U.S. patent application number 14/146888 was filed with the patent office on 2014-05-01 for multilayered packaging material.
The applicant listed for this patent is Nitya Prakash Khasat, Bakhtiar Alam Shah, Glenn Lee Vanderwende. Invention is credited to Nitya Prakash Khasat, Bakhtiar Alam Shah, Glenn Lee Vanderwende.
Application Number | 20140116005 14/146888 |
Document ID | / |
Family ID | 44558932 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140116005 |
Kind Code |
A1 |
Shah; Bakhtiar Alam ; et
al. |
May 1, 2014 |
MULTILAYERED PACKAGING MATERIAL
Abstract
A multilayered polymeric structure for use as a packaging
container comprising a first layer of oxygen barrier material and a
second protective layer bonded to the first layer where the oxygen
barrier layer material is selected from the group consisting of
saponified ethylene-vinyl acetate copolymer, polyamide, polyvinyl
alcohol, modification products thereof, and mixtures thereof, and
the second protective layer comprises a polymer and an inorganic
filler in an amount sufficient to further enhance the moisture
barrier property of the outer protective layer over what it would
be in the absence of the filler.
Inventors: |
Shah; Bakhtiar Alam; (Tinley
Park, IL) ; Khasat; Nitya Prakash; (Newark, DE)
; Vanderwende; Glenn Lee; (New Hope, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shah; Bakhtiar Alam
Khasat; Nitya Prakash
Vanderwende; Glenn Lee |
Tinley Park
Newark
New Hope |
IL
DE
PA |
US
US
US |
|
|
Family ID: |
44558932 |
Appl. No.: |
14/146888 |
Filed: |
January 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12802919 |
Jun 16, 2010 |
|
|
|
14146888 |
|
|
|
|
Current U.S.
Class: |
53/401 |
Current CPC
Class: |
B32B 1/02 20130101; B32B
27/20 20130101; B32B 27/08 20130101; B32B 7/12 20130101; B65B 55/00
20130101; B32B 2307/7246 20130101; B32B 2250/24 20130101; B32B
2307/7244 20130101; B32B 2264/10 20130101; B65D 81/264 20130101;
B32B 2250/40 20130101 |
Class at
Publication: |
53/401 |
International
Class: |
B65B 55/00 20060101
B65B055/00 |
Claims
1. A process for protecting an oxygen sensitive substance
comprising the step of enclosing the substance in a package, said
package comprising a laminated multilayer material where the
multilayer material comprises (i) a first layer of oxygen barrier
material having a first surface and an opposing second surface,
(ii) a protective second layer having a surface that is bonded to
at least a portion of the first surface of the first layer in a
face to face relationship, and; (iii) a protective third layer
having a surface that is bonded to at least a portion of the second
surface of the first layer in a face to face relationship, where
the oxygen barrier layer material is selected from the group
consisting of saponified ethylene-vinyl acetate copolymer,
polyamide, polyvinyl alcohol, and mixtures of the foregoing, the
protective second and third layers comprise a moisture barrier
polymer, and either one or both of the protective layers comprise
inorganic filler particles dispersed in the moisture barrier
polymer in an amount effective to show an enhancement of the rate
of recovery of the oxygen transmission rate of the structure after
a retort shock over what it would be in the absence of the filler
particles, where the filler particles comprise a material with a
moisture capacity of greater than 0.05% moisture by weight of
material, and where retort shock is a process in which the
structure is subjected to moisture vapor in the form of steam at a
temperature of at least 125.degree. C. for at least 33 minutes
impinging on the one or both of the protective layers.
2. The process of claim 1 in which the polymer is selected from the
group consisting of polypropylene, polystyrene, high-density
polyethylene, medium-density polyethylene, low-density
polyethylene, polyethylene terephthalate, polybutylene
terehthalate, polycarbonates, acrylonitrile-styrene-butadiene
copolymer, polyphenylene oxide, modification products and mixtures
thereof.
3. The process of claim 1 in which the multilayer material further
comprises a fourth and a fifth adhesive layers in between the first
and second, and first and third layers respectively.
4. The process of claim 26 in which the second layer further
comprises a skin layer adjacent to the side of the second layer
opposite to the first layer.
5. The process of claim 1 in which the third layer comprises a skin
layer adjacent to the side of the third layer opposite to the first
layer.
6. The process of claim 4 in which the second layer comprises a
skin layer adjacent to the side of the third layer opposite to the
first layer.
7. The process of claim 4 in which the skin layer comprises a
polyolefin.
8. The process of claim 4 in which the skin layer comprises a
polyolefin.
9. The process of claim 6 in which the skin layers on the second
and third layers comprise polyolefins.
10. The process of claim 3 in which the fourth and fifth layers
comprise an adhesive polymer.
11. The process of claim 10 in which the adhesive polymer comprises
a copolymer of ethylene and maleic anhydride.
