Note: Descriptions are shown in the official language in which they were submitted.
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Oriented polyolefin film with alkene block copolymer, a process for its
production and its use
Field of the invention
The present invention relates to an oriented polyolefin film with at least one
5 vacuole-containing layer. The invention also relates to a process for producing
the polyolefin film and to its use. The invention further relates to a method ofuse of block copolymers.
Description of Related Art
Polyolefin films are used for many diverse applications and can, broadly, be
10 divided into two groups, namely the transparent and non-transparent types of
films. Transparent films show of course the lowest possible opacity, while the
non-transparent types show such a high opacity that a meaningful measure-
ment of this parameter is not possible. In the case of non-transparent films, itis therefore their light transmission which is determined. Depending on the
15 degree of light transmission, a distinction is made between translucent and
opaque or white films.
Non-transparent films according to the state of the art contain, in at least onelayer, pigments or vacuole-initiating particles or a combination thereof, so that
the films show a reduced light transmission as compared with transparent
20 films.
Pigments are particles which essentially do not lead to the formation of vacuo-
les during the stretching of the film. The coloring action of the pigments is
caused by the particles themselves. The term "pigment" is in general tied to a
particle size of from 0.01 to at most 1 ,um and comprises both so-called "white
25 pigments", which confer a white color upon the films, and "color pigments"
which confer a coloration or a black color upon the film.
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Opaque films contain vacuole-initiating particles which are incompatible with
the polymer matrix and, on stretching of the films, cause the formation of
vacuole-like cavities, the size, nature and number of the vacuoles depending
5 on the material and on the size of the solid particles and on the stretching
conditions such as sL,etching ratio and stretching temperature. The vacuoles
reduce the density and provide the films with a characteristic pearlescent
opaque appearance which results from scattering of light at the vacuole/-
polymer matrix interfaces. In general, the mean particle diameter of the vacuo-
10 le-initiating particles is 1 to 10 ,um.
Conventional vacuole-initiating particles are inorganic and/or organic materialsincompatible with polypropylene, such as oxides, sulfates, carbonates or
silicates, and incompatible polymers such as polyesters or polyamides. The
term "incompatible materials" or "incompatible polymers" means that the mate-
15 rial or the polymer is present as a separate particle or as a separate phase inthe film.
The density of the non-transparent films can vary within wide limits and de-
pends on the nature and the quantity of the fillers. The density is in general
within the range from 0.4 to 1.1 g/cm3.
20 Such non-transparent films are described in detail in the following publications:
EP-A-0,004,633 describes a heat-sealable, opaque, biaxially oriented plastic
film which contains finely disperse solid, in particular inorganic, particles of a
size from 0.2 to 20 ,um and possesses at least one heat-sealing layer compo-
sed of a propylene/ethylene copoiymer. In addition to the inorganic particles,
25 opaque organic particles, for example those composed of crosslinked plastic,
are also suitable for providing opacity, the melting point of the plastic particles
being above the temperatures which arise during the manufacture of the film.
The sealability, the gloss and the imprintability of the film are said to be im-proved as compared with the state of the art. The mechanical properties of the
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film require improvement; in particular, the bending stiffness of these films inthe transverse direction is 10 to 20% higher than in the longitudinal direction.However, it is specifically the bending stiffness in the longitudinal direction that
is more important to the processor.
EP-A-0,083,495 describes a non-transparent, biaxially oriented film having a
glazed appearance and a surface gloss of more than 100% and containing at
least one spherical solids particle per vacuole. Furthermore, the film contains,on both surfaces of the core layer, a pore-free, transparent, thermoplastic
outer layer having a thickness which determines the optical character of the
film. Nylon is indicated, for example, as a material for the solids particle. As a
rule, the particles have a diameter which is greater than 1 ,Lm. In the case of
these films again, the mechanical properties, in particular the film stiffness, still
require improvement.
DE-A-4,211,413 describes films and moldings composed of a thermoplastic.
The thermoplastic is a thermoplastic elastomer and is composed of a partially
crystalline block copolymer and of a polymeric modifying agent. The multi-
phase alkene block copolymer has a copolymer content of 51 to 85%. The
hardness of the resulting film is very low and, due to the high content of
elastomeric copolymer in the block copolymer, the raw material is unsuitable
for oriented polypropylene films.
EP-A-0,564,846 describes a matt oriented polypropylene film which is provided
with its appearance by at least one one-sided co-extruded layer composed of
a blend of a block copolymer and other polymers.
DE-A-4,202,663 describes a non-oriented film which is composed of a blend of
a hetero-phase polyolefin, an ethylene/butylene copolymer and a propylene/-
butylene/ethylene terpolymer.
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Summary of the Invention
It is an object of the present invention to provide a non transparent poly-olefin
film in which the translucence or the opacity can be obtained by simple
measures and can be varied within wide limits. It is an additional object of the5 invention to provide a film which has good mechanical and homogeneous
optical properties. In particular it is an object of the invention to provide a film
of high stiffness and high tensile strength, particularly in longitudinal direction.
