U.S. patent application number 15/948568 was filed with the patent office on 2020-10-08 for aseptic and liquid food packaging with aqueous multibarrier coatings and methods of making same.
The applicant listed for this patent is Georgia-Pacific Bleached Board LLC. Invention is credited to Lori Jeanne Fortin.
Application Number | 20200317413 15/948568 |
Document ID | / |
Family ID | 1000003334776 |
Filed Date | 2020-10-08 |
![](/patent/app/20200317413/US20200317413A1-20201008-D00000.png)
![](/patent/app/20200317413/US20200317413A1-20201008-D00001.png)
![](/patent/app/20200317413/US20200317413A1-20201008-D00002.png)
United States Patent
Application |
20200317413 |
Kind Code |
A1 |
Fortin; Lori Jeanne |
October 8, 2020 |
ASEPTIC AND LIQUID FOOD PACKAGING WITH AQUEOUS MULTIBARRIER
COATINGS AND METHODS OF MAKING SAME
Abstract
Coatings for packaging materials and, more specifically, aqueous
coatings for paperboard substrates and methods of applying the
coatings. The aqueous coatings may include light blocking
particles.
Inventors: |
Fortin; Lori Jeanne;
(Peachtree Corners, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Georgia-Pacific Bleached Board LLC |
Atlanta |
GA |
US |
|
|
Family ID: |
1000003334776 |
Appl. No.: |
15/948568 |
Filed: |
April 9, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21H 19/826 20130101;
B65D 2565/387 20130101; D21H 19/38 20130101; D21H 5/22 20130101;
D21H 19/828 20130101; D21H 19/84 20130101; D21H 19/24 20130101;
D21H 5/003 20130101; D21H 19/824 20130101; B65D 65/42 20130101;
B65D 2565/382 20130101 |
International
Class: |
B65D 65/42 20060101
B65D065/42; D21H 21/36 20060101 D21H021/36; D21H 19/82 20060101
D21H019/82; D21H 19/84 20060101 D21H019/84; D21H 19/24 20060101
D21H019/24; D21H 19/38 20060101 D21H019/38; D21H 23/56 20060101
D21H023/56 |
Claims
1. A substrate for aseptic packaging, the substrate comprising at
least a first layer and a second layer, wherein the first layer is
disposed on a side of the substrate and the second layer disposed
on the first layer, wherein each layer comprises a composition
comprising an aqueous polymeric solution or dispersion dried to
form a continuous film to provide distinct barrier functions.
2. The substrate of claim 1, wherein the first layer composition
forms an oxygen gas barrier and the second layer composition forms
a moisture vapor or liquid barrier.
3. The substrate of claim 2, wherein the first layer composition
comprises a polyvinyl alcohol and the second layer composition
comprises an acrylic latex dispersion.
4. The substrate of claim 1, wherein the first and second layers
are coated on a side of the substrate intended for contact with
food or liquid contents for the aseptic packaging.
5. The substrate of claim 4, further comprising a third layer,
wherein the first, second, and third layers are coated on the side
of the substrate, the third layer disposed on the second layer and
being the top most layer.
6. The substrate of claim 1, wherein one of the first layer or the
second layer forms a barrier to light.
7. The substrate of claim 6, wherein the barrier to light
composition comprises a mixture of a carbon-black or aluminum
particles and the composition of the other layer comprises a second
polymer.
8. The substrate of claim 1, further comprising a third layer and a
fourth layer placed on a second side of the substrate opposite the
first and second layers.
9. The substrate of claim 1, wherein the substrate comprises a
layer of paper or paperboard.
10. A method of manufacturing aseptic packaging, comprising the
steps of: a. providing a substrate, wherein the substrate comprises
a layer of paper or paperboard; b. providing a first coating
composition; c. providing a second coating composition; and d.
forming a plurality of barrier layers on a first side of the
substrate.
11. The method of claim 10, wherein the forming a plurality of
barrier layers on a first side of the substrate comprises: i.
forming first barrier layer by coating the first coating
composition as a film onto a first side of the substrate and drying
the first coating composition; and ii. forming a second barrier
layer by coating the second coating composition as a film on top of
the first barrier layer and drying the second coating
composition.
12. The method of claim 11, before forming a plurality of barrier
layers, providing a third coating composition, and when forming the
plurality of barrier layers further comprises forming a third
barrier layer by coating the third coating composition as a film on
top of the second barrier layer and drying the third coating
composition.
13. The method of claim 12, wherein the third coating composition
is the same as the first coating composition.
14. The method of claim 10, wherein the forming a plurality of
barrier layers on a first side of the substrate comprises forming
the plurality of barriers simultaneously by applying the first and
the second coating compositions via curtain-coating or slide hopper
coating
15. The method of claim 10, wherein the combination of the first
barrier layer and the second barrier layer block oxygen and water
vapor.
16. The method of claim 10, wherein the plurality of barrier layers
forms a barrier to light.
17. The method of claim 10, wherein the first coating composition
comprises a solution comprising a polyvinyl alcohol and the second
coating composition comprises an acrylic latex dispersion.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to coatings for a variety
of aseptic and liquid food packaging materials that provide
improved total barrier properties for long-term storage. More
specifically, the present invention is directed to aqueous coatings
for packaging for foods and liquids and methods of applying the
coatings. The aqueous coatings may include light blocking
particles.
BACKGROUND OF THE INVENTION
[0002] Various materials have been used for the packaging of foods,
liquids, and other materials that need protection from handling,
moisture, water (liquid and vapor) oxygen, and light. Conventional
barrier layers or films that are intended to reduce or inhibit the
permeation of vapor typically include polyolefins, polyesters,
polyvinylidene chloride, acrylic polymers, styrene acrylate,
styrene butadiene, polyurethanes, polyamides, and metallic foils
(aluminum). Polyvinyl alcohol (PVOH) and copolymers such as
ethylene vinyl alcohol copolymer (EVOH) are known to have good
oxygen barrier properties, but the performance is highly dependent
on ambient relative humidity. Indeed, while a thin dispersion
coated layer of PVOH or EVOH or a similar polymer may be suitable
for packaging of dry products in a dry environment, such a layer is
not ideal for liquid packaging unless encapsulated by water-vapor
and liquid impervious layers. As such, a barrier layer including
polyvinyl alcohol or copolymers thereof typically include
additives, cross-linking agents, multivalent cations, and/or platy
fillers; however, even with such additives, the oxygen barrier
performance about 75 percent relative humidity is generally poor.
In addition, crosslinking the polymer or including additives to
improve the moisture resistance makes processing more difficult and
more expensive and also may run afoul of existing food safety
regulations for food packaging. Moreover, the crosslinking and
inclusion of additives may affect pot life and therefore
manufacturability.
[0003] Water-based polyurethanes can also have good oxygen barrier
properties, but lack high gas and moisture vapor barrier under high
humidity conditions. As such, a barrier layer including water-based
polyurethane typically includes an inorganic filler or requires
pre-treatment of the underlying substrate with a metal oxide layer
or the use of a metallized film. For example, U.S. Patent
Publication No. 2005/0084686 generally discloses aqueous gas
barrier coatings that include dispersed polyurethane resins and
layered inorganic materials, but the disclosure is limited to a
one-coat system on the surface of the substrate or within a
laminate system. U.S. Patent Publication No. 2008/0070043 generally
discloses aqueous gas barrier coatings that include a polyurethane,
but uses a metal oxide layer applied to the base film, i.e.,
underneath the coating, to achieve the desired gas water vapor
barrier properties.
[0004] Metallized substrates have also been independently employed
to provide a gas barrier. However, such metallized substrates are
typically expensive and, because of their low flexibility, are
commonly used as an intermediate layer of a laminated
structure.
