Note: Descriptions are shown in the official language in which they were submitted.
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Paper-type plastic film
The present invention relates to synthetic paper made from a coextruded,
biaxially oriented plastic film having improved initial tearability and
controllable
s tear propagation ability. The invention furthermore relates to a process for
the
production of the synthetic paper.
The success of biaxially oriented plastic films, in particular films
comprising
thermoplastic polymers and especially biaxially oriented polypropylene films,
is
io essentially based on their excellent 'rnechanical strength properties in
combina-
tion with comparatively low weight, good barrier properties and good weld-
ability. The polyolefin film protects the packed goods against rapid drying-
out
and against loss of aroma while using a very small amount of material.
15 What stands in the way of the consumer's need for hygienic, visually appeal-
ing, tightly sealed and robust packaging is the desire for easy and
controllable
opening. The latter is increasingly the subject of consumer complaints in the
case of packaging comprising polyolefin films and is regarded as a disadvan-
tage compared with paper packaging.
Uniaxially oriented films, such as, for example, tape products, exhibit
distinctly
low initial tear strength and/or a high tendency to split in the orientation
direction, and can therefore readily be torn initially and torn further in a
controlled manner in this direction. However, uniaxially oriented films are
unsuitable for many application areas, inter alia owing to deficient
mechanical
strengths in the transverse direction. The process of biaxial orientation
generates on the one hand the desired high strengths (moduli) in both
dimensions; on the other hand, however, the preferential directions are also
partially levelled out as a consequence of the process. This has the
consequence that, in order to open film packaging (for example cookie bags), a
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high force initially has to be overcome in order to tear the film. However,
once
the film has been damaged or partially torn, a tear propagates in an uncontrol-
lable manner, even on application of very low tensile forces. These deficient
service properties of excessively high initial tear strength and
uncontrollable
tear propagation behaviour reduce the acceptance of film packaging as a
replacement for paper in the end consumer market, in spite of the advantages
mentioned at the outset.
An attempt to solve this problem starts at the seal seam of the film
packaging.
to Thus, for example, EP 95/P003 describes a film which, instead of a heat-
sealing layer, has a peelable layer and in addition a special layer structure.
This makes it possible to re-open the film packaging in a controlled manner
where it was originally sealed, namely in the seam. This predetermined
breaking point provided is intended to prevent tears propagating in the film
in
an uncontrolled manner during opening.
A further solution that has been proposed is a multilayE:red structure with a
predetermined breaking point, i.e. with a layer which has particularly low
mechanical strength. On opening, the film initially tears at this
predetermined
2o breaking point. The tear propagates only in the weak layer. This principle
is
implemented both in the case of coextruded films and in the case of
multilayered laminates.
A further known possible solution is subsequent mechanical incorporation of a
predetermined breaking point in the form of a perforation cir notch.
In some cases, a tear-open tape (usually polyester) is used in order to
facilitate
controlled opening of the packaging. This solution is very expensive and has
therefore not become established everywhere on the market.
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The object of the present invention was to provide
a synthetic paper which combines the advantages of a
biaxially oriented plastic film with paper-like initial tear
and tear propagation behaviour. No additional measures such
as a tear-open tape or notch or a complex layer structure
should be necessary.
The object on which the invention is based is
achieved by a biaxially oriented polymer film having at
least one layer, where this layer is a fibre-containing
layer which is built up from a thermoplastic polymer and
contains natural fibres, polymer fibres or mineral fibres.
According to one aspect of the present invention,
there is provided a biaxially oriented polymer film
comprising at least one layer, wherein this layer is a
fibre-containing layer which is built up from a
thermoplastic polymer and contains cellulose fibres, cotton
fibres, polypropylene fibres, polyethylene fibres, polyester
fibres, polyamide fibres, polyimide fibres, wollastonite
fibres or fibres comprised of calcium silicate.
According to another aspect of the present
invention, there is provided a biaxially oriented polymer
film comprising at least one layer, wherein this layer is a
fibre-containing layer which is built up from a
thermoplastic polymer and contains natural fibres, polymer
fibres or mineral fibres, wherein the mineral fibre is not
asbestos fibre or glass fibre and wherein the thermoplastic
polymer is a polyolefin.
