U.S. patent application number 10/418524 was filed with the patent office on 2004-10-21 for multi-layer laminate structure.
Invention is credited to Shih, Keith S..
Application Number | 20040209021 10/418524 |
Document ID | / |
Family ID | 33159125 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040209021 |
Kind Code |
A1 |
Shih, Keith S. |
October 21, 2004 |
Multi-layer laminate structure
Abstract
A multi-layer structure for fabricating a beverage container
having two or more layers comprising paperboard and at least one
barrier layer formed of a blend of polyethylene, nylon and a
compatibilizer selected from maleic anhydride modified
polyethylene, zinc neutralized ethylene methacrylic acid, sodium
neutralized ethylene methacrylic acid, ethylene acrylic acid
copolymers, ethylene methacrylic acid copolymers and epoxy
functionalized polyethylene. The containers or cartons made from
the laminates containing the blend offer substantial heat
resistance and exhibit superior abuse resistance. The method and
process of making the blend and multi-layer structure are also
disclosed.
Inventors: |
Shih, Keith S.; (Loveland,
OH) |
Correspondence
Address: |
MCCARTER & ENGLISH LLP
CITYPLACE I
185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Family ID: |
33159125 |
Appl. No.: |
10/418524 |
Filed: |
April 18, 2003 |
Current U.S.
Class: |
428/34.2 |
Current CPC
Class: |
B32B 2307/7242 20130101;
C08L 23/04 20130101; B32B 2270/00 20130101; B32B 27/32 20130101;
C08L 23/0846 20130101; C08L 23/0884 20130101; B32B 27/10 20130101;
C08L 23/0876 20130101; B32B 27/18 20130101; B32B 27/34 20130101;
B32B 2439/70 20130101; C08L 51/06 20130101; Y10T 428/1303
20150115 |
Class at
Publication: |
428/034.2 |
International
Class: |
D21J 001/00 |
Claims
We claim:
1. Process for producing a compatibilized blend of polyethylene and
nylon which comprises forming a mixture of polyethylene, nylon, and
a compatibilizer which is a member selected from the group
consisting of maleic anhydride modified polyethylene, zinc
neutralized ethylene methacrylic acid, sodium neutralized ethylene
methacrylic acid, ethylene methacrylic acid copolymers, ethylene
acrylic acid copolymers and epoxy functionalized polyethylene and
heating said mixture in an extruder to a temperature which is
sufficient to form a homogeneous melt blend of said polyethylene,
nylon and compatibilizer.
2. A process according to claim 1 which comprises forming said
blend by separately introducing each of said polyethylene, nylon
and compatibilizer into said extruder for forming said mixture in
situ.
3. A process according to claim 1 which comprises forming said
blend by dry mixing said polyethylene, nylon and compatibilizer
prior to introduction into the extruder.
4. A compatibilized blend of polyethylene, nylon and a
compatibilizer which is a member selected from the group consisting
of maleic anhydride modified polyethylene, zinc neutralized
ethylene methacrylic acid, sodium neutralized ethylene methacrylic
acid, ethylene methacrylic acid copolymers, ethylene acrylic acid
copolymers and epoxy functionalized polyethylene.
5. A compatibilized blend according to claim 4 wherein said
polyethylene is a member selected from the group consisting of low
density polyethylene, linear low density polyethylene, metallocene
polyethylene and mixtures thereof.
6. A compatibilized blend according to claim 4 wherein said nylon
is a member selected from the group consisting of nylon 6, nylon 7,
nylon 8, nylon 11, nylon 12, nylon 6-6, nylon 6-9, nylon 6-10,
copolymer of nylon 6 and nylon 6-6, amorphous nylon, MXD6 nylon,
nylon nanoclay composite and mixtures thereof.
7. A compatibilized blend according to claim 4 wherein said nylon
is nylon 6.
8. A compatibilized blend according to claim 4 wherein said
polyethylene is low density polyethylene and said nylon is nylon
6.
9. A compatibilized blend according to claim 4 wherein said
compatibilizer is present in said blend in an amount of about 0.1
wt. % to about 15 wt. %.
10. A compatibilized blend according to claim 4 wherein said blend
contains less than about 40 wt. % of said polyethylene.
11. A compatibilized blend according to claim 4 wherein said blend
contains more than about 60 wt. % of said nylon.
12. A compatibilized blend according to claim 4 wherein said
compatibilizer is present in an amount of about 0.1 wt. % to about
15 wt. % said polyethylene is present in an amount of less than
about 40 wt. % and said nylon is present in an amount of more than
about 60 wt. %.