[0005] Indeed, as a result of the shortcomings of the conventional
coatings used in packaging materials for food and liquid materials,
the packaging material is generally always coated with a laminate,
i.e., a bulk core layer of paper or paperboard and an outer
laminate layer that includes multiple liquid barrier layers of
thermoplastics. And, in order to ensure that the packaging for
liquids and aseptic packaging has both water vapor barrier
properties and oxygen barrier properties, the outer laminate layer
generally includes at least one foil layer, e.g., aluminum foil. As
long as the aluminum foil is not damaged, the presence in the
laminate effectively prevents any molecules existing in the
environment around the package or in the packaged product from
migrating in any direction through the foil. In fact, there are few
known aseptic packaging materials or liquid packaging materials
that do not include a foil laminate and those known are typically
difficult to process because they require expensive co-extruded
layers or are much thicker than foil laminates and, thus, more
expensive to produce.
[0006] In addition to the use of laminates to provide barrier
properties to packaging materials, conventional barrier layers or
films for liquid packaging materials and those materials intended
for aseptic packaging are also commonly applied via melt extrusion
coating. However, as generally discussed above, melt extrusion
coating complicates processing of the packaging and increases the
expense. European Patent Publication No. 2 199 077 generally
describes aseptic packaging for liquid or wet food that includes a
core substrate, a first heat sealable polyolefin layer applied to
the outside of the core substrate, an oxygen gas barrier layer
formed by liquid film coating and applied to the inner side of the
core substrate, a water vapor barrier layer disposed on the oxygen
gas barrier layer, and a second heat sealable polyolefin layer
applied on to the water vapor barrier layer. The water vapor
barrier layer is laminated to the oxygen gas barrier layer via
direct extrusion or co-extrusion coating of the polyolefin-based
water vapor barrier layer. The second heat sealable polyolefin
layer is also directly extruded onto the water vapor barrier layer
or co-extrusion coated together with the water vapor barrier layer.
As such, even though this reference teaches a non-foil paper or
paperboard packaging laminate for aseptic packaging, the formation
of the packaging requires laminates and extrusion coating.
[0007] It has been recognized that barrier layers applied by liquid
film or aqueous coating may help to reduce complexity in converting
operations. In addition, such liquid film coating may reduce
overall material usage and eliminate manufacturing steps. However,
as discussed above, such liquid film coating applications only
exist in single water-based barrier layer coatings in combination
with melt extruded or laminated layers.
[0008] Moreover, while light shielding is typically accomplished
through the paperboard itself, manufacturers currently use an
additional metal foil lamination layer to further block light from
transmitting through the packaging. It would be advantageous to
eliminate the need for the additional lamination step and
accomplish the light shielding trait through aqueous coating.
[0009] As such, there remains a need in the art for aqueous
multi-barrier coatings and methods of application that reduce the
need for or completely eliminate additional extrusion or lamination
steps but still achieve the desired moisture resistance, water
vapor barrier properties, and light shielding.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to aqueous coating
compositions for use in packaging materials for aseptic and liquid
packaging, the packaging materials derived therefrom, and methods
of making the packaging materials. In an aspect, the invention is
directed to a packaging material having a substrate comprising at
least two layers thereon, wherein the at least two layers comprise
a first layer and a second layer disposed on the first layer,
wherein the first and second layers each comprise a composition
comprising an aqueous polymeric solution or dispersion, and wherein
the composition is dried to form a continuous film to provide
distinct barrier functions. In an aspect, the substrate can include
treated or untreated paper and/or paperboard.
[0011] The first and second layers can be different compositions
from one another. In an aspect, the first layer composition, coated
onto the substrate, can be used to form an oxygen gas barrier and
the second layer, coated on the first layer, can form a water
liquid and vapor barrier. In such instances, the first layer
composition can include an acrylic latex dispersion and the second
layer composition can include a polyvinyl alcohol. In other
embodiments, the first and second layers can form gas barriers and
barriers to light. In one aspect, the layers can be coated on the
inside side of a substrate (i.e., the side intended for contact
with the packaged liquid or food). If only one side of the
substrate is to be coated, it is preferable that the inside side of
the substrate be coated. In some instances, compositions are
applied at a wet thickness to the substrate of about 100 g/m.sup.2
or less. In another instances, the compositions are applied at a
dry thickness of about 30 g/m.sup.2 or less.
[0012] The substrate can also include a third layer composition
comprising an aqueous polymeric solution or dispersion. In such
instances, the first layer and the third layer can be same
composition, or different compositions. In other embodiments, the
substrate can include six layers, where the fourth, fifth, and
sixth layers are placed on a side of the substrate exposed to a
product contained in the packaging. In such aspects, the first and
fourth layers can have the same composition. In other aspects, the
substrate can include four layers of an aqueous polymeric solution
or dispersion compositions. In such aspects, the third and fourth
layers can be placed on a side of the substrate that is exposed to
the atmosphere.
[0013] In an aspect, the food packaging material can include least
two barrier providing layers, with the first layer forming a liquid
and water vapor barrier. In such aspects, the composition can
include an acrylic latex dispersion. In an aspect, the composition
of the second layer forms an oxygen gas barrier, and can be made of
a polyvinyl alcohol. In an embodiment, the liquid barrier layer can
be between the outer layer and the substrate. In other embodiments,
the oxygen barrier can between the substrate and the outer layer.
In instances where the substrate includes three layers, the second
layer can be between the first and third layers, with the first
layer adjacent the substrate and the third layer being the topmost
layer. In an aspect, the first, second, and third layers are coated
on the inside of the substrate. In an aspect, the third layer can
comprise an acrylic latex dispersion.
[0014] In an aspect, the compositions of the first and second
layers of the substrate of the food packaging product can vary. For
example, in one embodiment, the first layer comprises a
polyurethane latex dispersion and the composition of the second
layer comprises an acrylic latex dispersion. In such an embodiment,
the second layer can be the topmost layer, adjacent to the first
layer opposite the substrate, and vice versa. Further, the first
and second layers can be coated on the side of the substrate
intended for the interior of the container. In another aspect, the
composition of the first layer can include a mixture of polyvinyl
acetate dispersion and a carbon-black dispersion and the
composition of the second layer can include a polyolefin
dispersion.
[0015] In another embodiment, the compositions of the layers coated
on the substrate can include additives. For example, any of the
compositions of the layers can include additives. In such aspects,
the additives can include fillers designed to enhance barrier
characteristics, manufacturability, or other functions. For
example, the fillers can include light absorbing fillers, odor
control additives, light scattering particles (e.g., applied in a
polymeric matrix), scavengers (oxygen, CO2, ethylene, etc.),
thickeners, surfactants, inorganics, antimicrobials, preservatives,
friction control, anti-blocking, and the like.
[0016] In another aspect, the invention is directed at a method of
manufacturing aseptic packaging. The method can include the steps
of providing a substrate, providing a first and second coating
composition, and forming a plurality of barrier layers on a first
side of the substrate by forming a first barrier layer by coating
and drying the first coating composition as a film onto the
substrate, and forming a second barrier layer by coating and drying
the second coating as a film on top of the first barrier layer. In
one embodiment, the plurality of barrier layers can be coated
simultaneously. In an aspect, the substrate can include a layer of
paper or paperboard. In another aspect, the first composition can
include an acrylic latex dispersion. The second composition can
include a polyvinyl alcohol. The method can also include forming a
third barrier layer by coating and drying a third coating
composition on top of the second barrier layer. In such aspects,
the first and third compositions can be the same or different. In
some aspects, the first and second barrier layers are formed to
block oxygen and water vapor. In other aspect, the second layer can
form a barrier to light.