According to still another aspect of the present
invention, there is provided a method for producing the
polynler film as defined herein, wherein a mixture of
thermoplastic polymer and fibres is extruded on a cooling
roller to obtain a pre-film, and the pre-film is heated and
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stretched in longitudinal direction and transverse
direction.
According to yet another aspect of the present
invention, there is provided a use of the polymer film as
defined herein as a packaging film, a labeling film, a
laminating film or a metallizable film.
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Mineral fibres of asbestos or glass fibres, in particular long glass fibres,
are
excepted. The former are ruled out owing to their potential risk
(carcinogeneity,
respirability) for employees of film manufacturers and processors, the latter
are
disadvantageous owing to their high abrasiveness and the consequent wear of
1s machine parts.
The paper-like film can be made translucent to transparent or in the form of
an
opaque film, depending on the proposed application. For the purposes of the
present invention, "opaque film" means a non-transparent film whose light
zo transmission (ASTM-D 1003-77) is at most 70%, preferably at most 50%.
At least one layer of the films according to the invention contains mineral
fibres, such as wollastonite or polymer or natural fibres. This fibre-
containing
layer of the film, which contributes to the paper-like tear behaviour, is
built up
zs from thermoplastic polymers.
Possible thermoplastic polymers for the polymer matrix of the fibre-containing
layer are polyimides, polyamides, polyesters, PVC or polyolefins made from
olefinic monomers having from 2 to 8 carbon atoms. Particularly suitable are
30 polyamides and polyolefins, of which propylene polymers, ethylene polymers,
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butylene polymers, cycloolefin polymers or copolymers c:omprising propylene,
ethylene and butylene units or cycloolefins are preferred. In general, the
fibre-
containing layer comprises at least 50% by weight, preferably from 70 to 99%
by weight, in particular from 90 to 98% by weight, of the ttiermoplastic
polymer,
s in each case based on the weight of the layer.
Preferred polyolefins are propylene polymers. These propylene polymers com-
prise from 90 to 100% by weight, preferably from 95 to 100% by weight, in
particular from 98 to 100% by weight, of propylene and have a melting point of
120 C or above, preferably from 130 to 170 C, and generally have a melt flow
index of from 0.5 g/10 min to 15 g/10 min, preferably from 2 g/10 min to
10 g/10 min, at 230 C and a force of 21.6 N (DIN 53 735). Isotactic propylene
homopolymer having an atactic content of 15% by weight or less, copolymers
of ethylene and propylene having an ethylene content of 10% by weight or
ts less, copolymers of propylene with Ca-Ca-olefins having an olefin content
of
10% by weight or less, terpolymers of propylene, ethylene and butylene having
an ethylene content of 10% by weight or less and having a butylene content of
15% by weight or less are preferred propylene polymers for the core layer,
particular preference being given to isotactic propylene homopolymer. The
stated percentages by weight are based on the respective polymer.
Also suitable is a mixture of the said propylene homopolymers and/or
copolymers and/or terpolymers and other polyolefins, in particular made from
monomers having from 2 to 6 carbon atoms, where the mixture comprises at
least 50% by weight, in particular at least 75% by weight, of propylene
polymer.
Suitable other polyolefins in the polymer mixture are polyethylenes, in
particular HDPE, LDPE, VLDPE and LLDPE, where the proportion of these
polyolefins does not exceed 15% by weight, based on the polymer mixture, in
each case.
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Besides the thermoplastic polymer, the fibre-containing layer of the film
contains fibres in an amount of at most 50% by weight, preferably from 0.5 to
10% by weight, in particular from 1 to 5% by weight, based on the weight of
the
fibre-containing layer.
Various materials are basically suitable for the fibres. Suitable fibres are
those
made from thermoplastic polymers, from crosslinked thermoplastic polymers,
amorphous polymers, semi-crystalline polymers, stabilised natural fibres or
crystalline mineral fibres.
Fibres made from thermoplastic polymers, such as polyolefins, polyethylenes,
polypropylenes, cycloolefin polymers, copolymers, polyesters, polyamides,
polyimides or polyaramids, are suitable. It is also possible to use fibres
made
from crosslinked thermoplastic polymers, radiation-crosslinked or chemically
ts crosslinked thermoplastic polymers containing correspondingly reactive
groups. It is also possible to employ stabilised natural fibres, such as
cotton
fibres or cellulose fibres or crystalline mineral fibres, such as, for
example,
wollastonite or calcium silicates, for example TreminTM 939 from Quarzwerke
GmbH, Frechen, FRG, and other minerals having a corresponding morphology.
