Note: Descriptions are shown in the official language in which they were submitted.
- 1 -
Hoe 94/R 038
Heat-sealable, oriented, multilayer polyolefin film,
process for the production thereof, and the use thereof
The invention relates to an oriented, multilayer poly-
olefin film comprising a polyolefinic base layer and at
least one heat-sealable top layer. The films are
distinguished by low haze, high gloss and a low coeffi-
cient of friction.
The prior art describes transparent films having low
coefficients of friction. The demands on the processing
properties of the films and their smooth running through
automatic machines have constantly increased over the
years. For this reason, ever-lower coefficients of
friction are required, with the term "low" friction
values today covering an order of magnitude of from 0.3
to 0.1, while a friction of from 0.4 to 0.5 was regarded
as extremely low a few years ago.
DE-A-20 01 032 describes films made from various
thermoplastics whose surface-slip characteristics have
been improved by addition of carboxamides and anti-
blocking agents. Since it is not possible for a suffi-
cient amount of lubricant to be incorporated into the top
layers alone, the additional incorporation of the amides
into the base layer is recommended. These films have a
coefficient of friction in the range from 0.4 to 0.8 and
thus no longer meet today's quality requirements.
US-A-4,117,193 describes multilayer films comprising a
polypropylene base layer containing a lubricant, an
antiblocking agent and an antistatic. The top layer of
these films comprises a polymer blend and additionally
contains a lubricant and an antiblocking agent. The
~~~4~~z
- 2 -
polymer blend comprises an ethylene-butylene copolymer
and a polyolefinic resin such as HDPE or LDPE. It is
stated that the poor surface-slip characteristics of the
films cannot be sufficiently improved by the addition of
lubricants and antiblocking agents alone. For this
reason, the top layer is modified by addition of HDPE or
LDPE in combination with a lubricant and antiblocking
agent. According to the examples and comparative
examples, the reduction in the coefficient of friction is
essentially due to the addition of HDPE. Pure copolymeric
top layers with the same additive composition have
coefficients of friction of from 0.7 to 0.8. The films
combine excellent coefficients of friction with good
printability, but are highly unsatisfactory in haze and
gloss owing to the addition of the friction-reducing
polyolefinic resin.
EP-A-0 402 100 describes polypropylene films which
contain from 0.01 to 0.5% by weight of a spherical Si02
and from 0.3 to 5% by weight of a hydroxy fatty acid
glyceride. This invention relates to single-layer and
multilayer films. Multilayer embodiments contain the
combination of SiOz and glyceride both in the top layer
and in the base layer. It is stated that the selected
amounts of SiOZ and glyceride are essential for the
advantageous properties of the films and deviations from
these ranges no longer give the desired result. The films
are distinguished by good transparency, surface-slip
characteristics and adhesion to metal. However, they have
a coating on the surface after an extended storage time
which impairs the appearance of the films. This effect is
also known as blooming and is caused by migration of
certain additives, in particular the glycerides, to the
surface of the films.
EP-A-0 182 463 describes a multilayer film which contains
from 0.05 to 0.2% by weight of tertiary aliphatic amine
~:~.~4~2~
- 3 -
in the base layer and a combination of silicone oil and
SiOz in the heat-sealable top layer. According to the
description, the surprising interaction of SiOZ, silicone
oil and amine in combination with a selected top layer
thickness of less than 0.8 ~,m gives films having
coefficients of friction of 0.3 or less. In spite of this
excellent coefficient of friction, the processing proper
ties of the film are poor. In particular, it is not
printable and is therefore unsuitable for many
applications.
EP-A-0 143 130 discloses films which contain a
carboxamide in the base layer and likewise the com-
bination of silicone oil and Si02 in the top layer. Like
in the abovementioned EP-A-0 182 463, a synergistic
action of the three selected components on the coef-
ficient of friction is described. These films likewise
have poor processing properties in spite of their advan-
tageous surface-slip characteristics. Again, they lack
the important property of printability.
EP-A-0 242 055 describes the use of an infusible organo-
siloxane resin powder having a three-dimensional network
structure as antiblocking agent in films. Both the
silicone resin and the propylene polymer are employed in
the form of a powder comprising particles having a
virtually spherical shape, this particle shape being
characterized by a corresponding equation for the actual
degree of sphericity. The films are said to be improved
over the prior art with respect to their transparency,
antiblocking properties, sliding properties and
appearance. The propylene/antiblocking agent mixture can
also be employed as top layer material for coextruded
multilayer films. However, these coextruded multilayer
films are still unsatisfactory with respect to their
transparency and gloss values, in particular if the top
layers are applied in conventional thicknesses of greater
~~~~J~~
- 4 -
than 0.5 Vim. In addition, this antiblocking agent is very
much more expensive than conventional antiblocking
agents.
German Patent Application P 43 06 154.0 describes the use
of an organically coated Sio2 as antiblocking agent in
heat-sealable films. The coefficient of friction and
processing behavior of the film has been improved. This
specification makes no mention of the spatial shape of
the antiblocking particles.