It is a further particular object of the invention to provide a film with a highopacity and high whiteness at a given density.
10 It is also an object of the invention to provide a process for producing such film.
It is an additional object of the invention to provide a method of use for multi-
phase alkene block copolymers.
In achieving these and other readily apparent objects of the invention there is
15 provided an oriented polyolefin-film comprising at least one vacuole-containing
layer, wherein the vacuole-containing layer comprises a multiphase alkene
block copolymer.
Other objects of the invention also are achieved by providing a process for
producing a film comprising a vacuole-containing layer wherein the multiphase
20 alkene block copolymer, polymers and/or polymer blends are compressed
and heated in an extruder to form a melt or melts and said melts are extruded
through a flat die and the film thus obtained is drawn off by one or more rollers
and the film is then oriented from about 4:1to about 7:1 lenghtwise and from
about 6: 1 to about 11: 1 crosswise.
25 A further object of the invention is achieved by a method of use of alkene
block copolymer for the production of opaque films.
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These and other objectives of the invention will be readily apparent by referen-ce to the following detailed description of the preferred embodiments of the
invention.
Detailed Description of the preferred Embodiment.
5 The film according to the invention is a single-layer film or a multilayered film.
Single-layer embodiments have a structure like that of the vacuole-containing
layer, described below, of the multilayered film. Multilayered embodiments
contain at least two layers and always comprise the vacuole-containing layer
and at least one further layer, it being possible for the vacuole-containing layer
10 to form the base layer, the interlayer or the top layer of the multilayere~ film.
In a preferred embodiment, the vacuole-containing layer forms the base layer
of the film with at least one top layer and preferably top layers on both sides,it being possible, if desired, for a non-vacuole-containing or vacuole-containing
interlayer or interlayers to be present on one or both sides between the vacuo-
15 le-containing base layer and the top layer(s). In a further preferred embodi-ment, the vacuole-containing layer forms an interlayer of the multilayered film,which interlayer is located between the non-vacuole-containing base layer and
the top layer. Further embodiments with a vacuole-containing interlayer are of
five-layered structure and have vacuole-containing interlayers on both sides. In20 a further embodiment, the vacuole-containing layer can form a top layer on the
vacuole-containing or non-vacuole-containing base layer or interlayer. Within
the scope of the present invention, the base layer is that layer which makes up
more than about 40%, in particular more than about 50%, of the total film thick-ness. The top layer is the layer which forms the outermost layer of the film.
25 Depending on its intended use, the particular embodiment of the non-trans-
parent film can be translucent, opaque or white-opaque. Within the scope of
the present invention, non-transparent films are to be understood as those
films whose light transmission according to ASTM-D 1003-77 is less than about
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95%, preferably in the range from about 5 to about 80%. A distinction is made
between translucent and opaque and/or white-opaque types in accordance
with their light transmission. Translucent films have a light transmission of 95 to
70%, and opaque or white-opaque types have a light transmission of 69 to 0%,
preferably 69 to 5%, each measured according to ASTM-D 1003-77.
The vacuole-containing layer of the film according to the invention comprises
a multiphase alkene block copolymer, preferably a propylene block copolymer,
and, if appropriate, further added additives, each in effective quantities. The
amount of the alkene block copolymer in the vacuole-containing layer can vary
within wide limits, depending on the embodiment of the invention and on the
desired properties of the film. In general, the vacuole-containing layer com-
prises at least about 5 to 100% by weight, preferably about 10 to about 90%
by weight, in particular about 25 to about 70% by weight, of the alkene block
copolymer, based on to the weight of the vacuole-containing layer.
The multiphase alkene block copolymer is essentially composed of an elasto-
meric component and a partially crystalline component which are not com-
pietely miscible with one another and therefore form at least two phases.
Preferably, the block copolymer contains about 5 to about 45% by weight, in
particular about 5 to about 20% by weight, of the elastomeric component. The
crystalline component is in general a propylene polymer and, correspondingly,
the block copolymer contains about 55 to about 95% by weight, preferably
about 80 to about 95% by weight, thereof. The ethylene content of the block
copolymer is preferably in the range from about 2 to about 40% by weight, in
particular in the range from about 3 to about 25% by weight, and the propyle-
ne content is at least about 50% by weight, preferably about 70 to about 97%
by weight, of propylene. The ethylene content is determined by IR spectros-
copy. The above data in percent by weight are based in each case on the
weight of the block copolymer. The melting range of the block copolymer is
about 140 to about 180-C, preferably about 150 to about 170-C, and the melt
index is in the range from about 0.5 to about 8 g/10 minutes, preferably about
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2 to about 6 g/10 minutes (at 230C and a force of 21.6 N (DIN 53 735)).