2o For the purposes of the present invention, the term "mineral fibres" does
not
include glass fibres. As part of the investigations for the present invention,
it
was found that glass fibres are unsuitable for biaxially oriented films.
Amongst
other things, severe damage to dies and rolls of the BOPP plant occur on use
of thermoplastic polymers filled with glass fibres.
The fibre dirilensions, in particular the lengths and diameters, depend on the
specific area of application of the film and also on the film thickness. The
median values of fibre diameters are advantageously in the range from 1.5 to
50 pm, preferably from 3 to 20 pm, and the fibre length is in the range from'
10
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to 250 m, for example from 10 to 200 m, preferably from 20 to 50 m, and the
fibre L/D
ratio is in the range from 5 to 50, for example from 5 to 30, preferably from
10 to 30.
In a further embodiment, the fibres may be provided with a suitable coating.
In
particular, preferred coatings are those which improve the rheology and
compatibility of the fibres with the pplymer matrix. The coating may, if
desired,
contain a stabiliser, in particular in the case of polymer fibres. Preference
is
given to organic coatings for control of the compatibility with the polymer
matrix.
io
Of the fibres made from thermoplastic polymers, preference is given for
particular embodiments to matted fibres. These contain matting agents,
preferably titanium dioxide, which is added to the spin composition during
fibre
production, in order to reduce the natural gloss of the polymer fibres. This
1s gives Ti02-pigmented fibres, whose use in the fibre-containing layer of the
film
according to the invention is particularly preferred. These embodiments are
distinguished by increased whiteness and a particularly paper-like appearance.
The fibres must be substantially stable to the processing process, i.e. during
2o extrusion and subsequent orientation. In particular, the fibre structure
must be
substantially retained during production of the film. For this purpose, the
material, in particular "in the case of fibres made from thermoplastic
polymers,
should have a sufficiently high melting or softening point so that the fibre
retains its shape and does not melt at the processing temperature of the
25 respective matrix polymer. In one embodiment, the fibres have a melting
point which is at
least 5 C above the extrusion temperature of the matrix polymer or of the
polymer/fibre
mixture.
Surprisingly, the fibres effect a change in the tear behaviour in the
biaxially
oriented film. The tear behaviour of the film becomes much more similar to the
tear behaviour of paper. This effect is particularly surprising against the
3o background of expert knowledge on fibre-reinforced plastics. It is known to
add
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fibres to extrudates made from thermoplastics in the area of injection
moulding
in order to produce fibre-reinforced plastics. This improves the mechanical
properties of the extrudates, enabling the parts to be employed, in
particular, in
areas where particularly high mechanical loads occur. On application of this
s knowledge to biaxially oriented films, an increase in the mechanical
strength
would have been expected. However, such an increase in the strength or
rigidity of the film was not noted. By contrast, easier initial tearability
was
observed, i.e. lower mechanical strength was noted.
io This effect is particularly pronounced if the fibres are employed in an
interlayer
or in the base layer of the film. Fibres are less advantageous in a thin top
layer
of heat-sealable polymers. On the one hand, the initial tear force is only
reduced to an insignificant extent. On the other hand, the fibres as additives
to
the top layers may have an adverse effect on the heat-sealing properties and
15 the printability of the film.
Surprisingly, it has additionally been observed that thE: texture of the film
surfaces and - associated therewith - the optical appearance and haptic
properties of the film become paper-like. The paper-like property profile is
also
2o evident in the sound impression made on initial tearing. In addition,
particular
embodiments exhibit increased water vapour permeability i;breathability}.
If desired, the fibre-containing layer may additionally comprise pigments
and/or
vacuole-initiating particles in conventional amounts in each case.
For the purposes of the present invention, pigments are iricompatible
particles
which essentially do not result in vacuole formation on stretching of the film
and generally have a mean particle diameter in the range from 0.01 to a
maximum of 1 pm, preferably from 0.01 to 0.7 pm, in particular from 0.01 to
0.4 pm. The layer generally comprises pigments in an amount of from 1 to 15%
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by weight, preferably from 2 to 10% by weight, in each case based on the
weight of the layer.