13. A multi-layer laminate material having two or more layers
comprising at least one layer comprising a compatibilized blend
according to claim 4.
14. A laminated material comprising a paperboard substrate and a
layer formed of a compatibilized blend according to claim 4
deposited on one surface of the paperboard.
15. A beverage container comprising a multi-layered structure
comprising a paperboard substrate and at least one barrier layer
formed of a compatibilized blend according to claim 4.
16. A beverage container according to claim 15 wherein said barrier
layer is deposited on one surface of said paperboard.
Description
[0001] The present invention relates to multi-layer laminate
structures having two or more layers, at least one layer of which
comprises a blend of polyethylene, nylon and a compatibilizing
agent. More particularly this invention relates to a multi-layer
laminated material suitable for forming a beverage container
comprising a layer made of paperboard and a layer formed of a blend
of polyolefin, polyamide and a compatibilizing agent. The layer
comprising the blend may be deposited on one surface of the
paperboard or onto another layer preferably composed of a
polyester, polypropylene, polyethylene, ethylene vinyl alcohol
copolymer (EVOH), polyacrylonitrile, polyvinylidene chloride
(PVDC), or foil with or without an adhesive tie layer in between
them.
BACKGROUND OF THE INVENTION
[0002] Many foods, especially liquids, are susceptible to oxygen or
other gases that cause them to spoil, degrade, or change flavor.
Therefore, the package or container that is used to store the food
should have very good oxygen barrier properties to protect its
contents.
[0003] It is also very important that the package have very good
moisture barrier properties, so that moisture does not get in if
dry food is stored inside. In the case for liquid (or
water-containing) storage, the excellent moisture barrier
properties of the package will minimize the moisture transport out
of the package, as well. In paperboard-based packaging systems, the
required barrier properties can be provided by polymer resin
coatings applied on the paperboard.
[0004] The cellulosic materials in the paper based packages such as
gable top cartons are susceptible to moisture, which can weaken
their internal bonds and leads to bulging of the carton and a
perception of a spoiled and obsolete product on the shelf. The
weakening of the internal fibrous structure inside a paperboard can
happen through any one or any combination of the following three
mechanisms: 1) diffusion of moisture through the polymer resin
coating into the paperboard, 2) moisture wicking through pinholes
or defects generated by coating and the subsequent converting
processes, and 3) moisture wicking through unprotected raw edge at
the side seam or at the bottom seam.
[0005] If the paperboard becomes weakened due to the first
mechanism, a thick layer of moisture barrier such as polyethylene
or polypropylene can be applied on both sides of the paperboard to
overcome it. If the third mechanism causes the paperboard to
weaken, one can use the skiving technology to protect the raw edge.
Skiving is essentially done by 1) cutting out the outside polymer
layer along with a portion or all of the paperboard and 2) folding
the remaining polymer layer over and sealing it to the board to
protect the paperboard raw edge. Skiving is commonly done in gable
top cartons to effectively protect the paperboard raw edge.
[0006] Carton defects are often caused by blister or bubble
formation on the layer immediately adjacent to the paperboard at
the inside of the carton. This happens during heat sealing when
intensive heat is applied to the inside of the carton. Since
paperboard usually contains some amount of moisture, in equilibrium
with the outside environment, this intensive heat can vaporize the
moisture inside the paperboard. The outside carton surface is
usually coated with a layer of a moisture barrier such as
polyethylene. The temperature at the outside surface is not very
high so that this outside moisture barrier layer remains rather
rigid. Therefore, the vapor cannot escape through the outside
barrier layer. Since the inside surface temperature is very high,
the polymer layer immediately adjacent to the paperboard may be
"softened" enough so that blister or pinhole formation becomes
inevitable. Therefore, placing a layer of polymer with good heat
resistance and high melting or softening temperatures such as
polyamide (nylon) adjacent to the paperboard is a very important
and essential structure design to prevent this blister or pinhole
formation from happening.
[0007] After filling with the food contents, the gable-top cartons
or other shape containers made from these paperboard/polymer
laminates are generally packed inside corrugated boxes and these
boxes are stacked on top of each other in a pallet for
transportation. The transportation of milk or juice is usually done
in a refrigerated truck maintained at a temperature of
approximately 4.degree. C. The food contents, particularly the
liquid food such as juice and milk, can create a tremendous dynamic
load to the laminate structure and cause damage to the cartons due
to vibration or jittering of these boxes during transportation.
Typically the damage manifests itself in the form of leakage at the
bottom of the cartons. Polyamide or nylon polymers provide abuse
resistance to the structure due to their toughness. Other factors
such as the coating thickness (coat weight), adhesion of film to
paperboard, types of internal or surface sizing on the paperboard
can also affect the abuse resistance of the cartons or
containers.
