U.S. patent application number 11/790226 was filed with the patent office on 2007-08-23 for polymer film comprising a propylene random copolymer.
This patent application is currently assigned to Borealis Technology OY. Invention is credited to Markus Gahleitner, Pirjo Jaaskelainen, Manfred Kirchberger, Paivi Pitkanen.
Application Number | 20070197743 11/790226 |
Document ID | / |
Family ID | 8177835 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070197743 |
Kind Code |
A1 |
Jaaskelainen; Pirjo ; et
al. |
August 23, 2007 |
Polymer film comprising a propylene random copolymer
Abstract
The present invention relates in a first embodiment to a polymer
film comprising a propylene random copolymer with a total comonomer
content of 4.5 to 12 mol % wherein the sealing initiation
temperature SIT of the film is T.sub.m-30.degree. C. or less,
preferably T.sub.m-33.degree. C. or less, in a second embodiment to
a polymer film comprising a propylene random copolymer with a total
comonomer content of 4.5 to 12 mol % wherein the film is having a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, preferably 40% or more, in a
third embodiment to a polymer film comprising a propylene random
copolymer with a total comonomer content of 4.5 to 12 mol % wherein
the distribution of the comonomer in the random copolymer
determined according to TREF method is multimodal, preferably
bimodal, in a fourth embodiment to a polymer film comprising a
propylene random copolymer with a total comonomer content of 4.5 to
12 mol %, wherein the copolymer is having an elution interval of
50.degree. C. or more, and in a fifth embodiment to a polymer film
comprising a copolymer with a total comonomer content of 4.5 to 12
mol % wherein the random copolymer is a unimodal polymer and the
elution interval is determined by the equation Y.ltoreq.4.5m+16
wherein Y is the elution interval in .degree. C. and m is the
percentage of ethylene in the copolymer in wt. %.
Inventors: |
Jaaskelainen; Pirjo;
(Porvoo, FI) ; Gahleitner; Markus; (Neuhofen,
AT) ; Kirchberger; Manfred; (Prambachkirchen, AT)
; Pitkanen; Paivi; (Halkia, FI) |
Correspondence
Address: |
MILBANK, TWEED, HADLEY & MCCLOY LLP
INTERNATIONAL SQUARE BUILDING
1850 K STRET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
Borealis Technology OY
|
Family ID: |
8177835 |
Appl. No.: |
11/790226 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10481785 |
Apr 7, 2004 |
|
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PCT/EP02/07085 |
Jun 26, 2002 |
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11790226 |
Apr 24, 2007 |
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Current U.S.
Class: |
526/65 ;
526/348.1 |
Current CPC
Class: |
C08F 210/06 20130101;
Y10T 428/31909 20150401; C08J 2323/14 20130101; C08J 5/18 20130101;
C08F 210/06 20130101; C08F 2500/12 20130101; C08F 210/06 20130101;
C08F 4/6492 20130101; C08F 210/16 20130101; C08F 210/16 20130101;
C08F 2500/26 20130101 |
Class at
Publication: |
526/065 ;
526/348.1 |
International
Class: |
C08G 85/00 20060101
C08G085/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2001 |
EP |
01 115 469.7 |
Claims
1-3. (canceled)
4. A polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin having at least four
carbon atoms and a total comonomer content of 4.5 to 12 mol %,
wherein the distribution of the comonomer in the random copolymer,
determined according to TREF method using 1,2,4-trichlorobenzene as
an eluent, is multimodal or bimodal.
5. A polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin comprising at least
four carbon atoms and a total comonomer content 4.5 to 12 mol %,
wherein the copolymer has an elution interval determined according
to TREF method using 1,2,4-trichlorobenzene as an eluent of
50.degree. C. or more.
6. A polymer film according to claim 4 wherein the copolymer has a
melting temperature of T.sub.m of 135.degree. C. or higher.
7. A polymer film according to claim 4 wherein the copolymer has an
ethylene content of 5 wt % or lower.
8. A polymer film comprising a propylene random copolymer with the
comonomer being ethylene and a total comonomer content of 4.5 to 12
mol % wherein the random copolymer is a unimodal polymer and its
elution interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y
is the elution interval in .degree. C. determined according to TREF
method using 1,2,4-trichlorobenzene as an eluent and m is the
percentage of ethylene in the copolymer in wt %.
9-24. (canceled)
25. A polymer film according to claim 5, wherein the copolymer has
a melting temperature of T.sub.m of 135.degree. C. or higher.
26. A polymer film according to claim 5, wherein the copolymer has
an ethylene content of 5 wt % or lower.
27. A polymer film according to claim 6, wherein the copolymer has
an ethylene content of 5 wt % or lower.