Conventional pigments are materials such as, for example, aluminium oxide,
aluminium sulphate, barium sulphate, calcium carbonate, magnesium
carbonate, silicates such as aluminium silicate (kaolin clay) and magnesium
silicate (talc), silicon dioxide and titanium dioxide, of which white
pigments,
such as calcium carbonate, silicon dioxide, titanium dioxide and barium
sulphate, are preferably employed.
If desired, the layer may additionally comprise vacuole-initiating fillers,
generally in an amount of 1-15% by weight, preferably 2-10% by weight, in
particular 1-5% by weight.
For the purposes of the present invention, "vacuole-initiating fillers" are
solid
particles which are incompatible with the polymer matrix and result in the
formation of vacuole-like cavities on stretching of the films, where the size,
nature and number of the vacuoles are dependent on the size of the solid
particles and the stretching conditions, such as stretching ratio and
stretching
temperature. The vacuoles reduce the density, give the films a characteristic
mother-of-pearl-like, opaque appearance caused by light scattering at the
"vacuole/ polymer matrix" interfaces. In general, the vacuole-initiating
fillers
have a minimum size of 1 pm. In general, the mean particle diameter of the
particles is from 1 to 6 pm, preferably from 1,5 bis 3 pm.
The fibre-containing layer of the film according to the inverition may be the
only
layer of a single-layered embodiment of the paper-like plastic film. The fibre-
containing layer may also be the base layer of a multilayered embodiment of
the film. The fibre-containing layer is preferably an interlayer applied to
the
3o base layer. Correspondingly, multilayered embodiments of the paper-like
film
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additionally have a base layer or an interlayer or a top layer in addition to
the
fibre-containing layer.
These additional layers, which are generally fibre-free, are generally built
up
s from thermoplastic polymers. They comprise at least 70% by weight,
preferably
from 75 to 100% by weight, in particular from 90 to 98% by weight, of a thermo-
plastic polymer. Suitable thermoplastic polymers for these additional layers
are
basically the same polymers as described above for the fibre-containing layer.
io Suitable for the top layers are
copolymers of
ethylene and propylene or
ethylene and butylene or
propylene and butylene or
15 ethylene and another olefin having 5 to 10 carbon atoms or
propylene and another olefin having 5 to 10 carbon atoms or
a terpolymer of
ethylene and propylene and butylene or
ethylene and propylene and another olefin having 5 to 10 carbon atoms or
2o a mixture or blend of two or more of the said homopolyrriers, copolymers
and
terpolymers.
Of these, particular preference is given to
random ethylene-propylene copolymers having
25 an ethylene content of from 2 to 10% by weight, preferably from 5 to 8% by
weight, or
random propylene-l-butylene copolymers having
a butylene content of from 4 to 25% by weight, preferably from 10 to 20% by
weight,
30 in each case based on the total weight of the copolymer, or
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random ethylene-propylene-1-butylene terpolymers having
an ethylene content of from 1 to 10% by weight, preferably from 2 to 6% by
weight, and
a 1 -butylene content of from 3 to 20% by weight, preferably from 8 to 10% by
weight,
in each case based on the total weight of the terpolymer, or
a blend of an ethylene-propylene-l-butylene terpolymer and a propylene-
1-butylene copolymer
having an ethylene content of from 0.1 to 7% by weight
io and a propylene content of from 50 to 90% by weight
and a 1 -butylene content of from 10 to 40% by weight,
in each case based on the total weight of the polymer blerid.
The copolymers or terpolymers described above generally have a melt flow
is index of from 1.5 to 30 g/10 min, preferably from 3 to 15 g/10 min. The
melting
point is in the range from 120 to 140 C. The above-described blend of
copolymers and terpolymers has a melt flow index of from 5 to 9 g/10 min and a
melting point of from 120 to 150 C. All the melt flow indices indicated above
are measured at 230 C and a force of 21.6 N(DIN 53 735). Layers of
20 copolymers and/or terpolymers preferably form the top layers of heat-
sealable
embodiments of the film.
The total thickness of the film can vary within broad limits and depends on
the
intended application. The preferred embodiments of the paper-like film
25 according to the invention have total thicknesses of from 5 to 250 pm,
preferably from 10 to 100 pm, in particular from 20 to 60 Nm.
The thickness of the fibre-containing layer is selected independently of other
layers and is preferably in the range from 1 to 250 pm, iri particular from 3
to
3o 50 pm.
