Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
BARRIER PAPER OR BOARD
TECHNICAL FIELD
The present invention relates to pulp-based substrate layers having barrier
properties and
methods of obtaining such pulp-based substrate layers, in particular pulp-
based substrate
layers such as paper or paperboard having barrier properties.
PRIOR ART
Paper has been used for packaging applications from many decades. In the past,
due to
the lack of inherent barrier properties, paper has been used mostly as the
print carrier in
laminate and/or composite packaging solutions, where it is combined with other
materials
exhibiting barrier functionality, such as plastic films and/or aluminium
layers. The plastic
films can be either made from a single material or may be multilayer films
that incorporate
multiple layers of different polymers, and such plastic films can be applied
via extrusion
coating or via a lamination process. Aluminium layers can either be applied
either as thin
sheets of aluminium or may be applied via known deposition techniques such as
atomic
layer deposition. Also, combinations of plastic films and aluminium layers are
known in the
field of packaging.
In recent years, it has become possible to produce papers that have barrier
properties that
can compete with polymer films, while remaining recyclable.
Such barrier properties can be achieved via coating the paper with relatively
low amounts
of one or more dispersions, specifically one or more solutions, of a barrier
compound,
thereby reducing or replacing plastic film-based materials or metal layers in
the end product.
Furthermore, due to the light and thin nature of the layers formed upon drying
of these
waterborne dispersions or solutions, the barrier papers can be repulped and
recycled as
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paper.
Nevertheless, cost pressure in the packaging field demands for ever improved
performing
barrier papers, in which improved barrier properties must be achieved at the
same or even
lower cost.
EP 1 395 705 B1 discloses a process comprising forming a composite, multilayer
free
flowing curtain, the curtain having a solids content of at least 45 weight
percent, and
contacting the curtain with a continuous web substrate of base paper or base
board. No
overdrying is described.
EP 1 666 637 Al discloses a gas-barrier composite plastic film or sheet which
is obtained
by coating at least one side of a plastic film or sheet made of at least one
plastic selected
from the group consisting of polyolefins, polyesters, polyamides and
polystyrenes with a
coating material composition with a gas-barrier property at a coating weight
so as to give a
dry coat layer thickness of 0.1 to 100 pm. No overdrying is described.
SUMMARY OF THE INVENTION
The present invention provides a process that allows achieving improved
barrier properties,
such as VVVTR (Water Vapour Transmission Rate) or OTR (Oxygen Transmission
Rate), in
pulp based substrates without having to increase the amount of barrier
compound in the
barrier composition that is applied to the substrate and/or without having to
add further
barrier layers to the substrate. This allows achieving improved barrier
properties without an
increase in material cost.
It is an object of the present invention to provide a process for improving
the barrier
properties of a barrier layer comprised in a pulp-based substrate layer having
a barrier layer,
comprising the steps of
a) providing a pulp-based substrate layer having a layer of an
aqueous barrier
composition applied to it,
b) drying the pulp-based substrate layer having a layer of an
aqueous barrier
composition applied to it to form a pulp-based substrate layer having a
barrier layer, such
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that the moisture content of the pulp-based substrate layer having a barrier
layer is below
2.5 % by weight, preferably below 2 % by weight, preferably below 1.5 % by
weight, based
on the weight of the pulp-based substrate layer having a barrier layer.
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having, in this order,
a first barrier layer adjacent to the pulp-based substrate layer,
an inorganic barrier layer such as a metal layer adjacent to the first barrier
layer, where the
inorganic barrier layer is deposited via thin-film deposition,
a second barrier layer adjacent to the inorganic barrier layer,
optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of less than
1.5 g/(m2.d),
preferably of less than 1.0 g/(m2.d), and more preferably of 0.01 to 1.0
g/(m2.d) and/or an
OTR at normal conditions (23 C, 50%RH) of less than 1 cc/(m2.d), preferably of
less than
0.5 cc/(m2.d) and more preferably of 0.05 to 0.5 cc/(m2.d).
It is another object of the present invention to provide a packaging material
comprising at
least one pulp-based substrate layer having, in this order,
A primer layer adjacent to the pulp-based substrate layer,
a first barrier layer adjacent to the primer layer,
an inorganic barrier layer such as a metal layer adjacent to the first barrier
layer, where the
inorganic barrier layer is deposited via thin-film deposition,
a second barrier layer adjacent to the inorganic barrier layer,
optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of less than
1.5 g/(m2.d),
preferably of less than 1.0 g/(m2.d), and more preferably of 0.01 to 1.0
g/(m2.d) and/or an
OTR at normal conditions (23 C, 50 /ORH) of less than 1 cc/(m2.d), preferably
of less than
0.5 cc/(m2.d) and more preferably of 0.05 to 0.5 cc/(m2.d).