[0008] Polyolefins such as polyethylene or polypropylene have been
used to provide moisture barrier as well as heat sealing
properties. Generally speaking, a resin exhibiting excellent
moisture barrier properties does not have good oxygen barrier
properties and vice versa. Polyolefins are known to have poor
oxygen barrier performance. Therefore, multi-layer structures
containing both oxygen barrier layers and moisture barrier layers
have been developed to address these concerns. Ethylene vinyl
alcohol copolymer (EVOH) has excellent oxygen barrier properties
and has been used in packaging applications for oxygen sensitive
foods, such as orange juice. Other polymers such as polyethylene
terephthalate (PET), polyacrylonitrile, and polyvinylidene chloride
(PVDC), EVOH nanoclay composite, or polyamide nanoclay composite
could be used as the oxygen or aroma barrier. Nylon polymers have
also been used in paperboard packaging structures resulting in good
oxygen barrier performance for foods that require only moderate
protection from oxygen. However, nylon polymers are better known to
impart abuse resistance and heat resistance to the paperboard
structure. Aluminum foil has also been used in the laminate
structure to result in both excellent moisture and oxygen barrier
performance.
[0009] Paperboard/polymer laminate structures that consist of
layers of nylon polymers, polyolefins, and/or ethylene vinyl
alcohol copolymers (EVOH) are described in U.S. Pat. Nos.
3,972,467, 4,835,025, 4,888,222, 5,175,036, 5,958,534, 6,110,548,
and 6,383,582. While all of the prior arts patents addressed the
issues of oxygen and moisture barrier performance, none focused on
improving the abuse resistance of the cartons made from these
paperboard/polymer laminates.
[0010] The toughness of polyamides, particularly at low
temperatures, can be modified or improved by rubbers or elastomers.
The room temperature toughness of polyamides can also be improved
by introducing fillers such as calcium carbonate. Alternatively,
one could blend polyamides with another polymer having good
toughness properties. However, it may require the addition of a
compatibilizer in this blending approach if the polymer chosen is
not compatible with the polyamide(s). Polymers with good toughness
include but are not limited to linear low density polyethylene
(LLDPE), low density polyethylene (LDPE), metallocene polyethylene
(m-PE), zinc or sodium salts of ethylene methacrylic acid copolymer
(Surlyn.RTM.), and maleic anhydride modified polyethylene. It is
quite common that additional co-monomers with rubbery properties
and low glass transition temperatures are included in the
polymerization process of Surlyn.RTM. polymers and maleic anhydride
modified polyethylene to achieve excellent low temperature
toughness.
[0011] When blending Surlyn.RTM. polymers with polyamides, it may
not be necessary to add a compatibilizer because the polymer pairs
are compatible between themselves. When blending polyamide with
another polymer such as LDPE, it is necessary to add a third
component, the compatibilizer, to produce a compatible blend. The
role of compatibilizer is to reduce the interfacial surface energy
between the phase domains and hence reduce the phase domain sizes
of the blend. In an incompatible blend the phase domain sizes are
very large and the mechanical properties such as strength and
toughness are dramatically reduced.
[0012] Generally, blending polyamide with a low melting temperature
resin such as polyethylene would have a tendency to reduce the heat
resistance of the blend. It is essential that the modified
(toughened) polyamides maintain a substantial level of heat
resistance so that the paperboard will not blister or forms
pinholes during converting operation. The blends of the present
invention can be applied to the paperboard to form laminates with
substantial heat resistance and improved abuse resistance when the
laminates are made into the cartons or containers.
[0013] U.S. Pat. No. 3,373,222 discloses a blend of 40-60% by
weight of a polyamide and 40-60% by weight of a polyolefin resin,
and 2-10% by weight of a carboxylated polyethylene having an acid
number from 2.75 to 50. This blend is capable per se of being
shaped into various non-pinch crazing forms without any
difficulties. This is not what is contemplated by the present
invention but rather a blend to be applied to paperboard to form
laminates having improved heat and abuse resistance when formed
into cartons and containers.
SUMMARY OF THE INVENTION
[0014] It is therefore an object of the invention to provide a
compatible polyolefin-polyamide blend, which is substantially
resistant to heat and has improved toughness to be used in
multi-layer laminate structures.
[0015] Another object of the invention is to provide a multi-layer
laminate structure, particularly suitable for use for beverage
packaging purposes which has low permeability to gases, in
particular oxygen and vapors, in particular water vapor and at the
same time has improved physical properties such as abuse resistance
and is substantially resistant to heat.
