Note: Descriptions are shown in the official language in which they were submitted.
~92/119~2 ~ 9 2 ~ PCT/US92ioooo3
TITLE
BARRIER RESIN COATED LAMINATES
FIELD OF THE INVENTION
The invention relates to materials that have
improved heat seal properties. In particular, the
invention relates to metallized polymer films that
have improved heat seal properties for use in
packaging.
BACKGROUND OF THE INVENTION
Materials such as polymer film and metal
foil have been employed to protect products such as
food stuffs against the effects of oxidation and water
vapor permeation. The polymer films typically are
coated with polymeric, barrier layer compositions.
These barrier layer compositions typically include
coating additives such as aluminum silicates, talc,
waxes and the like to impart desired film properties
such as jaw release, printability, film slip and the
like. Unfortunately, these additives tend to reduce
the coating adhesion and heat seal properties of the
coated polymer film.
Metal foils such as aluminum foil also have
been used as packaging materials for products such as
food stuffs. Metal foils are useful for packaging due
to their low permeability to oxygen and water vapor.
Metal foils, however, are subject to significant cost
variability, have poor heat seal properties, and poor
flex-crack resistance.
The art has made efforts to improve the heat
seal properties of polymer films. In U.S. patents
3,896,066 and 3,985,065, the patentees apply a barrier
coating of a copolymer of vinylidene chloride to the
polymer substrate.
Japanese 6223174, published October 12,
1987, shows production of metallized sheets of paper
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and plastic. The process comprises applying a
polyvinylidene chloride copolymer of methacrylic '
ester, acrylonitrile, vinyl chloride, and methacrylic
acid onto the metallized surface of a sheet of paper
or plastic. The polyvinylidene chloride copolymer
then is oxidized.
Although the art has employed vinylidene
chloride copolymer barrier layers with polymeric
films, the`metallized polymer films which employ these
barrier compositions tend to be deficient as packaging
materials because of the effects of coating additives.
A need therefore exists for improved metallize~
packaging materials that employ barrier layer
compositions that include coating additives and which
overcome the deficiencies of the prior art materials.
SVMMARY OF THE INVENTION
The invention is directed to metallized
materials that have a a metallic coating on one or
more surfaces that show improved barrier layer coating
adhesion and heat seal properties. These metallized
materials include a coating of vinylidene copolymer on
the metallic coating. The polyvinylidene chloride
copolymer has at least 80% vinylidene chloride, at
least 4% of an ethylenically unsaturated acrylic
monomer, as well as coating additives for modifying
film properties.
In accordance with the invention, the
metallized materials that show improved barrier layer
coating adhesion and heat seal properties are made by
treating a substrate material that has at least one
metallic surface thereon with a formulated solution of
coating additives and vinylidene chloride copolynler.
The polyvinylidene chloride copolymer comprises at
least 80% by weight polyvinylidene chloride, at least
4% by weight of an ethylenically unsaturated acrylic
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ester. The solution of copolymer of vinylidene
chloride and coating additives forms a barrier layer
that imparts surprisingly improved adhesion and heat
seal properties to materials such as polyesters that
bear metal layers thereon.
Application of the aforedescribed solution
in accordance with the invention provides surprisingly
improved adhesion and heat seal properties. Such
substrate materials include, but are not limited to
plastics, regenerated cellulose, paper, metallizecl
plastics, metallized regenerated cellulose, metallized
paper and the like. Suitable plastics for use in the
invention include, but are not limited to polyesters,
polyolefins, polyamides, vinyl chlorides, copolymers
thereof, as well as blends thereof. Additional
examples of materials whose adhesive and heat seal
properties may be improved by the vinylidene chloride
copolymer of the invention include but are not limited
to metal foils such as aluminum foil.
The formulated solution of vinylidene
chloride copolymer and coating additives may be
applied to the substrate materials by any conventional
method known in the art. Such methods include solvent
solution coating, emulsion coating, melt coating, and
the like. Preferably, the vinylidene chloride
- copolymer is applied in a conventional coating tower
by passing the substrate material through a solvent
solution of formulated vinylidene chloride copolymer
and coating additives, and thereafter evaporating the
solvent to yield a layer of formulated vinylidene
chloride polymer and coating additives on the
substrate.
The substrate materials, preferably
metallized polymeric films, that are coated with the
formulated solution of vinylidene chloride copolymer
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and coating additives have particular utility in
packaging for materials such as foodstuffs. These
coated substrate materials can be employed as
produced. Alternatively, but without limitation, tl~e
coated metallized substrate materials may be used in
the form of a laminated film structure. The coatec1
substrate materials produced by the invention also may
be used in applications such as, but not limited to,
insulati~n materials for the construction industry.