EP-A-0 353 368 describes the use of the siloxane resin
powder described in EP-A-0 242 055 in combination with a
hydroxyfatty acid glyceride. These films are particularly
suitable for vacuum vapor deposition, but have very poor
gloss and transparency.
In applying the known teaching, it has been found that
some of the known antiblocking agents have adverse
effects on certain film properties. The antiblocking
agent impairs the transparency and the gloss of the film.
The improvement in friction is generally achieved at the
expense of an increase in surface roughness. Sio2 as
antiblocking agent in the production of the films results
in deposits on the die lip and in abrasion on the rolls.
This means that the die lip and the rolls must be cleaned
frequently, since the film otherwise runs poorly during
production and the deposits on the die lip result in
streaking on the film. In addition, problems occur during
3o corona treatment. The corona treatment breaks through in
the areas of the roll where Si02 abrasion has occurred
and results in the undesired phenomenon known as the
reverse-side effect. This causes unacceptable flaws
during further processing of the film, such as, for
example, printing or metallization.
CA 02154322 2005-07-04
29478-21
- 5 -
The present invention avoids or at least mitigates the
disadvantages of the films described in the prior art. In
particular, there is provided a multilayer film
which is distinguished by a combination of the following
properties:
~ high gloss
~ low haze
~ a low coefficient of friction
~ low surface roughness.
IO
The invention is achieved by a
multilayer film of the generic type specified at the
outset, wherein the heat-sealable top layer comprises at
least one amorphous polymer which is in the top layer in
the form of separated particles.
The base layer of the novel multilayer film essentially
comprises a polyolefin, preferably a propylene polymer,
and, if desired, further additives in effective amounts
in each case. In general, the base layer comprises at
least 50% by weight, preferably from 75 to 100% by
weight, in particular from 90 to 1000 by weight, of the
propylene polymer.
The propylene polymer comprises from 90 to 100% by
weight, preferably from 95 to 1000 by weight, in
particular from 98 to 100% by weight, of propylene and
has a melting point of 120°C or above, preferably from
150 to 170°C, and generally has a melt flow index of from
0.5 to 8 g/10 min, preferably from 2 to 5 g/10 min, at
230°C and a force of 21.6 N (DIN 53 735). Isotactic
propylene homopolymer having an atactic content of 15o by
weight or less, copolymers of ethylene and propylene
having an ethylene content of 10% by weight or less,
copolymers of propylene with C4-C8-a-olefins having an a-
olefin content of 10% by weight or less, terpolymers of
propylene, ethylene and butylene having an ethylene
~~ 5~ 32~
- 6 -
content of 10% by weight or less and 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 percentages by
weight given are based on the particular polymer.
Also suitable is a mixture of said propylene homopolymers
and/or copolymers and/or terpolymers and/or other poly-
olefins, in particular comprising monomers having 2 to 6
carbon atoms, where the mixture comprises at least 50% by
weight, in particular at least 75% by weight, of
propylene polymer. Other polyolefins which are suitable
in the polymer mixture are polyethylenes, in particular
HDPE, LDPE and LLDPE, where the proportion of these
polymers does not exceed 15% by weight in each case,
based on the polymer mixture.
In general, the base layer can contain lubricants,
antistatics, stabilizers and/or neutralizers in effective
amounts in each case, and also, if desired, hydrocarbon
resin.
In a white or opaque or white/opaque embodiment, the base
layer additionally contains pigments or vacuole-inducing
particles or a combination thereof. Such films have a
light transparency, measured in accordance with ASTM-D
1033-77, of at most 50%, preferably at most 70%.
Pigments are particles which result in essentially no
vacuole formation during stretching of the film. The
coloring action of the pigments is caused by the
particles themselves. The term "pigment" is generally
associated with a particle size of from 0.01 to a maximum
of 1 um and covers both "white pigments", which give the
films a white color, and "colored pigments", which give
the film a colored or black color. In general, the mean
particle diameter of the pigments is in the range from
~1~~322
0.01 to 1 Vim, preferably from 0.01 to 0.7 Vim, in particu-
lar from 0.01 to 0.4 Vim. The base layer generally con-
tains pigments in an amount of from 1 to 25% by weight,
in particular from 2 to 20% by weight, preferably from 5
to 15% by weight, in each case based on the base layer.
Conventional pigments are materials such as, for example,
aluminum oxide, aluminum sulfate, barium sulfate, calcium
carbonate, magnesium carbonate, silicates, such as
aluminum silicate (kaolin clay) and magnesium silicate
(talc), silicon dioxide and titanium dioxide, preference
being given to white pigments such as calcium carbonate,
silicon dioxide, titanium dioxide and barium sulfate.
