U.S. patent application number 09/901427 was filed with the patent office on 2001-11-08 for transparent multilayer polypropylene container with barrier protection.
Invention is credited to Curie, Kevin James, Davidson, Randolph Lee, Emre, Sahin.
Application Number | 20010038897 09/901427 |
Document ID | / |
Family ID | 26767067 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038897 |
Kind Code |
A1 |
Curie, Kevin James ; et
al. |
November 8, 2001 |
Transparent multilayer polypropylene container with barrier
protection
Abstract
A multilayer plastic container comprises a layer of a
polypropylene and a layer of EVOH directly adjacent the layer of
polypropylene wherein at least one of the polypropylene and EVOH
layers comprises an adhesive such as maleic anhydride concentrate
mixed therein to adhere the layer of polypropylene to the layer of
EVOH.
Inventors: |
Curie, Kevin James;
(Appleton, WI) ; Davidson, Randolph Lee; (Menasha,
WI) ; Emre, Sahin; (Appleton, WI) |
Correspondence
Address: |
Matthew E. Leno
McDermott, Will & Emery
31st Floor
227 West Monroe Street
Chicago
IL
60606
US
|
Family ID: |
26767067 |
Appl. No.: |
09/901427 |
Filed: |
July 9, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09901427 |
Jul 9, 2001 |
|
|
|
09293401 |
Apr 16, 1999 |
|
|
|
60082118 |
Apr 17, 1998 |
|
|
|
Current U.S.
Class: |
428/36.6 |
Current CPC
Class: |
B32B 27/08 20130101;
Y10T 428/31757 20150401; Y10T 428/1379 20150115; Y10T 428/1352
20150115; B65D 1/0215 20130101; Y10T 428/1383 20150115; Y10T
428/31746 20150401; B32B 27/32 20130101 |
Class at
Publication: |
428/36.6 |
International
Class: |
B32B 001/02 |
Claims
We claim:
1. A multilayer injection molded container comprising: a first
layer comprising polypropylene; and a second layer comprising a
material selected from the group consisting of EVOH and nylon,
directly adjacent to said first layer; wherein at least one of said
first and second layer further comprises an adhesive mixed
therein.
2. The container of claim 1 wherein said first layer contains
approximately 0.01% to 0.20% maleic anhydride.
3. The container of claim 1 wherein said first layer contains
approximately 0.015% maleic anhydride.
4. The container of claim 1 wherein said container has a haze value
of less than approximately 29% measured through a section of the
bottle having a total thickness of greater than approximately 15
mils.
5. The container of claim 1 wherein said container has a haze value
of approximately 10%-12% measured through a section of the bottle
having a total thickness of greater than approximately 15 mils.
6. The container of claim 1 wherein said second layer comprises
EVOH.
7. The container of claim 1 wherein said second layer comprises
MXD6 nylon.
8. The container of claim 1 wherein said second layer comprises
nylon 6.
9. The container of claim 1 wherein said second layer comprises
nylon 6/66.
Description
[0001] This application claims the priority of U.S. provisional
patent application Ser. No. 60/082,118 filed on Apr. 17, 1998, the
entirety of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to transparent multilayer
containers; specifically, to transparent multilayer containers
having a layer of polypropylene and a layer of a barrier material
which provides oxygen, carbon dioxide and moisture protection.
[0004] 2. Background Art
[0005] Many products that can be filled and stored in plastic
containers require carbon dioxide, oxygen and moisture barrier
protection to keep the products fresh for extended periods of time.
Such products include, by way of example only, certain carbonated
beverages, fruit juices, beer, sauces, ketchup, jams, jellies and
dry foods such as instant coffee and spices. Most commercially
acceptable transparent multilayer containers that provide carbon
dioxide and oxygen barrier protection are made of at least one
layer comprising a polyester such as polyethylene terephthalate
("PET") and a layer comprising ethylene vinyl alcohol copolymer
("EVOH"). The layer of EVOH in such containers provides excellent
carbon dioxide and oxygen barrier protection. EVOH can also act as
a chemical or fragrance barrier to keep flavors fresh for various
products such as orange juice.
[0006] PET has limited moisture barrier protection compared with
polypropylene. As a result, liquid products stored in PET
containers experience moisture loss resulting in product weight
loss and dry products stored in PET containers absorb more moisture
than products stored in polypropylene containers. In addition, PET
bottles have limited hot fill capabilities due to a low glass
transition temperature of PET. Additionally, the injection molding
process temperatures of PET and EVOH are significantly different
thus creating difficulties in molding these two materials together
in, for instance, multi-layer injection molding systems.