Having briefly summarized the invention, the
invention will now be described in detail by reference
to the following specification and non-limiting
examples. Unless otherwise specified, all percentages
are by weight and all temperatures are in degrees
Celsius.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, a
formulated solution of vinylidene chloride (VDC)
copolymer and up to 10% by weight of copolymer of
coating additives is applied to a metal bearing
substrate, preferably metallized polymer film, most
preferably metallized polyethylene terephthalate. The
VDC copolymer has at least 80%, but not more than 95%
vinylidene chloride. The balance of the vinylidene
chloride oopolymer comprises an ethylenically
unsaturated acrylate, preferably methyl methacrylate
(MMA). The ethylenically unsaturated acrylatc
comprises at least 4% of the VDC copolymer. Other
ethylenically unsaturated polyacrylates may be
employed in place of MMA or in combination with MMA.
Examples of suitable ethylenically unsaturated
acrylates include, but are not limited to, aliphatic
C2-C6 acrylates, aliphatic C2-C6 methacrylates, and
the like. Examples of ethylenically unsaturated
acrylates include, but are not limited to butyl
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acrylate, methyl acrylate, ethyl acrylate and the
like. Examples of aliphatic methacrylates include
methyl methacrylate, ethyl methacrylate, and the like.
Optionally, acrylonitrile (AN) may be included in the
vinylidene chloride copolymer provided that the
copolymer has at least 4~ of ethylenically unsaturated
polyacrylate. Preferably, the copolymer has 80 to 95%
vinylidene chloride and 4 to 20~ ethylenically
unsaturated acrylate, most preferably 88 to 92%
vinylidene chloride and 6 to 12% ethylenically
unsaturated acrylate.
The metal bearing materials that can be
coated with the formulated solution of vinylidene
chloride copolymer and coating additives preferably
are metallized polymers. Examples of suitable
polymers include polyesters, polyolefins, polyamides,
polyvinylchloride, copolymers thereof, and blends
thereof. Any oxidizable metal such as Fe, Cu, Al, Ti,
alloys thereof, and the like, most preferably
aluminum, may form the metal component of the
metallized polymer films. Most preferably, the
metallized polymeric film is aluminized polyethylene
terephthalate. Such metallized polymers are made by
processes known in the art, as described for example
in "Encyclopedia of Chemical Technology", Kirk-Othmer,
3rd Edition, Volume 15, pp. 264-265, the disclosure of
which is incorporated by reference. The metal bearin~
materials that may be coated, however, may be other
than metallized polymers. Examples of additional metal
bearing materials that may be employed in the
invention include metallized regenerated cellulose and
polyolefins such as metallized paper, metallized
oriented polypropylene, and the like.
The improved products of the invention are
preferably prepared by applying a coating solution of
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more than 90% by weight of a vinylidene chloride
copolymer that has at least four percent of
ethylenically unsaturated acrylate and up to 10% by
weight of coating additives to at least the metal
bearing surface of a metal bearing substrate.
Examples of coating additives include talc, waxes,
aluminum silicates, and the like. Alternatively, the
formulated solution of vinylidene chloride copolymer
may be applied to both the metal bearing surface and
the non-metal bearing surface of the substrate
material.
The formulated solution of vinylidene
chloride copolymer and coating additives preferably is
applied to the metallized substrate. Thereafter the
solvent of the vinylidene chloride copolymer solution
is evaporated to provide a coating of vinylidene
chloride copolymer and coating additives on at least
the metallized surface of the substrate. Application
of the solution of formulated polyvinylidene chloride
copolymer conveniently can be performed in a
conventional coating tower, as is known in the art.
Alternatively, but without limitation, the formulated
solution of vinylidene chloride copolymer and coating
additives may be applied by emulsion coating of a
solution of formulated vinylidene chloride copolymer
onto the substrate.
