 194 50 204 63
7 313 2 329 7
It was found that the use of two coatings improved both the MVTR and OVTR. It
was
also found that the use of two coatings comprising kaolin and polyvinyl
alcohol binder
5 was not able to improve the MVTR as much as when at least one coating
comprising
talc and styrene butadiene binder was used. The use of two coatings comprising
talc
and styrene butadiene binder was not able to improve the OVTR as much as when
at
least one coating comprising kaolin and polyvinyl alcohol binder was used. By
using
one coating comprising kaolin and polyvinyl alcohol and one coating comprising
talc
and styrene butadiene, both the MVTR and OVTR were improved.
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.
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The following numbered paragraphs define particular embodiments of the present
invention:
1. A substrate coated with:
a first coating comprising an alcohol-based binder and an inorganic
particulate material; and
a second coating comprising a latex binder and a phyllosilicate;
2. The substrate according to paragraph 1, wherein the substrate is paper.
3. The substrate according to paragraph 1 or paragraph 2, wherein the
alcohol-
based binder is polyvinyl alcohol.
4. The substrate according to any one of paragraphs 1 to 3, wherein the
inorganic
particulate material is selected from an alkaline earth metal carbonate or
sulphate (e.g.
calcium carbonate, magnesium carbonate, dolomite, gypsum), an aluminosilicate
(e.g.
hydrous kandite clay including kaolin, halloysite clay, ball clay, anhydrous
(calcined)
kandite clay including metakaolin, fully calcined kaolin and mica), talc,
perlite,
diatomaceous earth, magnesium hydroxide, aluminium trihydrate and combinations
thereof.
5. The substrate according to any one of paragraphs 1 to 4, wherein the
inorganic
particulate material is an aluminosilicate.
6. The substrate according to any one of paragraphs 1 to 5, wherein the
inorganic
particulate material is kaolin.
7. The substrate according to any one of paragraphs 1 to 6, wherein the
inorganic
particulate material has a shape factor equal to or greater than about 10, for
example
equal to or greater than about 30, for example equal to or greater than about
90.
8. The substrate according to any one of paragraphs 1 to 7, wherein the
inorganic
particulate material and alcohol-based binder are present in the first coating
in a weight
ratio of from about 5:1 to about 1:5, for example from about 2:1 to about 1:1.
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9. The substrate according to any one of paragraphs 1 to 8, wherein the
latex
binder is a styrene butadiene binder.
10. The substrate according to any one of paragraphs 1 to 9, wherein the
phyllosilicate is selected from clays (e.g. kaolin), talc, mica, chlorite,
pyrophyllite,
serpentine and combinations thereof.
11. The substrate according to any one of paragraphs 1 to 10, wherein the
phyllosilicate is talc.
12. The substrate according to any one of paragraphs 1 to 11, wherein the
phyllosilicate has an shape factor equal to or greater than about 10, for
example equal
to or greater than about 30, for example equal to or greater than about 90.
13. The substrate according to any one of paragraphs 1 to 12, wherein the
phyllosilicate and latex binder are present in the second coating in a weight
ratio of
from about 5:1 to about 1:10, for example from about 2:1 to about 1:1.
14. The substrate according to any one of paragraphs 1 to 13, wherein the
first
coating has a coat weight equal to or less than about 30 gsm (g/m2), for
example equal
to or less than about 15 gsm, for example equal to or less than about 10 gsm.
15. The substrate according to any one of paragraphs 1 to 14, wherein the
second
coating has a coat weight equal to or less than about 30 gsm (g/m2), for
example equal
to or less than about 15 gsm, for example equal to or less than about 10 gsm.
16. The substrate according to any one of paragraphs 1 to 15, wherein the
total coat
weight of the first and second coatings is equal to or less than about 50 gsm
(g/m2), for
example equal to or less than about 30 gsm, for example equal to or less than
about 20
gsm.
17. The substrate according to any one of paragraphs 1 to 16, wherein the
first and
second coatings are layered such that the first coating is closer to the
substrate than
the second coating (e.g. wherein the first coating is directly in contact with
the substrate
and the second coating is directly in contact with the first coating).
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18. The substrate according to any one of paragraphs 1 to 17, wherein the
first and
second coatings are layered such that the second coating is closer to the
substrate
than the first coating (e.g. wherein the second coating is directly in contact
with the
substrate and the first coating is directly in contact with the second
coating).
19. The substrate according to any one of paragraphs 1 to 18, wherein the
substrate
has a moisture vapour transmission rate (MVTR) equal to or less than about 200
gsm
(g/m2) per day, for example equal to or less than about 5 gsm (g/m2) per day,
for
example equal to or less than about 1 gsm (g/m2) per day, for example equal to
or less
than about 0.2 gsm per day.
20. The substrate according to any one of paragraphs 1 to 19, wherein the
substrate
has an oil vapour transmission rate equal to or less than about 200 gsm (g/m2)
per day,
for example equal to or less than about 8 gsm per day, for example equal to or
less
than about 5 gsm (g/m2) per day, for example equal to or less than about 1 gsm
(g/m2)
per day.
21. The substrate according to any one of paragraphs 1 to 20, wherein the
first
coating or the second coating or both comprise a surfactant.
22. Use of a first coating composition comprising an alcohol-based binder and
an
inorganic particulate material and a second coating comprising a latex binder
and a
phyllosilicate to coat a substrate.
23. A method of coating a substrate comprising coating the substrate with a
first
coating composition comprising an alcohol-based binder and an inorganic
particulate
material, and a second coating composition comprising a latex binder and a
phyllosilicate.
24. The use of paragraph 22 or the method of paragraph 23, wherein the first
and
second coating compositions are applied sequentially to the substrate.
25. The use of paragraph 22 or paragraph 24 or the method of paragraph 23
or 24,
wherein the first coating composition is applied to the substrate before the
second
coating composition is applied to the substrate (e.g. the first coating
composition is
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applied directly to the substrate and the second coating composition is
applied directly
to the first coating composition).
26. The use of paragraph 22 or paragraph 24 or the method of paragraph 23
or 24,
wherein the second coating composition is applied to the substrate before the
first
coating composition is applied to the substrate (e.g. the second coating
composition is
applied directly to the substrate and the first coating composition is applied
directly to
the second coating composition).
27. The use of any one of paragraphs 22, 24, 25 or 26 or the method of any one
of
paragraphs 23, 24, 25 or 26, wherein the substrate is as defined in any one of
paragraphs 1 to 21.
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