[0007] It is known to use polypropylene, instead of PET, for an
inner and outer layer of multilayer containers in extrusion blow
molding applications. One advantage of polypropylene over PET is
that polypropylene provides containers with better hot fill
properties. Furthermore, polypropylene and EVOH have relatively
similar melting temperatures, which makes it easier to maintain
proper injection molding or extrusion molding systems.
[0008] Unfortunately, however, polypropylene does not bond to EVOH
without the assistance of an additional agent. As a result, known
containers made with polypropylene and EVOH require a layer of an
adhesive between each layer of polypropylene and the layer of EVOH.
Accordingly, multilayer polypropylene containers with carbon
dioxide and oxygen barrier protection have typically had at least
five layers of material: a first layer of polypropylene, a first
layer of adhesive, a layer of EVOH, a second layer of adhesive and
a second layer of polypropylene.
[0009] Additionally, known polypropylene containers with barrier
protection have haze values of approximately 29%-35% or greater.
While it is known to injection stretch blow mold containers with a
single layer of clarified polypropylene to make a transparent
bottle having lower haze values, such containers do not have many
commercial purposes for food applications because they do not
provide significant carbon dioxide or oxygen barrier
protection.
SUMMARY OF THE INVENTION
[0010] The transparent containers of the present invention have a
layer comprising polypropylene and a layer comprising a barrier
material such as ethylene vinyl alcohol copolymer, nylon or a blend
of ethylene vinyl alcohol copolymer and nylon, adjacent to the
polypropylene layer wherein at least one of the polypropylene layer
and the barrier layer comprises an adhesive mixed therein.
[0011] It is one of the principal objectives of the present
invention to provide multilayer plastic containers that also
provide oxygen, carbon dioxide and moisture barrier protection
having a haze value of less than 25%.
[0012] It is another object of the present invention to provide
containers having a layer of a polypropylene/adhesive mixture and a
layer of barrier material directly adjacent the layer of
polypropylene/adhesive mixture.
[0013] It is another object of the present invention to provide
containers having a layer of a polypropylene and a layer of barrier
material/adhesive mixture directly adjacent the layer of
polypropylene.
[0014] It is another object of the present invention to provide
commercially acceptable, cost effective containers having a layer
comprising polypropylene and a layer comprising a barrier material
adjacent to the polypropylene layer, wherein the containers may be
used for carbonated beverages, fruit juices, sauces and beer.
[0015] It is still another object of the present invention to
provide a polypropylene bottle having at least two layers and
having a haze value of less than 25%.
[0016] It is further an object of the present invention to use two
different materials with similar melting temperature to provide
more compatible injection molding systems.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a perspective view of a multilayer container
according to the present invention.
[0018] FIG. 2 is a sectional view of a wall of the container shown
in FIG. 1.
[0019] FIG. 3 is a perspective view of a preform according to the
present invention that is used to make a multilayer container.
DETAILED DESCRIPTION OF THE DRAWINGS
[0020] Referring now to FIG. 1, there is shown a transparent,
multilayer plastic container, specifically a bottle 10, according
to the teaching of the present invention. The bottle 10 has a top
end 12 and a bottom end 14. A body portion 20 extends between the
top end 12 and the bottom end 14 and forms a cylindrical wall 22.
Although the container illustrated is a bottle, it is noted that
various other containers can be made according to the present
invention as well.
[0021] As best illustrated in the cross-sectional view of the
cylindrical wall 22 shown in FIG. 2, the bottle 10 is preferably
constructed of three layers, namely an inner layer 24, a middle
layer 26 and an outer layer 28. Both the inner layer 24 and the
outer layer 28, which are structural layers, are made of a material
comprising at least polypropylene. The polypropylene can be a
homopolymer or a copolymer. The comonomer can be selected from the
group consisting of ethylene, butylene, or other alpha-olefins from
C.sub.5-C.sub.8. A preferred comonomer is ethylene wherein the
ethylene is up to 3.0 weight % of the polypropylene copolymer. The
polypropylene may also contain additives such as clarifying agents.
Clarifying agents are exemplified by: Milliken Chemical, Division
of Milliken & Co.'s Millad 3988 clarifying agent or Mitsui
Toatsu Chemicals, Inc.'s NC4 clarifying agent. Other clarifiers
such as sorbitol and benzoates can also be used. Such clarifying
agents typically comprises 0.1-0.3% by weight of the polypropylene.