12. The process of claim 1 in which the filler particles comprise
fillers selected from the group consisting of talc, calcium
carbonate, calcium oxide, silica, barium sulfate, wollastonite,
mica, clay, kaolin, silica, diatomaceous earth, alumina, zinc
white, magnesium oxide, calcium sulfite, calcium sulfate, calcium
silicate, glass powders, glass fibers, silane-treated glass fibers,
asbestos, gypsum fibers, and combinations thereof.
13. The process of claim 1 in which the filler further comprises a
surface coating over at least a portion of its surface.
14. The process of claim 1 in which the filler is present in an
amount from 1.5% to 50% by weight of polymer plus filler in the
second layer, the third layer, or both.
15. The process of claim 12 in which the filler is present in an
amount from 10% to 40% by weight of polymer plus filler in the
second layer, the third layer, or both.
16. The process of claim 1 in which at least 10% of the filler
particles have an aspect ratio of between 1 and 120.
17. The process of claim 16 in which at least 10% of the filler
particles have an aspect ratio of between 5 and 40.
18. The process of claim 1 in which the filler particles have a
number average particle size in their smallest dimension of between
0.5 and 15 microns.
19. The process of claim 18 in which the filler particles have a
number average particle size in their smallest dimension of between
1.5 and 10 microns.
Description
PRIORITY DATA
[0001] This application is a divisional of U.S. application Ser.
No. 12/802,919, filed Jun. 16, 2010, and claims priority to that
application.
FIELD OF THE INVENTION
[0002] This invention relates to a multilayered structure useful
for packages, and more particularly relates to a multilayered
structure which is capable of retaining an oxygen barrier property
satisfactorily in the presence of a high humidity environment such
as a retort.
BACKGROUND OF THE INVENTION
[0003] Oxygen barrier resins such as saponified ethylene-vinyl
acetate copolymer (hereinafter referred to as "EVOH") have low
oxygen permeability and yet can be adversely affected by high
humidity and are liable to undergo an increase of oxygen
permeability under a highly humid atmosphere. Generally, packaging
structures are adapted to retain their oxygen barrier property by
including a protective layer, such as of a polyolefin or some other
barrier polymer having a low water absorption or low moisture
absorption on a layer of an oxygen barrier resin of high humidity
dependency thereby precluding direct exposure of the oxygen barrier
layer to water or moisture.
[0004] The dependence of the performance of a packaging structure
on humidity is an important property because packages are used to
store mammal foodstuffs, generally for humans or pets. Often
packages are subjected to a "retort process" in which the molded
package/container is subjected to excessive moisture as steam and
at elevated temperatures typically around 250.degree. F. (around
130.degree. C.) and the ingress of moisture through the outer
protective layers exponentially increases with temperature. This
effect leads to lowering of the efficiency of EVOH as the barrier,
an effect called "retort shock." Although this lowering is almost a
reversible process and the barrier efficiency generally returns to
almost its pre shock value, in order to meet the expectations of
the shelf life for the food contained in the retorted container the
thickness of the EVOH barrier layer must be increased, or lower
ethylene mole percent EVOH must be used. These are both expensive
alternatives and the most economical way to ensure shelf life is
still to protect the EVOH layer from the moisture/steam.
[0005] The present inventors have made the unexpected discovery
that addition of certain fillers in an effective level to a
protective layer results in faster recovery of the oxygen barrier
property of a packaging structure from moisture after retort
shock.
SUMMARY OF THE INVENTION
[0006] The invention is directed to a laminated multilayered sheet
structure for use in a packaging container, said structure
comprising: [0007] (i) a first layer of oxygen barrier material
having a first surface and an opposing second surface, [0008] (ii)
a protective second layer having a surface that is bonded to at
least a portion of the first surface of the first layer in a face
to face relationship, and; [0009] (iii) a protective third layer
having a surface that is bonded to at least a portion of the second
surface of the first layer in a face to face relationship, The
oxygen barrier layer material is selected from the group consisting
of saponified ethylene-vinyl acetate copolymer, polyamide,
polyvinyl alcohol, and mixtures of the foregoing. The protective
second and third layers comprise a moisture barrier polymer and
either one or both of the protective layers comprise inorganic
filler particles dispersed in the moisture barrier polymer in an
amount effective to show an enhancement of the rate of recovery of
the oxygen transmission rate (OTR) of the structure after a retort
shock over what the recovery rate would be in the absence of the
filler particles. The OTR is measured according to ASTM F-1307
measured on the structure, said method being hereby incorporated
here in its entirety by reference. The filler particles comprise a
material with a moisture capacity of greater than 0.05% moisture by
weight of material. The filler particles may comprise predominantly
the material with a moisture capacity of greater than 0.05%
moisture by weight of material, which means that over 90% of the
filler composition by weight is said material.
[0010] "Retort shock", as used here, is a process whereby the
structure is subjected to moisture vapor in the form of steam at a
temperature of at least 125.degree. C. for at least 33 minutes
impinging on the one or both of the filled protective layers.
