Note: Descriptions are shown in the official language in which they were submitted.
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Multilayar films with defined gas permeability and
their use as packaging material, in particular as
cheese-maturing packaging
The present invention relates to rnultilayer films which
are not used in the usual way to minimize permeability
to water vapor, gases, and aromas, but which have a
defined gas permeability and thus permit contents
packaged therein to enter into long-lasting, quality
retaining ec~uxlibrium with the external environment.
Very many products involved in daily life, and in
particular foods and drinks, are produced industrially
and packaged in an extremely wide variety of films
suitable for retaining the desired properties of the
respective contents fox the longest possible period of
time. The expiry date (ED) here is defined as the
day/month/year before which a packaged product is fully
satisfactory for use or consumption.
Prior art referred to is Joachim Nentwig: Kunststoff-
Fvlien [Polymer fzlms], Carl-Hanser Verlag 1994,
Munich, in relation to polymer films, Dr.Ing. Klaus
Stoeckhert: Polyamide, Polyamidfolien 'und lPolyamid-
verbundfolien [Polyamides, ~polyamide films, and
polyamide composite films], Neue Verpackung 8/1984, in
relation to polyamide films, H. wagner and P. Heckmann:
Orientierte Polypropylenfolien [Oriented polypropylene
films], Neue Verpackung 2/1979, in relation to
polypropylene films, and Dipl.-Ing. Hermann Hinsken:
Kunststoff-Verbundfolien [Polymer composite ~ilmsJ,
Neue Verpackung 2/1990 in relation to polymer composite
films_ f
Hot-sealable packaging films are used far producing
packaging which is intended for food or drink and wh~.ch
serves for the storage, the distribution, and the
hygienic self-service packaging of food or drink,
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different foods and drinks hors placing different
requirements upon the gas-permeability of the packaging
fzlms to be used. .
For example, the packaging of potato chips requires a
packaging film impermeable to water vapor, in order to
retain crispness. Baguettes or rolls packed under an
inert gas atmosphere need gas-tight packaging, so that
the inert gas is retained as fungistat, and so that
there is no C02 loss leading to a pseudovacuum which
deforms the product.
Composite films comprising a gas-barrier layer and
having oxygezx permeability < 2.0 cm~/m2 x day x bar have
proven successful for this purpose.
Particular requirements axe also placed upon the
industrial packaging of cheese in the form of pieces,
slices, or in ground or grated form, in particular when
the cheese-maturing process, the duration and intensity
of which differs according to type, lasts beyond the
moment of packaging, meaning that the cheese continues
to mature within the packaging, whereupon hermetically
sealed packaging would inflate as a result of evolution
of carbon dioxide.
Composite films suitable for this type of packaging are
composed of a, where appropriate, printed biaxially
oriented polyamide layer (PAB) as backing film with a
thiclazess of 12 or 15 dun, and of olefinic sealable
layers of thickness from 35 to 60 dam, the oxygen
permeability of which is from 30 to 50 cm3/m2 x day x
bar. For types of cheese from which gas evolution is
particulaz-ly marked, or fox products known to have a
short expiry time, biaxially oriented polyester films
(PET) are us~d instead of PAB backing films, the
resultant oxygen permeability being about 90 cm3/m2 X
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day x bar, the increased risk of fracture on creasing
being accepted here.
since biaxially oriented polyamide films are relatively
S expensive and, in particular when used as a backing
film, have disadvantages due to their hygroscopic
properties, there is a requirement fox replacement
packaging material which does not have these
disadvantages, for use in the cheese-packaging industry
in particular.
It was therefore an object of the present invention to
provide a packaging material, in particular packaging
films which have defined gas permeability and which are
suitable for packaged goods which evolve gases, for
example foods and drinks which continue to mature, in
particular cheese, and which do not have biaxially
oriented polyamide films as backing films, where the
entire packaging film is intended to have defined
oxygen permeability which depends on the contents, and
which is intended to be in the range c 100 crn°/m2 x day
x bar, particularly preferably in the range from 30 to
50 cm'/m2 x day x bar .
According to the invention, this object is achieved by
providing a multilayer film which comprises at least
a) one sealable layer as surface layer,
b) a layer with ~a layer thickness < 10 ~,un and based
on a semicrystalline polyamide mixture made from
m-xylylenediamine adipate and from an aliphatic
polyamide comprising dispersed, solid,
anisotropic, nano-scale, nucleating fillers which,
when the number average over all of the dispersed
fillers is taken, measure not more than 10 nm in
one of their dimensions and measure at least
100 nm in at least one other dimension and
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c) a backing layer made from plastic, with the
exception of a biaxially or~.ented backing layer
made from polyamide.
S The total thickness of the multilayer film of the
invention is preferably from 30 to 90 ~,un, particularly
preferably from 40 to 70 ).tm, where the layer b) made
from the polyamide mixture comprising the nano-scale
particles is [siG] preferably from 2 to 7 pm,
particularly preferably from 3 to 5 dun.