The middle layer 26 is preferably made of a material comprising at
least an ethylene vinyl alcohol copolymer (EVOH). The middle layer
26 of EVOH provides carbon dioxide and oxygen barrier resistance
that allows a product to be stored within the bottle 10 for an
extended period of time without spoiling. Note that while the
middle layer 26 is preferably made of a material comprising EVOH,
the middle layer can comprise any appropriate barrier material,
such as nylon or a blend of ethylene vinyl alcohol copolymer and
nylon as well without departing from the present invention. An
appropriate nylon is exemplified by MXD6, nylon 6 and nylon 6/66.
An appropriate adhesive (discussed in detail below) is chosen
dependant upon the material of the middle layer 26 to bond the
inner and outer layers 24, 28 thereto.
[0022] The inner and outer layers 24, 28 are the structural layers
of the bottle and provide additional moisture barrier protection
for the product to be contained in the bottle 10. The thickness of
the inner and outer layers 24, 28 and the thickness of the middle
layer 26 are determined by factors such as the type of product to
be filled in the container, the desired shelf life of the product,
etc. Typically the thickness of the layers are in the range of
between approximately 5 mils to 10 mils for each of the inner and
outer layers 24, 28 and between approximately 0.1 mils to 2.0 mils
for the middle layer 26.
[0023] The bottle 10 can be stretch blow molded from a preform 30
(FIG. 3), by using conventional stretch blow molding techniques. In
one embodiment, the preform 30 is made by an injection molding
process such as the injection molding processes described in U.S.
Pat. Nos. 4,511,528 and 4,712,990, which are hereby incorporated by
reference. Alternatively, the bottle may be made by extrusion blow
molding techniques such as the process described in U.S. Pat. No.
5,156,857, which is hereby incorporated by reference.
[0024] With regard to injection molding applications, the process
temperatures of polypropylene and EVOH are approximately the same.
Therefore, the process temperatures of the materials to comprise
the inner and outer layers 24, 28 and the materials to comprise the
middle layer 26 are also approximately the same despite the
addition of an adhesive (discussed in detail below) to at least one
of the inner and outer layers 24, 28 and the middle layer 26.
Accordingly, it is easier to maintain proper flow temperatures for
the material forming each layer 24, 26, 28 and, therefore, control
the flows of these layers having only two different materials as
opposed to controlling five layers of three distinct materials
(i.e., polypropylene, adhesive and EVOH) which may have different
process temperatures. The process temperature of the polypropylene
and EVOH is approximately between 180.degree.-235.degree. C. (with
or without the adhesive discussed in detail below). It is
specifically contemplated, however, that the present invention may
be accomplished with material other than the preferred
polypropylene and EVOH.
[0025] In order to bond each of the inner and outer layers 24, 28
to the middle layer 26, the material of at least one of the inner
and outer layers 24, 28 and the middle layer 26 comprises an
adhesive mixed therein. Thus, in a first embodiment of the present
invention, the inner and outer layers 24, 28 may comprise a mixture
of polypropylene and an adhesive ("polypropylene/adhesive mixture")
while the middle layer 26 is comprised of EVOH without an added
adhesive. Examples of this first embodiment are provided below.
[0026] In a second embodiment, the middle layer 26 may be made of a
material comprised of EVOH and an adhesive ("EVOH/adhesive
mixture") while the inner and outer layers 24, 28 are comprised of
a polypropylene without an added adhesive. Examples of this second
embodiment are provided below.
[0027] In a third embodiment, the inner and outer layers 24, 28 are
made of the polypropylene/adhesive mixture and the middle layer is
made of the EVOH/adhesive mixture.
[0028] Sufficient adhesion for purposes of this invention means
achieving a bond between the middle layer 26 and each of the inner
and outer layers 24, 28 to prevent delamination during forming of
the bottle 10 or other container and withstanding normal package
handling and distribution. For some applications, sufficient
adhesion would also mean a sufficient bond between the layers to
withstand hot filling of the container at temperatures of
190.degree.-210.degree. F. The amount of adhesive used must also
provide sufficient adhesion for purposes of injection molding the
preform and stretch blow molding the container from the preform.
Importantly, using the lowest possible percentage of adhesive is
desirable because the adhesive is relatively expensive compared to
polypropylene and EVOH.