In the context of the present invention, all values for MVTR are determined
and measured
at tropical conditions (38 C, 90% RH) according to ASTM F1249 and all OTR
values are
determined and measured at normal conditions (23 C, 50% RH) according to ASTM
D3985,
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unless stated otherwise.
It is another object of the present invention to provide a food item packaged
in a packaging
material according to the above.
Further embodiments of the invention are laid down in the dependent claims and
the
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described in the following with
reference to the
drawings, which are for the purpose of illustrating the present preferred
embodiments of the
invention and not for the purpose of limiting the same. In the drawings,
Fig. 1 shows a cross-section a packaging material according to one
embodiment of
the present invention, where a first barrier layer (2) and a second barrier
(3) are
arranged on top of a pulp-based substrate (1) and are adjacent to each other.
Fig. 2 shows a cross-section a packaging material according to
one embodiment of
the present invention, where a first barrier layer (2) and a second barrier
(3) are
arranged on top of a pulp-based substrate (1), where a inorganic barrier layer
(4) is in between the first barrier layer (2) and a second barrier (3) and
adjacent
to said barrier layers (2,3).
Fig. 3 shows a cross-section a packaging material according to
one embodiment of
the present invention, where a first barrier layer (2) and a second barrier
(3) are
arranged on top of a pulp-based substrate (1), where a primer layer (5) is in
between the pulp-based substrate (1) and a first barrier (2) and adjacent to
each
of them.
Fig. 4 shows a cross-section a packaging material according to
one embodiment of
the present invention, where a first barrier layer (2) and a second barrier
(3) are
arranged on top of a pulp-based substrate (1), where an inorganic barrier
layer
(4) is in between the first barrier layer (2) and a second barrier (3) and
adjacent
to said barrier layers (2,3) and where a primer layer (5) is in between the
pulp-
based substrate (1) and a first barrier (2) and adjacent to each of them.
DESCRIPTION OF PREFERRED EMBODIMENTS
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It is an object of the present invention to provide a process for improving
the barrier
properties of either a barrier layer comprised in a pulp-based substrate layer
having a barrier
layer, or of a barrier layer in a packaging material comprising a pulp-based
substrate layer
5 having a barrier layer, comprising the steps of
a) providing a pulp-based substrate layer having a layer of an aqueous
barrier
composition applied to it,
b) drying the pulp-based substrate layer having a layer of an aqueous
barrier
composition applied to it to form a pulp-based substrate layer having a
barrier layer, such
that the moisture content of the pulp-based substrate layer having a barrier
layer is below
2.5 % by weight, preferably below 2 % by weight, based on the weight of the
pulp-based
substrate layer having a barrier layer.
In the context of the present invention, the term "improving a barrier
property" means that a
barrier property of a layer with respect to at least one substance, such as
for example water
vapour or oxygen, is modified such as to allow for less diffusion of said
substance across
the layer. Specifically, in the case of water vapour and oxygen, such an
improvement is
expressed by lower numerical values in water vapour transmission rate and
oxygen
transmission rate, respectively.
It has been found that when a pulp-based substrate layer having a layer of an
aqueous
barrier composition applied to it is dried to a lower moisture content than
would usually be
required for mere drying and formation of a barrier film, the barrier
properties of the resulting
pulp-based substrate layer having a barrier layer are significantly improved.
The pulp-based substrate layer that are used in the process according to the
present
invention may be based on any type of pulp that is sourced from a plant such
as for example
softwood or hardwood. Exemplary types of pulp that may be comprised in the
pulp-based
substrate layer are chemical pulps such as kraft or sulphite pulps or are
chemi-
thermomechanical pulps.
In a preferred embodiment, the pulp-based substrate layer comprises both
hardwood and
softwood chemical pulp.
The process of the invention includes a step of providing a pulp-based
substrate layer
having a layer of an aqueous barrier composition applied to it. The layer of
an aqueous
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barrier composition can be applied via known techniques that may be used to
apply a liquid
coating, such as for example blade coating, rod coating, curtain coating,
reverse gravure
coating, gravure coating, spray coating, dip coating or air knife coating.
