Note: Descriptions are shown in the official language in which they were submitted.
1 23189-6435
Printable proP~lene-E~ _r based m_~ yer fllms_for packa~
The present lnventlon relates to multi-layer fllms which
are partlcularly suitable for use as packaging films, because they
have an adequate seal strength at relatlvely low seallng tempera-
tures.
Xt ls known that multi-layer fllms based on a polypropy-
lene film and sealing layers composed of polymers such as ionomer
reslns (for example Surlyn~) seal at relatively low temperatures
to glve an adequate strength. Thls also applies to multl-layer
films contalnlng sealing layers composed of ethylene/vlnyl acetate
copolymers.
However, both of the known multl-layer fllms have the
dlsadvantage that they no longer seal to glve adequate strength
after an electrical pretreatment necessary for the printlng of
fllms. Even if only one sealiny layer of a multi-layer film which
can be sealed on both sides ls sub~ected to electrical pretreat-
menk, the multl-layer film pretreated in this way can no longer be
used for a large number of types of packaglng involving wrapping,
namely not in the case of types of packaging ln which lt is
necessary to effect the sealing of a pretreated film surface to a
pretreated or non-pretreated fllm surface.
Surprisingly, the provlsion o~ the multl-layer ~ilms
according to the invention, whlch have an asymmetric structure,
has now made it possible to eliminate these disadvantages and to
make available multi-layer fllms which can be prlnted and sealed
without problems.
The present lnventlon therefore relates to heat-
sealable, at least monoaxially oriented multi.-layer films which
can be, if desired, printed and have an asymmetric structure,
composed of a film comprising, preferably consisting of a propy-
lene polymer as the base layer and two outer sealing layers~ of
whi.ch one sealing layer (1) comprises, preferably conslsts of an
ionomer resin or an ethylene/vinyl acetate copolymer and, if
appropriate, acrylic acid derivatlves, and the other sealing layer
(2) comprises, preferably
., ~
~3~ 9~94
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c~nsis~s o~ a copolymer formed fr~ e~hylene/arrylic
acid and, i~ appropria~e, acrylic acid derivatives, ~his
sealing layer being, if desired, prin~able.
Asyme~ric s~ruc~ure means ~ha~ ~he Lwo ou~er
sealing layers differ in ~heir chemical composition.
Py virtue of this asymmetric structure, these
multi-layer films according to the ;nvention produce seals
having adequate seal strength at relatively low tempera-
tures, even ~f they have been printed on one of their
surfaces.
The base layer of the sealable multi-layer films
according to the invention consists essentially of a pro-
pylene polymer containing uP to not more than 10~ by
~e;ght of a further ~-olefin having not more than 8 carbon
atoms, preferably ethylene.
It is preferable to employ an isotactic polypro-
pylene having a density of 0.9-0~91 g/cm3 and a melt index
of 1-4 9/10 minutes at 230C/ 21.6N (as specif;ed in DIN
53,735). The base layer can conta;n 3-15~ by weight,
preferably 8-12~ by weight, of an acldit;ve which ;s incom-
patible ~ith the propylene polymer, preferably an inor-
ganic additive, such as calcium carbonate, silicon dio~ide,
sodium aluminium silicate and/or titanium dioxide, whereby
an opalescent film is achieved.
Ionomer resins which can be employed for the pro-
duction of the sealing layer ~1) are the known
copolymers formed from -olef;ns, ,B-unsaturated mono-
carboxylic acids and, ;f appropriate, clerivatives of these
~,B-unsaturated monocarboxyl;c acids, preferably anhy-
dr;des, am;des or esters of lower aliphatic alcohols, the
carboxyl groups having been neutralized at least to the
extent of 10 mol% with metal ions~ Ions suitable for
salt formation are, in particular, monovalent, divalent
~5 and trivalent ions of metals of group I to III, IVa and
VIII of the periodic system of the elements (compare
"Handbook of Chemistry and Physics", Chemical Rubber
Publishing C~., 37th editi~n, paye 392).