The titanium dioxide particles comprise at least 95% by
weight of rutile and are preferably employed with a
coating of inorganic oxides, as is usually used as a
coating for Ti02 white pigment in papers or paints for
improving the light fastness. Particularly suitable
inorganic oxides include the oxides of aluminum, silicon,
zinc and magnesium or mixtures of two or more of these
compounds. They are precipitated from water-soluble
compounds, for example alkali metal aluminates, in
particular sodium aluminates, aluminum hydroxide,
aluminum sulfate, aluminum nitrate, sodium silicate or
salicylic acid, in the aqueous suspension. Coated TiOz
particles are described, for example, in EP-A-0 078 633
and EP-A-0 044 515.
The coating may also contain organic compounds containing
polar and nonpolar groups. Preferred organic compounds
are alkanols and fatty acids having 8 to 30 carbon atoms
in the alkyl group, in particular fatty acids and the
primary n-alkanols having 12 to 24 carbon atoms, and
polydiorganosiloxanes and/or polyorganohydrosiloxanes,
such as polydimethylsiloxane and polymethylhydrosiloxane.
_ g _
The coating on the TiOZ particles usually comprises from
1 to 12 g, in particular from 2 to 6 g, of inorganic
oxides, and if desired additionally from 0.5 to 3 g, in
particular from 0.7 to 1.5 g, of organic compounds, in
each case based on 100 g of TiOz particles. It has proven
particularly advantageous for the TiOZ particles to be
coated with A1203 or with A1Z03 and polydimethylsiloxane.
Opaque embodiments of the films contain vacuole-inducing
particles, which are incompatible with the polymer matrix
and result in the formation of vacuole-like cavities when
the films are stretched, the size, type and number of
vacuoles being dependent on the material and on the size
of the solid particles and the stretching conditions,
such as stretching ratio and stretching temperature. The
vacuoles give the films a characteristic mother-of-pearl-
like, opaque appearance caused by light scattering at the
vacuole/polymer matrix interfaces. In general, the mean
particle diameter of the vacuole-inducing particles is
from 1 to 6 ~,m, preferably from 1.5 to 5 ~Cm. The base
layer generally contains vacuole-inducing particles in an
amount of from 1 to 25% by weight.
Conventional vacuole-inducing particles in the base layer
are inorganic and/or organic materials which are incom-
patible with polypropylene, such as aluminum oxide,
aluminum sulfate, barium sulfate, calcium carbonate,
magnesium carbonate, silicates, such as aluminum silicate
(kaolin clay) and magnesium silicate (talc), silicon
dioxide and titanium dioxide, preference being given to
calcium carbonate, silicon dioxide and titanium dioxide.
Suitable organic fillers are the usual polymers which are
incompatible with the polymer of the base layer, in
particular those such as HDPE, polyesters, polystyrenes,
polyamides and halogenated organic polymers, preference
being given to polyesters, such as, for example, poly-
butylene or polyethylene terephthalates. For the purposes
- 9 -
of the present invention, "incompatible materials" or
"incompatible polymers" means that the material or
polymer is present in the film as separate particles or
as a separate phase.
White/opaque films to which vacuole-initiating particles
and pigments have been added contain the vacuole-initiat-
ing particles in an amount of from 1 to 10% by weight,
preferably from 1 to 5% by weight, and pigment in an
amount of from 1 to 7% by weight, preferably from 1 to 5%
by weight.
The density of the opaque or white films can vary within
broad limits and depends on the type and amount of the
fillers. The density is generally in the range from 0.4
to 1.1 g/cm3. Pigmented films have a density in the order
of 0.9 g/cm3 or above, preferably in the range from 0.9
to 1.1 g/cm3. Films containing only vacuole-initiating
particles have a density of less than 0.9 g/cm3. For
packaging films having a content of vacuole-initiating
particles of from 2 to 5% by weight, the density is in
the range from 0.6 to 0.85 g/cm3. For films having a
content of vacuole-initiating particles of from 5 to 14%
by weight, the density is in the range from 0.4 to
0.8 g/cm3. Films containing pigments and vacuole-initiat-
ing particles have a density in the range from 0.5 to
0.85 g/cm3, depending on the ratio between the pigment
content and the content of vacuole-initiating particles.
The novel multilayer film may contain (a) further inter-
layer(s) between the base layer and the top layer. This
(these) interlayer(s) which may be present essentially
comprises) propylene polymers or polypropylene mixtures,
as described above for the base layer. In principle, the
base layer and the interlayer(s) can comprise the same or
different propylene polymers or mixtures. The melt flow
indices of the polymers for the core layer and inter-
- 10 -
layers) should be as close as possible in magnitude. If
necessary, the MFI of the interlayer(s) can be somewhat
higher, with a maximum difference of 20%. If desired,
additives in effective amounts in each case can be added
to the interlayers.
In a preferred embodiment of the novel film, the prop-
ylene polymer of the base layer and/or interlayer is
peroxidically degraded.
A measure of the degree of degradation of the polymer is
the degradation factor A, which gives the relative change
in melt flow index, measured in accordance with
DIN 53 735, of the polypropylene; based on the starting
polymer.