The aqueous barrier composition may be applied to the pulp-based substrate
layer either
in-line at the time of the production of the pulp-based substrate layer on a
paper machine
or off-line after the pulp-based substrate layer, which may or may not already
have a primer
layer, has been produced, on a separate coating apparatus. In the case where
the pulp-
based substrate layer includes more than one barrier layer, the barrier layers
may be formed
either by subsequently running the pulp-based substrate layer through multiple
coating
apparatuses or by repeatedly running the pulp-based substrate layer through a
same
coating apparatus.
The coating apparatus is equipped with a coating unit which applies the
aqueous barrier
composition to the pulp-based substrate layer and with a drying unit which
dries the pulp-
based substrate layer and the aqueous barrier composition applied. The coating
unit may
be a blade coating, rod coating, curtain coating, reverse gravure coating,
gravure coating,
spray coating, dip coating, or air knife coating unit.
The aqueous barrier composition may be applied to the pulp-based substrate
layer in the
form of a liquid dispersion, specifically as a liquid solution, which may
preferably have a
solids content of up to 55% by weight, wherein the solids content may be more
preferably
between 5% by weight and 55% by weight, based on the weight of the aqueous
barrier
composition.
The pulp-based substrate layer may have any form or shape.
In one embodiment, the pulp-based substrate layer is in the form of a flat
web, for example
of paper or paperboard. This is mostly, but not necessarily, the case when the
aqueous
barrier composition is applied to the pulp-based substrate layer in a paper
machine, which
paper machine forms the pulp-based substrate layer as paper or paperboard and
applies
the aqueous barrier composition in-line. Alternatively, the aqueous barrier
composition is
applied to the pulp-based substrate layer in the form of a flat web in a
coating apparatus
comprising at least one coating unit, configured to apply the aqueous barrier
composition,
and a drying unit, configured to dry the pulp-based substrate layer having the
aqueous
barrier composition applied to it to the required moisture content. In order
to coat flat web
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shaped pulp-based substrate layers, the coating unit is preferably a blade
coating unit, rod
coating unit, curtain coating unit, reverse gravure coating unit, gravure
coating unit, spray
coating unit or air knife coating unit.
In another embodiment, the pulp-based substrate layer such as paper or
paperboard is not
in the form of a flat web, but is formed to a desired three-dimensional shape,
such as for
example a cup, a tray or a bottle. In this case, the aqueous barrier
composition is applied
to the pulp-based substrate layer in a coating apparatus comprising at least
one coating
unit, configured to apply the aqueous barrier composition, and a drying unit,
configured to
dry the pulp-based substrate layer having the aqueous barrier composition
applied to it to
the required moisture content. In order to coat three-dimensional shaped pulp-
based
substrate layers, the coating unit is preferably a spray coating unit, a
dipping coating unit or
a curtain coating unit.
In a preferred embodiment, the aqueous barrier composition may be applied to
the pulp-
based substrate layer on one side or both sides of the pulp-based substrate
layer.
The pulp-based substrate layer can be freely chosen in terms of base weight,
provided the
pulp-based substrate layer can be provided pin-hole free in order to avoid
holes in the
barrier layer. In the case the pulp-based substrate layer is a paper, the base
weight may be
preferably above 15 gsm and below 225 gsm, more preferably of 40 to 120 gsm,
whereas
in the case the pulp-based substrate layer is a paperboard, the base weight
may be
preferably above 225 gsm.
It is understood that the pulp-based substrate layer may be pre-coated or pre-
treated prior
to being provided in the process according to the invention in ways known in
particular in
the art of paper and/or paperboard production. For example, the pulp-based
substrate layer
may be calendared, pressed, smoothened or otherwise mechanically pre-treated
prior to
step a) and/or the pulp-based substrate layer may be provided with an internal
or external
sizing or a print coat or otherwise pre-treated prior to step a). As such, the
term pulp-based
substrate layer includes what is known as "base papers" in the packaging paper
field.
In a preferred embodiment, the aqueous barrier composition may be applied to
the pulp-
based substrate layer such as to arrive at a barrier layer having a grammage
of from 0.5
gsm to 15 gsm, preferably from 2 to 12 gsm, more preferably from 4 to 11 gsm
or from 4 to
10 gsm, Alternatively, the barrier layer may also have a grammage of from 9
gsm to 11
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gsm.