28. A polymer film according to claim 4, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
29. A polymer film according to claim 5, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
30. A polymer film according to claim 6, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
31. A polymer film according to claim 7, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
32. A polymer film according to claim 8, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
33. A polymer film according to claim 26, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
34. A polymer film according to claim 27, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
35. A polymer film according to claim 28, wherein the film has a
relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
36. A polymer film according to claim 4, wherein the film is having
a relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
37. A polymer film according to claim 5, wherein the film is having
a relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
38. A polymer film according to claim 6, wherein the film is having
a relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
39. A polymer film according to claim 7, wherein the film is having
a relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
40. A polymer film according to claim 8, wherein the film is having
a relative reduction of the static friction value (inside-inside)
from one to four days of 35% or more, or 40% or more.
41. A polymer film according to claim 26, wherein the film is
having a relative reduction of the static friction value
(inside-inside) from one to four days of 35% or more, or 40% or
more.
42. A polymer film according to claim 27, wherein the film is
having a relative reduction of the static friction value
(inside-inside) from one to four days of 35% or more, or 40% or
more.
43. A polymer film according to claim 28, wherein the film is
having a relative reduction of the static friction value
(inside-inside) from one to four days of 35% or more, or 40% or
more.
44. A polymer film according to claim 5, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
45. A polymer film according to claim 6, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
46. A polymer film according to claim 7, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
47. A polymer film according to claim 8, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
48. A polymer film according to claim 26, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
49. A polymer film according to claim 27, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
50. A polymer film according to claim 28, wherein the distribution
of the comonomer in the random copolymer determined according to
TREF method using 1,2,4-trichlorobenzene as an eluent is multimodal
or bimodal.
51. A polymer film according to claim 4, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
52. A polymer film according to claim 6, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
53. A polymer film according to claim 7, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
54. A polymer film according to claim 8, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
55. A polymer film according to claim 26, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
56. A polymer film according to claim 27, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
57. A polymer film according to claim 28, wherein the copolymer is
having an elution interval determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent of 50.degree. C. or
more.
58. A polymer film according to claim 4 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
59. A polymer film according to claim 5 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
60. A polymer film according to claim 7 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
61. A polymer film according to claim 8 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
62. A polymer film according to claim 27 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
63. A polymer film according to claim 28 with the comonomer being
ethylene and a total comonomer content of 4.5 to 12 mol % and
wherein the random copolymer is a unimodal polymer and its elution
interval satisfies the equation Y.ltoreq.4.5m+16 wherein Y is the
elution interval in .degree. C. determined according to TREF method
using 1,2,4-trichlorobenzene as an eluent and m is the percentage
of ethylene in the copolymer in wt %.
64. A polymer film according to claim 4, wherein the comonomer is
the propylene random copolymer is ethylene.
65. A polymer film according to claim 5, wherein the comonomer is
the propylene random copolymer is ethylene.
Description
[0001] The present invention relates to a polymer film comprising a
propylene random copolymer with the comonomer being ethylene or an
.alpha.-olefin, in particular ethylene, having at least four carbon
atoms and a total comonomer content of 4.5 to 12 mol %.
[0002] The production of films is one of the main applications of
propylene random copolymers. Such films, in turn, are applied
mainly for packaging purposes such as food packaging.
[0003] For these applications the properties of the film and hence
the properties of the polymer used for its production are
essential. Therefore, several modifications of processes for the
production of propylene random copolymers as well as the use of
several modified propylene random copolymers for films are
known.
[0004] For example, in EP 0 761 700 a gas phase process for the
production of propylene-ethylene random copolymer and the
production of a film thereof are disclosed. In U.S. Pat. No.
5,984,839 a propylene copolymer composition for films and a process
for the production thereof are disclosed. The copolymer composition
comprises a propylene homopolymer phase and a propylene/ethylene
copolymer phase.
[0005] Among the desired film properties there are good optical
properties as e.g. high transparency, low haze and high gloss, good
heat sealing properties and good mechanical properties.
[0006] Polymer films produced from known propylene random
copolymers still may be improved with respect to these properties,
in particular with respect to a combination of satisfactory values
for all or some of the above-mentioned properties.
[0007] It is therefore one object of the present invention to
provide a polymer film comprising a propylene random copolymer with
good optical properties such as high transparency, low haze and
high gloss. It is further an object of the invention to provide
such a film with good sealing properties, high softness and good
slip properties. Furthermore, it is an object of the present
invention to provide such a film having no or only low tendency to
blooming and a low degree of xylene solubles.
[0008] The present invention in a first embodiment provides a
polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin having at least four
carbon atoms and a total comonomer content of 4.5 to 12 mol %
wherein the sealing initiation temperature SIT of the film is
T.sub.m-30.degree. C. or less, preferably T.sub.m-33.degree. C. or
less.
