Note: Descriptions are shown in the official language in which they were submitted.
2~31295
Back~round of Invention
The present invention relates to paperboard lami-
nates, and more particularly to a non-foil paperboard lami-
nate useful for making containers for products such as fruit
or citrus juices, beverages and the like as well as
non-liquid dry products, wherein the laminate has good
oxygen barrier characteristics as well as the ability to
protect the products packaged therein against the 1088 of
essential oils, flavor and Vitamins. Paperboard coated with
low density polyethylene has been used for this purpose, but
it falls short of providing an acceptable container,
therefore additional barrier materials are required to
achieve the desired goal. It is well known that impermeable
materials such as aluminum foil, polar materials such as
polyamides, polyethylene terephthalates, polyvinylidene
chlorides, polyvinyl chlorides, etc., and highly crystalline
non-polar materials such as high density polyethylene and
polypropylene provide good gas barrier characteristics and
varying degrees of barrier to the absorption and/or
transmission of non-polar citrus juice flavor oils such as
d-Limonene et al. However, when additional barrier materials
are added to such structures, the manufacturing process
becomes comple~ because of the basic incompatibility of some
added materials with paperboard and low density
polyethylene. Nevertheless, polyethylene is the most
desirable material to have on both the inner and outer
surfaces of such a laminate in order to achieve reliable and
easy heat sealability when containers are formed.
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2~31~9~
U.S. Patents Nos. 4,789,575 and 4,802,943 disclose
a product and process for the manufacture of a laminate
structure having inner and outer layers of polyethylene
including an addit~onal barrier material, but the method for
making the laminate requires more complex manufacturing
steps than the present invention and achieves a structure
having less reliability in the field. U.S. Patent No.
4,513,036 discloses another structure having inner and outer
layers of polyethylnee, but the polypropylene barrier
material does not provide very good performance against the
1088 of essential oils and Vitamin C. Other prior art
related to the present invention is described in U.S. Patent
No. 4,289,830 which discloses a multi-layer, coextruded film
incorporating a barrier structure substantially as used in
the present ~nvention; a reprint from PLASTICS WORLD, July
1984 entitled "Barrier plastics challenge foil", which
discloses a barrier structure applied to paper substantially
as used in the present invention; and, a publication of
TAPPI PRESS entitled "High Barrier Polymers", presented at
the 1986 TAPPI Coextrusion Seminar, Marriott Hilton Head,
Hilton Head, SC, April 1-3 1986, whlch also shows a typical
barrier structure as disclosed herein in the form of a film.
Nevertheless, the invention disclosed and claimed herein is
deemed to be unobvious over the teachings of this prior art.
Summary of Invention
It is an ob~ect of the present invention to pro-
vide an improved heat-sealable, non-foil laminate for fruit
or citru~ ~uices, beverages and the like as well as
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2031~95
non-liquid dry products which is easy to manufacture and
which provides reliable performance in the field. In one
embodiment of the present invention, an existing commercial
structure for paperboard cartons comprising paperboard
sandwiched between two layers of low density polyethylene
(LDPE) is selected as the base material. Subsequently, in a
single manufacturing step, a symmetrical, five layer barrier
structure comprising LDPE/tie layer/ EVOH/tie layer/LDPE is
coextruded onto the surface of one of the layers of LDPE.
The coextrusion step can be accomplished without any inde-
pendent treat~ent to the LDPE layer of the base material
because the ad~acent LDPE/LDPE interfaces are compatible
with one another. In an alternative embodiment, the lami-
nate can be made in-line by selecting a paperboard sub-
strate, flame treating or corona discharge treating both
sides of the paperboard substrate, extrusion coating a layer
of LDPE onto the outer surface of the paperboard substrate,
extrusion coating a layer of LDPE onto the inner surface of
the paperboard substrate, and coextruding the aforementioned
five layer structure onto the inner layer of LDPE. The
final structure yields a construction which includes poly-
ethylene on its inner and outer surfaces to provide the most
desirable heat sealable characteristics, but which is much
simpler to manufacture than the prior art structures.
Carton~ constructed from the l~m~n~te of the present inven-
tion provide excellent gas barrier protection for dry pro-
ducts and significant flavor oil retention and prevention of
k`
2 ~31~-95
1088 of Vitamin C of the citrus juices contained therein,
resulting in an extended shelf like for the products.
8rief Description of Drawin~
FIGURE 1 is a cross-sectional elevation of the
laminate of the present invention;
FIGURE 2 is a block diagram representing a process
for m~ng the IA~nAte of the present inventlons and
FIGURE 3 is a block diagram representing an alter-
native process for manufacturing the laminate of the present
invention.
Detailed Description
In a preferred embodiment of the present invention
the laminate is prepared as follows:
Stepwise, the paperboard substrate is flame or
corona treated on both surfaces. Second, a layer of LDPE is
extrusion coated onto one surface of the paperboard at a
temperature in excess of 600 degrees F. to achieve a good
bond to the paperboard.
Thirdly, a layer of LDPE is extrusion coated onto
the other surface of the paperboard at the same temperature
as the first layer. And lastly, a five layer sandwich of
EVOH surrounded by Plexar tie layers and LDPE covering
layers is coextruded onto one of the first layers of LDPE
applied to the paperboard at a temperature substantially
le88 than 600 de8rees F. to prevent degradation of the EVOH
and tie layers.
The newly formed lAm~n~te is arranged 80 that the
five layer coextrusion becomes the inner surface or liquid
20~12~5
contact surface of any containers made from the laminate,
and the laminate is ~cored, cut into blanks, folded and side
seam heat-sealed in a conventional manner. The prepared
blanks are ready for filling and sealing on conventional
equipment in the normal manner. In an alternative
embodiment the five layer sandwich i~ coextruded directly
onto a base material comprising paperboard sandwiched
between two layers of low density polyethylene (LDPE).
The barrier laminate produced by the present in-
vention e~hibits excellent barrier properties and meets FDA
approval for use in food contact packag~ng. As an example,
the laminate of the present invention may comprise an
exterior coating of about 7-12 lbs/ream LDPE, paperboard of
varying th~ckness (depenting on carton size), an interior
coating of about 7-14 lbs/ream LDPE ant a coextrudet
sandwich layer applied to the interior coating of LDPE
comprising about 4-7 lbs/ream LDPE, 2-4 lbs/ream of an
adhesive tie layer (Plexar 177), 4-9 lbs/ream EVOH (Eval
EP), 2-4 lbs/ream tie layer (Plexar 177) and a product
contact layer of about 4-7 lbs/ream LDPE. The preferred
EVOH is sold under the product name Eval EP resin and is
available from Eval Company of America. The preferred tie
layer is Plexar 177 and is available from USI Corporation.
Any commercial extrusion grade of LDPE is suitable for use
in the present invention. Ream size is 3000 sheets 25X38
inches.
Even though EVOH is an excellent oxygen barrier,
its performance is greatly affected by relative humidity
293129S
(RH). Thus, for packaging a dry food product, the RH
susceptibility of the EVO~ can be reduced by increasing the
thickness of the LDPE layer adjacent to the coextrusion
layer. This permits modifications of the coat weights of
LDPE applied to the paperboard while still retaining a
symmetrical coextruded layer within the limits described.
It will thus be seen that the laminate of the pre-
sent invention provides barrier characteristics equivalent
to the most desirable products disclosed in the prior art,
but is much simpler and easier to manufactures than the la-
minates disclosed in the prior art. It should also be
understood that the coat weights set forth above in a
typical example may be reduced or modified as desired
depending upon the intended use for the product being
manufactured.