The multilayer films of the invention have defined
oxygen permeability < 100 cm3/m2 X day x bar, preferably
in the range fram 20 to 60, particularly preferably
from 30 to 50, cm3/m2 x day x bar. xt was entirely
surprising that this could be achieved using the
multilayer film structure of the invention comprising
the layer b) as barrier layer with a layer thickness
below 10 um, since, in contrast, when using biaxially
oriented polyamide backing films, similar: oxygen
permeability can only be achieved using the greater
layer thickness usually used for cheese packaging.
Layer c), the backing layer, may comprise the usual
plastics used for producing backing films, preferably
polyesters, such as polyethylene terephthalate, or
polyolefins, such as polypropylene.
The backing film preferably has biaxial orientation.
The backing film is preferably transparent. The layer
thickness is preferably from 10 to 25 um, particularly
preferably from 12 to 20 fun. That surface of the
backing film facing away from the remainder of the film
composite zaay have a sealable layer, preferably a hot-
sealable layer, which may be identical with the
sealable layer a).
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The sealable layer a) is pregerably a hot-sealable
layer which forms one surface layer of the multilayer
film of the invention. The layer a) is preferably
composed of polyolefins, particularly preferably of
polyethylene, of polypropylene, of an ethylene
propylene copolymer, of a mixture of polyolefins, of an
olefinic terpolymer, of a mixture of the polymers
mentioned, very particularly preferably of linear iow
density polyethylene (LLDPE), where appropriate mixed
with palybutene, or of polyvinyl acetate.
Each of the surfaces of the layer b) of the multilayer
film of the invention, which has a layer thickness of
c 10 dun, preferably a layer thickness of from 2 to
7 dun, has at least one adj scent layer, meaning that the
layer b) has no uncovered surface. The layer b) is
based on a semicrystalline polyamide mixture made from
m-xylylenediamine adipate and from an aliphatic poly-
amide, and has nano-scale, solid, anisotropic particles
dispersed therein and acting as nucleating fillers. The
dispersed nucleating fillers are preferably solid,
anisotropic particles which, when the numbex average is
taken for all of the dispersed particles, measure not
moxe than l0 nm in at least one freely selectable
dimension, preferably for every dispersed particle. It
is particularly preferable that the measurement of
these particles in at least one other dimension is in
the range from at least 100 nm to at most 1,000 nm.
Particular preference is given to the use of latnellar
particles whose thickness is < 10 nm, e.g.
phyllosilicates. These may have been selected from the
group consisting of phyllosilicates such as magnesium
silicate or aluminum silicate, montmarillonite,
saponite, beidellite, nontronite, hectorite,
stevensite. vermiculite, halloysite, and synthetic
analogues of these.
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The at least semicrystalline polyamide mixture ~.s
preferably composed of, based on the entire mixture of
the polyamides, from 60 to 98$ by weight, with
preference from 65 to 85~ by weight, of a semiaromatic
polyamide whose structure is composed of m-
xylylenediamine and adipic acid and, based on the
entire mixture of the polyamides, from 2 to 40$ by
weight, preferably from 15 to 35~ by weight, of an
aliphatic polyamide, such as nylon-6, nylon--11, nylon-
12, nylon-6, 6, nylon-6, 10, nylon-6/5, 6, particularly
preferably nylon-6, xhe layer b) comprises, based on
the aliphatic polyamide component, in each case S 10~
by weight, preferably from 1 to 5~ by weight, of nano-
scale, nucleating, solid particles, which are
particularly preferably added at an early stage during
the preparation of the respective aliphatic polyamide.
For reasons associated with process technology, each
surface of the layer b) preferably has a layer a) which
bas been bonded to the layer b) by way of an adhesion-
promoter layer, to increase adhesion. The adhesion-
promoter layer is preferably coextruded, and is
preferably based on a malefic-anhydride-grafted
polyethylene. To bond this composite to the respective
backing film c), it is preferable to use a solvent-free
polyurethane adhesive as adhesion promoter, preferably
applied at a layer thickness below 5 dun.
The backing film may moreover be a pigmented, printed,
or unprinted film, and the printing method here may use
a gravure printing machine or a flexel (sic] printing
machine. The print is preferably not arranged on the
external surfac~.
The multilayer film of the invention may be produced by
known techniques, such as adhesive lamination, sandwich
coating, or extrusion coating, and the backing film
here is preferably combined with the remainder of the
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film composite produced in a separate step of the
process_
This can be produced with the aid of multilayer blown-
film, flat-film, or coating or extrusion lamination
systems, preference being given here to blown or flat
film coextrusion.
