Note: Descriptions are shown in the official language in which they were submitted.
' 2154320
94/R 039 - 1 -
Non-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 non-heat-sealable top layer. The films are
distinguished by low haze, high gloss and a low coeffi-
cient of friction.
Transparent oriented polypropylene films are employed,
for example, in glass-lamination with paper or board. The
films are generally non-heat-sealable, since the lami-
nation takes place by the adhesive bonding of film and
paperboard.
This application makes high demands of the film appear-
ance and processing properties. The optical properties of
the film are principally described by the surface gloss
and the haze. For the processing properties, the fric-
tion, antistatic properties, abrasion behaviour, thick-
ness profile, roll make-up and flat lying of the film are
of great importance.
The prior art describes films having a low coefficient 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.
EP-A-0 124 310 describes films having a low coefficient
of friction which comprise a thick base layer and a thin
top layer containing finely divided inorganic particles.
- 2154320
- 2 -
The inorganic particles mentioned are SiOZ, aluminum
silicates, sodium aluminum silicates and carbon black.
The particle size is in the range from 0.2 to 5.0 ~,m. The
particles have an advantageous effect on the coefficients
of friction of the film. However, the film is still
highly unsatisfactory with respect to its roll make-up
and flat lying.
EP-A-0 350 168 describes a film having differentiated
sliding properties of the two surfaces. The top layers
are heat-sealable and contain Si02 as antiblocking agent.
EP-A-0 234 758 describes a multilayer polyolefin film
having good absorption capacity for water-based coatings.
The polypropylene top layer contains an antiblocking
agent and silicone oil. Si02, silicates, chalk, clay and
the like are described as suitable antiblocking agents,
but no detailed mention is made of the particle size of
the various antiblocking agents.
DE-A-35 17 795 describes multilayer polypropylene films
whose top layer contains a combination of amine, poly-
dialkylsiloxane and platelet-shaped inorganic pigment.
The film is distinguished by good antiblocking and
sliding properties. The platelet-shaped pigment has a
leaf structure. Suitable pigments are silicates and
carbonates.
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
2154320
- 3 -
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
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 Si02 as antiblocking agent in
heat-sealable films. The coefficient of friction and
processing behavior of the film have 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. Si02 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
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
CA 02154320 2005-06-30
29478-20
- 4 -
example, printing or metallization.
The present invention avoids or at least mitigates the
disadvantages of the films of the prior art. In par-
ticular, there is provided a multilayer film which
is distinguished by a combination of the following
properties:
~ high gloss
~ low haze
low abrasion
l0 ~ a low coefficient of friction
~ low surface roughness.
The invention is achieved by a
multilayer film of the generic type specified at the
outset, wherein the non-heat-sealable top layer includes
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 100% 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). Isotaetic
propylene homopolymer having an atactic content of 15% by
weight or less, copolymers of ethylene and propylene
having an ethylene content of 10o by weight or less,
copolymers of propylene with C4-C8-a-olefins having an a-
olefin content of 10% by weight or less and terpolymers
~~J~320
_ 5 _
of propylene, ethylene and butylene having an ethylene
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.
In general, the base layer can contain lubricants,
antistatics, stabilizers and/or neutralizers in effective
amounts in each case, and also, if desired, hydrocarbon
1o resin.
The novel multilayer film may contain (a) further inter-
layers) 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- _
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.
21J~32~
- 6 -
MF12
A =
MFI,
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.
The novel polyolefin film furthermore contains at least
one non-heat-sealable top layer. This top layer essen-
tially comprises non-heat-sealable polypropylene and at
least one amorphous polymer in the form of 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 propylene polymer.
The propylene homopolymer comprises from 95 to 100% by
weight, preferably from 98 to 100% by weight, of prop-
ylene and has a melting point of 140°C or above, prefer-
ably 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 15% by weight or less, copolymers of ethylene and
propylene having an ethylene content of 3% by weight or
less and copolymers of propylene with C4-C$-a-olefins
having an a-olefin content of 3% by weight or less are
~1~~3~0
preferred propylene polymers for the top layer, parti-
cular preference being given to isotactic propylene
homopolymer. The percentages by weight given are based on
the particular polymer.
If desired, 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%
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 ah 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 0%. 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
~1a~43~~
_8_
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
the top layer is in the range from 0.2 to 20 Vim, prefer-
ably from 0.5 to 1.5 Vim.
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:
f = A/ (rr/4) /D",~
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.
Surprisingly, the separated particles of amorphous
polymer in the homopolymer top layer have little adverse
effect on the excellent transparency of the film. It is
known from the prior art that the incorporation of
particulate fillers to a homopolymer base layer during
stretching results in the formation of vacuole-like
cavities in the layer (EP-A-0 083 495). The larger the
particle size of the fillers, the larger the vacuoles
CA 02154320 2005-06-30
29478-20
_ g _
formed. These filler-containing films have a charac-
teristic virtually opaque appearance due to the vacuoles.