[0009] The polymer film of this embodiment is showing superior
sealing properties due to the low SIT in relation to the melting
temperature T.sub.m.
[0010] The present invention in a second embodiment provides a
polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin having at least four
carbon atoms and a total comonomer content of 4.5 to 12 mol %
wherein the film is having a relative reduction of the static
friction value (inside-inside) from one to four days of 35% or
more, preferably 40% or more.
[0011] The polymer film of this embodiment is showing superior
processing properties due to the enhanced decrease of the static
friction values which allows for the film being further processed
within a shorter time after its production.
[0012] The present invention in a third embodiment provides a
polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin having at least four
carbon atoms and a total comonomer content of 4.5 to 12 mol %
wherein the distribution of the comonomer in the random copolymer
determined according to TREF method is multimodal, preferably
bimodal.
[0013] TREF (temperature rising elution fractionation) is a common
method to fractionate polyolefins according to their solubility
differences. It has been demonstrated for polypropylene that TREF
fractograms qualitatively reflect the distribution of isotacticity
in the polymer. The average length of isotactic chains increases
almost linearly with increasing elution temperature (P. Ville et
al., Polymer 42 (2001) 1953-1967). The results further showed that
TREF does not strictly fractionate polypropylene according to
tacticity but according to the longest crystallisable sequences in
the chain. The solubility of a polypropylene polymer chain hence is
influenced only by the concentration and distribution of sterical
defects.
[0014] According to the invention it has been found that a process
as described below provides for an even comonomer distribution in
the propylene copolymer. The comonomers act as sterical defects and
hence interrupt the sequence of isotactic propylene monomers. By an
even distribution of the comonomers an even distribution of
sterical defects is obtained, i.e. it is possible by this process
to tailor the defect distribution and hence the isotacticity
distribution of the polypropylene polymer.
[0015] It is hence possible to determine the comonomer distribution
and accordingly its modality by the TREF method which in detail is
described in the example section.
[0016] The term "modality of the comonomer distribution of the
copolymer" refers to the form of the curve in the TREF fractogram,
i.e. the appearance of the graph showing the polymer weight
fraction as a function of its solution temperature.
[0017] If the polymer is produced in a multistage process, e.g. in
the process described below by using different ethylene contents in
each reactor, the different polymer fractions produced in the
different reactors will each have their own comonomer distribution
which may considerably differ from one another. The TREF curve of
the resulting final polymer is then obtained as a superposition of
the TREF curves of the different polymer fractions.
[0018] Accordingly, this curve will for example show two or more
distinct maxima, a maximum and one or more shoulders, or will at
least be distinctly broadened compared to the curves for the
individual fractions. The TREF curve is having such a shape so that
for the person skilled in the art it is clear that the broadened
curve is originating from a superposition of two or more different
TREF curves and hence shows a multimodal ethylene distribution.
[0019] A polymer showing such a TREF curve is designated as having
a "multimodal comonomer distribution".
[0020] Accordingly, "bimodal comonomer distribution" is designating
the case that the TREF curve of the final polymer is originating
from two polymer fractions with different ethylene distributions.
This TREF curves for example is showing two different maxima, a
maximum and a shoulder or is distinctly broadened. It is having
such a shape so that for the person skilled in the art it is clear
that the curve is originating from a superposition of two different
TREF curves.
[0021] Preferably, the multimodal copolymer is having an elution
interval of 50.degree. C. or more.
[0022] The elution interval designates the temperature range of the
polymer elution determined from the TREF curve, i.e. the
temperature range T.sub.end-T.sub.start, wherein T.sub.end means
the temperature where the last polymer fraction is eluted, i.e. at
this temperature the polymer has been completely eluted from the
column, and T.sub.start means the temperature where the polymer
starts to elute, i.e. where the first fraction of the polymer is
eluted (eluted weight fraction >0).
[0023] Further preferred, the copolymer is having a melting
temperature T.sub.m of 135.degree. C. or higher.
[0024] Further preferred, the copolymer is having an ethylene
content of 5 wt. % or lower.
[0025] The present invention in a fourth embodiment provides a
polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin comprising at least
four carbon atoms, wherein the copolymer is having an elution
interval of 50.degree. C. or more.
[0026] Preferably, the copolymer in this embodiment is having a
melting temperature T.sub.m of 135.degree. C. or higher.
[0027] Further preferred, the copolymer in this embodiment is
having an ethylene content of 5 wt. % or lower.
[0028] The copolymer in this embodiment is preferably produced
according to the multistage process described below and further
preferred to all preferred embodiments of this process wherein the
ethylene content of the products from slurry reactor and gas phase
reactor are different.