Suitable monovalent metal ions are sc,dium,
5251
`` 131~3094
3 23189-6435
potassium, llthlum, caesium, sllver, mercury and copper. Suitable
dlvalent metal ions are berylllum, magnesium, calcium, strontlum,
barium , copper, cadmlum, mercury, tin, lead, iron, cobalt, nickel
and æinc. Suitable trivalent metal ions are aluminlum and iron.
It is preferable to use zinc lons and/or sodium ions for neutrali-
zatlon. The ionomer resln should consist of at least 50 mol% of
an ~-olefin, preferably ethylene. Preferred ionomer reslns con-
tain l to 25 mol% of the a,~-unsaturated monocarbo~ylic acid, at
least 10%, preferably 30%, of the carboxyl groups havlng been
neutrallzed by metal lons. Copolymers whlch are partlcularly
suitable for the productlon of the multi-layer fllms accordlng to
the lnventlon are those whlch have been formed from more than 80
mol% of ethylene and less than 20 mol% of acrylic acld and, if
appropriate, acryllc acld derlvatlves and whlch have been neutra-
llzed to the extent of at least 10%, preferably at least 30%, with
zlnc ions (Surlyn 1705~).
It ls also possible to use as the seallng layer (1)
material ethylene/vlnyl acetate copolymers in whlch the vinyl
acetate content ls 2-10% by welght, preferably 6-9% by weight, and
whlch have a melt index wlthln the range of 0.5-3 g~10 mlnutes at
190C/21.6 N (DIN 53,735), preferably wlthln the range of 1-2 g/10
mlnutes.
Copolymers formed from ethylene/acryllc acld and, if
approprlake, acrylic acld derivatives, such as acrylonitrile or
acrylic acld esters of lower allphatlc alcohols lCl-C4), are used
for the productlon of the seallng layer (2) whlch can also be
electrlcal dlscharge treated wlthout loslng lts sealablllty. The
copolymers used for seallng layer (2) are no or essentlally no
lonomer reslns. That means that the carboxyl groups are not or
essentially not neutra].lzed.
The copolymers preferably contain 1-20% by welght of
acryllc acld and, if appropriate, acrylic acld derivatives, ln
partlcular 3-10~ by weight of acryllc
. ~
1319094
acid and, if ~ppropria~e, acrylic acid deriva~ives. I~
is par~icularly preferable ~o employ copolymers
con~aining 6-9% by weigh~ of acrylic acid. Th~ m~lL
index of ~he sealing layer ma~erials should be wi~hin
~he range from 1 ~o 20~ preferably 3 to 15 and
par~icularly pref~rably 5 10, g/10 minu~es a~ 190Cl21.6
N, measured as specified in DIN 53,735.
Apart from the base layer and the outer sealing
layers, the multi-layer films according to the ;nvention
can also contain further layers, such as a gas barrier
layer and, if appropriate, adhesion-promoting layers.
Polymers which can be used for the product;on of the gas
barrier layer are the kno~n polymers, preferably ethylene/
vinyl acetate copolymers composed of 40 to 85 ~ol%, pre-
ferably 60 to 75 molZ, of vinyl acetate units which have
been saponified to the extent of at least 90%, preferably
more than 95 molZ. The ;ntrinsic viscosity values ~n] of
the polymers~ determined in a solvent mixture consist;ng
of 85% by weight of toluene and 15~ by ueight of water,
should pre~erably be between 0.07 and 0.17 l/g, part;cu-
larly preferably between 0.09 and 0.15 llg.
Polymers ~h;ch can be used for the production of
the gas barrier layer, in particular a barrier layer for
~5 o~ygen and/or aromas, are not only the ethylene/vinyl
alcohol polymers indicated, but also further polymers
having gas barrier properties, such ~sO for example, poly-
vinyl alcohol or polyamides. M;xtures of ethylene/vinyl
alcohol copolymers such as have been descr;bed above and
10-60~ by weight of the polymers ment;oned are particu-
larly su;table. Suitable polyamides are, in particular,
polyamide b and polyamide 12.