[0029] It has been found that the greater the percentage of
adhesive evenly distributed within any layer of the bottle 10
(referred to herein as a "mixed-adhesive layer"), the better that
layer will adhere to an adjacent layer. This correlation is due to
two facts. First, the adhesive force that a mixed-adhesive layer
may exert on an adjacent layer of a container depends, at least in
part, upon the amount of adhesive available at the outer surface of
that mixed-adhesive layer. Second, as the percentage of adhesive
agent evenly mixed and distributed throughout any composite
material used to construct a mixed-adhesive layer is increased, the
amount of adhesive agent which will be exposed at an outer surface
of that mixed-adhesive layer (and thereby made available for
adhesion to an adjacent layer) will also necessarily increase.
Additionally, the percentage of the adhesive agent in the
mixed-adhesive layer, which is exposed at the outer surface of that
mixed-adhesive layer, is inversely proportional to the thickness of
that mixed-adhesive layer. That is, a thinner mixed-adhesive layer
will produce greater adhesive potential from a given quantity of
adhesive agent, than will a relatively thicker mixed-adhesive layer
comprised of the same given quantity of adhesive agent.
[0030] From the foregoing it will be understood that because the
middle layer 26 of the present invention is thinner (preferably
between 0.1 and 2.0 mils) than each of the outer layers 24, 28
(preferably between 5 mils and 10 mils), mixing an adhesive into
the middle layer 26, as in the second preferred embodiment of the
present invention, will necessarily decrease the amount of adhesive
necessary to bond the inner and outer layers 24, 28 to the middle
layer 26 relative to the first embodiment of the present invention
in which the adhesive is dispersed within the inner and outer
layers 24, 28. Moreover, because the second embodiment of the
present invention only requires adhesive to be mixed into a single
layer rather than into two layers (as required by the first
embodiment of the present invention described above), the total
quantity of adhesive required for the second embodiment is further
reduced relative to the quantity of adhesive required for the first
embodiment. Regardless of which embodiment of the present invention
is employed, however, the amount of adhesive required to acquire
the requisite bonding of the middle layer 26 to both the inner and
outer layers 24, 28 is reduced relative to prior methods of bonding
polypropylene to EVOH which place an entire layer of adhesive
between each of the inner and outer layers 24, 28 and the middle
layer 26. Moreover, as discussed above, the complexity of molding
preforms to achieve such bonding is likewise reduced by elimination
of the adhesive layers.
[0031] In one embodiment of the present invention, bottles are made
having a haze value of less than approximately 29%. In another
embodiment, the bottles have a haze value of 10-12%. A haze value
is defined as the percent of total light which, in passing through
the specimen, deviates through forward scatter by more than 0.044
rad (2.5.degree.) on the average. The preferred test to obtain the
haze value of the bottle is ASTM Method D-1003 as defined in the
1995 Annual Book of ASTM Standards, Volume 8.01.
First Embodiment
[0032] The adhesive used to make the polypropylene/adhesive mixture
for the first embodiment of the present invention is a maleic
anhydride modified polypropylene. The amount of adhesive that must
be blended into the polypropylene depends on the maleic anhydride
concentration of the adhesive. Enough adhesive must be added such
that the resulting polypropylene/adhesive mixture has a maleic
anhydride content of approximately 0.01%-0.20% by weight of the
total mixture. (For example: 10% of adhesive containing 0.15%
maleic anhydride.) The polypropylene/adhesive mixture can contain
between 0-98% by weight polypropylene and between 2-100% by weight
adhesive. It has been found that the greater the percentage of
adhesive used, the better the layer of EVOH will adhere to the
structural layer. However, it has been found that sufficient
adhesion between the layers is achieved using
polypropylene/adhesive mixtures containing as low as approximately
0.01%-0.015% maleic anhydride. The middle layer 26, as provided by
the prescripts of first embodiment, is comprised of EVOH without
the presence of an adhesive therein.
[0033] The following are examples of the first embodiment of the
present invention:
EXAMPLE 1
[0034] A three-layer coinjection molded preform was made having
inner and outer structural layers 24 and 28 which are made from a
polypropylene/adhesive mixture containing about 85% polypropylene
and 15% adhesive and a middle layer 26 of EVOH. The polypropylene
was Solvay 4285. The adhesive was Morton EFM-2E02. The EVOH
selected for the middle layer 26 was Evalca LCE-105A (having a 44%
ethylene content). The preform was then stretch blow molded to form
a transparent container having a haze value of approximately 10-12%
measured through a section of the bottle having a thickness of
approximately 15-20 mils.