The elastomeric component of the block copolymer is in general an ethylene
copolymer, preferably an ethylene/propylene copolymer, which can, optionally,
be copolymerized with minor quantities (< 5% by weight) of a further comono-
5 mer. The ethylene content of the elastomeric component is in general about 20to about 95% by weight, preferably about 40 to about 70% by weight, based
on the weight of the elastomeric component. Suitable comonomers are propy-
lene, 1-alkenes having 4 to 10 carbon atoms, for example 1,3-butadiene, cyclic
olefins having 6 to 10 carbon atoms such as, for example, cyclopentene,
10 norbornene, cyclooctene or ethylidene-norbornene. The glass temperature TG
of the elastomeric component is in general below about 25 C, preferably
below about O C and in particular in the range from about -100-C to about
-10-C, and its crystallinity is less than about 5%, preferably less than about
3%, or it is almost 0%.
15 Surprisingly, vacuole-like cavities form in the polymer matrix during the biaxial
orienting of the films containing said block copolymer, without vacuole-initiating
fillers. In scanning electron micrographs, these vacuoles are clearly visible. It is
believed that, during the stretch-orienting of the film containing block copoly-mer, ruptures occur between the partially crystalline component, i.e. the propy-
20 lene polymer, and the elastomeric component, i.e. the ethylene/propylenecopolymer, whereby microcavities or vacuoles form, in the region of which the
visible light is refracted. This provides the film with a translucent or opaque
appearance and with a reduced density, which make it particularly suitable for
certain packaging purposes, in particular in the foodstuffs sector.
25 The preparation of the alkene block copolymers suitable according to the
invention is known per se and is described for example, in P. Galli,
T. Simonazi and D. del Duca, Acta Polymerica 39 (1988), No. 1/2, pages 81
to 90 which is incorporated herein by reference in its entirety. Furthermore,
these classes of polymers are common commercial products, for example
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~HOSTALEN PP made by Hoechst AG.
In a further preferred embodiment of the invention, the vacuole-containing layerin general comprises, in addition to the alkene block copolymer, a propylene
polymer in a quantity of up to about 95% by weight, preferably about 10 to
about 90% by weight, in particular about 30 to about 75% by weight, each
basedon the weight of the layer. Depending on the propylene polymer/multi-
phase alkene block copolymer ratio, the content of the elastomeric component
in the vacuole-containing layer is from about 2 to about 15% by weight, prefe-
rably about 4 to about 10% by weight, basedon the weight of the layer.
The propylene polymer contains about 90 to about 100% by weight, preferably
about 95 to about 100% by weight, in particular about 98 to about 100% by
weight, of propylene based on the weight of the polymer and has a melting
point of about 120-C or higher, preferably about 150 to about 175-C, and in
general has a melt index from about 0.5 g/10 minutes to about 10 g/10 minu-
tes, preferably about 2 g/10 minutes to about 8 g/10 minutes, at 230 C and
a force of 21.6 N (DIN 53 735).
Isotactic propylene homopolymer having an atactic fraction of about 15% by
weight and less, copolymers of ethylene and propylene with an ethylene
content of about 10% by weight or less, copolymers of propylene with
C4-C8-olefins with an olefin content of about 10% by weight or less, terpolymersof propylene, ethylene and butylene with an ethylene content of about 10% by
weight or less and a butylene content of about 15% by weight or less repre-
sent preferred propylene polymers for the vacuole-containing layer, isotactic
propylene homopolymer being particularly preferred. The indicated percentag-
es by weight relate to the particular polymer.
Furthermore, a blend of the said propylene homopolymers and/or copolymers
and other polyolefins, in particular having about 2 to about 10 carbon atoms,
is suitable as the polypropylene. The blend can contain at least about 50% by
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weight, in particular at least about 75% by weight, of a propylene polymer.
Suitable other polyolefins in the polymer blend are polyethylenes, in particularHDPE, MDPE, VLDPE, LDPE and LLDPE, the content of these polyolefins in
each case not exceeding about 15% by weight, relative to the polymer blend.
In a further preferred embodiment, both the alkene block copolymer used in
the vacuole-containing layer and the propylene polymer which may have been
added can be partially degraded, during granulation by the addition of organic
peroxides. A measure of the degree of degradation of the polymer is the so-
called degradation factor A, which indicates the relative change in the melt
index of the polypropylene according to DIN 53 735, relative to the starting
polymer.
A MFI2
MFIl
MFI, = Melt index of the propylene polymer before the addition of the
organic peroxide
MFI2 = Melt index of the propylene polymer degraded by the peroxide
1 5 mechanism
In general, the degradation factor A of the propylene polymer used is in the
range from about 3 to about 15, preferably about 6 to about 10.
Dialkyl peroxides are particularly preferred organic peroxides, an alkyl radicalbeing understood as the usual saturated straight-chain or branched lower alkyl
radicals having up to 6 carbon atoms. In particular, 2,5-dimethyl-2,5-di(t-butyl-
peroxy) hexane or di-t-butyl peroxide are preferred.
In a further embodiment of the invention, the film according to the invention
additionally comprises, in the layer containing a block copolymer and/or in
another layer, fillers known per se, in general in a quantity from about 1 to
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about 30% by weight, relative to the weight of the particular layer. Within the
scope of the present invention, the term "fillers" comprises the usual vacuole-
initiating solid particles, called "solid particles" below, and pigments.