[0017] This summary does not limit the scope of the claimed subject
matter. Furthermore, the claimed subject matter is not constrained
to the limitations that solve any or all disadvantages noted in any
part of this disclosure. Features, aspects and advantages of the
present invention are understood with reference to the following
description, appended claims and accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Further features and advantages of the invention can be
ascertained from the following detailed description that is
provided in connection with the drawing(s) described below:
[0019] FIG. 1 is a cross-section of an embodiment of a packaging
material produced according to the invention;
[0020] FIG. 2 is a cross-section of another embodiment of a
packaging material produced according to the invention;
[0021] FIG. 3 is a cross-section of another embodiment of a
packaging material produced according to the invention; and
[0022] FIG. 4 is a cross-section of another embodiment of a
packaging material produced according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention is directed to aqueous coating
compositions for use in packaging materials for aseptic and liquid
packaging, the packaging materials derived therefrom, and methods
of making the packaging materials. As used herein, "aseptic
packaging" refers to packaging in which a previously sterilized
food is packed in a similarly previously sterilized package under
aseptic conditions. An aseptic package is distinguishable from
other types of liquid packaging in that the contents of the package
may be stored in the package for up to months and even longer at
ambient temperature, without the contents deteriorating or being
ruined. However, packaging in which the food must, throughout its
entire storage time in the package, be kept refrigerated (at most
approx. 8.degree. C.) in order not to deteriorate or be completely
ruined is also contemplated for use with the present invention.
Moreover, retortable packages that are intended to be filled with
food and, after sealing, be subjected to a heat treatment for the
purposes of extending shelf-life at elevated temperature in an
atmosphere of high relative humidity are also contemplated for use
with the present invention. The aqueous coating compositions
described herein may be applied to suitable substrates to achieve
improved moisture resistance, water vapor barrier, oxygen barrier,
and light shielding.
[0024] The packaging materials of the present invention may include
multiple barrier layers applied via aqueous coating onto an
untreated or pre-treated substrate. For example, according to some
aspects of the invention, a packaging material of the present
invention may include a substrate and at least two aqueous coating
barrier layers disposed thereon. In other aspects, a packaging
material of the present invention may include a substrate and at
least three aqueous coating barrier layers disposed thereon. In an
aspect, such coatings are applied in-line on the same machine
forming the paper base. The coating compositions, packaging, and
methods of making are described in greater detail below.
Aqueous Coating Compositions
[0025] The aqueous coating compositions may vary depending on the
objective of the barrier layer formed therefrom and the placement
of the particular barrier layer in the multi-barrier layer coating
system.
Polymeric Dispersions and Solutions
[0026] The aqueous coating compositions described herein may be in
the form of a continuous phase solution. That is, the
barrier-forming polymeric components of the aqueous formulation are
completely dissolved in the base solvent (e.g., water). In this
aspect, the polymer resin is dissolved in an aqueous medium, for
example, water. In another embodiment, the aqueous coating
compositions described herein may be in the form of a dispersion.
That is, the polymer resin is dispersed (for example, is present as
small particles) in an aqueous medium such as water.
[0027] In one aspect, the aqueous coating compositions may include
acrylic latex dispersions. Without being bound by any particular
theory, it is believed that the use of acrylics in the aqueous
coating composition of the invention may provide superior liquid
and water vapor barrier properties. For instance, an aqueous
coating layer including the use of one or more acrylic latex
dispersions is resistant to aqueous liquids and provides a moisture
vapor barrier. Additionally, the use of one or more acrylics in the
aqueous coating composition of the invention provides superior heat
sealing characteristics. Suitable examples of acrylic polymers
useful in forming acrylic latex dispersions for use with the
present invention include, but are not limited to, acrylic
polymers, styrene-acrylic copolymers, styrene-acrylic acrylonitrile
terpolymers, and derivatives thereof. Examples of commercially
available acrylic latex dispersions for use with the present
invention include JONCRYL.RTM. 74, 89, 537, and 538 from BASF
Corporation, ACRONAL.RTM. dispersions from BASF Corporation,
RHOPLEX.TM. dispersions from The Dow Chemical Company, and
dispersions from Mallard Creek Polymers, Trinseo, Archroma, and
Synthomer.
[0028] In another embodiment, the aqueous coating composition of
the invention includes a polyvinyl alcohol (PVOH) solution, an
ethyl vinyl alcohol (EVOH) solution, or combinations thereof.
Without being bound by any particular theory, since PVOH and EVOH
have high oxygen gas barrier properties, are relatively easy to use
as a liquid film coating, and have high odor barrier properties, it
is believed that the use of an aqueous coating including PVOH,
EVOH, or a combination thereof in at least one coating layer will
improve overall barrier properties of packaging material for
aseptic and liquid packaging. One example of a commercially
available PVOH for use in this aspect of the invention includes
SELVOL.TM. Polyvinyl Alcohol 21-205 Solution from Sekisui Specialty
Chemicals America, LLC. An example of a commercially available EVOH
for use in this aspect of the invention includes EXCEVAL.TM.
RS-2117 from Kuraray.
[0029] In this aspect, the coating composition may include, along
with the PVOH, EVOH, or combination thereof, a polymer or compound
with functional carboxylic acid groups. Suitable examples of such a
polymer with functional carboxylic acid groups include, but are not
limited to ethylene acrylic acid copolymer (EAA), ethylene
methacrylic acid copolymers (EMAA), or mixtures thereof. If
included, this polymer may be present in an amount of about 1
percent to about 20 percent by weight of the dry coating,
preferably about 5 percent to about 15 percent by weight of the dry
coating. The coating composition may also include inorganic
compounds such as metal oxides.
[0030] In yet another embodiment, the aqueous coating composition
of the invention includes a polyurethane latex dispersion. As used
herein, the term "polyurethane" refers to a polymer including
multiple urethane (--NH--C(O)--O--) linkages within the backbone
and, optionally, urea linkages (NH--C(O)--NH--) within the
backbone. As used herein, a "polyurethane latex dispersion" refers
to a polyurethane resin that, when neutralized, forms a stable
dispersion in water or a water-miscible solvent. In this regard,
the water-miscible solvent may be a single solvent or a blend of
solvents, e.g., methanol, ethanol, propanol, and combinations
thereof. The water-miscible solvent may also be a mixture of water
and at least one water-miscible solvent.
[0031] Without being bound to any particular theory, the use of
certain polyurethane latices in the aqueous coating composition of
the invention confers an array of beneficial properties to the
packaging material. For example, the polyurethane latex dispersion
can provide good oxygen-barrier properties, high flexibility, and
good adhesion with various substrates. In this aspect, the
polyurethane latex dispersion may incorporate a neutralizable acid
group or other anionic hydrophilic group that may be neutralized
with a neutralizing agent. Suitable polyurethanes generally include
the reaction product of at least one isocyanate-containing
component, a polyisocyanate, and at least one isocyanate-reactive
component, e.g., a hydroxy-terminated component or an
amine-terminated component. Any isocyanate-containing component
available to one of ordinary skill in the art is suitable for use
according to the present invention including, but not limited to,
4,4'-diphenylmethane diisocyanate (MDI); polymeric MDI;
carbodiimide-modified liquid MDI; 4,4'-dicyclohexylmethane
diisocyanate (H.sub.12MDI); p-phenylene diisocyanate (PPDI);
m-phenylene diisocyanate (MPDI); toluene diisocyanate (TDI);
3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI);
isophoronediisocyanate (IPDI); hexamethylene diisocyanate (HDI);
naphthalene diisocyanate (NDI); xylene diisocyanate (XDI);
p-tetramethylxylene diisocyanate (p-TMXDI); m-tetramethylxylene
diisocyanate (m-TMXDI); ethylene diisocyanate;
propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate;
cyclohexyl diisocyanate; 1,6-hexamethylene-diisocyanate (HDI);
dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;
cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methyl
cyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of
2,4,4-trimethyl-1,6-hexane diisocyanate (TMDI); tetracene
diisocyanate; napthalene diisocyanate; anthracene diisocyanate;
isocyanurate of toluene diisocyanate; uretdione of hexamethylene
diisocyanate; and mixtures thereof.