[0011] In one embodiment, the moisture barrier polymer is selected
from the group consisting of polypropylene, polystyrene,
high-density polyethylene, medium-density polyethylene, low-density
and linear low density polyethylene, polyethylene terephthalate,
polybutylene terehthalate, polycarbonates,
acrylonitrile-styrene-butadiene copolymer, polyphenylene oxide,
modification products and mixtures thereof.
[0012] The second layer or the third layer may further comprise a
skin layer adjacent to the surfaces of the second layer or third
layer that are opposite to the first layer. Any of the skin layers
may further comprise polyolefins, and the skin layer or layers may
be pigmented.
[0013] The second layer, the third layer or both may further be
bonded to the oxygen barrier (first) layer by an intermediate layer
that comprises a polymeric adhesive suitable to bond the first
layer to the second and/or third layers. The intermediate polymer
layer may comprise a copolymer of ethylene and maleic anhydride.
The filler particles used in the invention comprise filler
materials that have an ability to absorb or adsorb moisture to the
extent of 0.05% or greater, or 0.08% or greater, or even 1.0% or
greater by weight of material and may be selected, for example and
without limitation, from the group consisting of calcium carbonate,
calcium oxide, silica, barium sulfate, wollastonite, mica, clay,
kaolin, silica, diatomaceous earth, alumina, zinc white, magnesium
oxide, calcium sulfite, calcium sulfate, calcium silicate, glass
powders, glass fibers, silane-treated glass fibers, asbestos,
gypsum fibers, and combinations thereof.
[0014] The filler particles further may further comprise a surface
coating over at least a portion of their surface.
[0015] An effective amount of filler particles is an amount that
renders the required enhancement of recovery of OTR after retort
shock. In a still further embodiment of the structure of the
invention, the filler particles are typically present in an amount
from 1.5% to 50%, or even 10% to 40% by weight of polymer plus
filler in the second or third layers or both. Some or all of the
filler particles may further have an aspect ratio of greater than
1:1. In a still further embodiment the filler particles have a
number average particle size in their smallest dimension of between
0.5 and 15 microns or even between 1.5 and 10 microns.
[0016] The invention is further directed to a container that
comprises a structure according to any of the embodiments described
above. For example a container comprising walls in which the walls
comprise a multilayered polymeric structure. The structure
comprises a first layer of oxygen barrier material and second and
third protective layers bonded to the first layer on either side of
the first layer. The oxygen barrier layer material is selected from
the group consisting of saponified ethylene-vinyl acetate
copolymer, polyamide, polyvinyl alcohol, modification products
thereof, and mixtures thereof, and the second and third protective
layers independently comprise one or more polymers. At least one of
the second and third protective layers is a filled protective layer
comprising inorganic filler particles dispersed in the filled
protective layer in an amount effective to further enhance the
moisture barrier property of the filled protective layer over what
it would be in the absence of the filler. As described above, the
filler particles used in the invention may comprise filler
materials that have a moisture capacity of greater than 0.05% by
weight of materials, via an ability to absorb or adsorb moisture to
the extent of 0.05% or greater, or 0.08% or greater, or even 1.0%
or greater or greater by weight of material.
[0017] The effective amount of inorganic filler particles required
to be dispersed in the moisture barrier polymer may be defined by
the amount sufficient to show an increase in the rate of recovery
of the oxygen transmission rate (OTR) of the package over what it
would be in the absence of the filler particles after exposure to
steam, for example at a temperature of at least 125.degree. C. for
at least 33 minutes. The OTR is measured according to ASTM F-1307
measured on the structure, said method being hereby incorporated
here in its entirety by reference. An enhanced rate of reduction in
the OTR after exposure to steam when filler particles are present
in a protective layer means that an effective amount of particles
is present.
[0018] The invention is further directed to a process for
protecting an oxygen sensitive substance comprising the step of
enclosing the material in a package. The package comprises a
structure according to any of the embodiments described above. For
example the multilayer material comprises a first layer of oxygen
barrier material and a second protective layer and in one
embodiment even a third protective layer bonded to the first layer.
The oxygen barrier layer material is selected from the group
consisting of saponified ethylene-vinyl acetate copolymer,
polyamide, polyvinyl alcohol, modification products thereof, and
mixtures thereof, and the second protective layer comprises a
polymer and inorganic filler particles dispersed in the polymer in
an amount sufficient to further enhance the moisture barrier
property of the filled layer over what it would be in the absence
of the filler, as described above.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 shows a not to scale representation of a cross
section of a two layered embodiment of the present invention.
[0020] FIG. 2 shows a not to scale representation of a cross
section of a three layered embodiment of the present invention.
[0021] FIG. 3 shows a not to scale representation of a cross
section of a five layered embodiment of the present invention.
[0022] FIG. 4 shows a plot of oxygen transmission rate for samples
prepared according to the invention, and control samples with no
filler.