Solid particles are incompatible with the polymer matrix and, on stretching of
5 the films, lead to the formation of additional vacuole-like cavities, the size,
nature and number of these vacuoles depending on the size of the solid
particles and the stretching conditions such as the stretching ratio and
stretching temperature. Due to light scattering at the "vacuole/polymer matrix"
interfaces, the additional vacuoles contribute to the opaque appearance of the
10 film. As a rule, the usual solid particles have a minimum size of 1 ,um, in order
to lead to an effective, i.e. opacifying quantity of vacuoles. In general, the
mean particle diameter of the solid particles is 1 to 6,um, preferably 1.5 to
5 ,um. The chemical character of the solid particles plays a subordinate role.
Usual solid particles are inorganic and/or organic materials which are incom-
15 patible with polypropylene, such as alumina, aluminum sulfate, barium sulfate,calcium carbonate, magnesium carbonate, silicates such as aluminum silicate
(kaolin clay) and magnesium silicate (talc), silica and titanium dioxide, amongst
which calcium carbonate, silica and titanium dioxide are used preferentially.
Suitable organic solid particles are those commonly used which are incompat-
20 ible with the polymer of the base layer, in particular polyolefins such as HDPE,polybutene, polyesters, polystyrenes, polyamides and halogenated organic
polymers, polyesters such as, for example, polybutylene terephthalate being
preferred. "Incompatible materials or incompatible polymers" means within the
scope of the present invention that the material or the polymer is present in the
25 film as a separate particle or as a separate phase.
Within the scope of the present invention, pigments comprise those particles
which essentially do not cause formation of vacuoles during stretching. The
coloring action of the pigments is caused by the particles themselves. The
term "pigment" is in general tied to a particle size of from 0.01 to at most 1 ,um
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and comprises both so-called "white pigments", which confer a white color
upon the films, and "color pigment" which confer a coloration or a black color
upon the film. In general, the mean particle diameter of the pigments is in the
range from about 0.01 to about 1 ,Lm, preferably about 0.01 to about 0.7 ,lLm,
5 in particular about 0.01 to about 0.4 ,um.
Conventional pigments are materials such as, for example, alumina, aluminum
sulfate, barium sulfate, calcium carbonate, magnesium carbonate, silicates
such as aluminum silicate (kaolin clay) and magnesium silicate (talc), silica and
titanium dioxide, carbon black, graphite, and other color pigments which are
10 thermally stable up to 300C, amongst which white pigments such as calcium
carbonate, silica, titanium dioxide and barium sulfate are preferentially used.
The preferred titanium dioxide particles are composed to the extent of at least
about 95% by weight of rutile and are preferably used with a coating of in-
organic oxides, such as is normally used as a coating for TiO2 white pigment
15 in papers or paints, in order to improve the light fastness. Particularly suitable
inorganic oxides include the oxides of aluminum, silicon, zinc or magnesium,
or mixtures of two or more of these compounds. They are precipitated from
water-soluble compounds, for example an alkali metal aluminate, in particular
sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum-nitrate,
20 sodium silicate or silica, in the aqueous suspension. TiO2 particles having acoating are described, for example, in EP-A-0,078,633 and EP-A-0,044,515.
If desired, the coating also contains organic compounds having polar and non-
polar groups. Preferred organic compounds are alkanols and fatty acids
having about 8 to about 30 carbon atoms in the alkyl group, in particular fatty
25 acids and primary n-alkanols having about 12 to about 24 carbon atoms, and
also polydiorganosiloxanes and/or polyorganohydrogensiloxanes such as
polydimethylsiloxane and polymethylhydrogensiloxane.
The coating on the TiO2 particles is usually composed of about 1 to about
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12 9, in particular about 2 to about 6 9, of inorganic oxides and, optionally,
about 0.5 to about 3 g, in particular about 0.7 to about 1.5 g, of organic
compounds are additionally present, in each case relative to 100 9 of TiO2
particles. It has proved to be particularly advantageous if the TiO2 particles are
5 coated with Al2O3 or with Al2O3 and polydimethylsiloxane.
Depending on the intended use of the film or the current fashion, the films
according to the invention may, additionally to the alkene block copolymer,
contain only solid particles or only pigments or a combination of solid particles
and pigments in one of the film layers. All the quantity data below relating to
10 the fillers are percentages by weight (% by weight) and relate to the weight of
the particular layer.
Films which are additionally finished only with pigment contain the latter in
general in a quantity from about 2 to about 25% by weight, in particular about
3 to about 20% by weight, preferably about 5 to about 15% by weight.
15 Preferred pigments are white pigments, in particular TiO2 and BaSO4 having a
mean particle diameter from about 0.01 to about 0.7 ,um, in particular about
0.01 to about 0.4 ,um.
.
Films which are additionally finished only with vacuole-initiating solid particles
contain the latter in general in a quantity from about 1 to about 25% by weight,20 preferably about 2 to about 14% by weight. Preferred vacuole-initiating particles
are CaCO3, SiO2, polyamides and incompatible polyolefins such as, for
example, polyethylene terephthalates or polybutylene terephthalates. CaC03,
in particular CaCO3 having a mean particle diameter of from about 1 to about
5 ,um, preferably about 2 to about 5 ,um, is particularly advantageous.