[0032] Any hydroxy-terminated component available to one of
ordinary skill in the art is suitable for use in forming the
polyurethane latex dispersion including, but not limited to,
polyether polyols, hydroxy-terminated polybutadiene (including
partially/fully hydrogenated derivatives), polyester polyols,
polycaprolactone polyols, and polycarbonate polyols. Any
amine-terminated component available to one of ordinary skill in
the art is suitable for use in forming the polyurethane latex
dispersion including, but not limited to,
3,5-dimethylthio-2,4-toluenediamine and isomers thereof
3,5-diethyltoluene-2,4-diamine and isomers thereof, such as
3,5-diethyltoluene-2,6-diamine;
4,4'-bis-(sec-butylamino)-diphenylmethane;
1,4-bis-(sec-butylamino)-benzene,
4,4'-methylene-bis-(2-chloroaniline);
4,4'-methylene-bis-(3-chloro-2,6-diethylaniline);
polytetramethyleneoxide-di-p-aminobenzoate; N,N'-dialkyldiamino
diphenyl methane; p,p'-methylene dianiline; m-phenylenediamine;
4,4'-methylene-bis-(2-chloroaniline);
4,4'-methylene-bis-(2,6-diethylaniline);
4,4'-methylene-bis-(2,3-dichloroaniline);
4,4'-diamino-3,3'-diethyl-5,5'-dimethyl diphenylmethane;
2,2',3,3'-tetrachloro diamino diphenylmethane; trimethylene glycol
di-p-aminobenzoate; and mixtures thereof. The polyurethane latex
dispersion may also include a curative that is an amine-terminated
component or a hydroxy-terminated component. The polyurethane may
be saturated or unsaturated.
[0033] The polyurethane latex dispersion may be formed according to
any method known in the art including the one-shot technique or the
prepolymer technique. In particular, in the one-shot technique, the
isocyanate-containing component, isocyanate-reactive component, and
curing agent are reacted in one step. The prepolymer technique
involves a first reaction between an isocyanate-containing
component and an isocyanate-reactive component to produce a
prepolymer, and a subsequent reaction between the prepolymer and
hydroxy and/or amine-terminated curing agent. In one embodiment,
the polyurethane latex dispersion includes a prepolymer formed from
the reaction product of an isocyanate and a polyol or a polyamine,
which is then emulsified and reacted with an amine-terminated or
hydroxy-terminated component. A particularly suitable commercially
available polyurethane latex dispersion is TAKELAC.TM.WPB-341 from
Mitsui Chemicals. Other examples of suitable commercially available
polyurethane dispersions include, but are not limited to,
BAYHYDROL.RTM. polyurethane dispersions from Covestro, SANCURE.TM.
from Lubrizol, LUPHEN.RTM., EPOTAL.RTM., and EMULDUR.RTM. from the
BASF Corporation, and polyurethane dispersions from Alberdinck
Boley.
[0034] In still another embodiment, the aqueous coating composition
includes a chlorinated polymer. For example, the aqueous coating
composition may include a polyvinylidene chloride (PVdC) based
latex. More specifically, the PVdC may be a homopolymer of PVDC and
its copolymers and blends. Examples of copolymers suitable for use
in this aspect of the invention include those with polyvinyl
chloride (PVC) and chlorinated PVC (CPVC) and other copolymers
containing any moiety derived from copolymerization with an active
double bond such as an alkene, haloalkene or any of the acrylic
containing monomers. Most commonly, in a latex dispersion, VdC is
copolymerized with methyl methacrylate, methyl acrylate, butyl
acrylate and/or acrylonitrile. One example of a commercially
available family of PVdC copolymers for use with the present
invention is DIOFAN.RTM. from Solvay Specialty Polymers. Another
example of a commercially available PVdC for use with the present
invention is DARAN.RTM. PVdC dispersions available from Owensboro
Specialty Polymers, Inc.
[0035] In yet another embodiment, the aqueous coating composition
includes a polyolefin dispersion. The polyolefin dispersion may be
made by polymerizing olefins such as ethylene, propylene, butene-1,
pentene-1,4-methylpent-1-ene, and the like, in any conventional
manner. In an aspect, using mechanical dispersion technology
developed by Dow (commonly practiced under the BLUEWAVE.TM. mark),
large polyolefin pellets are processed with a specially designed
high-temperature polymer dispersant system. Water and neutralizer
are added, resulting in a High Internal-Phase Emulsion (HIPE) that
locks in the particle size needed for thin-film coatings. The
emulsion is then diluted with water to create a stable suspension
of polymer particles that are approximately 1 micron in diameter.
These particles remain suspended in water until applied to a
surface. Non-limiting examples of polyolefins suitable for use in
this aspect of the invention include high-density polyethylene
(HDPE), polypropylene, low-density polyethylene (LDPE), very
low-density polyethylene (VLDPE), linear low-density polyethylene
(LLDPE), polybutylene (PB), and blends thereof. Examples of
commercially available polyolefin dispersions for use with the
present invention include HYPOD.TM. polyolefin dispersions from The
Dow Chemical Company or Aquaseal dispersions available from
Paramelt.
[0036] In still another embodiment, the aqueous coating composition
may include a polyester aqueous dispersion. The present invention
contemplates the use of any aliphatic, semi-aromatic, or aromatic
polyester. Non-limiting examples of polyesters suitable for use in
this aspect of the invention include polyethylene terephthalate,
polybutylene terephthalate, polytrimethylene terephthalate,
polyethylene terephthalate, vectran, and their derivatives.
Examples of commercially available polyester aqueous dispersions
for use with the present invention include EvCote.TM. polyester
aqueous dispersions from AkzoNobel and Eastek.TM. polyester aqueous
dispersions from Eastman Chemical Company. The aqueous coating
composition may also include aqueous dispersions of biodegradable
polyesters. Biodegradable polyesters are advantageous in that such
polyesters are biocompatible and have short degradation times. In
one embodiment, the biodegradable polyester is an aliphatic
polyester. Examples of aqueous dispersions of biodegradable
polyesters for use with the aqueous coating systems of the present
invention include, but are not limited to, polylactic acid,
polyhydroxyalkanoate, polyglycolic acid, poly- -caprolactone,
polyhydroxybutyrate, and poly(3-hydroxy valerate).
[0037] In another embodiment, the aqueous coating composition may
include styrene butadiene. Examples of commercially available
styrene butadiene products include GenFlo from Omnova Solutions as
well as products from BASF, Trinseo and Synthomer. In still another
embodiment, the aqueous coating composition includes vinyl polymers
or copolymers derived from moieties such as ethylene (for example,
ethylene vinyl acetate), polystyrene, polyacrylonitrile, and
polyvinyl acetate. One example of a commercially available
polyvinyl acetate dispersion for use with the present invention is
SUNBOND.TM. 3410 from Omnova Solutions.
[0038] The polymeric solutions and dispersions discussed above may
be present in the aqueous coating composition in varying weight and
volume percentages. The weight and volume percent of the polymeric
solutions and dispersions will depend on the other components
present in the composition. However, the volume percentage should
be selected so that the barrier-providing polymeric solution or
dispersion component forms a continuous and contiguous arrangement,
in order to form an interconnected network. In addition, the volume
percentage of the polymeric component should be selected so as to
maintain the mechanical integrity of the substrate to be coated. In
one embodiment, the polymeric component is present in the aqueous
coating composition, on a dry volume basis, in an amount of about
35 volume percent to about 100 volume percent. In another
embodiment, the polymeric component is present in the aqueous
coating composition, on a dry volume basis, in an amount of about
50 volume percent to about 99 volume percent. In still another
embodiment, the polymeric component is present in the aqueous
coating composition, on a dry volume basis, in an amount of about
75 volume percent to about 95 volume percent.