[0016] It is another object of the invention to provide a
multi-layer laminate material having two or more layers comprising
paperboard and at least one barrier layer formed of a blend of
polyolefin, polyamide and a compatibilizer.
[0017] It is another object of the invention to provide a
multi-layer structure comprising paperboard and at least one
barrier layer formed from a blend of polyamide, polyolefin and a
compatibilization agent deposited on one surface thereof.
[0018] In accordance with the invention, there is provided a blend
comprising polyolefin, preferably polyethylene, a polyamide,
preferably nylon 6 and a compatibilization agent selected from
maleic anhydride modified polyethylene, zinc neutralized ethylene
methacrylic acid copolymer, sodium neutralized ethylene methacrylic
acid copolymer, ethylene acrylic acid copolymer, ethylene
methacrylic acid copolymer and epoxy functionalized
polyethylene.
[0019] The invention also provides a process for producing the
blend and a multi-layer laminate structure including the same which
comprises mixing the polyolefin, polyamide and compatibilization
agent, heating and blending the mixture to form a melt and
extruding the melt onto paperboard or another material by the
extrusion coating or extrusion lamination process.
[0020] The process can be carried out by, first pre-blending the
polyolefin, polyamide with a sufficient amount of a
compatibilization agent in a mixer to make a dry blend, and then
introducing the dry blend into the extruder hopper. A single screw
extruder equipped with a mixing section such as a Maddock mixer is
sufficient to make a compatible blend. Alternatively the
polyolefin, polyamide and compatibilization agent can be
pre-compounded in a twin screw extruder, a single screw extruder
equipped with a mixing screw, or an internal mixer and pelletized.
These pellets can then be fed directly into the extruder for
extrusion coating. In the instance when the pre-compounded blend is
used, it is not necessary to equip the single screw extruder on the
extrusion coating line with any mixing element.
[0021] In both instances, the mixture is heated and the melt blend
is extruded as a coating or film onto the paperboard. It is of
course possible for the melt blend to be extruded onto another
layer of a multi-layer structure other than directly onto the
paperboard.
[0022] The obtained blend compositions and the multi-layer
structures produced therewith may be converted into packaging
materials intended for the packaging of beverages which require low
water vapor transmission rates and low gas, particularly oxygen and
flavor permeabilities, and improved abuse resistance.
DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
[0023] The blends of polyolefin, polyamide and compatibilization
agent are obtained by a melt blending process using a single screw
extruder in a extrusion coating line or co-extrusion coating line,
as long as the extruder is equipped with a mixing section.
Alternatively the blend can be pre-compounded off-line by a
twin-screw extruder, a single screw extruder equipped with a mixing
section, or an internal batch mixer. The blend obtained is then
palletized. These pellets are then fed into the extruder hopper of
the single extruder in the extrusion coating line for the
subsequent processing. Polyolefins that may be used are
polyethylene homopolymers such as but not limited to low density
polyethylene, linear low density polyethylene, metallocene
polyethylene, and high density polyethylene; polypropylene
homopolymers, copolymer of propylene with ethylene, and rubber
modified (impact modified) polypropylene. Most preferred as the
polyolefin is low-density polyethylene such as Tenite 1924P from
Eastman Chemical Company or MarFlex.TM. PE 4517 from Chevron
Phillips Chemical Company. The polyolefin resin may be used in the
form of granules or powders.
[0024] Polyamides that may be used are nylon 6, nylon 7, nylon 8,
nylon 11, nylon 12, nylon 6-6, nylon 6-9 and nylon 6-10, copolymers
of nylon 6 and nylon 6-6, amorphous nylon such as the one sold by
DuPont under the trade name of Selar PA, MXD6 nylon such as sold by
Mitsubishi Gas Chemical Company, and polyamide nanoclay composites.
The preferred polyamide is nylon 6 such as Capron.RTM. B73QP
manufactured by Honeywell Plastics The compatibilization agents can
be maleic anhydride modified polyethylene, such as Fusabond.RTM.,
polymers from DuPont or Tymor.RTM. resins from Rohm and Haas, zinc
or sodium neutralized ethylene-methacrylic acid copolymers such as
Surlyn.RTM., ionomers from DuPont, modified Surlyn.RTM. ionomers
with additional functional groups, ethylene acrylic acid copolymers
such as Primacor.RTM. polymers from Dow Chemical Company, ethylene
methacrylic acid copolymers such as Nucrel.RTM. polymers from
DuPont, or epoxy functionalized polyethylene such as Lotader.RTM.
polymers from Atofina. The preferred compatibilizer is maleic
anhydride modified polyethylene such as Tymor.RTM. 1N06 from Rohm
and Haas or Surlyn.RTM. ionomer such as Surlyn.RTM. 1857 from
DuPont for a blend of nylon 6 and LDPE.