25 Films which are additionally finished with vacuole-initiating solid particles and
with pigment contain solid particles in a quantity from about 1 to about 10% by
weight, preferably about 1 to about 5% by weight, and a pigment in a quantity
from about 1 to about 7% by weight, preferably about 1 to about 5% by
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weight. For such film types, a combination of CaCO3 as solid particles and
TiO2 as pigment is preferred.
The density of the films according to the invention can vary within wide limits
and depends inter alia on the nature and quantity of the block copolymer and
on the quantity of fillers which may have been added. The density is in general
below the calculated density of the individual components of the film, i.e. the
density of the film is reduced. In general, the films have a density of at most
about 1.5 g/cm3, and preferably the density is in the range from about 0.4 to
about 1.3 g/cm3, in particular about 0.5 to about 1.0 g/cm3.
The embodiment, according to the invention, of the film comprises at least one
further vacuole-containing or non-vacuole-containing layer which can be the
base layer, an interlayer or a sealable or non-sealable top layer of the multi-
layered film. In principle, the vacuole-containing layer according to the inven-tion and the other layer or layers can have the same structure or a different
1 5 structure.
The other layer comprises in general about 75 to about 100% by weight, in
particular about 90 to about 99.5% by weight, of olefinic polymers having
about 2 to about 10 carbon atoms, i 3ach case relative to the w. eight of the
other layer, and, if appropriate, additives in effective quantities in each case.
Examples of such olefinic polymers are
a propylene homopolymer or
a copolymer of
ethylene and propylene or
ethylene and 1-butylene or
propylene and 1-butylene or
a terpolymer of
ethylene and propylene and 1-butylene or
a mixture of two or more of the said homo-, co- and terpolymers or
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a blend of two or more of the said homo-, co- and terpolymers, optio-
nally mixed with one or more of the said homo-, co- and terpolymers,
a propylene homopolymer or
random ethylene/propylene copolymers with
an ethylene content from about 1 to about 10% by weight,
preferably about 2.5 to about 8% by weight, or
random propylene/1-butylene copolymers with
a butylene content from about 2 to about 25% by weight,
preferably about 4 to about 20% by weight,
each relative to the total weight of the copolymer, or
randQm ethylene/propylene/1-butylene terpolymers with
an ethylene content from about 1 to about 10% by weight,
preferably about 2 to about 6% by-weight, and
a 1-butylene content from about 2 to about 20% by weight,
preferably about 4 to about 20% by weight,
each relative to the total weight of the terpolymer, or
a blend of an ethylene/propylene/1-butylene terpolymer and a
propylene/1-butylene copolymer
with an ethylene content from about 0.1 to about 7% by weight
and a propylene content from about 50 to about 90% by weight
and a 1-butylene content from about 10 to about 40% by weight,
each relative to the total weight of the polymer blend,
being particularly preferred.
The propylene homopolymer used in the other layer or layers contains about
97 to about 100% by weight of propylene and has a melting point of 140-C or
hi~her, preferably 150 to 170 C, isotactic homopolypropylene having an n-
heptane-soluble content of 6% by weight and less, relative to the isotactic
homopolypropylene, being preferred. The homopolymer has in general a melt
index of about 1.5 g/10 minutes to about 20 g/10 minutes, preferably about
2.0 9/10 minutes to about 15 9/10 minutes. The indicated weight percentages
relate to the polymer.
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The copolymers used in the other layer or layers and described above have in
general a melt index from about 1.5 to about 30 g/10 minutes, preferably from
about 3 to about 15 9/10 minutes. The melting point is preferably in the range
from about 120 to about 140-C. The terpolymers used in the layer or layers
have a melt index in the range from about 1.5 to about 30 9/10 minutes,
preferably from about 3 to about 15 9/10 minutes, and a melting point in the
range from about 120 to about 140-C. The blend of co- and ter-polymers,
described above, has a melt index from about 5 to about 9 9/10 minutes and
a preferred melting point from about 120 to about 150 C. All the melt indices
given above are measured at 230 C and at a force of 21.6 N (DIN 53 735).
Other layers of co- and/or ter-polymers form preferably the top layers of
sealable embodiments of the film.
In principle, the other layer can additionally contain the pigments described
above for the vacuole-containing layer in corresponding quantities. Embodi-
ments with a vacuole-containing other layer contain the vacuole-initiating fillers
described above in corresponding quantities.
Optionally, all the above-described top layer polymers can be partially degra-
ded during granulation by the addition of organic peroxides, in the same way
as described above for the vacuole-containing layer. ln general, the same
peroxides as described above for the vacuole-containing layer are used here.
The degradation factor A is in general in the range from about 3 to about 15,
preferably about 6 to about 10.
The total thickness of the film can vary within wide limits and depends on the
intended use. The preferred embodiments of the film according to the invention
have overall thicknesses from about 5 to about 200,um, about 10 to abpit
100 ~m and especially about 20 to about 80 ,Lm being preferred. The thickness
of the interlayer or interlayers, which may be present, is about 2 to about
12 ,um, independently of one another in each case, interlayer thicknesses from
about 3 to about 8 ,um, in particular about 3 to about 6 ,um, being preferred.