[0039] In each of the coating compositions discussed above, the
coating composition includes about 99 percent to about 60 percent
of the dispersion, latex, or mixture by weight of the dry coating
composition. In one embodiment, the coating composition includes
about 99 percent to about 70 percent of the dispersion, latex, or
mixture by weight of the dry coating composition. In another
embodiment, the coating composition includes about 99 percent to
about 75 percent of the dispersion, latex, or mixture by weight of
the dry coating composition. In still another embodiment, the
coating composition includes about 95 percent to about 80 percent
of the dispersion, latex, or mixture by weight of the dry coating
composition.
Additives
[0040] Any of the coating systems discussed herein may include one
or more additives. In one embodiment, the polymeric solutions and
dispersions of the present invention may include one or more light
absorbing or scattering fillers. As used herein, the term "light
absorbing filler" refers to an additive that is capable of
absorbing light and providing opacity to the substrate after
application of the aqueous coating composition, for example, the
packaging material ultimately formed using the aqueous coating
composition. Non-limiting examples of light absorbing fillers
contemplated for use with the present invention include metal
flakes, metal paste, metal nanoparticles, carbon black, dyes,
pigmented colorants, titanium dioxide, and hollow sphere particles
such as the commercially available ROPAQUE.TM. hollow sphere
polymeric pigments from The Dow Chemical Company and Expancel
Microspheres from AkzoNobel.
[0041] In one embodiment, the polymeric solutions and dispersions
of the present invention may include aluminum flakes, paste, or
nanoparticles as a light reflecting filler. For example, the
aqueous coating composition may include a polyolefin dispersion and
aluminum flakes or paste. One example of a commercially available
aluminum paste for use with the present invention is STAPA IL
HYDROLAN 801 55900/G from Eckart GmbH. The aluminum flakes may be
present in the aqueous coating composition, on a dry weight basis,
in an amount of about 10 percent to about 90 percent by weight of
the coating composition. In another embodiment, the aluminum flakes
may be present in the aqueous coating composition, on a dry weight
basis, in an amount of about 12 percent to about 83 percent by
weight of the coating composition. In still another embodiment, the
aluminum flakes may be present in the aqueous coating composition,
on a dry weight basis, in an amount of about 25 percent to about 75
percent by weight of the coating composition. In yet another
embodiment, the aluminum flakes may be present in the aqueous
coating composition, on a dry weight basis, in an amount of about
35 percent to about 65 percent by weight of the coating
composition. The aluminum flakes may also be present in the aqueous
coating composition, on a dry volume basis, in an amount of about 2
volume percent to about 65 volume percent. In another embodiment,
the aluminum flakes may be present in the aqueous coating
composition, on a dry volume basis, in an amount of about 10 volume
percent to about 50 volume percent. In still another embodiment,
the aluminum flakes may be present in the aqueous coating
composition, on a dry volume basis, in an amount of about 15 volume
percent to about 40 volume percent.
[0042] In another embodiment, any of the polymeric solutions and
dispersions of the present invention may include carbon black, for
example, a carbon black dispersion, as a light absorbing filler.
For example, the aqueous coating composition may include a mixture
of a polyvinyl acetate dispersion and a carbon-black dispersion.
One example of a commercially available carbon black dispersion for
use with the present invention is AQUABLAK.RTM. 8328 from Solution
Dispersions. The carbon black may be present in the aqueous coating
composition, on a dry weight basis, in an amount of about 5 percent
to about 80 percent by weight of the coating composition. In
another embodiment, the carbon black may be present in the aqueous
coating composition, on a dry weight basis, in an amount of about 9
percent to about 77 percent by weight of the coating composition.
In still another embodiment, the carbon black may be present in the
aqueous coating composition, on a dry weight basis, in an amount of
about 15 percent to about 65 percent by weight of the coating
composition. In yet another embodiment, the carbon black may be
present in the aqueous coating composition, on a dry weight basis,
in an amount of about 20 percent to about 55 percent by weight of
the coating composition. The carbon black may also be present in
the aqueous coating composition, on a dry volume basis, in an
amount of about 2 volume percent to about 65 volume percent. In
another embodiment, the carbon black may be present in the aqueous
coating composition, on a dry volume basis, in an amount of about
10 volume percent to about 50 volume percent. In still another
embodiment, the carbon black may be present in the aqueous coating
composition, on a dry volume basis, in an amount of about 15 volume
percent to about 40 volume percent.
[0043] The coating compositions may also include additives such as
thickeners, surfactants, inorganics, oxygen scavengers, scavengers
for other gases such as carbon dioxide or ethylene, antimicrobials,
preservatives, friction control, anti-blocking, colorants,
dispersion stabilizers, and combinations thereof.
[0044] Inorganic additives are also contemplated for use in the
aqueous coating compositions of the invention. Examples of
inorganic additives suitable for use with the present invention
include, but are not limited to, calcium carbonate, talc, clays,
and nanoparticulates such as nanoparticulate clays. In one
embodiment, the inorganic additive is a platy nanoparticulate,
i.e., a particulate with a high aspect ratio and a low particle
size. In this aspect, the aspect ratio of the inorganic additive
may be greater than about 20 in its exfoliated form. In one
embodiment, the aspect ratio of the inorganic additive ranges from
about 50 to about 10,000. In another embodiment, the aspect ratio
of the inorganic additive ranges from about 50 to about 5,000. In
yet another embodiment, the nanoparticulate preferably has a
particle size in at least one dimension of less than about 100 nm.
In one embodiment, the nanoparticulate has a particle size of about
50 nm or less. In another embodiment, the nanoparticulate has a
particle size of about 20 nm or less. For example, the
nanoparticulate may have a particle size of about 5 .mu.m or less.
Without being bound by any particular theory, it is believed that
the use of such play nanoparticulates improve the barrier
properties by creating a more difficult path for gas molecules to
traverse the barrier coating.
[0045] Suitable nanoparticulates include, but are not limited to,
kaolin, kaolinite, antigorite, smectite, vermiculite, bentonite,
illite, mica, laponite, dickite, nacrite, halloysite, antigorite,
chrysotile, pyrophyllite, montmorillonite, hectorite, saponite,
sauconite, sodium tetrasilicic mica, sodium taeniolite, margarite,
vermiculite, phlogopite, xanthophyllite, atapulgite, zeolite,
boehmite, diatomaceous and fuller's earth, calcined aluminium
silicate, hydrated aluminium silicate, magnesium aluminium
silicate, sodium silicate, magnesium silicate, and combinations
thereof.
[0046] When included, the inorganic additive may be present in an
amount of about 5 percent to about 40 percent by weight of the dry
coating composition. In one embodiment, the inorganic additive is
present in an amount of about 10 percent to about 40 percent by
weight of the dry coating composition. The inorganic additive may
also be present in the aqueous coating composition, on a dry volume
basis, in an amount of about 2 volume percent to about 65 volume
percent. In another embodiment, the inorganic additive may be
present in the aqueous coating composition, on a dry volume basis,
in an amount of about 10 volume percent to about 50 volume percent.
In still another embodiment, the inorganic additive may be present
in the aqueous coating composition, on a dry volume basis, in an
amount of about 15 volume percent to about 40 volume percent.
[0047] When included, the dispersion stabilizer may be present in
an amount of about 1 percent or less by weight of the dry coating
composition.
Packaging Materials Formed According to the Invention
[0048] The packaging materials formed according to the invention
may include multiple barrier layers formed from the coating
compositions of the invention. For example, in one embodiment, the
packaging material may include at least two barrier layers formed
from the aqueous coating compositions of the invention. In another
embodiment, the packaging material may include at least three
barrier layers formed from the aqueous coating compositions of the
invention. The multiple barrier layers may be coated on a single
side of the substrate or may be coated on both sides of the
substrate. Various embodiments are described below.