[0025] The blend will preferably contain less than 40% by weight of
the polyolefin, preferably polyethylene, more than 60% by weight of
the polyamide preferably nylon 6 and from about 0.1 weight % to
about 15 weight % of the compatibilization agent. A particularly
preferred blend contained 90% by weight of the nylon 6,
approximately 8.5% by weight of the LDPE, and approximately 1.5% by
weight by weight of the compatibilizer.
[0026] The process of the invention is most advantageously
performed by the use of an extrusion coating line having at least a
single screw extruder equipped with a mixing section. The three
components are pre-blended (dry blended) in a mixer before being
introduced into the extruder. A single screw extruder equipped with
a mixing section, such as a Maddock mixer, is sufficient to melt
blend the polyethylene, nylon 6 and compatibilization agent.
Alternatively the dry blend can be pre-compounded in a twin-screw
extruder, in a single screw extruder equipped with a mixing
section, or in an internal mixer. The melt blend formed is then
pelletized and the pellets fed directly into a single screw
extruder for extrusion coating or film coating operations. In the
instance when the pre-compounded blend is used, there is no need to
equip the single screw extruder on the extrusion coating or film
casting line with any mixing element.
[0027] In order to obtain an optimal mixing of the polyethylene,
nylon 6 and compatibilization agent during the extrusion process,
they should all be in their molten states. In general, a practical
melt processing temperature for polyethylenes is in the range of
from about 130.degree. C. and upwards, for the compatibilizers in
the range of from about 110.degree. C. and upwards, and for
polyamides in the range from about 220.degree. C. and upwards. In
order to get good mixing between these components, the temperature
of the extruder barrel section at which the mixing section is
located should be above 220.degree. C. However, the processing
temperatures must not be so high that any substantial degree of
degradation of the polymer resins will take place. The temperature
of the melt should therefore not exceed about 320-330.degree.
C.
[0028] While the present invention is directed to polyamide and
polyolefin blend barrier layers for paperboard substrates, the
invention is not limited to the extrusion of such layer on
cellulosic substrates. Accordingly, the substrate may be comprised
of only paperboard, polymer films, aluminum foil, and their
combination. The blend of polyamide and polyolefin layer may also
be applied to polymeric materials such as thermoplastics and many
other materials where there is a desire to reduce the oxygen,
moisture, and/or flavor vapor transport through the material.
[0029] Examples of such paperboard include but are not restricted
to bleached paperboard, unbleached paperboard, kraft, sulfide, and
multi-ply board. The basis weight of paperboard could vary from 20
lbs/3,000 square foot (or 20 lbs/ream) to 500 lbs/ream.
[0030] Various coatings or treatments may be applied to the
paperboard before or after co-extrusion coating with the blend of
polyamide and polyolefin. These coatings or treatments could
include sizing agents, primers and other wet-end and off-line
additives. Other methods known to those of ordinary skill may be
used to obtain a container such as single or multi-layer polymer
structure or plastic container containing the blend of this
invention. Examples of such a rigid or flexible container could be
plastic bottles, jars, pouches, and bags.
[0031] A particularly preferred substrate for inclusion in the
laminate structures of the invention is a bleached paperboard made
by International Paper Company with basis weights in the range of
120 lbs/ream to 400 lbs/ream and more preferably in the range of
140 lbs/ream to 290 lbs/ream.
[0032] The method of making a paperboard/polymer laminate structure
containing at least a layer of polyamide and polyolefin blend is
preferably carried out using the extrusion coating process. The
blend can be prepared on-line. In a preferred method, a gravimetric
or volumetric blender is used to meter the three components
(polyamide, polyolefin, and compatibilizer) to the proper
proportions and mix them to form the dry blend. The dry blend is
then introduced into the extruder hopper via a conveying device. A
single screw extruder equipped with a mixing section, such as a
Maddock mixer, serves to melt blend the polyamide, polyolefin, and
the compatibilizer to form a stable melt curtain for extrusion
coating operation. Alternatively one can use gravimetric or
volumetric feeders to directly feed the individual resin in the
right proportions to the extruder.
[0033] Alternatively the blend could be prepared off-line. The
blend can be compounded or melt blended in a twin screw extruder, a
single screw extruder equipped with the mixing section, or in an
internal batch mixer such as a Banbury mixer. The melt blend formed
is then pelletized. The pellets are then fed into an extruder for
extrusion coating or extrusion lamination operations.