MFIZ
A=
A?Fh
25
MFI~ = melt flow index of the propylene polymer before
addition of the organic peroxide
MFI2 = melt flow index of the peroxidically degraded
propylene polymer.
In general, the degradation factor A of the propylene
polymer employed is in a range from 3 to 15, preferably
from 6 to 10.
Particularly preferred organic peroxides are dialkyl
peroxides, where the term alkyl radical is taken to mean
a conventional saturated, straight-chain or branched
lower alkyl radical having up to six carbon atoms.
Particular preference is given to 2,5-dimethyl-2,5-di(t-
butylperoxy)hexane and di-t-butyl peroxide.
- 11 -
The novel polyolefin film furthermore contains at least
one heat-sealable top layer. This top layer essentially
comprises heat-sealable polymers of a-olefins having 2 to
carbon atoms and amorphous polymer in the form of
5 separated particles and, if desired, further additives in
effective amounts in each case. In general, the top layer
comprises from 75 to virtually 100% by weight, in
particular from 90 to 99.5% by weight, of the heat-
sealable a-olefinic polymer.
Examples of such a-olefinic polymers are
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 said homopolymers,
copolymers and terpolymers or
a blend of two or more of said homopolymers, a
copolymers and terpolymers, if desired mixed with
one or more of said homopolymers, copolymers and
terpolymers,
particular preference being given to
random ethylene-propylene copolymers having
an ethylene content of from 1 to 10% by weight,
preferably from 2.5 to 8% by weight, or
random propylene-1-butylene copolymers having
a butylene content of from 2 to 25% by weight,
preferably from 4 to 20o by weight,
in each case based on the total weight of the
copolymer, or
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
- 12 -
a 1-butylene content of from 2 to 20% by
weight, preferably from 4 to 20% by weight,
in each case based on the total weight of the
terpolymer, or
a blend of an ethylene-propylene-1-butylene ter-
polymer and a propylene-1-butylene copolymer
having an ethylene content of from 0.1 to 7% by
weight
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 blend.
The above-described copolymers generally have a melt flow
index of from 1.5 to 30 g/10 min, preferably from 3 to
15 g/10 min, and a melting point in the range from 120 to
140°C. The terpolymers generally have a melt flow index
in the range from 1.5 to 30 g/10 min, preferably from 3
to 15 g/10 min, and a melting point in the range from 120
to 140°C. The above-described blend of copolymers and
terpolymers generally 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 abovementioned melt flow indices are measured at
230°C and a force of 21.6 N (DIN 53 735).
If desired, all the above-described top layer polymers
can have been peroxidically degraded in the same way as
described above for the base layer, in principle using
the same peroxides. The degradation factor for the top
layer polymers is generally in the range from 3 to 15,
preferably from 6 to 10.
According to the invention, the top layer of the film
contains at least one amorphous polymer in the form of
separated particles, generally in an amount of at most 5%
z~~~~~~
- 13 -
by weight, preferably from 0.001 to 3% by weight, in
particular from 0.01 to 2% by weight, based on the weight
of the top layer. It has been found that the amorphous
polymer, which is a polymeric solid per se and, as a raw
material, has no particle character, is, surprisingly, in
the top layer in the form of separated particles.
For the purposes of the present invention, amorphous
polymers are taken to mean polymers which are solids at
room temperature in spite of an irregular arrangement of
the molecular chains. They are essentially non-crystal-
line, and their degree of crystallinity is generally less
than 5%, preferably less than 2%, or is Oo. Particularly
suitable amorphous polymers are those whose glass
transition temperature T~ is in. the range from 70 to
300°C, preferably from 80 to 250°C, in particular from
100 to 200°C, or whose Vicat softening temperature T~
(VST/B/120) is from 70 to 200°C, preferably from 80 to
180°C. In general, the amorphous polymer has a mean
molecular weight Mw in the range from 500 to 500,000,
preferably from 1000 to 250,000, in particular from 3000
to 200,000.
The refractive index of the amorphous polymer is
generally in the range from 1.3 to 1.7, preferably from
1.4 to 1.6. It is particularly advantageous here if the
refractive index of the amorphous polymer is in a certain
ratio to the refractive index of the polyolefin of the
top layer. In general, the refractive indices of the
amorphous polymer and the polyolefin of the top layer
differ by at most 0.1 units, preferably by at most
0.05 units.
The amorphous polymer is, surprisingly, present in the
resultant film in the form of separated particles, which
are clearly evident in transmitted-light photographs of
the film surface. The particle size of the particles in
- 14 -
the top layer is in the range from 0.2 to 20 ~,m, prefer-
ably from 0.5 to 1.5 ~Cm.
It has been found that the particles of amorphous polymer
are generally approximately spherical. For the purposes
of the present invention, the term approximately
spherical particles covers particles which satisfy the
following condition:
i o f = AI (nI4) I o~
in which f is greater than 0.5, preferably from 0.7 to 1,
and A is the cross-sectional area in mmz and D~X is the
maximum diameter of the cross-sectional area in mm. The
factor f is a measure of the degree of sphericity of the
particles. The closer the value of f to 1, the closer the
shape of the particles to the ideal spherical shape.