In the process according to the present invention, the drying of the pulp-
based substrate
layer having a layer of aqueous barrier composition applied to it to form a
pulp-based
substrate layer having a barrier layer is carried out such that the moisture
content of the
pulp-based substrate layer having a barrier layer is below 2.5 % by weight or
of from 0.5 to
2.5 % by weight, preferably below 2 % by weight or of from 0.5 to 2 % by
weight, more
preferably below 1.5 `)/0 by weight or of from 0.5 to 1.5 c/o by weight, based
on the weight of
the pulp-based substrate layer having a barrier layer.
It is understood that before drying, the moisture content of the pulp-based
substrate layer
having the aqueous barrier composition applied to it is in excess of 2.5 % by
weight, or in
excess of 5 % by weight based on the weight of the pulp-based substrate layer
and the
aqueous barrier composition applied to it. It was determined that the pulp-
based substrate
layer having the aqueous barrier composition applied to it usually has, due to
the amount
of water added by way of the aqueous barrier composition, a moisture content
of about 9%
by weight when the pulp-based substrate layer is a paper via appropriate
measurements or
calculations. When it is a paperboard, due to the higher grammage, the
moisture content
will be lower but in any case in excess of 2.5 % by weight.
The moisture content may be measured either in-line in the paper machine via a
calibrated
moisture content measuring apparatus configured to correlate the measured
moisture
content to the moisture content as measured according to the Tappi T412
standard; or it
may be measured off-line by sampling and measuring the moisture content
according to
Tappi T412. It is understood that the person of ordinary skill in the art will
be able to correlate
the in-line measured moisture content to the moisture content according to a
Tappi 412 in
order to calibrate the in-line moisture content measuring apparatus.
In the process according to the present invention, the moisture content of
pulp-based
substrate layer and the layer barrier layer is below 2.5 % by weight,
preferably below 2 %
by weight, more preferably below 1.5 % by weight, based on the weight of the
pulp-based
substrate layer. The moisture content may be determined according to Tappi
T412. It is
understood that due to the differential water retention properties between the
pulp-based
substrate layer and the aqueous barrier composition, the measured moisture
content is the
sum of the individual fractions of moisture content contained in the pulp-
based substrate
layer and the barrier layer, respectively, at the time of measurement and it
is not easily
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possible to attribute accurately the fraction of the overall moisture content
originating from
the pulp-based substrate layer or the aqueous barrier composition. It has
however been
found that when the overall measured moisture content of the pulp-based
substrate layer
and the barrier layer is below the above given thresholds, the barrier
properties of the pulp-
based substrate layer having a barrier layer are improved when compared to
barrier
properties of a pulp-based substrate layer having a barrier layer that has
been dried to a
more conventional moisture content above the above given thresholds.
In the pulp-based substrate layer having a barrier layer, obtained via the
process according
to the invention, a VVVTR at tropical conditions (38 C, 90% RH) of less than
10 g/(m2.day),
and preferably of less than 5 g/(m2.day) and more preferably of between 1 and
5 g/(m2.day)
when measured according to ASTM F1249 may be achieved with a barrier layer
having a
thickness of about 5 microns or less, or between 1 to 5 microns, which is an
unexpectedly
low VVVTR for a thickness of about 5 microns or less. A OTR (23 C, 50% RH) of
less than
0.2 cc/(m2.day), more specifically of between 0.05 and 0.1 cc/(m2.day) may be
achieved
with a barrier layer having a thickness of about 1 micron or less when
measured according
to ASTM D3985, which is an unexpectedly low OTR for a thickness of about 5
microns or
less.
The above barrier properties are achieved without including a metal or
inorganic layer in the
pulp-based substrate layer having a barrier layer. However, it may desirable
to even further
improve the overall barrier properties of the pulp-based substrate layer
having a barrier
layer, obtained via the process according to the invention, by the addition of
a metal layer,
a non-metallic inorganic layer, or both.
In an embodiment of the process according to the present invention, the
aqueous barrier
composition comprises a barrier compound, preferably in the form of an aqueous
dispersion, specifically in the form of an aqueous solution, of a barrier
compound. The
barrier compound may be any one compound, in particular an organic compound,
that is
able to improve the barrier properties such as for example OTR or VVVTR of the
pulp-based
substrate layer when formed into a layer on the pulp-based substrate layer.