DETAILED DESCRIPTION OF THE INVENTION
[0023] When an amount, concentration, or other value or parameter
is given as either a range, preferred range, or a list of upper
preferable values and lower preferable values, this is to be
understood as specifically disclosing all ranges formed from any
pair of any upper range limit or preferred value and any lower
range limit or preferred value, regardless of whether ranges are
separately disclosed. Where a range of numerical values is recited
herein, unless otherwise stated, the range is intended to include
the endpoints thereof, and all integers and fractions within the
range. It is not intended that the scope of the invention be
limited to the specific values recited when defining a range.
[0024] The invention is directed to a laminated multilayer sheet
structure that is suitable for protective packaging. The terms
"multilayer sheet structure" and "multilayer barrier structure" and
"multilayer barrier material" and "multilayer structure" as used
herein are synonymous. In one embodiment the present invention
comprises an oxygen barrier layer in contact with and bonded in
face to face contact to at least one protective layer. By "sheet
structure" is meant herein that the structure has two dimensions
that are significantly larger than a third, thickness, dimension
such that two opposing surfaces of the structure defined by the
larger dimensions can be identified. In one embodiment the present
invention comprises an oxygen barrier layer in contact with and
bonded in face to face contact to at least one protective layer
over a portion or all of their surfaces. By "face to face" is meant
that one surface of one layer is in contact over at least a
portion, and even over all, of the surface with one surface of a
second layer.
[0025] When used as packaging, the structure will typically have a
thickness in the range 0.1 to 10 mm, preferably 0.1 to 5 mm and
more preferably 0.1 to 2 mm.
[0026] In the two layer embodiment as shown in FIG. 1, the
multilayer sheet structure comprises a oxygen barrier layer (1) and
a protective layer (2). In a three layer embodiment, for example
shown figuratively in FIG. 2, the multilayer structure comprises an
oxygen barrier layer (1) sandwiched between two protective layers
(2) and (3). The bonding of the oxygen barrier layer and the
protective layer or layers can be enabled by use of one or more
adhesive layers located in between the layers to be bonded. The
protective layers may each also be in contact with a further skin
layer as shown in FIG. 3. The skin layers (4) and (5) serve to
provide a desired surface appearance to the multilayer, or to
provide a substrate for any desired pigmentation. Each layer of the
multilayer structure will be described in more detail below.
[0027] The multilayer structure of the invention can be made by any
technology known to one skilled in the art. For example, and
without limitation, coextrusion, coinjection molding, or extrusion
blow molding are processes that can be uses to fabricate the
structure of the invention.
[0028] In a preferred embodiment, the invention is directed to a
multilayered sheet structure for use in a packaging container, said
structure comprising: [0029] (i) a first layer of oxygen barrier
material having a first surface and an opposing second surface,
[0030] (ii) a protective second layer having a surface that is
bonded to at least a portion of the first surface of the first
layer in a face to face relationship, and; [0031] (iii) a
protective third layer having a surface that is bonded to at least
a portion of the second surface of the first layer in a face to
face relationship,
[0032] The oxygen barrier layer material is selected from the group
consisting of saponified ethylene-vinyl acetate copolymer,
polyamide, polyvinyl alcohol, and mixtures of the foregoing. The
second and third protective layers comprise a moisture barrier
polymer and either one or both of the protective layers comprise
inorganic filler particles dispersed in the moisture barrier
polymer in an amount effective to show an enhancement in the rate
of recovery of the oxygen transmission rate (OTR) of the structure
over what it would be in the absence of the filler particles after
a retort shock. "Retort shock", as used here, is a process whereby
the structure is subjected to moisture vapor in the form of steam
at a temperature of at least 125.degree. C. for at least 33 minutes
impinging on the one or both of the filled protective layers.
[0033] The rate of recovery of OTR may be measured directly and OTR
at two different times after retort shock compared. Alternatively,
the rate of recovery of OTR can measured by the integral of a plot
of oxygen transmission rate versus time where time is measured from
the end of the retorting process for at least 50 hours and
enhancement means that the integral in the presence of particles is
less than that in the absence of particles.
[0034] The structure of the invention shows an enhancement of the
rate of recovery of the oxygen transmission rate of the structure
after a retort shock over what the recovery rate would be in the
absence of the filler particles The filler particles comprise a
material with a moisture capacity of greater than 0.05%, or 0.08%,
or even 1.0% moisture by weight of material. In one embodiment the
filler particles may comprise predominantly the material with a
moisture capacity of greater than 0.05%, or 0.08%, or even 1.0%
moisture by weight of material, where "predominantly" means that
over 90%, or even 95% of the filler composition by weight is said
material. The moisture capacity of the filler material may be due
to adsorption of moisture on the material surface or absorption
into the bulk of the material. The scope of the present invention
is not to be limited by the mechanism by which the filler particles
pick up moisture. Either mechanism, or any other mechanism, by
which the material takes up moisture may contribute to moisture
capacity.
Oxygen Barrier Layer
[0035] Examples of the material for this layer include saponified
ethylene-vinyl acetate copolymers, polyamides, polyvinyl alcohol,
modification products and mixtures thereof. Among the materials
enumerated above, the saponified ethylene-vinyl acetate copolymer
having an ethylene content in the range of 25 to 50 mol % and a
saponification degree of not less than 96% is a preferred
embodiment. By increasing the ethylene content beyond 25 mol %, the
molding properties, for example in extrusion molding and blow
molding, are improved. By holding down the ethylene content below
50 mol %, the oxygen barrier property is enhanced.