Suitable amorphous polymers having the property profile
described above are a multiplicity of generally trans-
parent polymers. Examples thereof are atactic polystyrene
(T~ - 95 to 105°C, preferably 100°C), poly-a-methyl
styrene (T~ - 170 to 180°C, preferably 175°C), poly-
acrylates, in particular polymethyl methacrylate
(T~ = 115 to 130°C, preferably 122°C), amorphous
homopolymers and copolymers of polycyclic olefins
(T~ = 70 to 300°C depending on composition and molecular
weight), polyvinylcarbazole (T~ =180 to 220°C, prefer-
ably 200°C), atactic polyvinylcyclohexane (T~ - 130 to
150°C, preferably 140°C), polyvinyl chloride (T~ = 65 to
90°C, preferably 80°C), polyacrylonitrile (T~ - 100 to
110°C, preferably 106°C), specific types of rubber, in
particular cyclorubber (T~ = 70 to 120°C) , uncrosslinked,
partially crosslinked and crosslinked dispersions of
amorphous polymers (T~ from 70 to 200°C depending on
polymerization partner and degree of polymerization).
CA 02154322 2005-07-04
29478-22
- 15 -
Suitable cycloolefin copolymers are known per se and are
described in EP-A-0 407 870, EP-A-0 485 893,
EP-A-0 503 422 and DE-A-40 36 264.
The cycloolefin polymers employed are built up from one
or more cycloolefins, where the cycloolefins employed are
generally substituted or unsubstituted cycloalkenes
and/or polycycloalkenes, such as, for example, bi-, tri-
or tetracycloalkenes. The cycloolefin polymers may also
be branched. Such products can have a comb or star
structure.
Particular preference is given to cycloolefin copolymers
Z5 containing at least one polycyclic olefin of the formulae
I to VI below:
Rt
CN
HC "~ ~ CH
R3 ~ C...._R;
HC ~~ /CH~R~
CH
CH ~ ~ CH2
He ~ CH
(it):
R3 - C! R,~ ~ CHZ
HC I CHI
1"~ CH ~ CH2
- 16 -
R
C H ~ C H ---.~ C H
HC ~ NCH ' (I11~.
RS--C~ Ri
Ry -C~R~
~H ~ y
HC ~ / CH ~ CH ~ R
1"~ C H
R~
CH H'
HC ' ~H CH ~ 'CH CH
(IY).
R C R R~ C-- Ra
gs -- C-R,
I CH
HC ~CH~ IH ~CH\ CH~ R
~ C / 'H
R=
J y
/ C H -.
I H ~ CH' CH
HC
~Y).
R R
HC~ ~H ~GH_", CH ~"tH\Ri
I
Rt
RZ
I A1
C H -..' r..r" ~ H "_ /
CH _ CH ~ CH CH
~ R7~C R (YI).
HC-~ ~H ~CH~ C1~..-~CH~ ~H~CH~ ~
I . R
R~
The radicals R~ to R8 in the formulae I to VI may be
identical or different and are H, C6-C2o-aryl, C~-C2o-
alkyl, F, Cl, Br, I or a monocyclic olefin of the formula
VII below
in which n is a number from 2 to 10.
z~ ~~3zz
- 17 -
Cii - CN ( Y i I )
..
(c~z)~ .
The cycloolefin polymers are preferably prepared with the
aid of transition-metal catalysts, which are described in
the abovementioned specifications. Preference is given to
the preparation processes of EP-A-0 407 870 and
EP-A-0 485 893, since these processes give cycloolefin
polymers having a narrow molecular weight distribution
(M',1/M~ - 2 ) . This avoids the disadvantages such as
migration, extractability or tack of the (or caused by
the) low-molecular-weight constituents.
A particularly good property profile is achieved using
cycloolefin polymers which have a moderate to high
molecular weight in the range from 1000 to 200,000,
preferably from 2000 to 180,000, in particular from 3000
to 150,000. The molecular weight is regulated during the
preparation by using hydrogen and a specific choice of
the catalyst and reaction conditions.
The novel multilayer film comprises the above=described
base layer and at least one top layer and, if desired,
further layers. Preference is given to three-layer
embodiments, which have a top layer on both sides of the
base layer, it being possible for these top layers to be
identical or different in thickness and composition.
Preference is also given to five-layer embodiments, which
contain a base layer, interlayers applied to both sides
of the base layer and top layers on both sides.
The overall thickness of the novel multilayer polyolefin
film can vary within broad limits and depends on the
intended use. It is preferably from 5 to 70 Vim, in
- 18 -
particular from 10 to 15 Vim, the base layer making up
from about 50 to 90% of the total film thickness.
The thickness of the top layers) is greater than 0.2 ~,m
and is preferably in the range from 0.3 to 2 Vim, in
particular greater than from 0.5 to 1 Vim, where top
layers on both sides can have identical or different
thicknesses.
