Note: Descriptions are shown in the official language in which they were submitted.
CA 02110440 2003-09-19
Description
Polypropylene molding composition for producing calendered
films
The present invention relates to a molding composition for
producing polypropylene films by calendering, which molding
composition consists of a homopolymer or copolymer of
propylene and a thermoplastic fluoropolymer with a fluorine
content of at least 50o and a melting point below the
customary processing temperature of polypropylene.
The production of films from polypropylene is carried out
predominantly by extrusion, such as, for example, by film
blowing or by extrusion via a slit die with subsequent
cooling on metal rolls (chill-roll process). By comparison,
the calendering process, which is customary in PVC film
production for producing especially high-quality films, has
only a minor importance. Although the production of
calendered films from polypropylene was described for the
first time as long as over 30 years ago, because of unsolved
technical problems the process has scarcely become
widespread.
Polypropylene molding compositions tend to adhere very
intensively at the temperatures customary for calendering.
This makes it necessary to add relatively large amounts of
release agents, which lead to undesired secondary effects,
such as, for example, to roll deposits and therefore to poor
surface qualities of the films or to impairment of the
transparency or weldability of the films.
The low melt elasticity of the polypropylene in comparison
limits the polypropylene grades coming into consideration
for calendering to those with a high melt viscosity.
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However, these PP grades have a high tendency to
crystallize, leading to disturbing surface structures which
reduce the quality.
It is known the polypropylene grades suitable for producing
calendered films must have a MFI 230/21.6 of 0.4 to 2.0 g/10
min, and they must be stabilized so that their melt flow
index does not rise above 2.4 g/10 min during processing
(cf. EP 40 298).
Moreover, a process for producing PP calendered films is
known in which the polypropylene has a MFI 230/21.6 of 0.2
to 1.0 g/10 min and additional release agents such as
siloxanes, polyoctamers and metal salts of carboxylic acids
are added (cf. DE 32 40 338).
Also known is a polyolefin molding composition for producing
calenderized films, in which suitable polypropylene grades
have, for example, a MFI 230/21.6 of 0.5 g/10 min (cf. DE 40
28 407). The said molding compositions contain a stabilizer
system composed of phosphites or sulfur compounds in
conjunction with a phenolic antioxidant which has the
function of suppressing an increase of the MFI value during
the course of processing and thus of suppressing a
relatively intense adhesion tendency of the polyolefin.
According to the prior art, PP grades with a high melt
viscosity, that is to say with a MFI 230121.6 of less than
5g/10 min, are accordingly necessary for producing
calendered films from polypropylene, additional stabilizers
and lubricants and release agents being advantageously used.
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It is known that the processing behavior of polyolefins is
improved by the addition of fluoropolymers, which are
obtainable from tetrafluoroethylene, vinylidene fluoride,
hexafluoropropene, vinyl fluoride and
chlorotrifluoroethylene (cf. US 31 25 547). The addition of
these fluoropolymers, in specific polyolefins, preferably in
LLDPE (Linear Low Density Polyethylene), increases the
flowability of the polymer melt. In addition, in processing
operations in which the polymer melt is subject to high
shearing, such as, for example, in film blowing through
narrow annular dies, they improve the surface quality of the
extrudate by preventing the occurrence of melt fracture
(shark-skin).
Finally, the addition of small amounts of vinylidene
fluoride to PP molding composition has been disclosed (cf.
JP 61/085 457). These small amounts are intended to produce
extruded films with improved slipping properties.
It has now been found that specific fluorine-containing
polymers, in very small amounts, reduce the adhesion
tendency of PP molding compositions in such a manner that
even polypropylene with a significantly higher MFI can
advantageously be processed on calenders to produce films
and the addition of other lubricants and release agents is
in general superfluous.
The invention thus relates to a polypropylene molding
composition for producing calendered films which comprises
99.5 to 99.999% by weight of a homopolymer or copolymer of
polypropylene with a MFI 230/2.16 of 2.0 to 25g/10 min and
0.001 to 0.5% by weight of a fluorine-containing
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thermoplastic polymer with a fluorine content of at least
50o and a melting point of below 250°C.
The polypropylene molding composition according to the
invention comprises 99.5 to 99.999, preferably 98 to 99.5, o
by weight of a homopolymer or copolymer of propylene with a
MFI 230/2.16 of 2.0 to 25g/10 min, preferably 4 to 15 g/10
min. The copolymers of propylene include, for example,
ethylene/propylene copolymers, propylene/1-butene copolymers
and propylene/isobutylene copolymers. Mixtures of
homopolymers or copolymers of propylene with terpolymers of
propylene, ethylene and a diene are also possible.
Furthermore, the molding composition according to the
invention consists of 0.001 to 0.5, preferably 0.02 to
0.040, by weight of a fluorine-containing thermoplastic
polymer with a fluorine content of at least 50%, preferably
more than 700, and a melting point below the customary
processing temperature of the polypropylene, that is to say
below 250°C, preferably below 190°C, and in particular from
100 to 130°C.