Suitable barrier
compounds may be chosen from polymers barrier compounds that may be man-made
or
natural such as for example polyesters, polyolefins or polyamides. In
particular, the man-
made polymer barrier compounds may be chosen among PVDC, PE, PP, PET, PA,
PVOH,
EVOH, PVC, PVA, PLA, PHA, styrene acrylate and styrene butadiene,
nanocellulose,
cellulose nanocrystals or cellulose nanofibrils. In another embodiment, the
aqueous barrier
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composition further comprises, in addition to the above-mentioned polymers
compounds,
one or more inorganic barrier compounds. The inorganic barrier compounds may
be chosen
from mineral barrier compounds such as nanopigments, which are preferably
plateled-
shaped, such as for example nanoclays. In the case where inorganic barrier
compounds
5 are comprised in the aqueous barrier composition, the aqueous barrier
composition is
preferably an aqueous solution of a barrier compound such as a water-soluble
polymer
compound, where the inorganic barrier compound is dispersed in.
The aqueous barrier composition may in a preferred embodiment further include
a wax. In
10 a preferred embodiment, when a wax is comprised in the aqueous
barrier composition, the
aqueous barrier composition may preferably be in the form of an aqueous latex,
such as for
example a styrene butadiene latex or styrene acrylic latex. Waxes are not
soluble in an
aqueous environment such as aqueous solutions or water. It is understood that
the wax
suitable for the aqueous barrier composition can be man-made or a natural wax,
for
example man-made wax such as polyethylene wax or alkane wax or for example
natural
wax such as a wax ester.
The aqueous barrier composition may be in the form of an aqueous dispersion of
a barrier
compound. It is understood that "a barrier compound" means one or more barrier
compounds, i.e. one single barrier compound or a combination of two or more
different
barrier compounds. In a preferred embodiment the aqueous dispersion of a
barrier
compound may comprise one barrier compound or more barrier compounds such as
for
example two different man-made and/or natural polymer compounds. An example of
an
aqueous dispersion of a barrier compound is an aqueous dispersion of PVDC.
Other
examples are aqueous dispersions of styrene butadiene, styrene acrylic,
polyethylene co-
polymer or polyvinylacetate. It is understood that the term aqueous dispersion
of a barrier
compound also encompasses, without being limited to, an aqueous latex of a
barrier
compound. Examples of an aqueous latex of a barrier compound are latex of
styrene
butadiene or latex of styrene acrylic.
In an embodiment of the process according to the invention, after the drying
step b), the
process further comprises the step c) of moisturizing the pulp-based substrate
layer having
a barrier layer, such that the moisture content of the pulp-based substrate
layer having a
barrier layer is 3.5 % by weight or more, or between 3.5% and 6% by weight,
based on the
weight of the pulp-based substrate layer and the barrier layer. This might be
necessary
under certain circumstances if the pulp-based substrate layer having a barrier
layer is
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subsequently converted or printed immediately downstream of the paper machine
or at a
later stage since a moisture content of less than 3% by weight leads to
increased brittleness
and loss of flexibility in the pulp-based substrate layer. Increasing the
moisture content
above 3 % by weight improves the flexibility of the pulp-based substrate
layer. Furthermore,
moisturizing reduces curl and removes static charges from the pulp-based
substrate layer.
Moisturizing may be achieved by applying steam, water mist, water or an
aqueous coating,
preferably on the reverse side of the pulp-based substrate layer, i.e. the
side of the pulp-
based substrate layer opposite to the side having the barrier layer. It has
been observed
that that even though the moisturizing step increases moisture content after
drying in step
b., it does not negatively affect the barrier properties of the pulp-based
substrate layer
having a barrier layer. In some instances, after the drying step b), the
moisture content of
the pulp-based substrate layer having a barrier layer may further be increased
to 4.5 % by
weight or more, or between 4.5% and 6% by weight, based on the weight of the
pulp-based
substrate layer and the barrier layer.
Optionally, the moisturizing step may be followed by a further drying step to
adjust the
moisture content to a predetermined moisture content above 3 c/o by weight,
preferably to
3% by weight to 5% by weight. Particularly but not exclusively, when the
remoistening is
done via the application of a further coating layer or of water (pure or
otherwise) on the
reverse side of the pulp-based substrate layer, drying is preferred in order
to avoid blocking,
wrinkling or opposite curl.
In a preferred embodiment of the process according to the present invention,
drying the
pulp-based substrate layer having a layer of aqueous barrier composition
applied to it to
form a pulp-based substrate layer having a barrier layer is achieved by
exposing the pulp-
based substrate layer having a layer of aqueous barrier composition to heat,
radiation or
underpressure, or a combination of two or more thereof. Heat may be applied
for example
via hot air or steam, radiation may be in the form of infrared radiation or
microwave radiation.
It is understood that the same options may be employed in the further drying
step after the
moisturizing step.