In accordance with the preferred method for
applying the formulated solution of viny1idclle
chloride copolymer, the copolymer of vinylidene
chloride and ethylenically unsaturated monomer,
preferably MMA, is dissolved in a solvent such as
tetrahydrofuran (THF), toluene, methyl ethyl ketone,
nonpolar solvents such as l,~-dibromopropane,
bromobenzene, alpha-chloronaphthalene,
2-methylnaphthalene, o-dichlorobenzene, polar aproctic
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W^92/11952 ~1 U ~ 9 2 0 PcT/us92/nono3
solvents such as tetramethylene sulfoxide, N-methyl
pyrrolidone, trimethylene sulfide, isopropyl
sulfoxide, N-acetyl pyrrolidine, N,N-dimethyl
acetamide, or mixtures thereof. Preferably, the
solvent is a mixture of at least 15% THF, the balance
being toluene, most preferably 60-75% THF and 25-~0%
toluene. The formulated solution of vinylidene
chloride copolymer then is applied to at least the
metal bearing surface of a polymer substrate,
preferably polyester, most preferably polyethylene
terephthalate, in an air drying, laboratory-scale
coating tower. The inlet temperature and the outlet
temperature of the coating tower may be in the ranqe
of 70 C to 130-C. Preferably, the inlet temperature
is 120-C and the outlet temperature is 80 c. q'he
coated polyethylene terephthalate is passed through
the coating tower at the rate of 30 to 90 feet per
minute, preferably 90 feet per minute.
The coated materials achieved by the
invention have properties which make them particularly
suited for use as packaging materials for foodstuffs
where deterioration due to oxidation and change of
moisture content is a concern. In the examples that
follow, properties are determined by the tests
described below.
Heat seal strength is measured by cutting
three samples of the coated metallized substrates that
measure l x lO inches. These samples are cut with the
grain or machine direction of the film running in the
long dimension of the sample. The samples are taken
from the east, west and center edges of the coated,
metallized substrate. Each sample is folded in half
in the machine direction. The halves of the sample
are sealed together at each end at right angles to the
grain by applying a 0.75 inch wide sealing bar under
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carefully controlled conditions of temperature,
pressure and contact time. The resulting three sets
of strips are tested by opening each set at the free
end, placing them in a Suter testing machine, and
pulling them apart while maintaining the folded end
perpendicular to the pull direction. The highest
force in grams required to pull the strips apart is
taken as a measure of the heat seal bond strength.
Heat seals are measured on the coated material as is.
The laminate bond strength is measured by
laminating a film sample to a 2-mil thick polyethylene
film by using an adhesive such as a two-component
curing type adhesive system. The adhesive coating
weight applied is typically 1-1.5 lb dry solids per
1~ ream. A heated pressure-nip roll is set at a
lamination temperature of 170-220-F, typically 215-F.
While preparing the laminate of sample film
to polyetherylene film, 15 or more sheets of release
paper are inserted between the film sample and the
polyethylene film at approximately 5 ft intervals to
provide non-bonded areas in the laminate in order to
assist initiation of delamination during bond strength
tests. Typically, the laminates are cured at 25C for
at least 7 days before being tested for bond strength.
After the laminates are cured, both sides
are reinforced from outside with a polyimide adhesive
tape to prevent the test films from tearing. Five
1 x 8 inch specimens per test are cut with the long
dimension parallel to the web direction. Samples are
obtained from various locations across the web width.
The laminate sample is tested "as is" for bond
strength, or tested after being moisture conditioned.
The moisture conditioning can be done in two
ways. Samples with the non-bonded starting area
exposed are conditioned in an enclosed dessicator at
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40-C for 1, 3, or 7 days, respectively. The bottom of
each dessicator is filled with water.
The laminate bond strength is recorded as
"grams per inch width" by pulling apart the two films
of the laminate (as separated by the release paper) in
a tensile machine while holding the tail of the
specimen at right angles to the direction of pull 50
that a constant shear peel is established. The bond
strength reported for one sample is typically an
average value of five film specimens tested under
duplicating conditions.
Without further elaboration, it is believed
that one skilled in the art can, using the preceding
description, utilize the present invention to its
fullest extent. The following preferred specific
embodiments are, therefore, to be construed as merely
illustrative, and not limitative of the remainder of
the disclosure in any way whatsoever. In the
following examples, all temperatures are set forth in
degrees Celsius; unless otherwise indicated, all parts
and percentages are by weight.
EXAMPLE 1
A. Preparation of the Formulated Solution -
The vinylidene chloride copolymer employed has the
following weight percentage composition: vinylidene
chloride 91.3, acrylonitrile 1.8, methyl methacrylate
6.9; A formulated solution of 90.64% of the
copolymer, 1.01% talc, 8.12% waxes, and a 0.23%
aromatic polyester resin is prepared in a solvent of
65% THF and 35% toluene. The mixture is heated to
40 C to 45 C until the polymer is dissolved. The
solid content of the bath solution is 18%. The
aromatic polyester resin used in the formulated
solution is prepared by trans-esterifying the
bis-(ethylene glycol) esters of terephthalic acid,
WO92/11952 ~ 9 2 ~ PCT/US92/OoO~
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isophthalic acid, adipic acid, and azelaic acid using
a tetraisopropyl titanate catalyst and following the
procedures of U.S. patent 2,892,747.