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The apparent density of the film is in the range from 0.3 to 1.5 g/cm3
(measurement method in accordance with DIN).
For the purposes of the present invention, the base layer is the layer that
makes up more than 50% of the total thickness of the film. Its thickness is
given
by the difference between the total thickness and the thickness of the top
layer(s) and interlayer(s) applied and can therefore vary within broad limits
analogously to the total thickness. Top layers form the outermost layer of the
to film.
In order to improve certain properties of the polypropylene film according to
the
invention still further, both the base layer and the interlayer(s) and the top
layer(s) may comprise additives in an effective amount in each case,
preferably
is hydrocarbon resin and/or antistatics and/or antiblocking agents and/or
lubricants and/or stabilisers and/or neutralising agents which are compatible
with the polymers of the core layer and the top layer(s), with the exception
of
the antiblocking agents, which are generally incompatible.
2o The invention furthermore relates to a process for the production of the
multi-
layered film according to the invention by the extrusion process, which is
known per se. The conditions during the production process depend on the
respective polymer matrix which forms the principal consti-tuent of the film.
The
process for the production of a polypropylene film is described in detail
below
25 as an example.
In this process, the melts corresponding to the individual layers of the film
are
coextruded through a slot die, the film obtained in this wa~y is taken off on
one
or more roll(s) for solidification, the film is subsequently biaxially
stretched and
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heat-set and, if desired, correspondingly surface-treated on the surface layer
provided for the surface treatment.
Biaxial stretching (orientation) is preferred and can be carried out
simultaneously or successively, with successive biaxial stretching, in which
stretching is firstly carried out longitudinally (in the machine direction)
and then
transversely (perpendicular to the machine direction), being particularly
favourable.
to Firstly, as usual in the coextrusion process, the polymer or polymer
mixture of
the individual layers is compressed and liquefied in an extruder, it being
possible for the fibres and any additives added to be already present in the
polymer. The melts are then pressed simultaneously through a slot die (flat-
film
die), and the extruded single- or multilayered film is takein off on one or
more
1s take-off rolls, during which it cools and solidifies.
The film obtained in this way is preferably then stretched longitudinally and
transversely to the extrusion direction, which results in orientation of the
molecule chains. The stretching in the longitudinal direction is preferably
20 carried out at from 3:1 to 7:1 and the stretching in the transverse
direction is
preferably carried out at from 5:1 to 12:1. The Iongltudinal stretching is
advantageously carried out with the aid of two rolls runnirig at different
speeds
corresponding to the target stretching ratio, and the transverse stretching is
carried out with the aid of a corresponding tenter frame. For biaxial
stretching,
25 stretching can in principle also be carried out sirnultaneously in the
longitudinal/transverse directions. These simultaneous stretching processes
are known per se in the prior art.
The biaxial stretching of the film is followed by its heat se'lting (heat
treatment),
30 in which the film is held at a temperature of from 110 to 150 C for about
0.5 to
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s. The film is subsequently wound up in a conventional manner using a
wind-up device.
It has proven particularly favourable to keep the take-off roll or rolls by
means
5 of which the extruded film is also cooled and solidified, at a temperature
of from
10 to 90 C, preferably from 20 to 60 C.
In addition, the longitudinal stretching is advantageously carried out at a
temperature of less than 140 C, preferably in the range frcim 125 to 135 C,
and
io the transverse stretching at a temperature of above 140 C, preferably at
from
145 to 160 C.
If desired, as mentioned above, one or both surface(s) of the film can be
corona- or flame-treated by one of the known methods after the biaxial
rs stretching.
If desired, the film can be coated, melt-coated, varnished or laminated by
suitable coating processes in subsequent processing steps in order to impart
further advantageous properties.
The plastic film according to the invention is distinguished by relatively
easy
initial tearability. The force that has to be applied to initiate a tear at
the film
edge is significantly reduced. Undesired distension at the edge does not occur
on initial tearing, so that the film withstands the initial teeiring. Initial
tearing of
the film is significantly easier and the tears can then be propagated in a
more
controlled manner. In addition, it also exhibits paper-like character with
respect
to appearance, haptic properties and water vapour permeability.