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The indicated values relate in each case to one interlayer. This thickness of the
top layer or layers is selected independently of the other layers and is prefera-
bly in the range from about 0.1 to about 10,um, in particular about 0.2 to
about 5 ,um, preferably about 0.3 to about 2 ,um, and top layers applied to both5 sides can be identical or different with respect to thickness and composition.The thickness of the base layer results correspondingly from the difference of
the overall thickness of the film and the thickness of the applied top layer(s)
and interlayer(s) and can therefore vary within wide limits analogously to the
overall thickness.
10 In order to improve certain properties of the polyolefin film according to the
invention even further, both the single-layer film and the vacuole-containing
layer, the other layer, the base layer(s), the interlayer(s) and/or the top layer(s)
of the multilayered film can, in each case in an effective quantity, contain
additives, optionally low-molecular weight hydrocarbon resins compatible with
15 the polymer and/or preferably antistatic agents and/or anti-blocking agents
and/or lubricants and/or stabilizers and/or neutralizing agents as well as anti-blocking agents. All the quantity data in the explanation below in percent by
weight (% by weight) relate in each case to the layer or layers, to which the
additive can have been added.
20 A low-molecular weight resin is preferably added, for example for improving the
water vapor permeability (WVP) and- for improving the film stiffness. Hydro-
carbon resins are low-molecular polymers whose molecular weight is in
general in the range from about 300 to about 8,000, preferably about 400 to
about 5,000, preferably about 500 to about 2,000. The molecular weight of the
25 resins is thus markedly lower than that of the propylene polymers which form
the main component of the individual film layers and in general have a
molecular weight of more than 100,000. The content of the resin is in a range
from about 1 to about 30% by weight, preferably about 2 to about 10% by
weight. The softening point of the resin is between about 60 and about 180C
(measured according to DIN 1995-U4, corresponding to ASTM E-28),
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preferably above about 100 to about 160C. Amongst the numerous low-
molecular resins, the hydrocarbon resins are preferred, and in particular in theform of the petroleum resins, styrene resins, cyclopentadiene resins and
terpene resins (these resins are described in Ullmanns Encyklopadie der
5 techn. Chemie [Ullmann's Encyclopedia of Industrial Chemistry], 4th edition,
volume 12, pages 525 to 555). Suitable petroleum resins are described in
numerous publications such as, for example, EP-A-0, 180,087, which is
incorporated herein by reference.
Preferred antistatic agents are alkali metal alkane sulfonates, polyether-
10 modified, i.e. ethoxylated and/or propoxylated polydiorganosiloxanes
(polydialkyl-siloxanes, polyalkylphenylsiloxanes and the like) and/or the
essentially straight-chain and saturated aliphatic tertiary amines with an
aliphatic radical having about 10 to about 20 carbon atoms, which are
substituted by ~-hydroxy-(C,-C4)-alkyl groups, N, N-bis-(2-hydroxyethyl)-
alkylamines having about 10 to about 20 carbon atoms, preferably about 12 to
about 18 carbon atoms, in the alkyl radical being particularly suitable. The
effective quantity of antistatic agent is in the range from about 0.05 to about
0.3% by weight.
Lubricants are higher aliphatic acid amides, higher aliphatic acid esters, waxes20 and metal soaps as well as polydimethylsiloxanes. The effective quantity of
lubricant is in the range from about 0.1 to about 3% by weight. Particularly
suitable is the addition of higher aliphatic acid amides in the range from about0.15 to about 0.25% by weight in the base layer and/or in the top layers. A
particularly suitable aliphatic acid amide is erucic acid amide. The addition of25 polydimethylsiloxanes in the range from about 0.3 to about 2.0% by weight is
preferred, in particular of polydimethylsiloxanes having a viscosity from about
10,000 to about 1,000,000 mm2/s.
The stabilizers used can be the conventional compounds having a stabilizing
action for ethylene polymers, propylene polymers and other c~-olefin polymers.
2l5s27~
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The added quantity thereof is between about 0.05 and about 2% by weight.
Phenolic stabilizers, alkali metal/alkaline earth metal stearates and/or alkali
metal/alkaline earth metal carbonates are particularly suitable. Phenolic
stabilizers are preferred in a quantity from about 0.1 to about 0.6% by weight,
5 in particular about 0.15 to 0.3% by weight, and with a molecular mass of more
than about 500 g/mol. Pentaerythritol tetrakis-3-(3,5-di-tertiarybutyl-4-hydroxy-
phenyl)-propionateor1,3,5-trimethyl-2,4,6-tris(3,5-di-tertiarybutyl-4-hydroxyben-
zyl)benzene are particularly advantageous.