[0034] In the extrusion coating process a moving paperboard is
coated with single or multi-layer polymer melt fed through the
extrusion coating die. The paperboard/polymer melt laminate is then
subsequently passed through a nip roll/chill roll in order to cool
it down before it is wrapped up in the winding station. If a
multi-layer polymer is involved, it may be necessary to place a tie
layer or tie between two dissimilar polymer layers. For instance,
it may be necessary to place a tie layer between a polyamide layer
and a polyolefin layer. Another example is to co-extrude EVOH with
LDPE, it is necessary to place a tie layer between these two
polymer layers. Depending on the polymer layers used in forming the
multi-layer structure, the choice of tie layer may change. For
instance, maleic anhydride modified polyethylene is suitable to be
used as a tie layer between polyamide and polyolefin. However,
maleic anhydride modified polyethylene may not be suitable as the
tie layer between polyester and polyethylene. When co-extruding
polyamide and EVOH together, one may eliminate the use of a tie
layer because the adhesion between polyamide and EVOH is generally
good. Generally speaking the tie layer used for polyamide and
another resin can also be used as the tie layer between the blend
of polyamide and polyolefin and same specific resin. Therefore,
maleic anhydride modified polyethylene is suitable for use as a tie
layer between the blend of polyamide and polyolefin and
polyethylene. The preferred tie layer resin in this case is maleic
anhydride modified polyethylene such as Plexar.RTM. 5125 from
Equistar Chemical Company.
[0035] It may be necessary to apply a treatment to the paperboard
surface in order for it to adhere to the hot polymer melt. The
usual treatment is flame treatment so that polar species are
induced on the paper surface. The flame treatment is usually done
on-line. Other surface treatment includes corona discharge, and
ozone treatment. These treatments can be done on-line or
off-line.
[0036] In the case of a multi-layer co-extrusion coating, various
polymer melts from different extruders flow through the heated
pipes to a feed block. Each polymer melt is converted into a
layered form inside the feed block. Various molten polymer layers
are then combined at the exit of the feed block before the
combination enters into the extrusion-coating die. An alternative
method is to use the multiple manifold die and to allow the layers
to combine inside the die. The layers are combined at or close to
the final land of the die, and they exit as one integral layer. A
third approach combines both the feed block and multiple manifolds
to provide even better processing control.
[0037] Another method of making a paperboard/polymer laminate
structure containing a least a layer of polyamide and polyolefin
blend is to use the extrusion lamination process. In this process,
a solid polymer laminate that has been pre-formed elsewhere is fed
along with the moving paper web through an extrusion die. A polymer
hot melt layer (as an adhesive layer) is directed through the
extrusion die and deposited between the paperboard and the
laminate. The paperboard/adhesive/laminate is then passed through
the nip roll and the chill roll to cool down before it was wound on
the roll at the winding station. It may be necessary to apply a
surface treatment on the laminate film surface in order for it to
stick to the adhesive layer.
[0038] It may also be necessary to apply a surface treatment on the
paperboard for the same reason. The surface treatment for the
laminate film can be corona discharge or ozone treatment and can be
done either on-line or off-line. As for the surface treatment for
paperboard, it can be flame, corona discharge, or ozone.
[0039] An alternative method is to use adhesive lamination, where
an adhesive, a primer or glue is applied between two adjacent
layers or substrates during the lamination process.
[0040] The following structures were prepared and illustrate
preferred laminates of the invention:
1 Structure #1 12 polyolefin 10 paperboard 14 polyolefin/polyamide
blend (compatibilized) 16 tie 18 polyolefin
[0041] 12 designates a polyolefin gloss layer for printing (5-20
lbs/ream, preferably 12 lbs/ream). 10 is the paperboard (100-300
lbs/ream, preferably of 125-285 lbs/ream). 14 is a compatibilized
blend of polyamide (nylon) and polyolefin with a coat weight of
2-20 lbs/ream, preferably 5 lbs/ream. 16 is a tie layer having a
coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream, and 18 is
another polyolefin layer (heat sealing layer) in food contact,
having a coat weight of 10-25 lbs/ream, preferable in the range
between 12-20 lbs/ream.