In a preferred embodiment of the process according to the present invention,
drying the
pulp-based substrate layer having a layer of aqueous barrier composition
applied to it to
form a pulp-based substrate layer having a barrier layer is achieved by
heating the pulp-
based substrate layer having a layer of aqueous barrier composition to a
temperature of at
least 100 C, preferably at least 115 C, more preferably at least 130 C. This
may be done
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at ambient pressure, i.e. without control of pressure, or at underpressure,
i.e. control of
pressure such that the pressure is below ambient pressure. In the case where
underpressure is used, the drying time at the same drying temperature can be
further
reduced as compared to the case where drying is carried out at ambient
pressure and/or
the drying temperature at the same drying time can be further reduced as
compared to the
case where drying is carried out at ambient pressure. Since the pulp-based
substrate layer
can be heated in excess of 100 C, it means that the substrate does not suffer
from thermal
shrinkage as most polymer films such as for example PET, PE or PP, commonly
used in
barrier film packaging.
In a preferred embodiment of the process according to the present invention,
the pulp-based
substrate layer having a layer of an aqueous barrier composition further
comprises an
intermediate layer positioned between the layer of a barrier composition and
the pulp-based
substrate layer. In a preferred embodiment, the intermediate layer positioned
between the
layer of a barrier composition and the pulp-based substrate layer is a primer
layer, which
primer layer is preferably chosen such as to smoothen and close the surface on
the side of
the pulp-based substrate layer to which the aqueous barrier composition is to
be applied.
In the case where an aqueous barrier composition is to be applied on the
opposite side as
well, a primer layer may or may not be present on that side, and if so,
positioned between
the respective layer of a barrier composition and the pulp-based substrate
layer.
In a preferred embodiment of the process according to the present invention,
in step a), the
pulp-based substrate layer having a layer of an aqueous barrier composition
applied to it
has an intermediate layer such as a primer layer positioned between the pulp-
based
substrate layer and the layer of the aqueous barrier composition. The
intermediate layer
such as a primer layer may smoothen the underlying pulp-based substrate layer,
close any
pores or pinholes, and provide flexibility that allows for easier converting.
As such the
intermediate layer or primer layer may have any composition, provided it can
achieve at
least one of the above functions, and may for example, comprise starch in
either unmodified
or modified form, man-made polymer dispersions, or even barrier compounds.
In a preferred embodiment of the process according to the present invention,
the pulp-based
substrate layer having a barrier layer further comprises an inorganic barrier
layer or a metal
barrier layer, wherein the inorganic barrier layer or a metal barrier layer
may be adjacent to
the barrier layer. The inorganic barrier layer or a metal barrier layer is
preferably deposited
via techniques known as thin-film deposition techniques. In a preferred
embodiment of the
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process according to the present invention, the inorganic barrier layer or a
metal barrier
layer is deposited via either chemical deposition, such as atomic layer
deposition, or
physical deposition. It is understood that the inorganic barrier layer or
metal barrier layer
may only be applied once the pulp-based substrate layer having a barrier layer
has been
formed or before the aqueous barrier composition is applied to the pulp-based
substrate
layer. It is not possible to apply the inorganic barrier layer via thin-film
deposition to the
undried aqueous barrier composition.
In a preferred embodiment of the process according to the present invention,
after step c),
the process further comprises the step d) of applying an inorganic barrier
layer or a metal
barrier layer to the barrier layer via thin-film deposition.
In the case where a metal barrier layer is deposited, the metal is preferably
aluminium. In a
preferred embodiment of the process according to the present invention, the
metal barrier
layer is of aluminium.
In the case where an inorganic barrier layer is deposited, the inorganic
barrier is preferably
chosen from metal oxides such as aluminium oxide or silica, e.g. AlxOy or
SiOx.
When the inorganic barrier layer or a metal barrier layer surface is
deposited, the surface
on which it is deposited on may or may not have been surface treated before
the deposition
of the inorganic barrier layer or a metal barrier layer. Exemplary surface
treatments are
plasma treatment or corona treatment.
In a preferred embodiment of the process according to the present invention,
the inorganic
barrier layer or the metal barrier layer is adjacent to and deposited directly
onto the barrier
layer.