[0036] The oxygen barrier layer (1) can also be made of multiple
extruded layers of the same or different barrier materials. In an
example of this structure, the barrier layer will be extruded from
a multilayer die and the resulting extrudate bonded into a single
layer, preferably by application of pressure and heat.
Protective Layers
[0037] Examples of the material use in the construction of these
layers include homo and copolymers from the family of polypropylene
resins, polystyrene and rubber modified polystyrene, linear and
branched polyethylenes regardless of the resin density (for example
high-density of density above 0.94, medium-density polyethylene of
density above 0.92 to 0.94, and low-density and linear low density
polyethylene of density 0.92 and below), polyethylene
terephthalate, polybutylene terephthalate, polycarbonates,
acrylonitrile-styrene-butadiene copolymer, modification products
and mixtures thereof. The polymer used for the protective layer is
not limited, however, and, for example, nylon (polyamide) can also
be used in this application.
[0038] If there is more than one protective layer in the structure,
then at least one of the protective layers has filler particles
incorporated therein and dispersed in the polymer, in an amount
effective to increase the moisture barrier property of the layer or
to reduce the oxygen transmission rate of the first layer after
moisture exposure when compared to a structure that has no filler
particles in either protective layer. For example, in a two layer
structure, the protective layer will have filler incorporated
therein. In a three layer structure as described above, one or both
of the protective layers will have filler incorporated therein.
[0039] The filler particles in the at least one protective layer
comprise a material with a moisture capacity of greater than 0.05%,
or 0.08%, or even 1.0% moisture by weight of material. The filler
particles may comprise predominantly the material with a moisture
capacity of greater than 0.05%, or 0.08% or even 1.0% moisture by
weight of material, where "predominantly" means that over 90% or
even 95% of the filler composition by weight is said material. The
moisture capacity of the filler material may be due to adsorption
of moisture on the material surface or absorption into the bulk of
the material. The scope of the present invention is not to be
limited by the mechanism by which the filler particles pick up
moisture. Either mechanism, or any other mechanism, by which the
material takes up moisture may contribute to moisture capacity. The
filler particles of the invention may also comprise a blend of a
first set of particles with the moisture capacity specified above,
and a second set particles with moisture capacity less than 0.05%
by weight of the second set of particles. In certain embodiments,
the weight percentage of the first set of particles by weight of
total particles can be at least 20%, or 40%, or 60% or even
80%.
[0040] Further, it is possible to add to the polymer composition in
any layer of the structure of the invention appropriate amounts of
various additives, such as antioxidants, weathering agents,
antistatic agents, foaming agents, colorants, and the like.
[0041] The method of preparing the polymer plus filler composition
of the present invention is not particularly restricted. Kneading
machines commonly employed for plastics or rubbers, such as a
Banbury mixer, a single-screw extruder, a twin-screw extruder, a
roll mill, etc., can be used. The resulting blended composition can
be molded into desired molded products by thermoforming extruded
sheet or film, injection molding, extrusion molding, blow molding,
etc. in a manner known to one skilled in the art. Filler can be
compounded in the carrier resin off or in line with the sheet
extrusion process.
[0042] The filler can be a high aspect ratio filler, a low aspect
ratio filler or a mixture of both types of filler. The term "aspect
ratio" of a particle is defined herein as a ratio of a largest
dimension of the particle divided by a smallest dimension of the
particle. The aspect ratios can be determined by scanning under an
electron microscope and visually viewing the outside surfaces of
the particles to determine the lengths and thicknesses of the
particles. The use of single digits and the use of two digits to
describe aspect ratio herein are synonymous. For example the terms
"5:1" and "5" both have the same meaning. A low aspect ratio filler
is defined as being a filler having an aspect ratio of from 1:1 to
about 3:1 and such fillers can also be used in the structure of the
invention. Examples of low aspect ratio fillers may include calcium
carbonate, barium sulfate, or combinations thereof. Commercially
available calcium carbonate includes OMYACARB FT.RTM., available
from OMYA Inc. of Alpharetta, Ga. One example of commercially
available barium sulfate is BARITE 2075.RTM., available from Polar
Minerals in Mentor, Ohio.
[0043] All of the filler particles may further have an aspect ratio
of 1, or between 1 and 120, or even between 3 and 40. The number
average aspect ratio of the filler particles may further have an
aspect ratio of between 1 and 120, or even between 3 and 40. In a
further embodiment at least 10% and preferably at least 30% and
even 50% or 70% of the filler particles have an aspect ratio of
between 1 and 120, or even between 3 and 40. Blends of fillers may
be therefore used in which one filler has a high aspect ratio and
another filler has a low aspect ratio.