The thickness of any interlayer(s) present is, in each
case independently of one another, from 1 to 12 Vim,
preferably from 2 to 8 Vim, in particular from 3 to 6 Vim.
The values given are each based on one interlayer.
In addition to this selected top layer additive, the
novel multilayer film may additionally contain
neutralizers, stabilizers, lubricants, hydrocarbon resins
and/or antistatics in one or more layers. The percentages
by weight given below relate to the weight of the
respective layer to which the additive has been added.
Neutralizers are preferably dihydrotalcite, calcium
stearate and/or calcium carbonate having a mean particle
size of at most 0.7 Vim, an absolute particle size of less
than 10 ~,m and a specific surface area of at least
40 mz/g. In general, the neutralizer is added in an
amount of from 0.02 to O.lo by weight.
Stabilizers which can be added are the conventional
stabilizing compounds for polymers of ethylene, propylene
and other a-olefins. The amount in which they are added
is between 0.05 and 2% by weight. Particularly suitable
are phenolic stabilizers, alkali/alkaline earth metal
stearates and/or alkali/alkaline earth metal carbonates.
Phenolic stabilizers are preferred in an amount of from
0.1 to 0.6% by weight, in particular from 0.15 to 0.3% by
215322
- 19 -
weight, and having a molecular weight of greater than
500 g/mol.Pentaerythrityltetrakis[3-(3,5-di-tert-butyl
4-hydroxyphenyl)propionate] and 1,3,5-trimethyl-2,4,6
tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene are
particularly advantageous.
Lubricants are higher aliphatic acid amides, higher
aliphatic acid esters, waxes and metal soaps, and poly-
dimethylsiloxanes. The effective amount of lubricant is
in the range from 0.1 to 3% by weight. The addition of
higher aliphatic acid amides in the range from 0.15 to
0.25% by weight to the base layer and/or the top layers
is particularly suitable. A particularly suitable ali-
phatic acid amide is erucamide.
Hydrocarbon resins are low-molecular-weight polymers
whose molecular weight is generally in the range from 300
to 8000, preferably from 400 to 5000, in particular from
500 to 2000. The molecular weight of the resins is thus
significantly lower than that of the propylene polymers
which form the principal component of the individual film
layers and generally have a molecular weight of greater
than 100, 000. The hydrocarbon resins are preferably added
to the base layer and/or the interlayer(s) . The effective
amount of low-molecular-weight resin is from l~to 20% by
weight, preferably from 2 to 10% by weight, based on the
layer.
The low-molecular-weight resin recommended is a natural
or synthetic resin having a softening point of from 60 to
180°C, preferably from 80 to 150°C, determined in accor-
dance with ASTM E-28. Of the numerous low-molecular-
weight resins, preference is given to hydrocarbon resins,
specifically in the form of petroleum resins, styrene
resins, cyclopentadiene resins and terpene resins (these
resins are described in Ullmanns Encyklopadie der
technischen Chemie [Ullmann's Encyclopedia of Industrial
CA 02154322 2005-07-04
29478-21
- 20 -
Chemistry], 4th Edition, Volume 12, pages 525 to 555).
Suitable petroleum resins are described in numerous
specifications, such as, for example, EP-A-0 180 087.
Preferred antistatics are alkali metal alkanesulfonates,
polyether-modified, i.e. ethoxylated and/or propoxylated,
polydiorganosiloxanes (polydialkylsiloxanes, polyalkyl-
phenylsiloxanes and the like) and/or the essentially
straight-chain and saturated, aliphatic, tertiary amines
containing an aliphatic radical having 10 to 20 carbon
atoms which are substituted by ~-hydroxy-(C~-C4)-alkyl
groups, N,N-bis(2-hydroxyethyl)alkylamines having 10 to
20 carbon atoms, preferably 12 to 18 carbon atoms, in the
alkyl radical being particularly suitable. The effective
amount of antistatic is in the range from 0.05 to 3% by
weight. A further preferred antistatic is glycerol
monostearate.
The invention furthermore relates to the production of
the novel multilayer films by the coextrusion process,
which is known per se.
In this process, as is customary in coextrusion, the
polymer or polymer mixture of the individual layers is
compressed and liquefied in an extruder, it being
possible for any additives added to be present in the
polymer or polymer mixture already or to be added via the
masterbatch method. The melts corresponding to the
individual layers of the film are then coextruded simul-
taneously through a flat-film die (slot die), and the
extruded multilayer film is drawn off over one or more
take-off rolls, where it cbols and solidifies.
The resultant film is then stretched longitudinally and
transversely to the extrusion direction, which results in
orientation of the molecule chains. The stretching is
2~5~322
- 21 -
preferably from 4:1 to 7:1 in the longitudinal direction
and from 7:1 to 11:1 in the transverse direction. The
longitudinal stretching is expediently carried out with
the aid of two rolls running at different speeds
corresponding to the desired stretching ratio, and the
transverse stretching is expediently carried out with the
aid of an appropriate tenter frame.