The multilayer films of the invention having defined
gas permeability, i.e. barrier function, within a
certain gas permeability range, give excellent results
when printed, since the level of hygroscvpic properties
of the barrier layer has been minimized, and provide
the necessary retention of pattern-repeat distance and
register, and in particular in combination with a
biaxially oriented polypropylene backing film, has
reduced water-vapor permeability and thus reduced loss
in weight from a product packaged therein, and the
multilayer films of the invention are therefore
particularly suitable as packaging material, very
particularly preferable as packaging material for foods
or drinks which evolve gases; e_g. cheese.
The present invention therefore also provides the use
of the multilayer films of the invention as a packaging
material, preferably for foods or drinks which evolve
gases, in particular as a packaging material for
cheese.
The present invention also provides a packaging made
from a multilayer film of the invention for foods ox
drinks which evolve gases, preferably cheese, very
particularly preferably a packaging for maturing
cheese. This packaging may be produced on either
horizontal or vertical automatic packaging machines
with the aid of the multilayer films of the invention.
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Test methods
Oxygen permeability is determined in accordance with
the draft of DIN 53380, Part 3, 3uly 1989 issue, using
the carrier gas method. It is defined as the Nml
quantity of oxygen which diffuses in 24 hours through
one square meter of film under a pressure difference of
one bar at a prescribed temperature and humidity.
It is measured using the Oxtran 100 device from Mocon
Instrument Laic]. Unless otherwise specified, oxygen
permeability is stated in cm'/ma*d*bar at 23°C and 75~
relative~humidity td = day).
mhe haze stated is the quantity of light in ~ which is
reemitted in the form of scattered light after the film
has been illuminated by a central beats, based on the
entire amount of transmitted light. The test uses
Procedure A of the RSTM test standard D 100361.
The seal strength determined is the force ~.x~; N, based
on the test strip width of 15 mm, required to split a
seal seam produced under defined conditions (pressure,
temperature, time).
Seal3.ng conditions: pressure 5 N/cm2 [sic], time 0.5
sec, temperature from 105 to I70°C, in steps of five
Kelvin.
Test ecLuipment: Brugger sealer
Test strip cutter with cutting width 15 mm tensile
strength testing machine with measurement range 10 N
and separation velocity 100 mm/min.
Examples
.All of the substances ment3.oned axe commerc:Lally
available traded products.
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Example 1
An 8-layer blown-film extruder is used to caextrude a
mixture of, based on the entire mixture of the
polyamides, 80~ by weight of a polyamide composed of m-
xylylenediamine az~d adipic acid (PA 1~D6) and, based an
the entire mixture of the polyamides, 20~c by weight of
nylon-6 which, based on nylon-6, [lacuna] 2$ by weight
of a lamellar aluminum phyllosilicate as a central
layer b) of thickness 4 ym embedded between, in each
case, an adhesion-promoter layer and a layer a)
composed of linear low-density polyethylene. The melt
temperature was 270°C, and the expansion ratio far the
coextruded blown film was 1:1.6.
The resultant blown film, separated to give two webs,
electrically pre-treated on one side and Wound up, was
laminated an a commercially available laminating
system, using a solvent-free polyurethane adhesive
(Primacor 1420 from DOW) to a polyethylene
terephthalate (PET) backing film with a th:Lckz~ess og
12 ym or to a biaxially oriented polypropylene (BOPP)
backing film with a layer thickness of 15 dun or to a
polypropylene backing film coextruded with a sealable
layer composed of polyethylene and biaxially stretched,
with a thickness of 20 um.
The methods stated above were used to determine the
oxygen permeability, the haze, and the seal strength of
the resultant multilayer films of the invention. The
appropriate values can be found in Table 1 below.
Structure of blowxa film A
LLDPE Adhesion B0~ by weight PA MXD 6*, Adhesion LLDPE
of
15 promoter 20~ by weight of nylon-6 promoter 23
a tun
4 jun with 2% by weight of 4 ~.ua
nano articles 4
**
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*MXD 6-6121, Mitsubishi
** Nanaparticles of aluminum silicate
LLDPE - lineaz~ low-density polyethylene
Table 1
Backing Blown Oxygen Haze Seal
film film erm. stx.
PET 7.2 A 37 7 23 +
BOPP 15 A 42 8 25 +
Coex gOPP A 44 9 26 +
2 0 ~1m
+ suitable for cheese packaging in any forza
PET ~ polyethylene terephthalate
30 BOPP = biaxially oriented polypropylene
Coex Bopp ~- biaxially oriented coextrudate with a hot-
sealable polyethylene layer of thickness 5 dun
Comparative Example 1
The type of commercially availabl~ packaging film
usually used for cheese packaging, composed of
biaxially oriented polyamide (PAHy and of a sealable
layer composed of linear low-density polyethylene
exhibits the values stated in Table 2 far oxygen
permeability, haze, and seal strength, these having
been determined by the methods stated above.
Table 2
Backing Sealable Oxygen Haze Seal
film la er perm. str.
PAB 15 um LLDPE 42 8 32
50
suitable for cheese packaging in any fount