It was therefore extremely surprising that the novel
films have virtually unimpaired transparency, since a
person skilled in the art would have expected the forma-
tion of vacuoles in the homopolymer top layer due to the
separated, amorphous particles and thus a considerable
increase in the haze of the film. Furthermore, it has
been found, entirely unexpectedly, that the novel film
to exhibits virtually no abrasion phenomena during produc-
tion or further processing.
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-methylsty-
rene (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 (TG - 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 I20°C), uncrosslinked,
partially crosslinked and crosslinked dispersions of
amorphous polymers (TG from 70 to 200°C depending on
polymerization partner and degree of polymerization).
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-
zm~~zo
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
containing at least one polycyclic olefin of the formulae
I to VI below:
R~
CH ~
HC CH~
3 - ~_ 4 ( I )'
IIR R I
CH
HC ~ I / R~
CH
HC ~CH ~ / CHZ
I CH
R3 - C-R~ ( CHZ
HC I CH
CH / CH2
R~
HC ~ CH ~ ~ CH 'CH
I CH
Rs-C- R6 ( I I I ) .
~~ RS C R~ I
-CH ~ CH' CH
HC I I CH ' R
215320
CH Rt
HC ~CH~CH~~H'CH~ I \CH~
R - I-R, Rs-C-R6 R~_C- Rs ( (IYj,
CH\ I /CH\ I /CH\R'
HC NCH / CH \ C /H
RZ
l R~
' CH
HC' I H ~ CH' NCH .
. C R4 I . (Y)
HC_ IH ~CH_ CH ~CH\Rt
R~
R~
l RI
' CH CH ~
HC' IH ~ CH ' ~CH~ I CH
R C R ~ R~ C Rs~ (YI~
HC' I ~ CH _ ' CH_ I CH
CH CH CH I ~R ~
l
RZ
The radicals R' to R$ in the formulae I to VI may be
identical or different and are H, C6-C2o-aryl, C~-C2o-
alkyl, F, C1, Br, I or a monocyclic olefin of the formula
VII below
CH - CH (Y(1)
(CHz,n . . .
in which n is a number from 2 to 10.
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
215320
- - 12 -
EP-A-0 485 893, since these processes give cycloolefin
polymers having a narrow molecular weight distribution
(Mw/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 3 to 100 Vim, in
particular from 5 to 60 Vim, the base layer making up from
about 50 to 97% of the total film thickness.
The thickness of the non-heat-sealable top layers) is
greater than 0.1 ~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 ~cm.
215~3~0
- 13 -
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 m2/g. In general, the neutralizer is added in an
amount of from 0.02 to 0.1% 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
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.
CA 02154320 2005-06-30
29478-20
- 14 -
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
to amount of low-molecular-weight resin is from 1 to 20% by
weight, preferably from 2 to 100 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
2o resins are described in Ullmanns Encyklopadie der
technischen Chemie ~Ullmann's Encyclopedia of Industrial
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 o-hydroxy-(C'-C4)-alkyl
groups, N,N-bis(2-hydroxyethyl)alkylamines having 10 to
20 carbon atoms, preferably l2 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
21a~~2~
- 15 -
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 cools 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
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.
215420
- 16 -
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
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
2~~432~
- 17 -
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-
s 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
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. Novel films additionally containing a lubri-
cant, such as, for example, fatty acid amide, in
215%320
- 18 -
particular erucamide, have an even further reduced
coefficient of sliding friction. In the case of the novel
film containing 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 100 to 150, preferably from 110 to 145. The haze of
transparent embodiments is in the range from 0.2 to 2.5,
preferably in the range from 0.4 to 2Ø
The invention is now described in greater detail with
reference to working examples.
Example 1
A three-layer film having an overall thickness of 20 ~m
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
~I~~320
- 19 -
isotactic propylene homopolymer having an n-heptane-
soluble content of 4.0% by weight and a melting point of
160°C.
The top layers contained 0.05% by weight of a cyclic
olefin copolymer having a T~ of 174 ° C and a mean mole-
cular weight of 34,000. Each of the top layers was 0.4 ~m
thick.
Example 2
Example 1 was repeated, but the top layer contained 0.15%
by weight of the same cycloolefin copolymer.
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:
215~3~0
.,. - 2 0 -
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.
Meltinct point
DSC measurement, maximum of the melting curve, heating
rate 20°C/min.
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
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
z1~~320
- 21 -
proportional electrical quantity. The measur.,ement value
is dimensionless and must be specified together with the
angle of incidence.
2154320
- 22 -
m
T CO
O O O O O O
Q t~ M t~ O I~ T
O O O O O O
O-.~- m ~ ~ ~ N r N
O
U
O. Q O O O O O O
O O ""
U
c~
0
O L
j, CO f~ O O N
T
T O O T T T
J Q
N
cu
H I
L
> ~ O I~ tn ~ f~
'O T T T DO T
~ T
_
rt~
. Q
d
O ~ N N N N
N ~ T T T T T
T
Q..
~ U ~ 'a
s
t1
n a a n
T U C'~ ti'
U U U
u! u~ wUQm