Biaxial stretching of the film is followed by heat-
setting (heat treatment), the film being kept at a
temperature of from 100 to 160°C for about 0.5 to
10 seconds. The film is subsequently wound up in the
conventional manner by means of a wind-up unit.
It has proven particularly favorable to keep the take-off
roll or rolls, by means of which the extruded film is
also cooled and solidified, at a temperature of from 20
to 90°C.
The temperatures at which longitudinal and transverse
stretching are carried out can vary. In general, the
longitudinal stretching is preferably carried out at from
100 to 150°C and the transverse stretching is preferably
carried out at from 155 to 190°C.
If desired, one or both surfaces of the film can, as
mentioned above, be corona- or flame-treated by one of
the known methods after the biaxial stretching.
In the case of corona treatment, the film is expediently
passed between two conductor elements serving as
electrodes, such a high voltage, usually alternating
voltage (about 10 to 20 kV and 20 to 40 kHz, being
applied between the electrodes that spray or corona
discharges can occur. The spray or corona discharge
ionizes the air above the film surface and reacts with
the molecules of the film surface, causing formation of
~~'5~3~2
- 22 -
polar inclusions in the essentially nonpolar polymer
matrix.
For flame treatment with a polarized flame (cf.
US-A-4,622,237), a direct electric voltage is applied
between a burner (negative pole) and a chill roll. The
level of the applied voltage is between 500 and 3000 V,
preferably in the range from 1500 to 2000 V. The applied
voltage gives the ionized atoms increased acceleration,
and they hit the polymer surface with greater kinetic
energy. The chemical bonds within the polymer molecule
are more easily. broken, and formation of free radicals
proceeds more rapidly. Heating of the polymer here is
substantially less than in the case of standard flame
treatment, and films can be obtained in which the heat-
sealing properties of the treated side are even better
than those of the untreated side.
The amorphous polymers can be incorporated into the top
layer or top layers of the film either as pure granules
or as granulated concentrate (Masterbatch), by premixing
the polyolefin granules or powder of the top layers)
with the amorphous polymer and subsequently feeding the
mixture to the extruder. In the extruder, the components
are mixed further and warmed to the processing tempera-
ture. It has been found that the lubricant properties and
the appearance of the film also depend on the extrusion
conditions (temperature and shear). Surprisingly, the
lubricant properties and appearance of the film vary with
the conditions in the extruder under otherwise identical
conditions with respect to raw materials and stretching
process. It is essential for the novel process for the
production of the film that the extrusion temperature for
the top layers) is above the glass transition tempera-
ture/Vicat softening temperature of the amorphous
polymer. In general, the extrusion temperature for the
top layers) is at least 10°C, preferably from 15 to
~1~~~~2
- 23 -
180°C, in particular from 20 to 150°C, above the T~ or T~
of the amorphous polymer.
It is assumed that the amorphous polymer liquefies under
the usual extrusion conditions for film production and
then surprisingly separates during the extrusion into
particulate particles of a certain size, depending on the
viscosity of the polyolefin of the top layer and the
viscosity of the amorphous polymer at the selected
extrusion temperature, and does not agglomerate. The
amorphous polymer, which is simply added as solid, is
thus, after the extrusion and orientation, in the form of
separated particles in the top layer of the film which
act as antiblocking agent.
The novel film has better gloss and haze than known films
having low coefficients of friction and is likewise
distinguished by a low coefficient of friction and low
surface roughness. The coefficient of sliding friction of
lubricant-free embodiments of the novel films is
generally in the range from 0.3 to 0.7, preferably from
0.3 to 0.5. Films additionally containing a lubricant,
such as, for example, fatty acid amide, in particular
erucamide, have an even further reduced coefficient of
sliding friction. In the case of the novel film contain-
ing erucamide in the base layer, this is generally in the
range from 0.05 to 0.3, preferably from 0.1 to 0.2. The
gloss of the novel film is in the range from 90 to 130,
preferably from 105 to 130. The haze of transparent
embodiments is in the range from 0.9 to 3.0, preferably
in the range from 0.9 to 2Ø
The invention is now described in greater detail with
reference to working examples.
215~~~~
- 24 -
Example 1
A three-layer film having an overall thickness of 20 ~Cm
and an ABA layer structure, i.e. the base layer B was
surrounded by two identical top layers A, was produced by
coextrusion and subsequent stepwise orientation in the
longitudinal and transverse directions.
The film was subjected to one-sided corona treatment on
the roll side before rolling up. The roll side is the
side of the film with which it is in contact with the
first take-off roll. The surface tension on this side as
a consequence of this treatment was from 39 to 40 mN/m.
All layers contained 0.13% by weight of pentaerythrityl
tetrakis[4-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]
(~Irganox 1010) as stabilizer and 0.06% by weight of
calcium stearate as neutralizer.