Suitable fluorine-containing polymers are produced by
copolymerization of vinylidene fluoride and
hexafluoropropylene or by terpolymerization of vinylidene
fluoride, hexafluoropropylene and tetrafluoroethylene. Such
fluoropolymers preferably have a fluorine content of over
500, in particular of more than 68~ and a melting point
below the customary processing temperature of the
polypropylene, that is to say less than 230°C. A
particularly preferred fluoropolymer is composed of
tetrafluoroethylene, vinylidene fluoride and
hexafluoropropylene with a fluorine content of
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68 to 76~ and a melting point of less than 185°C,
particularly preferably from 100 to 130°C.
The molding composition according to the invention can
additionally contain further additives, such as, for
example, antioxidants, for example alkylated monophenols,
alkylated hydroquinones, hydroxylated thiodiphenyl ethers,
alkylidene bisphenols, benzyl compounds, acylaminophenols,
(3-(5-t-butyl-4-hydroxy-3-methylphenyl)-propionates, (3-(3,5-
di-t-butyl-4-hydroxyphenyl) propionamides, UV absorbers and
light stabilizers, for example 2-(2'-
hydroxyphenyl)benzotriazoles, 2-hydroxybenzophenones, oxalic
diamides, possibly substituted benzoates, acrylates, nickel
compounds, sterically hindered amines (HALS), metal
deactivators, phosphates and phosphonites, peroxide-
scavenging compounds, basic costabilizers, nucleating
agents, fillers and reinforcing agents, plasticizers,
optical brighteners, flameproofing agents, antistatic
agents, blowing agents, lubricants and pigments.
For metering in the fluorine-containing polymer, all methods
come into consideration which are otherwise customary for
the addition of additives. For example, it is possible
continuously to add the fluoropolymer to the polypropylene
during preparation, compounding or processing. It is
especially advantageous to choose methods permitting an
especially uniform distribution of the fluoropolymers;
incorporation using kneaders, Banbury mixers, or mixing
extruders can be quoted as examples in this regard. It is
advantageous to produce a more highly concentrated mixture
of fluoropolymer and polypropylene which contains, for
example, 0.1 to 20~ by weight of fluoropolymer, in
particular 1 to 3$ by weight of
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fluoropolymer, and, after its production is in the form of a
powder, beads or cylindrical pellets. This master batch can
then be metered into the polypropylene, for example in the
plastication extruder, in the course of film production and
results in a very homogenous distribution of the active
substance, even on machines without special mixing elements.
Using the molding composition according to the invention, it
is possible to produce, by calendering, polypropylene films
of high quality. For example, it is possible to produce
calendered films by plasticating a polypropylene molding
composition and drawing out the plastic state on a film
calender, wherein a molding composition is used which
comprises 99.5% to 99.999% by weight of a homopolyer or
copolymer of propylene with a MFI 230/2.16 of 2.0 to 25 g/
10 min and 0.001 to 0.5% by weight of a fluorine-containing
theromplastic polymer with a fluorine content of at least
50% and a melting point of below 250°C. The addition of
fluoropolymers is not only effective as regards the release
effect, but also results in significantly fewer deposits and
provides an improved take-off behavior in comparison to the
use of conventional lubricants.
The following examples are intended to explain the invention
in greater detail.
A 4-roll, L-type laboratory calender from Schwabenthan with
a roll width of 35 cm and a roll diameter of 15 cm was used.
The rolls are electronically heated. The following settings
were made for all tests:
2l~Ot~40
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Roll Temperature (C) Speed (rpm)
Heating roll 1 150 10
Heating roll 2 170 12
Heating roll 3 170 15
Heating roll 4 120 18
Cooling roll 1 15 18
Cooling roll 2 15 18
The polypropylene was plasticated by
means of a twin-
screw extruder.
The temperature
was chosen
in dependence
on the temperature
PP grade at
used such
that the
melt
the die outlet 200C in each case.
was
Furthermore, a two-roll mill with a roll width of 30 cm
and a roll diameter of 15 cm was used. Speed 15120 rpm,
temperature 190°C.
Example/Compara-
tive Amounts in g
example
A 1 H C D 2 E F
PP 1 200 200 200 200
PP 2 200 200 200 200
AO 1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
AO 2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Fluoropolymer 0.1 0.1
Ca stearate
Montan wax 0.2 0.2
0.1 0.1
PP 1 PP homopolymer (1~I 230/2.16 5 g/10 min)
PP 2 PP homopolymer (ICI 230/2.16 12 g/10 min)
AO 1 bas[3,3-bas-4-(4'-hydroxy-3'-t-butylphenyl)
butanoic acid] ethylene glycol ester
A02 tri(2,4-di-t-butylphenyl) phosphate
Fluoro- terpolymer of 40% tetrafluoroethylene, 40%
polymer vinylidene fluoride and 20% hexafluoropropene
Montan partly saponified ester wax of montanic acids
wax with 1,3-butanediol
211040
Results:
l.) Rollingtests (two-roll
mill)
Example/ Adhesion-free Ease of take-off
of
Comp. time (min.) the roll hide
A 13 poor
1 24 good
B 5 poor
C 22 moderate
D 6 poor
2 12 good
E <1 very poor
F il moderate
2. Calendering
tests
Example/ Ease of Roll Take-off
Comp. take-off depositsbehavior
of
the film
A moderate none irregular
take-off line
1 good none smooth, straight
take-off line
8 moderate slight irregular take-off
depositline
C good slight somewhat irregular
deposittake-o!! line
D adheres
immediately
2 moderate- cone slightly curved
good take-off line
E adheres
immediately
F adheres
immediately