The anti-blocking agents are preferably added to the top layers. Suitable anti-
10 blocking agents are inorganic additives such as silica, calcium carbonate,magnesium silicate, aluminum silicate, calcium phosphate and the like and/or
incompatible organic polymers such as polyamides, polyesters, poly-
carbonates and the like, and benzoguanamine/formaldehyde polymers, silica
and calcium carbonate are preferred. The effective quantity of anti-blocking
agent is in the range from about 0.01 to about 10% by weight, preferably
about 0.1 to about 5% by weight. The mean particle size is between about 1
and about 6,um, in particular about 2 and about 5,um, particles having a
spherical shape, as described in EP-A-0,236,945 and DE-A-3,801,535, being
particularly suitable.
20 Neutralizing agents are preferably calcium stearate and/or calcium carbonate
of a mean particle size of at most about 0.7 ,um, an absolute particle size of
less than about 10 ,um and a specific surface area of at least about 40 m2/g.
In general, the neutralizing agent is added in a quantity from about 0.02 to
about 0.1% by weight.
25 The invention also relates to a process for producing the film according to the
invention by the extrusion process known per se. Within the scope of this
process, the procedure is such that the block copolymers, which may be
mixed with the propylene polymers, are fed to the extruder either in the pure
form or as a granulated concentrate (masterbatch) and then compressed and
2ls527~
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heated. The melts corresponding to the film or to the individual layers of the
film are then extruded or co-extruded through a sheet die, and the film thus
obtained is drawn off for solidification on one or more roller(s). The film is then
oriented, thermofixed and, if appropriate, corona-treated or flame-treated on
5 the surface intended for treatment.
It has proved to be particularly advantageous to hold the draw-off roller or
rollers, by means of which the extruded film is also cooled and solidified, at atemperature from about 10 to about 90 C, preferably about 20 to about 60 C.
The initial film thus obtained is stretched preferably longitudinally and transver-
10 sely to the direction of extrusion, which causes biaxial orienting of the moleculechains. The biaxial orienting can be carried out simultaneously or successively,
it being particularly advantageous in successive biaxial stretching first to stretch
longitudinally (in the machine direction) and then transversely (perpendicularlyto the machine direction). The stretching is preferably about 4:1 to about 7:1
in the longitudinal direction and preferably about 6:1 to about 11:1 in the
transverse direction. The longitudinal stretching will advantageously be carriedout by means of two rollers running at different speeds, corresponding to the
desired stretching ratio, and the transverse stretching by means of a
corresponding tenter frame.
20 The temperatures at which the longitudinal and transverse stretching are
carried out can vary within a wide range. In general, the longitudinal stretching
is carried out at about 90 to about 150 C, preferably about 100 to about
140-C, and transverse stretching is carried out at about 140 to about 190 C,
preferably about 150 to about 180-C.
25 The biaxial stretching of the film is followed by its thermofixing (heat treatment),
the film being held for about 0.5 to about 10 seconds at a temperature from
about 110 to about 130 C. Subsequently, the film is wound up in the
conventional manner on a winding-up device.
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Optionally, one or both surface(s) of the film can, as mentioned above, be
corona- or flame-treated after the biaxial stretching by one of the known me-
thods, an electric direct voltage being applied between a burner (negative
pole) and a cooling roller for a flame treatment with a polarized flame
(cf. US-A-4,622,237 which is incorporated by reference). The level of the
applied voltage is between about 500 and about 3,000 V, preferably in the
range from about 1,500 to about 2,000 V. The ionized atoms obtain an
increased acceleration by the applied voltage and impinge onto the polymer
surface with a higher kinetic energy. The chemical bonds inside the polymer
molecules are more easily broken, and the formation of the free radicals
proceeds faster. The thermal stress on the polymer is in this case far lower
than in the case of the standard flame treatment, and films can be obtained, in
which the sealing properties of the treated side are even better than those of
the untreated side.
For the alternative corona treatment, the film is passed through between two
conductor elements serving as electrodes, such a high voltage, in most cases
an alternating voltage (about 10,000 V and about 10,000 Hz), being applied
between the electrodes that spray discharges or corona discharges can take
place. The air above the film surface is ionized by the spray discharge or
corona discharge and reacts with the molecules of the film surface, so that
polar inclusions are produced within the substantially non-polar polymer matrix.The treatment intensities are within the conventional range, 38 to 45 mN/m
being preferred.
The films according to the invention are distinguished by an isotropic bending
stiffness; that is, the bending stiffness of the film in the longitudinal and
transverse directions is approximately of the same magnitude. The difference
is in general not more than about 10%, based on the value in the transverse
direction.
The invention will now be explained in even more detail by reference to embo-
215S279
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diment examples.
Example 1
By co-extrusion and subsequent stepwise orienting in the longitudinal and
transverse directions, an opaque three-layer film of symmetrical structure was
5 produced with an overall thickness of 40,um. The top layers each had a
thickness of 0.6 ,lLm.
A base layer (= vacuole-containing layer):
100 %by weight of XHOSTALEN PPN 1752 propylene block
copolymer having an MFI of 1.5 9/10 minutes,
measured at 230 C under a load of 21.6 N, and
having an ethylene content of 6.5% by weight.