The base layer B essentially comprised a propylene
homopolymer having an n-heptane-soluble content of 4% by
weight and a melting range of from 160 to 162°C. The melt
flow index of the propylenehomopolymer was 3.4 g/10 min
at 230°C and a load of 21.6 N (DIN 53 735). The base
layer contained 0.12% by weight of erucamide having a
melting range of from 78 to 82°C and 0.12% by weight of
N,N-bis-ethoxyalkylamine (~Armostat 300).
The polyolefinic top layers essentially comprised an
ethylene-propylene-1-butene terpolymer containing 3.5% by
weight of ethylene, 88.5% by weight of propylene and 8%
by weight of 1-butene. The top layers contained 0.05% by
weight of a cyclic olefin copolymer having a T~ of 174°C
and a mean molecular weight of 34, 000. Each of the top
layers was 0.8 ~Cm thick.
Example 2
Example 1 was repeated, but the top layer contained 0.15%
by weight of the same cycloolefin copolymer.
21~~322
- 25 -
Comparative Example 1
Example 1 was repeated, but the antiblocking agent
employed was 0.15% by weight of a crosslinked silicone
resin powder having a mean particle diameter of 2 ~m
(~Tospearl 20 from Toshiba Silicone Co., Ltd.).
Comparative Example 2
Example 1 was repeated, but the antiblocking agent
employed was 0.15% by weight of an organically coated
silicon dioxide having a mean particle diameter of 2 ~m
(~Sylobloc 44 from Grace).
Comparative Example 3
Comparative Example 1 was repeated, but the top layer
contained 0.33% by weight of the silicone resin powder.
Comparative Example 4
Comparative Example 2 was repeated, but the top layer
contained 0.33% by weight of the coated silicon dioxide.
The properties of the films of the examples and compara-
tive examples are summarized in the table below.
The following measurement methods were used to
characterize the raw materials and the films:
Melt flow index
The melt flow index was measured in accordance with
DIN 53 735 at a load of 21.6 N and at 230°C.
Meltinc~point
DSC measurement, maximum of the melting curve, heating
rate 20°C/min.
Determination of the minimum sealing temperature
Heat-sealed samples (seal seam 20 mm x 100 mm) are
produced using a Brugger HSG/ET sealing unit by sealing
~~~~3zz
- 26 -
a film at different temperatures with the aid of two
heated sealing jaws at a sealing pressure of 10 N/cm2 and
a sealing time of 0.5 s. Test strips 15 mm in width are
cut out of the sealed samples. The T-seal seam strength,
i.e. the force necessary to separate the test strips, is
determined using a tensile testing machine at a take-off
rate of 200 mm/min, the seal seam plane forming a right
angle with the tension direction. The minimum sealing
temperature is the temperature at which a seal seam
strength of at least 0.5 N/15 mm is achieved.
Seal seam strength
For the measurement, two film strips 15 mm in width were
laid one on top of the other and sealed for 0.5 s at
130°C and a sealing pressure of 1.5 N/mm2 (Brugger NDS
unit, sealing jaws heated on one side). The seal seam
strength was determined by the T-peel method.
Friction
The friction was determined in accordance with
DIN 53 375. The coefficient of sliding friction was
measured 14 days after production.
Surface tension
The surface tension was determined by the ink method
(DIN 53 364).
Roughness
The roughness was determined in accordance with DIN 4768
at a cut-off of 0.25 mm.
Haze
The haze of the film was measured in accordance with
ASTM-D 1003-52. The Holz haze measurement was carried out
in accordance with ASTM-D 1003-52, but, in order to
utilize the optimum measurement range, the measurement
was carried out on four film layers lying one on top of
2~~~32~
- 27 -
the other and using a 1° slit diaphragm instead of a 4°C
pinhole diaphragm.
Gloss
The gloss was determined in accordance with DIN 67 530.
The reflector value was measured as an optical parameter
for the surface of a film. In accordance with the
ASTM-D 523-78 and ISO 2813 standards, the angle of
incidence was set at 20 ° or 60 ° . A light beam hits the
planar test surface at the set angle of incidence and is
reflected or scattered thereby. The light beams incident
on the photoelectronic receiver are indicated as a
proportional electrical quantity. The measurement value
is dimensionless and must be specified together with the
angle of incidence.
- 2~
'~~ ~a-
r5
a
m _ ~ ~ N
m In O O T O T
O
3 Q (tnD.O tI~T ~ M
O
Q O O O O
C 07
~U m ~ T T M T M
V Q O O O O O
U
m
' ~ N N ~ N N
M T T T T T T
O
U
Z Q N ~1 CO N CO CO
1 T T T T T T
L O ~ T T T T T T
'
T
~ ~
M
O
O_ T CO ~ tn N I~-
T M M ~' M
T
H' N
Q
L
N Ln ~ tI7 M T
~t N N M M
C
O ~ ~ C~~C'~~M N
N
T T T T T T
N
_N
N Q
_O
C
O p
N N ~ O O O O
p
T T T T T T
L
u'~ U opC Q
T M
ti! t,NU U U n a n a
U U
U Q m