2 Structure #2 22 polyolefin 20 paperboard 24 polyamide/polyolefin
blend 26 tie 28 polyolefin 30 polyolefin 32 tie 34 EVOH* 36 tie 38
polyolefin *EVOH or polyamide or blend of polyamide and
polyolefin
[0042] 22 designates a polyolefin gloss layer for printing (5-20
lbs/ream, preferably 12 lbs/ream). 20 is the paperboard (100-300
lbs/ream, preferably in the range of 125-285 lbs/ream). 24 is a
compatibilized blend of polyamide (nylon) and polyolefin having a
coat weight of 2-20 lbs/ream, preferable 5 lbs/ream. 26 is a tie
layer having a coat weight of 1-5 lbs/ream, preferably 1.5
lbs/ream. 28 is polyolefin layer having a coat weight of 6-30
lbs/ream, preferably 28 lbs/ream, 30 is also a polyolefin layer
having a coat weight of 1-7 lbs/ream, preferably 4 lbs/ream. 32 is
another tie layer with a coat weight of 1-5 lbs/ream, preferably
1.5 lbs/ream, 34 can be one of the following: 1) ethylene vinyl
alcohol copolymer (EVOH) containing 26-44 mol % ethylene, 2)
polyamide such as nylon 6, nylon 66, nylon 10, nylon 6-10,
amorphous nylon, MXD6 nylon, 3) a compatibilized blend of polyamide
and polyolefin. The coat weight of this layer, 34, is between 0.5-7
lbs/ream, preferably 2-4 lbs/ream. 36 is another tie layer having a
coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream and 38 is the
food contact polyolefin layer having a coat weight of 1-7 lbs/ream,
preferably 4 lbs/ream.
3 Structure #3 42 polyolefin 40 paperboard 44 polyamide/polyolefin
blend 46 EVOH 48 tie 50 polyolefin 52 tie 54 EVOH 56 tie 58
polyolefin
[0043] 42 designates a polyolefin gloss layer for printing (5-20
lbs/ream, preferably 12 lbs/ream). 40 is the paperboard (100-300
lbs/ream, preferably 125-285 lbs/ream), 44 is a compatibilized
blend of polyamide (nylon) and polyolefin having a coat weight of
2-20 lbs/ream, preferably 5 lbs/ream. 46 is an ethylene vinyl
alcohol copolymer (EVOH) having a coat weight of between 0.5-10
lbs/ream, preferably 3-6 lbs/ream. 48 is a tie layer. The coat
weight of this tie layer, 48, is between 0.5-15 lbs/ream,
preferably 8 lbs/ream. 50 is a polyolefin layer having a coat
weight of 1-20 lbs/ream, preferably 4-10 lbs/ream. 52 is another
tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5
lbs/ream. 54 is another EVOH layer with a coat weight of 1-10
lbs/ream, preferably 3 lbs/ream. 56 is another tie layer having a
coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream. 58 is the
food contact polyolefin layer having a coat weight of 1-20
lbs/ream, preferably 4-10 lbs/ream.
EXAMPLE 1
[0044] Multi-layer paperboard/polymer laminates were produced at
the pilot scale co-extrusion line. Two structures were made. The
control structure (Run 1) had the following multi-layer
construction:
[0045] Run 1--LDPE (gloss finish)/paperboard/nylon 6/tie
layer/LDPE
[0046] Run 2 had the following multi-layer construction:
[0047] Run 2--LDPE (gloss finish)/paperboard/blend of nylon 6 and
LDPE/tie/LDPE
[0048] In both runs, 12 lbs/ream of the gloss LDPE coating were
used. The paperboard basis weight was 265 lbs/ream in both runs. In
Run 1, the coat weight of nylon 6 was 5 lbs/ream and in Run 2 the
coat weight of the blend of nylon 6 and LDPE was also 5 lbs/ream.
The coat weight for the tie layer in both structures was 1.5
lbs/ream. The coat weight for the LDPE on the matte side (also the
food contact side) was 14 lbs/ream for both structures. The blend
was made up of approximately 90 wt % nylon 6, 1.5 wt %
compatibilizer, and 8.5 wt % LDPE. During the co-extrusion coating
process, the polymer to paperboard adhesion was checked by the
cross cut method.
[0049] 1) Using a sharp knife or razor blade, a first light cut of
the polymer coating on the paperboard was made. A second similar
cut was made so as to form an "X" shape between the two cuts.
[0050] 2) the knife edge was used for starting the polymer
separation from the paperboard at the center of the "X" cut.
[0051] 3) The polymer was grasped and then slowly pulled to cause
separation of the coating from the paperboard.
[0052] 4) The degree of fiber tear on the polymer film surface was
observed and a rating of excellent, good, fair, and poor in
descending order was assigned based thereon.
[0053] Excellent adhesion was found for both samples on both the
gloss side coating (LDPE to paperboard) and the matte side coating
(laminate to paperboard), as we observed 100% fiber tear when we
pulled the film away from the paperboard.