In a preferred embodiment of the process according to the present invention,
after step d),
the process further comprises the step e) of applying a further layer of
aqueous barrier
composition to the inorganic barrier layer or a metal barrier layer and drying
the resulting
stack of layers having the further layer of aqueous barrier composition
applied to it to form
a further barrier layer such that the moisture content of the resulting stack
of layers having
a further barrier layer is below 2.5 c/o by weight, preferably below 2 % by
weight, based on
the weight of the resulting stack of layers having a barrier layer. The
aqueous barrier
composition and the further aqueous barrier composition may have the same
composition
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or may have different compositions.
It is understood that the pulp-based substrate layer having a barrier layer
may further be
coated with a functional layer such as for example a sealing layer which
further may or may
not be a printable layer.
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having a barrier layer obtained by the
process as
described above, for example a wrapping paper for perishable goods such as
snacks,
candy, nuts, cereals, chocolate, frozen confectionery, toffee, potato chips,
dried fruit, cakes,
tea leaves, whole bean or ground coffee, pepper, spices, cured meats, dairy
products, fresh
food such as vegetables, fruit and meat, dry pet food, tobacco, dehydrated
foods, non-foods
such as vitamins or minerals, household or personal care products, for
example.
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having, in this order,
a first barrier layer adjacent to the pulp-based substrate layer,
an inorganic barrier layer such as a metal layer adjacent to the first barrier
layer, where the
inorganic barrier layer is deposited via thin-film deposition,
a second barrier layer adjacent to the inorganic barrier layer,
optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of less than
1.5 g/(m2.d),
preferably of less than 1.0 g/(m2.d), and more preferably of 0.01 to 1.0
g/(m2.d).
In a preferred embodiment, the first and second barrier layer have the same
composition or
have a different composition.
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having, in this order,
primer layer adjacent to the pulp-based substrate layer,
a first barrier layer adjacent to the primer layer,
an inorganic barrier layer such as a metal layer adjacent to the first barrier
layer, where the
inorganic barrier layer is deposited via thin-film deposition,
a second barrier layer adjacent to the inorganic barrier layer,
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optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of less than
1.5 g/(m2.d),
5 preferably of less than 1.0 g/(m2.d), and more preferably of 0.01 to 1.0
g/(m2.d). In a
preferred embodiment, the first and second barrier layer have the same
composition, and
preferably comprise PVDC or a nanopigment. It is expected that PVDC will be
phased out
to be replaced in the coming years with other barrier compounds having the
same or better
barrier properties and that are more environmentally friendly.
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having, in this order,
a barrier layer adjacent to the pulp-based substrate layer,
optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of 1 to 5
g/(m2.d).
It is a further object of the present invention to provide a packaging
material comprising at
least one pulp-based substrate layer having, in this order,
a primer layer adjacent to the pulp-based substrate layer,
a barrier layer adjacent to the primer layer,
optionally a sealing layer such as a heat- or cold- sealing layer adjacent to
the second
barrier layer, wherein the combined amount of the first barrier layer and the
second barrier
layer ranges from 4 gsm to 11 gsm, preferably from 9 to 11 gsm, and wherein
the packaging
material exhibits a VVVTR at tropical conditions (38 C, 90% RH) of 1 to 5
g/(m2.d).
It is understood that in the above packaging materials, the respective barrier
layers are
preferably obtained by applying an aqueous barrier composition to either the
pulp-based
substrate layer, the primer layer or the inorganic barrier layer as may be the
case and then
drying the resulting stack of layers having the aqueous barrier composition
applied to it such
as to form a stack of layers having a barrier layer and such that the moisture
content of the
resulting stack of layers having a barrier layer is below 2.5 % by weight,
preferably below 2
% by weight, based on the weight of the stack of layers having a barrier
layer. For the
avoidance of doubt, the stack of layers includes the pulp-based substrate
layer.
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EXPERIMENTAL DATA
Comparative Example 1
A base paper of 70 gsm was coated with an aqueous dispersion of PVDC such as
to achieve a coat weight of 10 +/- 1 gsm and dried until a moisture content of
3% was
reached. In general, a person of ordinary skill in the art will know how to
achieve a given
coat weight when provided with an aqueous barrier composition having a certain
solids
content of barrier compound by applying the appropriate amount of barrier
composition to
the base paper.
The resulting barrier paper exhibited a WVTR at tropical conditions (38 C, 90%
RH) of about 3 to 5 g/(m2.d), when measured according to ASTM F1249 and OTR at
normal
conditions (23 C,50%RH) of higher than 5 cc/(m2.d.).
Example 1
A base paper of 70 gsm was coated with an aqueous dispersion of PVDC such as
to achieve a coat weight of 10 +/- 1 gsm and dried until a moisture content of
1.7% was
reached.