Suitable mixt~res are also mixtures such as those
described in EP 0,064,330 A 1 and EP 0,063,006 A 1, in
which mixtures of ethylenetvinyl alcohol copolymers and
polyamides containing, in addition, suitable plastic;zers
are used for the product;on of the gas barrier layers~
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~3~l9094
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If the multi-layer films accorcling to the inven-
tion do contain gas barrier layers, as a rule aclequate
lamination adhesion is only achieved with the help of
adhesion-promot;ng ~ayers. It is preferable to employ
modified polyolef;ns for the product;on of such adhes;on-
promot;ng layers. These are, in particular, homopoly
olefins or copolyolefins containing carboxyl groups, such
as, for example, polypropylene or polyethylene containing,
grafted on, at least one monomer from the group compris-
ing r~B-monounsaturated dicarboxylic acids, such as~ for
example, maleic acid, fumaric acid or itaconic acid or
anhydrides, esters, am;des or imides thereof. Other
suitable copolymers are copolymers of ethylene with r~,B-
unsaturated carboxylic acids, such as acrylic acid ormethacrylic acid, and/or metal salts thereof ~zinc or so-
dium) and/or alkyl-tC1-C4) esters thereof or corresponding
graft polymers of the monomers mentioned on polyolefins,
such as polyethylene or polypropylene, or partially sapon-
ified ethylene/vinyl acetate copolymers which ha~e op-
tionally been graft-polymeri~ed with a monomer of the
acids mentioned above and which have a low degree of
sapon;fication, or mixtures thereof.
It is particularly preferable to use, for the pro-
duction of adhesion-promoting layers, polyoLefins, such
as poLypropylene or copolymers of propylene and ethyLene
containing not more than 1X by weight of grafted-on mono-
unsaturated dicarboxylic acid anhydrides, such as maleic
anhydride, or saponif;ed copolymers thereof, if appro-
priate mixed with polyoLef;ns.
The adhesion-promoting polymer can also be incor-
porated ;nto the sealabLe layer or into the gas barrier
layer. It is possibLe to impart a finish to the layers
of the muLti-layer f;lms accord;ng to the invention using
customary add;t;ves and auxiliaries, such as, for example,
slip agents, anti-bLocking agents and antistatic agents,
in customary amounts.
Thus ;t is possibLe to empLoy poLydiorganosiloxanes
or mixtures thereof having a kinematic viscosity of at least
100 mm2/second at 25C. Suitable polydiorganosiloxanes are
polydialkylsiLoxanes, polyalkylvinylsiloxanes, olefin-
~ 5251
i319094
-- 6 --
modified siloxane oils, polyether-modified siloxane oils
and olefin/polyether-mod;fied silicone oils, ethoxy-
modified silicone oils and alcohol-modified silicone
oils, and polydialkylsiloxanes having, preferably, C1-C4
in the alkyl group.
Polydime~hylsiloxane is particularly suitable.
The polydiorganos;loxanes should preferably have a kine-
matic viscosity of at least 105 mm2/second at 25C, par-
ticularly preferably at least 106 mm2/second. It is also
possible to employ, for imparting a finish to the layers,
the knovn unsaturated fatty acid amides, saturated fatty
acid amides, such as, for example, stearamide or erucamide,
and also the thermoplastic polymers ~hich are incompatible
with the polymers of the layer materials, such as, for
e~ample, polyamide 12, or ;norganic spacing matèrials,
such as SiO2 or CaC03~ and/or antistatic compounds, such
as long-chain, aliphatic, tertiary amines which can, if
appropriate, be monounsaturated, such as ethoxylated ter-
tiary amines, particularly preferably an N,N-bis-(hydroxy-
ZO ethyl)-tC12-C16)-alkylamide.
The multi-layer films according to the invention
can be produced by a customary process, such as lamination,
coating and/or melt (co)extrusion.
The multi-layer films according to the invention
are at least monoax;ally oriented; preferably, they are
subjected to biax;al stretching. In this regard, the
longituclinal stretching is preferably carr;ed out in a
ratio of 5:1 to 7:1 and the transverse stretching in a
ratio of 7:1 to 10:1.
The multi-layer films according to the invention
preferably have a total thickness of 19-100 ~m~ particu-
larly preferably 20-50 ~m, it being necessary for the base
Layer to have a thickness of 20-50 ~m and the heat-sealable
layers to have, preferably, a thickness of 0.8-2 ~m, par-
ticularly preferably 1.2-1.5 ~m.