B. Coating of the Metallized Substrate - A
conventional solvent coating tower is used to apply
the formulated solution to both the metallized and
non-metallized surfaces of a 1/2 mil aluminized
polyethylene terephthalate film moving at 90 feet per
minute. The formulated solution is placed in a ~ip
tank maintained at 40-C and transferred to the
metallized polyethylene terephthalate by a doctor
roll. The doctor roll setting is 0.003 inches. Inlet
and outlet tower temperatures of the coating tower are
120C and 80-C respectively. Inlet and outlet tower
15 air supply is 250 and 300 cubic feet per minute
respectively.
The coating weight is determined by the
weight difference between the coated and uncoated
samples. The coated samples are tested for heat seal
and laminate bond strength properties both as is, and
after conditioning. Conditioning entails leaving the
samples in a dessicator for periods of either 24
hours, 72 hours, or 1 week. The bottom of the
dessicator is filled with water. The results are -
shown in Table 1.
EXAMPLE 2
The procedure of Example 1 is followed
except that the vinylidene chloride copolymer has the
following weight percentage composition: vinyiidene
30 chloride 90.5, methyl methacrylate 9.5. The heat seal
and laminate bond strength properties are shown in
Table 1.
EXAMPLE 3
The procedure of Example 1 is followed
except that the vinylidene chloride copolymer has the
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following weight percentage composition: vinylidene
chloride 90.9, methyl methacrylate 9.l. The heat seal
and laminate bond strength properties are shown in
Table l.
EXAMPLE 4
The procedure of Example l is followed
except that the vinylidene chloride copolymer has the
following weight percentage composition: vinylidene
chloride 91.6, acrylonitrile 4.0, methyl
methacrylate 4.4. The heat seal and laminate bond
strength properties are shown in Table l.
COMPARISON EXAMPLE l
The procedure of Example l is followed
except that the vinylidene chloride copolymer has tl1e
following weight percentage compositon: vinylidene
chloride 92.l, acrylonitrile 5.5, methyl methacrylate
2.5. The heat seal and laminate bond strength
properties are shown in Table l.
COMPARISON EXAMPLE 2
The procedure of Comparison Example l is
followed except that no coating additives are includec1
in the formulated solution. The vinylidene chloride
copolymer employed has the following weight percentage
composition: vinylidene chloride 92.l, acrylonitrile
5.5, methyl methacrylate 2.5. The heat seal and
laminate bond strength properties are show in in
Table l.
COMPARISON EXAMPLE 3
The procedure of Comparison Example 2 is
followed except that the vinylidene chloride copolymer
has the following weight percentage composition:
vinylidene chloride 90.5, methyl methacrylate 9.5.
The heat seal and laminate bond strength properties
are shown in Table l.
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TABLE 1
METALLIZED SIDE
COATING HEAT SEAL METALLIZED SIDE
WEIGHT STRENGTH LAMINATE BOND STRENGTH (gm/in)
(q/m2) (qm/in) AS IS CONDITIONED CONDITIONED
EXAMPLE
1 2.0 220 384 4671 3183
2 2.1 277 518 290l 6383
3 2.1 170 218 l92l 3763
4 2.1 293 443 4l9l 4413
COMPARATIVE EXAMPLE
1 2.4 57 120 432 353
. 2 2.6 177 275 1282 1333
3 2.3 167 344 2412 2193
d---l Ctr dfll~llnldn~le h~mpl ~ condltlon-d In ~ de~slc~tor ~t 40 C ~or 2~ hours -Bo~om o~
Cured lunln~ mpl ~ condltlon-d In de~lc~tor a~ 40 C for 72 ho~rs ao~o~n of
Cured l~mln~n ~mple~ condl~loned In ~ de~lc-~or ~t ~O C for I v~k aot~n of
d-~lc~o~ flll~d vl~h w ~
Table 1 shows that the heat seal and
laminate bond strength properties of the coated
metallized side improve significantly.as the quantity
of methyl methacrylate in the vinylidene chloride
copolymer contains at least 4% MMA or more. This
improvement occurs despite the presence of coating
additives.
From the foregoing description, one skilled
in the ,art can easily ascertain the essential
characteristics of this invention, and without
departing from the spirit and scope thereof, can make
various changes and modifications of the invention to
adapt it to various usages and conditions.
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