The following measurement methods were used in ordE~r to characterise the
fibres and the films:
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The following method was used for characterisation of the median values of
fibre length/diameter and L/D ratio:
A sufficiently thin coat of the fibre material to be investigated is observed
under
a microscope. The magnification should be selected in a suitable way so that a
representative ensemble can be investigated. With the aid of suitable software
support, the individual fibres can be measured with respec:t to their length,
their
diameter and thus also their UD ratio. Through definii:ion of suitable sub-
lo ensembles, discrete distributions of fibre length and diameter can be set
up,
enabling evaluation of the median values.
Weight per unit area:
The weight per unit area is determined in accordance with DIN EN ISO 536.
Modulus of elasticity:
The moduli of elasticity in the longitudinal and transverse directions are
determined in accordance with DIN EN ISO 527-1 and 527-3.
2o Tear propagation strength:
The tear propagation strength in the longitudinal and treinsverse directions
is
determined in accordance with ASTM D1938-85.
Initial tear resistance:
The initial tear resistance in the longitudinal direction is determined in
accordance with ASTM D1004-66.
Coefficient of dynamic friction i/o
The coefficient of friction at the limit of sliding of the inside of the film
(i) against
its outside (o) was determined in accordance with DIN 53375.
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Water vapour permeability
The water vapour permeability was determined in accordance with DIN 53122
Part 2 at 37.8 C and 90% relative humidity.
All fibre types employed are listed below with their characteristic
properties.
Table (fibre characterisation)
Weight average Weight avei-age UD
Fibre Nature length diameter ratio
type [Nml INm]
A Cellulose 197 20 10
B Cellulose 18 15 1
C Cotton 390 16 23
D Cotton 510 17 29
E Nylon 6.6 620 20 30
F Wollastonite 66 8 8
G Wollastonite 50 7 7
The invention is now explained by the following examples.
Example 1: Fibres in the interlayers of a five-layered film having a
transparent
base layer
A transparent five-layered film was produced via the corresponding process
steps, i.e. after coextrusion, the film was taken off and cooled over a first
take-
off roll and a further triple roll, subsequently stretched in the longitudinal
direction, stretched in the transverse direction, set and corona-treated, with
the
following conditions being selected:
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Extrusion: extrusion temperature 250 C
Longitudinal stretching: stretching roll T= 120 C
Longitudinal stretching by the factor 4.5
Transverse stretching: heating zone T 170 C
stretching zone T = 165 C
Transverse stretching by the factor 8
Setting: temperature T = 155 C
Corona treatment: voltage: 10,000 V
to frequency: 10,000 Hz
The base layer of the film essentially comprised a propylene homopolymer. In
the interlayers, either propylene homopolymer or a propylene-ethylene
copolymer was employed. The interlayers contained various fibres in an
amount of up to 30% by weight. The top-layer material en-iployed on both sides
was a heat-sealable copolymer. AIl layers comprised conventional stabilisers
and neutralisers.
The multilayered film produced in this way had a surface tension of from 40 to
2o 41 mN/m (top side) directly after production. The films hacf a thickness of
about
35 - 43 pm. The thickness of the top layers was in each case about 0.7 pm; the
thickness of the two interlayers was in each case about 3 pm. The films
exhibited a paper-like appearance with all fibre typE:s used. The initial
tearability was significantly reduced. The films sounded like paper on initial
tearing and further tearing. Their coefficient of friction was reduced.
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Comparative Example 1
In comparison with Example 1, a film having the same layer structure as
described in Example 1was produced. The only difference was that no fibres
were added to the interlayers.