[0044] All or any of either the first or second set filler
particles as defined above may further have an aspect ratio of
between 3 and 120 or 5 and 120 or 10 and 120, or even between 3 and
40 or 5 and 40 or 10 and 40. The number average aspect ratio of the
first or second set or both of filler particles may further have an
aspect ratio of between 3 and 120 or 5 and 120 or 10 and 120, or
even between 3 and 40 or 5 and 40 or 10 and 40. In a further
embodiment at least 10% and preferably at least 30% and even 50% or
70% of the filler particles have an aspect ratio of between 3 and
120 or 5 and 120 or 10 and 120, or even between 3 and 40 or 5 and
40 or 10 and 40.
[0045] There is no particular limitation to the upper or lower
limit of the number average aspect ratio of either set of filler
particles. The inventors have discovered that high aspect ratio
fillers are particularly effective when included in at least one
protective layer of the present invention, and the structure of the
invention mat comprise layers with different fillers which may have
the aspects ratios defined above, or have an aspect ratio of 1. The
high aspect ratio fillers of the present invention may have, for
example, preferably have an aspect of from about 3:1 to about
100:1, and more preferably from about 10:1 to about 50:1. The high
aspect filler may for example be talc, mica, wollastonite, or
combinations thereof Commercially available talc materials include
JETFIL.RTM. 575, available from Luzenac America of Englewood, Colo.
Commercially available mica materials include SUZOREX.RTM. 325-PP,
available from Zemex Industrial Minerals, Inc. Commercially
available wollastonite include the NYGLOS.RTM. series of
wollastonite, available from NYCO Minerals Inc. of Calgary,
Alberta, Canada.
[0046] The filled polymer layer of the structure may be formed by
direct compounding and extrusion of a polymer with at least one
particulate mineral filler, for example, using a twin screw
extruder. Irrespective of the method used to incorporate the filler
into the polymer, examples of particulate mineral fillers that may
be used include, but are not limited to, talc, calcium carbonate,
calcium oxide, silica, barium sulfate, wollastonite
(Ca.sub.3(Si.sub.3O.sub.9)), mica, clay, kaolin or combinations
thereof. For example, the filled polymer layer may comprise calcium
carbonate and polypropylene. A protective layer comprising at least
one particulate mineral filler and polymer as claimed here in
combination with the oxygen barrier layer of the invention provides
much improved recovery form retort shock and hence protection of
the oxygen barrier layer as compared to a non-filled neat
protective layer in combination with the oxygen barrier layer.
[0047] One example of a commercial calcium carbonate material is
ground calcium carbonate under the tradename of Omyacarb FT,
available from Omya, Inc, and Camel Fine ST, available from Imerys.
It is contemplated that other types of calcium carbonate may be
used including precipitated calcium carbonate. Commercially
available barium sulfate includes Barite 1075, available from Polar
Minerals, Atlanta, Ga. Commercially available wollastonite may be
obtained from NYCO, Calgary, Alberta, Canada. Commercially
available mica materials include ALBASHIELD.RTM. 15, available from
Zemex Industrial Minerals, Inc.
[0048] It is contemplated that other additives may be added to the
protective layer or layers if used. For example, titanium dioxide
(TiO.sub.2) may be added the polymer layer to provide a whitening
effect. Other additives, such as other pigments, may be added to
the substrate. The layer may also include recycled material, either
post consumer or manufacturing scrap, for example.
[0049] Other examples of fillers to be used in the present
invention are not particularly limited to the above, and include
inorganic fillers, such as silica, diatomaceous earth, alumina,
zinc white, magnesium oxide, calcium sulfite, calcium sulfate,
calcium silicate, glass powders, glass fibers (inclusive of
silane-treated glass fibers), asbestos, gypsum fibers, and the
like.
[0050] These fillers may be used either individually or, if
desired, in combination thereof. In view of a favorable balance
between moisture resistance and other properties of the resulting
composition, talc and/or mica are preferably used as fillers.
[0051] The filler used in the invention may also be coated. In
accordance with one aspect of the invention, surface treatment of
the fillers, in particular those which are hydrophilic, includes
reaction of the filler surface with organosilanes, modified
oligomers and a wide variety of surfactants. Typically, the entire
surface of the filler is treated with surfactant.
[0052] The filler-containing polymer composition of the protective
layer or layers of the present invention typically contains from
1.5 to 50% by weight, and preferably from 10 to 40% by weight, of
the above-described filler.
[0053] There is no particular limit on the size of the filler
particles used in the present in the invention, except that they be
effective at reducing moisture permeability of the protective layer
or layers. The fillers used in the present invention preferably
have a number average smaller dimension of between 0.5 microns and
50 microns, and more preferably from 1.5 microns to 10 microns.
Adhesive Layer
[0054] This layer bonds the oxygen barrier layer to the protective
layer or layers as described above. Examples of the material for
this layer include polar group-containing modified polyolefins
obtained by graft modifying polyethylene, polypropylene, or
ethylene-vinyl acetate copolymer with unsaturated carboxylic acids,
or unsaturated polycarboxylic acids or anhydrides thereof;
ethylene-vinyl acetate copolymer and saponification products
thereof; ethylene-ethylacrylate copolymer, ethylene-acrylic acid
copolymer, ethylene-methacrylic acid copolymer, ionomers obtained
by cross-linking such copolymers with metallic ions; and block
copolymers of styrene with butadiene. These are preferably
synthetic resins compatible with synthetic resins used for forming
the oxygen barrier layer and the protective layers.