[0054] The coated paperboard was converted into blanks using a side
seam sealing machine and a skiver. A blue dye (methylene blue)
alcohol solution was used to check the side seam quality,
particularly the pinhole resistance. The visual examination lead to
a ranking of one of the following five in descending order:
excellent, very good, good, fair, and poor. These blanks were then
fed into the milk filling machine (H-100 filler by Evergreen) for
carton conversion and filing. 2% low fat milk was used to fill the
half-gallon size cartons with standard J bottom. A red dye (Scarlet
Moo) aqueous solution was used to check the pinhole resistance of
the board at the bottom of the carton. In this test, unfilled empty
carton was filled with the red dye solution and sat for 2 minutes.
The red dye solution was then poured out of the carton. The bottom
portion of the carton was wiped cleaned with an absorbent tissue
and then visually examined for existence of pinholes. The visual
examination lead to a ranking of one of the following five in
descending order: excellent, very good, good, fair, and poor. Both
the side seam pinhole resistance and bottom pinhole resistance
tests reveal the heat resistance of the coated boards.
[0055] The cartons filled with the milk were stored in the cold
room at approximately 4.degree. C. for two days. Then these cartons
were subjected to the distribution abuse resistance test. This is
an in-house developed test method to simulate the vibration and
jittering of the cartons experienced during transportation. The
test is designed to compare the relative bottom durability or
distribution abuse resistance of cartons to a control group within
a study. Data are not to be used for comparison between studies. A
total of 40 cartons are used for each test. The tester essentially
consists of a shaker table. The variables in this tester are rpm of
the motor and duration of the test. The testing conditions were:
210 rpm for 15 minutes, 225 rpm for 15 minutes, 250 rpm for 15
minutes, and 270 rpm for 15 minutes. After the test, the bottom of
each carton was visually examined to detect leakage. The total
number of leakage (for a total of 40 cartons) was then recorded as
the distribution abuse resistance of the cartons. Table 1 lists all
of the test results.
4TABLE 1 Results of the adhesion test, pinhole resistance test, and
distribution abuse resistance test. Abuse resistance Adhesion to
Adhesion to Pinhole Pinhole (# leaks out paperboard paperboard
resistance resistance of 40 (gloss side) (matte side) (side seam)
(bottom) cartons) Run 1 excellent excellent excellent very good 17
Run 2 excellent excellent excellent very good 4
EXAMPLE 2
[0056] Multi-layer paperboard/polymer laminates were produced at
the co-extrusion line. Two structures were made. The control
structure (Run 3) had the following multi-layer construction:
[0057] Run 3--LDPE (gloss finish)/paperboard/nylon 6/tie
layer/LDPE
[0058] Run 4 had the following multi-layer construction:
[0059] Run 4--LDPE (gloss finish)/paperboard/blend of nylon 6 and
LDPE and compatibilizer/tie/LDPE
[0060] In both runs, 12 lbs/ream of the gloss LDPE coating were
applied. The paperboard basis weight was 265 lbs/ream in both runs.
In Run 3, the coat weight of nylon 6 was 5 lbs/ream and in Run 4
the coat weight of the blend of nylon 6 and LDPE was also 5
lbs/ream. The coat weight for the tie layer in both structures was
1.5 lbs/ream. The coat weight for the LDPE on the matte side (also
the food contact side) was 14 lbs/ream for both structures. The
blend was made up of approximately 80 wt % nylon 6, 5 wt %
compatibilizer, and 15 wt % LDPE.
[0061] The adhesion test, pinhole resistance test, and distribution
abuse resistance test for both structures (from Run 3 and Run 4)
were carried out as described in Example 1. The results are listed
in Table 2.
5TABLE 2 Results of the adhesion test, pinhole resistance test, and
distribution abuse resistance test. Abuse resistance Adhesion to
Adhesion to Pinhole Pinhole (# leaks out paperboard paperboard
resistance resistance of 40 (gloss side) (matte side) (side seam)
(bottom) cartons) Run 3 excellent excellent excellent very good 10
Run 4 excellent excellent excellent very good 5
[0062] Articles made from the multi-layer laminate structure
comprising the compatibilized blends of polyolefin (polyethylene)
and polyamide (nylon 6) and paperboard, according to the present
invention are possessed of superior distribution abuse resistance
and subsantial heat resistance. When combining the compatibilized
blend of nylon 6 and LDPE with a high oxygen barrier such as EVOH,
polyester, polyacrylonitrile, polyvinylidene chloride, or a foil
and a high moisture barrier such as LDPE or a foil, the resultant
structure is suitable for use in beverage packaging and
particularly for packaging juices and punches that require a high
barrier against moisture and gases, such as oxygen and against
flavor components.
* * * * *