Table 1
Film properties of the films in accordance with Example! 1 and Comparative
Example 1
Fibre type used D c B A Comp. Example
Fibre concentration [%] 2.5 2.5 2.5 2.5 No fibres
Weight per unit area [g/m2] 27.6 27.9 33.2 30.5 34.3
Mod. of elasticity, longitudinal [N/mmz] 1700 1700 1900 1700 1900
Mod. of elasticity, transverse [N/mmZ] 4600 4900 5000 4600 5400
Initial tear strength [N] 6.9 7.2 8.0 7.9 9.6
Tear prop. strength, longitudinal [mN] 96 124 156 144 164
Tear prop. strength, transverse [mN] 44 32 44 80 60
Dynamic coeff. of friction i/o 0.35 0.4 0.35 0.3 0.5
Example 2: Fibres in the core layer of a transparent five-layered film
A film was produced as described in Example 1. In contrast to Example 1, the
fibres were now incorporated into the base layer of the film. The interlayers
remained fibre-free. Via the corresponding process steps after coextrusion,
the
extruded, transparent five-layered film was taken off and cooled over a first
take-off roll and a further triple roll, subsequently stretched in the
longitudinal
direction, stretched in the transverse direction, set and corona treated, with
the
following conditions being selected:
Extrusion: extrusion temperature 250 C
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Longitudinal stretching: stretching roll T 114 C
Longitudinal stretching by the factor 4.5
Transverse stretching: heating zone T 172 C
stretching zone T = 160 C
Transverse stretching by the factor 8
Setting: temperature T = 150 C
Corona treatment: voltage: 10,000 V
frequency: 10,000 Hz
to The multilayered film produced in this way had a surface tension of from 40
to
41 mN/m (top side) directly after production. The films hacl a thickness of
about
38 - 42 pm. The thickness of the top layers was in each case about 0.7 pm; the
thickness of the two interlayers was in each case about 3 pm. Irrespective of
the fibre type used, the films of Example 2 exhibit a paper-like appearance.
is The initial tearability is significantly reduced. The film sounds like
paper on
initial tearing and further tearing. Its coefficient of friction is reduced.
Comparative Example 2
A film was produced as described in Example 2. In contrast to Example 2, the
20 film contained no fibres in the base layer.
Table 2
Film properties of Example 2 and Comparative Example 2
Fibre type used F F Comp. Example
Fibre concentration [%] 7.5 5.0 No fibres
Weight per unit area [g/mz] 38.1 36.4 34.6
Mod. of elasficity, longitudinal [N/mm2] 1700 1800 2000
Mod. of elasticity, transverse [N/mm2] 2800 3000 3500
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Initial tear strength/longitudinal [N] 7.7 8.1 9.4
Tear prop. strength, longitudinal [mN] 88 128 124
Tear prop. strength, transverse [mN] 40 28 60
Dynamic coeff. of friction i/o 0.30 0.32 0.45
Example 3: Fibres in the interlayers of a five-layered film having an opaque
core layer
A film was produced as described in Example 1. In contrast to Example 1, the
base layer additionally comprised calcium carbonate and titanium dioxide.
Via the corresponding process steps after coextrusion, the extruded, opaque
five-layered film was taken off and cooled over a first takE:-off roll and a
further
triple roll, subsequently stretched in the longitudinal direction, stretched
in the
io transverse direction, set and corona treated, with the following conditions
being
selected:
Extrusion: extrusion temperature 240 C
Longitudinal stretching: stretching roll T= 114 C
is Longitudinal stretching by the factor 4.5
Transverse stretching: heating zone T 172 C
stretching zone T = 160 C
Transverse stretching by the factor 8
Setting: temperature T = 150 C
20 Corona treatment: voltage: 10,000 V
frequency: 10,000 Hz
The multilayered film produced in this way had a surface tension of from 40 to
41 mN/m (top side) directly after production. The films ha<i a thickness of
about
25 32 - 44 pm. The thickness of the top layers was in each case about 0.7 pm;
the
thickness of the two interlayers was in each case about 3 pm. Irrespective of
the fibre type used, the films of the example exhibit a sirniiar appearance.
The
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initial tearability is significantly reduced. The film sounds like paper on
initial
tearing and further tearing. Its coefficient of friction is reduced. The film
having
an increased fibre concentration in the interlayer (type F; 15%) exhibits a
significantly increased water vapour permeability (about 50%).
Comparative Example 3
A film was produced as described in Example 3. In contrast to Example 3, the
interlayers contained no fibres.
Table 3 (film properties)
Fibre type used F D c B Comp. Example
Fibre concentration [%] 15.0 2.5 2.5 2.5 No fibres
Weight per unit area [g/mZ] 29.7 20.4 26.4 26.3 30.8
Mod. of elasticity, longitudinal [N/mm'] 1500 1100 1200 13000 1600
Mod. of elasticity, transverse [N/mmZ] 2400 2200 2300 2300 2900
Initial tear strength [N] 5.2 6.8 6.4 6.7 8.5
Tear prop. strength, longitudinal [mN] 82 56 84 68 94
Tear prop. strength, transverse [mN] 63 52 36 40 55
Dynamic coeff. of fric6on i/o 0.25 0.35 0.3 0.4 0.55
WVP (37.8 C and 90% r.h.) 7.8 - - - 6.8
Example 4: Fibres in the core layer of a five-layered film having an opaque
core layer
A film was produced as described in Example 2. In contrast to Example 2, the
film now additionally comprised calcium carbonate and titanium dioxide in its
base layer.