Containers
[0055] The present invention is also directed to a container that
is constructed using the multilayer sheet structure of the
invention as described above as a wall of the container. A
container will generally comprise a lid and a body, where the body
is constructed of walls. The lid can be constructed of the
multilayer barrier construction disclosed herein, or metal or any
suitable barrier material. The body of the container comprises a
wall or walls that are constructed according to the multilayer
barrier material structure or structures described above.
[0056] For example, in one embodiment of the container of the
invention the outside and inside walls of the container wall will
generally comprise over at least a part of their surfaces a
pigmented skin that is between 0 to 25% of the thickness of the
container wall. The skin is bonded to a protective layer. At least
one, and preferably both, of the protective layers in the container
wall comprise filler or fillers as described above. The protective
layers then comprise 5 to 40% of the thickness of the
container.
[0057] An oxygen barrier layer, preferably EVOH, comprises 1 to 10%
of the thickness of the container wall. Adhesive layers as
described above bond the oxygen barrier layer to at least one and
preferable two protective layer or layers. In this embodiment the
adhesive layer constitutes 1 to 5% of the thickness of the
container.
[0058] The pigmented skin is preferably a polyolefin or a blend of
several polyolefins, the term "polyolefin" being as understood by
one skilled in the polymer arts as being a polymer of an
unsaturated hydrocarbon (olefin.) The pigmented skin contains
pigment to provide the desired coloration for the multilayer
surface, and one skilled in the art will be able to easily identify
appropriate pigments for use in this application. At least one of
the protective layers is filled as described in the barrier
structure above and comprises a polymer, filler particles as
described above, and optionally regrind or recycled materials. The
container may be made by a thermoforming or molding process, but
any process known to one skilled in the art will suffice to make
the container.
[0059] The adhesive layer is preferably a functionalized extrudable
thermoplastic resin, e.g., maleated or otherwise functionalized
olefins. One skilled in the art will understand what resin may be
used to compatibilize the oxygen barrier and the protective layer.
In some cases mineral filler can be added to the outer skin layers
or these layers can be eliminated.
[0060] The container of the invention can be manufactured by
thermoforming of the multilayered barrier barrier. Thermoforming of
polyolefins, for example, is well known. Generally, a sheet of the
polyolefin is formed or shaped by heating the sheet above the
softening temperature of the polyolefin, fitting the sheet along
the contours of a mold with pressure supplied by vacuum or other
force, and removing the shaped article from the mold after cooling
below its softening point.
[0061] Thermoforming methods such as pressure forming, vacuum
forming, or plug-assist vacuum forming are often useful in
packaging products. In general terms, thermoforming involves
heating of a thermoplastic film or laminate and forming the film or
laminate into a desired shape for holding a product to be inserted.
This sheet of a film or laminate is usually referred to as a
forming web. Various systems and devices are used in a
thermoforming process, often accompanied by vacuum-assist and
plug-assist components to provide the proper forming of the forming
web into a predetermined shape.
[0062] A packaging container according to the present invention may
therefore comprise a container formed by deforming a multilayer
sheet as described above according to a thermoforming method, and a
lid made of a resin or of a metal or of another suitable barrier
material and adapted for sealing the holding container.
[0063] The container can also be formed by other methods, for
example and not limited to, coinjection molding, extrusion blow
molding, laminated sheet thermoforming, and any other method known
to one skilled in the art.
Method for Protecting Substances
[0064] The invention is also directed to a method for protecting an
oxygen sensitive substance, such as a foodstuff, comprising the
step of enclosing the material in a package. The package comprises
a laminated multilayer sheet structure according to any of the
embodiments that are described above. For example in one embodiment
the multilayer material comprises a first layer of oxygen barrier
material and a second protective layer bonded to the first layer in
a face to face relationship by one surface on each of the first
layer and the protective layer.
[0065] The oxygen barrier layer material is selected from the group
consisting of saponified ethylene-vinyl acetate copolymer,
polyamide, polyvinyl alcohol, modification products thereof, and
mixtures thereof, and the second protective layer comprises a
protective polymer and an inorganic filler dispersed in the polymer
in an amount sufficient to further enhance the rate of recovery of
the multilayer sheet structure after retort shock as defined above.
Enhancement means The OTR of the sheet structure recovers more
quickly after retort shock in the presence of inorganic filler than
in its absence. The filler particles comprise a material with a
moisture capacity of greater than 0.05% moisture by weight of
material. The filler particles may comprise predominantly the
material with a moisture capacity of greater than 0.05%, or 0.08%,
or even 1.0% of moisture by weight of material. In one embodiment,
over 90% or even 95% of the filler composition by weight is said
material.