[0049] The underlying substrate may be paper, paperboard, or any
fibrous board base conventionally used in aseptic packaging, liquid
packaging, or retortable packaging. As such, the term "substrate"
includes, without limitation, materials such as packaging films
(including antiseptic, corrosion protective, vacuum and controlled
atmosphere packages), paper, paperboard, carton, and other fibrous
board bases used for packaging. The substrate may have a thickness
of from about 100 .mu.m up to about 600 .mu.m. For instance, in the
case of aseptic packaging, the substrate may have a caliper from
about 9 pt. to about 20 pt. In the case of gable top cartons, the
substrate may have a caliper from about 14 pt. to about 22 pt. The
surface weight of the substrate may vary depending on factors such
as the machine design and manufacturing conditions. However, in one
embodiment, the surface weight of the substrate may be about 50
g/m.sup.2 to about 500 g/m.sup.2. In one embodiment, the surface
weight of the substrate is about 200 g/m.sup.2 to about 300
g/m.sup.2. In another embodiment, the surface weight of the
substrate is about 50 g/m.sup.2 to about 150 g/m.sup.2. For
example, the surface weight of the substrate may be about 75
g/m.sup.2 to about 125 g/m.sup.2.
[0050] The substrate may be untreated or pre-treated. However, as
used herein, when the substrate is pre-treated, the pre-treatment
will be considered part of the substrate. A variety of
pre-treatments may be used depending upon the identity and utility
of the substrate. In one embodiment, a size press application may
be applied in order to improve the holdout properties of the
substrate. In another embodiment, the substrate may be coated with
clay and/or calcium carbonate and a styrene-acrylate binder. In
another embodiment, a pigmented smoothing layer and/or other
pre-coats can be applied in the substrate. In still another
embodiment, the paperboard may be calendared to improve smoothness.
The substrate can be treated and/or selected to have other
characteristics, including, but not limited to, flexibility
(resistance to score cracking), brightness, and anti-wicking
properties. In yet another embodiment, an adhesion promoter may be
applied to the substrate.
[0051] In an aspect, the packaging material includes a substrate
that has a first layer coated on a first side of the substrate, and
a second layer coated on the first layer, placing the first layer
between the substrate and the second layer. In an aspect, the
second layer is oriented to be in contact with the contents that
the packaging material is used to contain. In such aspects, the
second layer can be configured to be a liquid and vapor barrier and
the first layer is an oxygen gas barrier. In such instances, the
barriers are placed closest to the most likely occurrence of
exposure in which they are trying to block, protecting the adjacent
layers to potential exposure to which they could be sensitive too.
For example, when the packaging material is used to contain a food
item, which can include liquid and other vapors, the second layer,
acting as a vapor and liquid barrier, can operate more efficiently
to block the adjacent materials from crossing into the first layer.
Likewise, the first layer, being adjacent the substrate and hence
oxygen from exterior exposure, can prevent oxygen from entering or
reaching the second layer and the food items.
[0052] In one embodiment, as shown in FIG. 1, the packaging
material 10 has barriers layers 14, 16, 18 on only one side of the
substrate 12. However, in other aspects, the substrate 12 can be
surrounded by three barrier layers on each side. As shown, the
packaging material 10 includes a first aqueous coating layer 14
formed from a first aqueous coating composition, a second aqueous
coating layer 16 formed from a second aqueous coating composition,
and a third aqueous coating layer 18 formed from a third aqueous
coating composition. In this aspect, the third aqueous coating
layer 18 is the topmost layer, i.e., the layer exposed to the
atmosphere or packaged food, the second aqueous coating layer 16 is
located in between the third aqueous coating layer 18 and the first
aqueous coating layer 14, and the first aqueous coating layer 14 is
the bottommost layer, i.e., the layer disposed directly on the
substrate 12. The first, second, and third aqueous coating
compositions 14, 16, 18 respectively may be the same or different.
For example, in one embodiment, the first aqueous coating
composition 14 is the same as the third aqueous coating composition
18, but different from the second aqueous coating composition
16.
[0053] In another embodiment, as shown in FIG. 2, the packaging
material 20 includes a first aqueous coating layer 24 formed from a
first aqueous coating composition and a second aqueous coating
layer 26 formed from a second aqueous coating composition. In this
aspect, the second aqueous coating layer 26 is the topmost layer,
i.e., the layer exposed to the atmosphere or the packaged food or
liquid, and the first aqueous coating layer 24 is the bottommost
layer, i.e., the layer disposed directly on the substrate 22. The
first and second aqueous coating compositions may be the same or
different. For example, in one embodiment, the first aqueous
coating composition is different from the second aqueous coating
composition.
[0054] In one embodiment, the packaging material 10 includes a
first aqueous coating layer 14 formed from a coating composition
including an acrylic latex dispersion, a second aqueous coating
layer 16 formed from a coating composition including PVOH, EVOH, or
a combination thereof, and a third aqueous coating layer 18 formed
from a coating composition including the acrylic latex dispersion.
In this aspect, as shown in FIG. 1, the third aqueous coating layer
18 is the topmost layer, i.e., the layer exposed to the atmosphere
and/or the packaged food or liquid, and the first aqueous coating
layer 14 is the bottommost layer, i.e., the layer disposed directly
on the substrate 12. Without being bound to any particular theory,
since PVOH, EVOH, or a combination thereof has good oxygen barrier
properties but poor moisture vapor barrier properties and moisture
resistance and acrylics have good liquid barrier and heat seal
properties, the second aqueous coating layer 16 resides between
coating layers 14 and 18 that each include an acrylic latex
dispersion. Indeed, the PVOH, EVOH, or combination thereof is
encapsulated with a moisture-resistant coating (i.e., the acrylic
latex dispersion) in order to minimize or mask the
humidity-dependence of the internal PVOH/EVOH oxygen barrier
performance. This three-layer coating configuration may also be
applied to the inside of a substrate, i.e., the third aqueous
coating layer 18 is exposed to the contents of the packaging rather
than the atmosphere.
[0055] In another embodiment, the packaging material 20 includes a
first aqueous coating layer 24 formed from a coating composition
including a polyurethane latex dispersion and a second aqueous
coating layer 26 formed from a coating composition including an
acrylic latex dispersion. In this aspect, as shown in FIG. 2, the
second aqueous coating layer 26 is the topmost layer, i.e., the
layer exposed to the atmosphere, and the first aqueous coating
layer 24 is the bottommost layer, i.e., the layer disposed directly
on the substrate 22. Without being bound to any particular theory,
since water-based polyurethanes have high oxygen resistance but are
often limited to non-direct-contact food packaging applications
from a health and safety perspective, a second (top) layer formed
from the acrylic dispersion is sufficient to achieve the desired
overall oxygen barrier properties, liquid barrier, and heat seal
properties. This two-layer coating configuration may also be
applied to the inside of a substrate, i.e., the second aqueous
coating layer 26 is exposed to the contents of the packaging rather
than the atmosphere.
[0056] In yet another embodiment, the packaging material 20
includes a first aqueous coating layer 24 formed from a coating
composition including a polyvinylidene chloride-based latex and a
second aqueous coating layer 26 formed from a coating composition
including a polyolefin dispersion. Without being bound to any
particular theory, since polyvinylidene chloride-based polymers
have high oxygen and moisture vapor barrier properties and
polyolefin dispersions have desirable liquid barrier and heat seal
properties, this two-layer coating system will provide the desired
overall barrier properties. This two-layer coating configuration
may also be applied to the inside of a substrate, i.e., the second
aqueous coating layer 26 is exposed to the contents of the
packaging rather than the atmosphere.
[0057] In still another embodiment, the packaging material 20
includes a first aqueous coating layer 24 formed from a coating
composition including a mixture of a polyvinyl acetate dispersion
and a carbon-black dispersion and a second aqueous coating layer 26
formed from a coating composition including a polyolefin
dispersion. Without being bound to any particular theory, since
polyvinyl acetate has desirable heat seal and oxygen barrier
properties, carbon-black provides light shielding properties, and
polyolefin dispersions have desirable liquid barrier and heat seal
properties, this two-layer coating system will provide the desired
overall barrier and light shielding properties. This two-layer
coating configuration may also be applied to the inside of a
substrate, i.e., the second aqueous coating layer 26 is exposed to
the contents of the packaging rather than the atmosphere.