The resulting barrier paper exhibited a VVVTR at tropical conditions (38 C,
90%
RH) of about 1.5 to 2.5 g/(m2.d), when measured according to ASTM F1249 and a
OTR at
normal conditions (23 C,50c/oRH) of between 0.5-2.5 cc/(m2.d.).
Comparative Example 2
A base paper of 80 gsm was coated with an aqueous dispersion of SBR (styrene-
butadiene rubber) and wax latex mixture such as to achieve a coat weight of 6
+/- 1 gsm
and dried until a moisture content of 2.8 % was reached.
The resulting barrier paper exhibited a VVVTR at tropical conditions (38 C,
90%
RH) of about 28 to 40 g/(m2.d), when measured according to ASTM F1249.
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Example 2
A base paper of 80 gsm was coated with an aqueous dispersion of SBR and wax
latex mixture such as to achieve a coat weight of 6 +/- 1 gsm and dried until
a moisture
content of 1.8% was reached.
The resulting barrier paper exhibited a WVTR at tropical conditions (38 C, 90%
RH) of about 3 g/(m2.d), when measured according to ASTM F1249.
Comparative Example 3
A base paper of 80 gsm was coated with an aqueous solution of polyvinyl
alcohol
such as to achieve a coat weight of 3 +/- 1 gsm and dried until a moisture
content of 3.2%
was reached.
The resulting barrier paper exhibited a VVVTR at ambient conditions (23 C, 50%
RH) of about 2.5 g/(m2.d), when measured according to ASTM F1249.
Example 3
A base paper of 80 gsm was coated with a aqueous solution of polyvinyl alcohol
such as to achieve a coat weight of 3 +/- 1 gsm and dried until a moisture
content of 3.2%
was reached.
The resulting barrier paper exhibited a VVVTR at ambient conditions (23 C, 50%
RH) of about 1 g/(m2.d), when measured according to ASTM F1249.
Comparative Example 4
A base paper of 80 gsm was first coated with an aqueous solution of
predominantly
polyvinyl alcohol such as to achieve a coat weight of 2 +/- 1 gsm and dried
until a moisture
content of 3.4% was reached. Then, a second coating with an aqueous dispersion
of SBR
and wax latex mixture such as to achieve a coat weight of 7 +/- 1 gsm and
dried until a
moisture content of 3.5% was reached.
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The resulting barrier paper exhibited a VVVTR at tropical conditions (38 C,
90%
RH) of about 18 to 23 g/(m2.d), when measured according to ASTM F1249.
The resulting barrier paper exhibited a OTR (23 C, 50% RH) of above 3
cc/(m2.d).
Example 4
A base paper of 80 gsm was first coated with an aqueous solution of
predominantly
polyvinyl alcohol such as to achieve a coat weight of 2 +/- 1 gsm and dried
until a moisture
content of 2.0% was reached. Then, a second coating with an aqueous dispersion
of SBR
and wax latex mixture such as to achieve a coat weight of 7 +1- 1 gsm and
dried until a
moisture content of 1.4% was reached.
The resulting barrier paper exhibited a WVTR at tropical conditions (38 C, 90%
RH) of about 2.5 g/(m2.d), when measured according to ASTM F1249.
The resulting barrier paper exhibited a OTR (23 C, 50% RH) of about 0.1
cc/(m2.d).
Example 5
A base paper of 100 gsm having a moisture content of about 4 % by weight was
coated with an aqueous barrier composition comprising about 50 % by weight of
a barrier
compound and about 50 % by weight of water. The aqueous barrier composition
was
applied to the base paper at a wet coating weight of about 20 gsm to achieve a
barrier layer
having a dry coating weight of about 10 gsm, and the base paper having the
aqueous barrier
composition applied to it was then dried to a moisture content of about 2 % by
weight, to
form a base paper having barrier layer. After the drying, the base paper
having barrier layer
was re-moisturized to a moisture content of about 4.5 % by weight. The
detailed amounts
used can be found in Table 1.
Table 1
Basepa per Coating Drying Remoistening
water
(gsm) 4.0 14.0 2.2 5.0
solid (gsm) 96.0 106.0 106.0 106
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Total
(gsrn) 100.0 120.0 108.2 111.0
Moisture
content (%
by weight) 4.0 11.7 2.0 4.5
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LIST OF REFERENCE SIGNS
1 pulp-based substrate 4 inorganic barrier
layer
2 first barrier layer 5 primer layer
3 second barrier layer
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