[0066] The process of the invention may also be directed in another
embodiment to a use of a laminated multilayer sheet structure as
described above that comprises a moisture barrier protective layer
or layers as described above, and either one or both of the
protective layers comprise inorganic filler particles dispersed in
the protective layer or layers in an amount sufficient to show an
reduction of the oxygen transmission rate (OTR) of the structure
over what it would be in the absence of the filler particles after
exposure to steam, for example at a temperature of at least
125.degree. C. for at least 33 minutes. The OTR is measured
according to ASTM F-1307 measured on the structure, said method
being hereby incorporated here in its entirety by reference. A
reduction in the OTR means that after exposure to steam, either the
initial OTR after steam treatment, and/or later OTR after sample
aging, is lower than it would be in the absence of the filler
particles.
[0067] The protective polymer of the process may for example be
selected from the group consisting of polypropylene, polystyrene,
high-density to medium-density polyethylenes, low-density
polyethylene, polyethylene terephthalate, polybutylene
terehthalate, polycarbonates, acrylonitrile-styrene-butadiene
copolymer, polyphenylene oxide, modification products and mixtures
thereof.
[0068] The process of the invention may also utilize a laminated
multilayer structure that further comprises a protective third
layer bonded to the first layer in a face to face relationship and
to the surface of the first layer opposite to that bonded to the
second layer. The protective layers may also further have skin
layers as described above bonded to them on the faces opposite to
the first layer. The skin layers on the second and third layers may
comprise polyolefins.
[0069] The filler used in the protective layer of the process may
be selected from the group consisting of talc, calcium carbonate,
barium sulfate, wollastonite, mica, clay, kaolin, silica,
diatomaceous earth, alumina, zinc white, magnesium oxide, calcium
sulfite, calcium sulfate, calcium silicate, glass powders, glass
fibers, silane-treated glass fibers, asbestos, gypsum fibers, and
combinations thereof. The filler may further comprise a surface
coating over at least a portion of its surface. The filler may be
present in an amount from 5% to 50% or even 10% to 40% by weight of
polymer plus filler in the outer layer.
[0070] The filler particles may have an aspect ratio of between 1
and 120, and even between 3 and 40. All of the filler particles may
further have an aspect ratio of between 1 and 120, or even between
3 and 40. The number average aspect ratio of the filler particles
may further have an aspect ratio of between 1 and 120, or even
between 3 and 40. In a further embodiment at least 10% and
preferably at least 30% and even 50% or 70% of the filler particles
have an aspect ratio of between 1 and 120, or even between 3 and
40.
[0071] The filler particles may also have a number average particle
size in their smallest dimension of between 0.5 and 15 microns,
even between 1.5 and 10 microns.
EXAMPLES
[0072] (i) Moisture Capacity
[0073] The moisture capacity of typical fillers was measured by
drying filler samples were dried at 110 C for 24 hours to achieve
same level of moisture content as a starting point. After cooling
down period in dessicator for one hour they were exposed to 90%
relative humidity at 40.degree. C. Moisture absorption was measured
by weight gain and expressed as a percentage of the mineral weight.
The following table summarizes the results.
TABLE-US-00001 Mineral Weight % water uptake. Ca.Carbonate 0.12
Mica 0.4 Inoganic Feldspathic minerals 0.3
[0074] (ii) Oxygen Transmission Rate (OTR)
[0075] A 0.045 inch (1.14 mm) thick multilayer sheet was extruded
with following seven layer structure: [0076] (i) Outer layer of
virgin PP (5% of thickness of sheet.) [0077] (ii) Protective layer
of polypropylene with 30% calcium carbonate in overall total
multilayered structure as measured by TGA. The calcium carbonate
had a mean particle size of 2 microns and an aspect ratio of 1:1.
[0078] (iii) Maleic anhydride grafted PP adhesive (2% of thickness
of sheet.) [0079] (iv) EVOH (5% of thickness of the total sheet
width.) [0080] (v) Maleic anhydride grafted PP Adhesive (2% of
thickness of sheet.) [0081] (vi) Same as layer (ii). [0082] (vii)
Outer layer of virgin PP (5% of thickness of sheet.)
[0083] Oxygen transmission rate was measured on containers from
examples 2 and 3 and the control that were placed on a Mocon 2/21
(Mocon Inc., Minneapolis, Minn.) for 10 days according to ASTM
F-1307, hereby incorporated in its entirety by reference. (Mocon
Inc., Minneapolis, Minn.) FIG. 4 shows the results of the oxygen
transmission rate (OTR) testing. The transmission rate in the
carbonate filled sample has an OTR that is approximately that of
the unfilled sample after retort, or steam treatment. but the
filled sample then recovered more quickly to a lower OTR than the
unfilled sample.
[0084] These results show the effectiveness of the filled samples
at lowering OTR after resort shock, and in particular the
effectiveness of the sample containing filler with a high moisture
capacity. The calcium carbonate sample showed a faster recovery
than the control sample after resort shock.
* * * * *