[0058] In yet another embodiment, the packaging material 20
includes a first aqueous coating layer 24 formed from a coating
composition including a polyvinylidene chloride-based latex and a
second aqueous coating layer 26 formed from a coating composition
including a polyolefin dispersion and aluminum flake. Without being
bound to any particular theory, since polyvinylidene chloride-based
polymers have high oxygen and moisture vapor barrier properties,
polyolefin dispersions have desirable liquid barrier and heat seal
properties, and aluminum flake provides light shielding properties,
this two-layer coating system will provide the desired overall
barrier properties. This two-layer coating configuration may also
be applied to the inside of a substrate, i.e., the second aqueous
coating layer 26 is exposed to the contents of the packaging rather
than the atmosphere.
[0059] In another embodiment, as shown in FIG. 3, the packaging
material 30 includes a first aqueous coating layer 34a formed from
a first aqueous coating composition, a second aqueous coating layer
36a formed from a second aqueous coating composition, and a third
aqueous coating layer 38a formed from a third aqueous coating
composition. In this aspect, the third aqueous coating layer 38a is
the topmost layer, i.e., the layer exposed to the atmosphere, and
the first aqueous coating layer 34a is the bottommost layer, i.e.,
the layer disposed directly on the substrate 32. The packaging
material also includes a fourth aqueous coating layer 34b formed
from a fourth aqueous coating composition, a fifth aqueous coating
layer 36b formed from a fifth aqueous coating composition, and a
sixth aqueous coating layer 38b formed from a sixth aqueous coating
composition. In this aspect, the sixth aqueous coating layer 38b is
the topmost layer, i.e., the layer exposed to the packaged product,
and the fourth aqueous coating layer 34b is the bottommost layer,
i.e., the layer disposed directly on the substrate 32. The various
coating layers may be formed of the same or different aqueous
coating compositions. For example, in one embodiment, the first and
third aqueous coating compositions are the same as the fourth and
sixth aqueous coating compositions and the second and fifth aqueous
coating compositions are the same. However, other configurations
are contemplated. For example, while not shown, the substrate 32
may have only two aqueous coating layers on the inside of the
packaging, i.e., the side of the substrate that contacts the
packaged contents. The aqueous coating compositions layered on the
inside of the substrate may differ from the aqueous coating
compositions layered on the outside of the substrate. In the
alternative, only one of the aqueous coating compositions layered
on the inside of the substrate may differ from the aqueous coating
compositions layered on the outside of the substrate.
[0060] In another embodiment, the packaging material 40 includes a
first aqueous coating layer 44a formed from a first aqueous coating
composition and a second aqueous coating layer 46a formed from a
second aqueous coating composition. In this aspect, as shown in
FIG. 4, the second aqueous coating layer 46a is the topmost layer,
i.e., the layer exposed to the atmosphere, and the first aqueous
coating layer 44a is the bottommost layer, i.e., the layer disposed
directly on the substrate 42. The packaging material also includes
a third aqueous coating layer 44b formed from a third aqueous
coating composition and a fourth aqueous coating layer 46b formed
from a fourth aqueous coating composition. In this aspect, as shown
in FIG. 4, the fourth aqueous coating layer 46b is the topmost
layer, i.e., the layer exposed to the packaged product, and the
third aqueous coating layer 44b is the bottommost layer, i.e., the
layer disposed directly on the substrate 42. The various coating
layers may be formed of the same or different aqueous coating
compositions. For example, in one embodiment, the first aqueous
coating composition is the same as the third aqueous coating
composition. In another embodiment, the fourth aqueous coating
composition may be a different aqueous coating composition than any
of the first, second, or third aqueous coating compositions.
Wet Thickness
[0061] The aqueous coating compositions may be applied to the
untreated or pre-treated substrates at a wet thickness of about 100
g/m.sup.2 or less for each layer. In one embodiment, the aqueous
coating compositions may be applied to the untreated or pre-treated
substrates at a wet thickness of about 50 g/m.sup.2 or less. In
another embodiment, the aqueous coating compositions may be applied
to the untreated or pre-treated substrates at a thickness of about
10 g/m.sup.2 to about 50 g/m.sup.2. In yet another embodiment, the
aqueous coating compositions may be applied to the untreated or
pre-treated substrates at a wet thickness of about 2 g/m.sup.2 to
about 25 g/m.sup.2.
Dry Thickness
[0062] The aqueous coating compositions may be applied to the
untreated or pre-treated substrates at a dry thickness of about 30
g/m.sup.2 or less for each layer. In one embodiment, the aqueous
coating compositions may be applied to the untreated or pre-treated
substrates at a dry thickness of about 20 g/m.sup.2 or less. In
another embodiment, the aqueous coating compositions may be applied
to the untreated or pre-treated substrates at a thickness of about
2 g/m.sup.2 to about 20 g/m.sup.2. In yet another embodiment, the
aqueous coating compositions may be applied to the untreated or
pre-treated substrates at a dry thickness of about 5 g/m.sup.2 to
about 15 g/m.sup.2.
Coating Method
[0063] The aqueous coating compositions may be applied to the
substrate using a variety of known techniques, including but not
limited to spraying, rod coating, roll coating, blade coating, slot
die coating, gravure coating (direct, reverse, and offset),
flexographic coating, size press (puddle and metered), slide
hopper, and curtain-coating. In one embodiment, the barrier layers
are formed by applying the aqueous coating compositions by rod
coating. In another embodiment, the barrier layers are formed by
applying the aqueous coating compositions with a technique that
allows for the deposition of multiple layers simultaneously. For
example, the barrier layers may be formed by applying the aqueous
coating compositions via curtain-coating or slide hopper coating.
However, it is also contemplated that not all barrier layers are
applied to the substrate using the same technique, e.g., a first
barrier layer may be applied via rod coating, a second barrier
layer may be applied via curtain-coating, etc.
Properties
[0064] Once applied to the underlying packaging material, the
coating systems described herein provide packaging containers for
aseptic packaging and liquid packaging with improved total barrier
properties for long-term storage as well improved recyclability.
The coating systems of the invention may also reduce costs
associated with manufacturing. In one embodiment, the packaging
containers are able to preserve the qualities of the packaged
contents, i.e., nutritional value, hygienic safety and taste, at
ambient conditions for at least 3 months. In another embodiment,
the packaging containers are able to preserve the qualities of the
packaged contents, i.e., nutritional value, hygienic safety and
taste, at ambient conditions for at least 4 months. In most aseptic
cases, however, the packaging is able to preserve the contents for
longer periods than that. In addition, the coating systems of the
invention are moisture-resistant and provide superior oxygen
barrier properties and heat sealing characteristics.
Suitable Uses
[0065] As previously discussed, the multiple barrier layers
described herein are intended for use in aseptic packaging, liquid
packaging, and retortable packaging. Indeed, packaging containers
of the single use disposable type for liquid foods such as milk,
fruit juices, and the like intended for long term ambient storage
are contemplated. Similarly, packaging of liquid food products
intended for chilled storage and distribution are also
contemplated. Likewise, packaging intended to be durable for
sterilization of filled packages in autoclave of retort treatment
such as for soups, pastes and semi-solid food are also
contemplated.
EXAMPLES
[0066] The following non-limiting examples are merely illustrative
of the preferred embodiments of the present invention, and are not
to be construed as limiting the invention, the scope of which is
defined by the appended claims.
[0067] In each of the examples, various coating systems of the
present invention were applied to a substrate, for example,
paperboard. Table 1 below provides the wet and dry thicknesses of
each of the coating layers applied in the examples.