B top layers:
99.67% by weight of random ethylene/propylene copolymer having a C2
content of 3.5% by weight
0.33% by weight of SiO2 of a mean particle size of 2 ,um as anti-
blocking agent
The production conditions in the individual process steps were:
Extrusion: Temperatures A layer: 280 C
B layers: 280 C
Temperature ofthe draw-off roller: 30 C
Longitudinal stretching:
Temperature: 122 C
Longitudinal stretching ratio: 6.0
Transverse stretching:
Temperature: 155 C
Transverse stretching ratio: 8.0
21~527~
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Fixing: Temperature: 140 C
Convergence: 15%
Example 2
For comparison with Example 1, CaCO3 as filler and propylene homopolymer
5 were additionally incorporated into the base layer, so that the composition of the base layer was as follows:
93% by weight of ~HOSTALEN PPN 1752
4.9% by weight of chalk of the Millicarb type having a mean diameter of
3,umr in the form of the ~MULTIBASE PPH 7012A
masterbatch
2.1% by weight of homopolymer from the ~Multibase PPH 7012A
masterbatch
Comparison Example 1
A three-layer film was produced as described in Example 1, but the base layer
15 did not contain any block copolymer and had the following composition:
95.1% byweight of ~XP 123 AC polypropylene homopolymer made by
Statoil
4.9 % by weight of chalk of the ~MILLICARB type made by Omnya having
- a mean particle diameter of 3,um, added in the form of
the ~MULTIBASE PPH 7012A masterbatch
The following measurement methods were used for characterizing the raw
materials and the films:
Melt index
The melt index was measured analogously to DIN 53 735 at 21.6 N load and
230 C.
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Melting point
DSC measurement, maximum of the melting curve, heating-up rate
20 C/minute.
Density
5 The density is determined according to DIN 53 479, method A.
Gloss
The gloss was determined according to DIN 67 530. The reflector value was
measured as the optical parameter for the surface of a film. Analogously to the
standards ASTM-D 523-78 and ISO 2813, the angle of incidence was set to
10 60 C or 85 C. A light beam strikes the planar test surface under the set angle
of incidence and is reflected and/or scattered by the surface. The light beams
striking the photo-electronic receiver are indicated as a proportional electrical
value. The measured value is dimensionless and must be reported together
with the angle of incidence.
2lss274
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Opacity and whiteness
The opacity and the whiteness are determined by means of the electric
remission photometer "ELREPHO" made by Zeiss, Oberkochem (Germany),
standard light type C, 2 C normal observer. The opacity is determined
according to DIN 53 146. The whiteness is defined as WG = RY + 3RZ - 3RX.
WG = whiteness; RY, RZ, RX = corresponding reflection factors when using
the Y, Z and X color measurement filter. A pressed piece of barium sulfate
(DIN 5033, part 9) is used as a white standard. A detailed description is given,for example, in Hansl Loos "Farbmessung" [Color Measurement], Verlag Beruf
und Schule, Itzehoe (1989).
Light transmission
The light transmission is measured analogously to ASTM-D 1003-77.
Mean molecular weight and dispersity of the molecular masses
The mean molecular masses (Mw, Mn) and the mean dispersity (MW/Mn) of the
molecular masses were determined analogously to DIN 55 672, Part 1, by
means of gel permeation chromatography. In place of THF, ortho-dichloroben-
zene was used as eluant. Since the olefinic polymers to be examined are
insoluble at room temperature, the erltire measurement is carried out at
elevated temperature (~ 135C).
Crystallinity
The crystallinity was determined by means of X-ray methods. In this case, the
corrected diffracted X-ray intensities were set to be proportional to the fractions
of the amorphous and crystalline phases.
Glass temperature
The samples were examined by means of DSC (Differential Scanning Calori
metry). The heating-up rate was 20 K/minute. In order to eliminate the thermal
history in the specimen, the specimen was first heated in DSC apparatus to a
temperature above the glass temperature TG. rapidly cooled and then heated
again (second heating-up). The temperature for the glass transition was taken
215527~
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- 25 -
as half the step height from the thermogram for the second heating-up.
Vicat softening point
The Vicat softening point VST/B/120 was measured according to ISO 306,
DIN 53 460.
5 Bending stiffness
The measurement is carried out in accordance with DIN 53 121, but with a
different setting of a bending angle of 15-C and a measuring length of 1 mm.
Tensile strength
The tensile strength is determined in accordance with DIN 53 455.
10 Shrinkage
The shrinkage is determined in accordance with DIN 53 377. The specimen is
treated for 5 minutes at 130-C.
Ethylene content
The ethylene content of the copolymer was determined by means of IR
15 spectroscopy. In this case, the extinctions per mm at 732 cm~1 were measured
on pressed plates of about 350 ,um thickness. The allocation of the extinctions
per mm to ethylene contents was carried out with the aid of a calibration curve
which is based on 13C-NMR data.
While there is shown and described herein certain specific structure
20 embodying the invention, it will be manifest to those skilled in the art thatvarious modifications and rearrangements of the parts maybe made without
departing from the spirit and scope of the underlying inventive concept and
that the same is not limited to the particular forms herein shown and
described.
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