Via the corresponding process steps after coextrusion, the extruded, opaque
five-layered film was taken off and cooled over a first takE:-off roll and a
further
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triple roll, subsequently stretched in the longitudinal direction, stretched
in the
transverse direction, set and corona treated, with the following conditions
being
selected:
Extrusion: extrusion temperature 245 C
Longitudinal stretching: stretching roll T 114 C
Longitudinal stretching by the factor 4.5
Transverse stretching: heating zone T= 170 C
stretching zone T = 160 C
io Transverse stretching by the factor 8
Setting: temperature T = 150 C
Corona treatment: voltage: 10,000 V
frequency: 10,000 Hz
is The multilayered film produced in this way had a surface tension of from 40
to
41 mN/m (top side) directly after production. The films had: a thickness of
about
40 - 52 pm. The thickness of the top layers was in each case about 0.7 pm; the
thickness of the two interlayers was in each case about 3 pm. Irrespective of
the fibre type used, the films of the example exhibit a similar appearance.
The
20 initial tearability is significantly reduced. The film sound:; like paper
on initial
tearing and further tearing.
Comparative Example 4
A film was produced as described in Example 4. In contrast to Example 4, the
25 base layer now contained no fibres.
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Table 4 (film properties)
Fibre type used E Comp. Example
Fibre concentration [%] 1.5 No fibres
Weight per unit area [g/m2] 30.4 31.1
Mod. of elasticity, longitudinal [N/mm2] 1156 1 700
Mod. of elasticity, transverse [N/mm2] 2600 3000
Initial tear strength [N] 7.7 8.6
Tear prop. strength, longitudinal [mN] 92 76
Tear prop. strength, transverse [mN] 68 52
s Example 5: Fibres in the core layer and interlayers of a five-layered film
having an opaque core layer
A film was produced as described in Example 4. In contrist to Example 4, the
film additionally contained fibres in the interiayer in an amount of up to 30%
by
io weight, i.e. both the base layer and the interlayer coritained fibres in
this
example.
Via the corresponding process steps after coextrusion, the extruded, opaque
five-layered film was taken off and cooled over a first takE:-off roll and a
further
15 triple roll, subsequently stretched in the longitudinal direc:tion,
stretched in the
transverse direction, set and corona treated, with the foliowing conditions
being
selected:
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Extrusion: extrusion temperaiture 245 C
Longitudinal stretching: stretching roll T 114 C
Longitudinal stretching by the factor 4.5
Transverse stretching: heating zone T= 170 C
stretching zone T = 160 C
Transverse stretching by the factor 8
Setting: temperature T = 150 C
Corona treatment: voltage: 10,000 V
frequency: 10,00C1 Hz
The multilayered film produced in this way had a surface tension of from 40 to
41 mN/m (top side) directly after production. The films hacl a thickness of
about
40 - 48 pm. The thickness of the top layers was in each case about 0.7 Nm; the
thickness of the two interlayers was in each case about 3 pm. Irrespective of
is the fibre type used, the films of the example exhibit a sirriilar
appearance. The
initial tearabitity is significantly reduced. The film sounds like paper
during
initial tearing and further tearing. Its coefficient of friction is reduced.
Table 5 (film properties)
Fibre type used F F G G Comp. Example
Fibre concentration [%] in interlayer 7.5 7.5 7.5 7.5 No fibres
Fibre concentration [%] in core layer 5.0 2.5 5.0 2.5
Weight per unit area [g/mZ] 28.8 29.0 32.9 31.6 29.4
Mod. of elasticity, longitudinal [N/mmT] 1100 1300 1200 1400 1500
Mod. of elasficity, transverse [N/mmz] 1600 2000 1700 2100 2600
Initial tear strength [N] 6.3 6.7 5.9 7.0 8.5
Tear prop. strength, longitudinal [mN] 124 116 124 112 100
Tear prop. strength, transverse [mN] 232 156 60 64 58
WVP (37.8 C and 90% r.h.) 7.3 7.0 7.5 6.8 6.5