The multi-layer films according to the invention
W~ 5251
~3~9~9~
are particularly suitable for use as packag;ng material,
in particular as wrapp;ng films, preferably for foodstuffs,
and they can be pr;nted and prov;ded with peel;ng strips
for this purpose.
In the examples which follo~, the follo~ing test
methods were used to determine the values:
The haze was determined as specified in ASTM D 1003 - 52.
The gloss of the film was determined by using a photo-
electric glossmeter devised by Dr. B. Lange, Berlin, con-
sisting of a low-voltage incandescent lamp and a condensing
lens rhich illuminates the samPle at an angle of less than
45, and a second leg at an angle of less than 45 to the
plane of measurement, fitted with a diaphragm aperture and
a photocell. An indicator device ~microammeter) which is
capable of fine regulat;on and which also contains the
current supply and the automatic voltage regulator for the
incandescent lamp is connected. The gloss is defined as
the percentage proportion of light reflected in a conven-
tional manner at an angle of less than 45, relative to a
surface-silvered mirror as a 100% standard. When testing
the gloss, a polished black sheet of glass is placed on
the glossmeter as an intermedia~e s;tandard, because the
silvered mirror standard is not resistant in tarnishing
caused by atmospheric pollution. This sheet has exactly
5% of the gloss of a surface-s;lvered sheet ~f mirror
glass .
The galvanometer reading of the photoceLl of the
glossmeter is adjusted by means of the control poten-
tiometer via the black glass intermediate standard, in
order to increase the accuracy of reading the graduation
of the scale. The film to be tested is laid flat under
the glossmeter, above matt black photographic paper,
transversely to the direction of running, relative to the
optical axis of the glossmeter, and measurements are car-
ried out at five satisfactory points. The gaLvanometerreading is divided by 1û and the average value is
WW 5251
~319~9~
calculated.
The strength of the seals is determined by test;ng
their seal strength at a sealing pressure of S0 N/cm2. In
this context, seal strength ;s to be understood as meaning
the force required to separate a seal produced under def-
inite conditions ~50 N/cm pressure and a duration of
seal;ng of 0.5 seconds) at the temperatures indicated in
Table 1n The seal strength is quoted in N and relates to
a test strip 15 mm wide.
The scratch resistance is determined by measuring
the haze deter~ined when using the Ulbricht globe. In
this determination, the haze of a film is measured before
and after scratching. The scratch;ng is effected by means
of 40 9 of dust-free silicon carbide, which is sprinkled
~ithin a definite time snto a film inclined to the hori-
zontal at 45.
Example 1
A sealing layer composed of an ethylene/acrylic
acid copolymer in which the carboxyl groups have been neu-
tralized with zinc ions is applied by a conventional pro-
cess to one surface (A) of a base film composed of poly-
propylene of density 0.905 g/cm3, melt index 3.3 9/10 min-
utes at 230C/21-6 N and melting range 160-166C, and an
ethylene/acrylic acid copolymer containing 3 mol% of
acrylic acid is applied to the other surface (~), and the
laminate is stretched so that a composite film is obtained
~hich has been stretched longitudinally by a rat;o of 5:1
and stretched transversely by a ratio of 10:1.
The base films have a th;ckness of 17.4 ~m and the
sealing layers each have a thickness of 1.3 ~m.
Before the seal s~rength, the gloss and the scratch
resistance are determined, the sealing layer consisting
of the ethylene/acrylic acid copolymer is subjected to
electrical pretreatment (corona treatment). The experi-
mental results are entered in Table 1.
~ 5251
131909~
Example 2 (comparison)
~. ~
A multi-layer film is produced as indicated in
Example 1, but both surfaces of the base film composed of
polypropylene are furnished w;th an ethylene/acrylic acid
S copolymer in which ~he carboxyl groups have been neutral-
ized with zinc ions. A sealing layer is again subjected
to electrical pretreatment analogously to Example 1. The
experimental results are entered in Table 1.
WW 5Z51
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