TABLE-US-00001 TABLE 1 Example or Approximate Approximate
Comparative Coating Meyer wet dry Example material Rod thickness,
.mu. thickness, .mu. 1, C, 2, E ALD 15 34 16 1, B PVA 25 57 12 2, D
PUL 15 34 10 3, 5 DIOFAN .RTM. 15 34 17 B204 3, 5 HYPOD .TM. 15 34
15 9105 and 9105/Aluminum 4 SUNBOND .TM. 12 27 14 3410/C-black
Example 1: Three Layer Coating System
[0068] A solid bleached sulfate pre-coated with a composition
including calcium carbonate and styrene-acrylate binder was used as
the underlying substrate. The substrate was coated with an aqueous
dispersion as shown in Table 2 below. Each coating layer was
applied using a Meyer rod having the size designated in Table 2.
After each coating, the layer was dried by forced air in a box oven
at 200.degree. F.
[0069] Moisture vapor transmission rate (MVTR) was measured via the
wet cup technique with the coated layers (if present) oriented
toward the liquid-filled water receptacle and placed in standard
Tappi conditions.
TABLE-US-00002 TABLE 2 Example 1 Comp. Ex. A Comp. Ex. B Comp. Ex.
C Bottom Layer ALD.sup.1 -- PVA.sup.2 ALD.sup.1 Meyer Rod Size 15
25 15 Middle Layer PVA.sup.2 -- -- ALD.sup. Meyer Rod Size 25 15
Top Layer ALD.sup.1 -- -- -- Meyer Rod Size 15 MVTR 60 644 635 57
(g/m.sup.2/day) .sup.1Joncryl .RTM. 74-A from BASF Corporation.
.sup.2Selvol .RTM. Polyvinyl Alcohol 21-205 Solution from Sekisui
Specialty Chemicals America, LLC.
[0070] As shown above, the composition and method of the present
invention resulted in a MVTR an order of magnitude less than
Comparative Examples A and B. In addition, when comparing the
results of Example 1 and the results of Comparative Example C, it
can be seen that a middle PVA layer, which is resistant to oxygen
transmission, does not disrupt or change the MVTR.
Example 2: Two Layer Coating System
[0071] A solid bleached sulfate pre-coated with a composition
including calcium carbonate and styrene-acrylate binder was again
used as the underlying substrate. The substrate was coated with an
aqueous dispersion as shown in Table 3 below. Each coating layer
was applied using a Meyer rod having the size as designated in
Table 3. After each coating, the layer was dried by forced air in a
box oven at 200.degree. F.
[0072] Moisture vapor transmission rate (MVTR) was measured via the
wet cup technique with the coated layers (if present) oriented
toward the liquid-filled water receptacle and placed in standard
Tappi conditions. Oxygen Transmission Rate (OTR) was measured in
accordance with ASTM D3985.
TABLE-US-00003 TABLE 3 Example 2 Comp. Ex. D Comp. Ex. E Bottom
Layer PUL.sup.1 PUL.sup.1 ALD.sup.2 Meyer Rod Size 15 15 15 Top
Layer ALD.sup.2 -- -- Meyer Rod Size 25 MVTR (g/m.sup.2/day) 99 180
95 OTR (cc/m2/day) 185 6400 8900 .sup.1Takelac .RTM. WPB-341 from
Mitsui Chemicals America, Inc. .sup.2Joncryl .RTM. 74-A from BASF
Corporation.
[0073] As shown above, the composition and method of the present
invention resulted in a MVTR an order of magnitude less than
Comparative Example D. In addition, when comparing the results of
Example 2 and the results of Comparative Example E, it can be seen
that an additional layer of PUL does not degrade the MVTR.
Moreover, the two-layer system of Example 2 resulted in a large
improvement in OTR.
Example 3: Two Layer Coating System with Heat-sealable Layer Over
Oxygen Barrier
[0074] An uncoated paper substrate was used as the underlying
substrate. A first layer of polyvinylidene chloride (Diofan.RTM. B
204 from Solvay Specialty Polymers USA, LLC) was applied to the
substrate with the wet and dry thicknesses shown in Table 1 via a
Meyer rod having a size of 15. The layer was then dried by forced
air in a box oven at 200.degree. F. A second layer including a
polyolefin dispersion (Hypod.RTM. 9105 from Dow Chemical Company)
was then applied over the first layer with a wet and dry thickness
of shown in Table 1 via a Meyer rod having a size of 15 and dried
in the same manner as the first layer. The resulting coated
substrate was visually inspected and found to be defect-free and
smooth.
Example 4: Two Layer Coating System with Heat-sealable Layer Over
Light-Blocking Layer
[0075] A solid bleached sulfate pre-coated with a composition
including calcium carbonate and styrene-acrylate binder was used as
the underlying substrate. The substrate was then coated with a
mixture of a polyvinyl acetate dispersion and a carbon-black
dispersion as shown in Table 4 below. The mixture was applied at
the wet and dry thicknesses shown in Table 1 using a Meyer rod
having a size of 12. After coating, the light-blocking layer was
dried by forced air in a box oven at 200.degree. F. A polyolefin
dispersion was then applied over the first layer at the wet and dry
thicknesses shown in Table 1 using a Meyer rod having a size of 15
and dried in the same manner as the first layer.
TABLE-US-00004 TABLE 4 Example 4 Bottom Layer Polyvinyl Acetate
Disperson.sup.1 20 g Carbon-Black Dispersion.sup.2 4.5 g Meyer Rod
Size 12 Top Layer Polyolefin dispersion.sup.3 Meyer Rod Size 15
.sup.1SUNBOND .TM. 3410 from Omnova Solutions, Inc. .sup.2Aquablak
.RTM. 8328 from Solution Dispersions .sup.3Hypod 9105 .TM. from The
Dow Chemical Company.
[0076] The resulting coated substrate was visually inspected and
found to be defect-free and smooth.
Example 5: Two Layer Coating System with Light-Blocking Layer Over
Oxygen/Moisture Vapor Layer
[0077] A polyvinylidene chloride-based latex dispersion was applied
to an uncoated paper substrate at the wet and dry thicknesses shown
in Table 1 using a Meyer rod having a size of 15. After coating,
the layer was dried by forced air in a box oven at 200.degree. F. A
mixture of a polyolefin dispersion and aluminum flake (as shown in
Table 5 below) was then applied over the first layer at the wet and
dry thicknesses shown in Table 1 using a Meyer rod having a size of
15 and dried in the same manner as the first layer.
TABLE-US-00005 TABLE 5 Example 5 Bottom Layer Polyvinylidene
Chloride- based Disperson.sup.1 Meyer Rod Size 15 Top Layer
Polyolefin Dispersion.sup.2 20 g Aluminum Flake.sup.3 l.7 g
.sup.1Diofan .RTM. B 204 from Solvay Specialty Polymers USA, LLC.
.sup.2Hypod 9105 .TM. from The Dow Chemical Company. .sup.3STAPA IL
HYDROLAN 801 5590/G Aluminum Paste from Eckart GmbH.
[0078] The resulting coated substrate was visually inspected and
found to be defect-free with a metallic appearance (like a foil),
smooth, and having improved opacity as compared with the uncoated
paper substrate.
[0079] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing measurements.
Furthermore, when numerical ranges of varying scope are set forth
herein, it is contemplated that any combination of these values
inclusive of the recited values may be used. The invention
described and claimed herein is not to be limited in scope by the
specific embodiments herein disclosed, since these embodiments are
intended as illustrations of several aspects of the invention. Any
equivalent embodiments are intended to be within the scope of this
invention. Indeed, various modifications of the invention in
addition to those shown and described herein will become apparent
to those skilled in the art from the foregoing description. Such
modifications are also intended to fall within the scope of the
appended claims. All patents and patent applications cited in the
foregoing text are expressly incorporated herein by reference in
their entirety.
* * * * *