EXAMPLE 2
[0035] A multilayer coinjection molded preform was made as in
Example 1 except that the percentages of polypropylene and adhesive
in the inner and outer layers 24 and 28 were 90% polypropylene and
10% adhesive. The preform was stretch blow molded to form a
transparent container having a haze value of approximately between
10-12% measured through a section of the container having a
thickness of approximately 15-20 mils.
EXAMPLE 3
[0036] A three-layer container was made by a coextrusion blow
molding process. The layers were extruded together to form a tube.
The tube was blow molded in a mold to form the container. The
layers 24 and 28 were made from a polypropylene/adhesive mixture
containing about 90% polypropylene and 10% adhesive. The
polypropylene was Montell SR256M. The adhesive is Morton EFM-2E02.
The EVOH selected for the middle layer 26 was Evalca LCE105A.
EXAMPLE 4
[0037] A multilayer coinjection molded preform was made as in
Example 1 except that the EVOH used was Evalca LCF-104AW (having a
32% ethylene content). The preform was then stretch blow molded to
form a transparent container.
EXAMPLE 5
[0038] A multilayer coinjection molded preform was made as in
Example 1 except that the EVOH used was Evalca LCL 101A (having a
27% ethylene content). The preform was then stretch blow molded to
form a transparent container.
EXAMPLE 6
[0039] A multilayer coinjection molded preform was made as in
Example 1 except that the EVOH used was Nippon Gohsei Soamol
DC3203. The preform was then stretch blow molded to form a
transparent container.
EXAMPLE 7
[0040] A multilayer coinjection molded preform was made as in
Example 1 except that the barrier was nylon, specifically
Mitsubishi's MXD6-6121 nylon. The preform was then stretch blow
molded to form a transparent container.
EXAMPLE 8
[0041] A multilayer coinjection molded preform was made as in
Example 1 except that the polypropylene was Fina 7426MZ. The
preform was then stretch blow molded to form a transparent
container.
EXAMPLE 9
[0042] A multilayer coinjection molded preform was made as in
Example 1 except that the polypropylene was Montell SR256M. The
preform was then stretch blow molded to form a transparent
container.
EXAMPLE 10
[0043] A multilayer coinjection molded preform was made as in
Example 1 except that the polypropylene/adhesive mixture layer was
100% Mitsui Admer QB510A. The preform was then stretch blow molded
to form a transparent container.
[0044] The bottles made in Examples 1-10 of the first embodiment
above are transparent, exhibit good strength and provide excellent
carbon dioxide, oxygen and moisture barrier protection. The bottles
can also withstand being hot filled.
Second Embodiment
[0045] The EVOH/adhesive mixture used for the middle layer 26 of
the second embodiment was comprised of Evalca XEP403 resin. The
inner and outer layers 24, 28 are comprised of polypropylene
without the presence of a maleic anhydride therein.
[0046] The following are examples of the second embodiment of the
present invention:
EXAMPLE 1
[0047] A three-layer coinjection molded preform was made having
inner and outer structural layers 24 and 28 made from 100%
polypropylene. The polypropylene was Solvay 4285. The middle layer
26 was made from 100% Evalca XEP403 resin. The preform was then
stretch blow molded to form a transparent container.
EXAMPLE 2
[0048] A multilayer coinjection molded preform was made as in
Example 1 of the second embodiment except that the polypropylene
used for the inner and outer structural layers 24 and 28 was Fina
7426MZ and the middle layer 26 was comprised of Evalca XEP403
having 100 ppm of Cobalt. The preform was then stretch blow molded
to form a transparent container.
[0049] The bottles made in Examples 1 and 2 of the second
embodiment are transparent, exhibit good strength and provide
carbon dioxide, oxygen and moisture barrier protection.
[0050] From the foregoing description, it will be apparent that the
transparent multilayer polypropylene containers having a barrier
layer of the present invention have a number of advantages, some of
which have been described above and others of which are inherent in
the transparent multilayer polypropylene containers of the present
invention. Also, it will be understood that modifications can be
made to the transparent multilayer polypropylene containers having
a barrier layer of the present invention without departing from the
teachings of the invention. Accordingly the scope of the invention
is only to be limited as necessitated by the accompanying
claims.
* * * * *