[0029] The present invention in a fifth embodiment provides a
polymer film comprising a propylene random copolymer with the
comonomer being ethylene or an .alpha.-olefin comprising at least
four carbon atoms, wherein the random copolymer is a unimodal
polymer and the elution interval is determined by the equation
Y.ltoreq.4.5m+16 wherein Y is the elution interval in .degree. C.
and m is the percentage of ethylene in the copolymer in wt. %.
[0030] Such unimodal polymers are preferably produced by the
multistage process described below wherein the ethylene content of
the products from the slurry reactor and the gas phase reactor is
the same.
[0031] It is preferred that a polymer film according to any of the
second to fifth of the above-described embodiments is having a
sealing initiation temperature SIT of T.sub.m-30.degree. C. or
less, preferably T.sub.m-33.degree. C. or less.
[0032] It is further preferred that a polymer film according to any
of the first, third, fourth or fifth of the above-described
embodiments is having a relative reduction of the static friction
value (inside-inside) from one to four days of 35% or more,
preferably 40% or more.
[0033] It is further preferred that a polymer film according to any
of the first and second of the above-described embodiments
comprises a propylene random copolymer wherein further the
distribution of the comonomer in the random copolymer determined
according to TREF method is multimodal, preferably bimodal.
[0034] It is further preferred that a polymer film according to any
of the first and second of the above-described embodiments
comprises a propylene random wherein the copolymer is having an
elution interval of 50.degree. C. or more.
[0035] It is further preferred that a polymer film according to any
of the first and second of the above-described embodiments
comprises a propylene random copolymer wherein the random copolymer
is a unimodal polymer and the elution interval is determined by the
equation Y.ltoreq.4.5m+16 wherein Y is the elution interval in
.degree. C. and m is the percentage of ethylene in the copolymer in
wt. %.
[0036] In the following, preferred embodiments for all of the
above-mentioned embodiments one to five, where appropriate, of the
inventive polymer film are given.
[0037] It is particularly preferred that the comonomer in the
propylene random copolymer used for the production of the inventive
film is ethylene.
[0038] Further preferred, the total ethylene content of the
copolymer is 3 wt. % or more, more preferably 5 wt % or more.
[0039] Further preferred, the total ethylene content of the
copolymer is 9 wt. % or less, more preferably 8 wt. % or less.
[0040] In many applications, it is desired that the tensile modulus
of the film is low so that "soft" films are obtained. It is
therefore preferred that the inventive polymer film is having a
tensile modulus in the machine direction (MD) of 400 MPa or less,
preferably 350 MPa or less.
[0041] The polymer film according to the present invention
preferaby is having a thickness of 10 to 500 .mu.m, more preferably
of 20 to 200 .mu.m
[0042] Preferably, the propylene random copolymer used for the
production of the inventive film has an MFR.sub.2 of 1 to 20,
preferably of 2 to 12.
[0043] It is further preferred that the content of xylene solubles
of the inventive polymer film is from 4 to 15 wt. %, more preferred
from 6 to 10 wt. %.
[0044] In a further embodiment of the inventive polymer film, the
film further comprises a nucleating agent. Such nucleating agents
are for example sodium benzoate (CAS 532-32-1);
1,3:2,4-bis(3,4-dimethylbenzylidene)-sorbitol (CAS 135861-56-2,
Millad 3988). The application of a nucleating agent increases the
crystallisation rate of the polymer film. They are predominantly
used for the production of thicker films for improving the optical
properties thereof and/or for the improvement of the ageing
properties of films.
[0045] The inventive polymer film can be produced by any film
making process known to the skilled person. In particular, the film
can be produced by a cast process, a cast process with subsequent
orientation of the film leading to a biaxial oriented polypropylene
(BOPP) film, a roll stack process or a blown film process.
[0046] It is preferred that the inventive polymer film is produced
in a cast process or a process leading to BOPP or a blown film
process.
[0047] In case the film is produced by a cast process it is
preferred that the polymer before film forming is subjected to a
"controlled rheology" (visbreaking) process. This is done in order
to obtain required values for e.g. MFR.sub.2, polydispersity index
PI and M.sub.w/M.sub.n of the polymer.
[0048] Visbreaking of the copolymer is normally carried out in the
molten stage of the polymer in single- or twin-screw extruders in
the presence of free radical initiators such as peroxides,
preferably in an inert atmosphere. Visbreaking processes are well
known to the skilled person. Usually, visbreaking e.g. leads to a
significant increase in the MFR.sub.2 value.
[0049] It is further preferred that the propylene random copolymer
after visbreaking is having an MFR.sub.2 value of 6.0 to 12.0 g/10
min.
[0050] In case the film is produced in a blown film process the
polymer usually is not subjected to a visbreaking process before
film making. The MFR.sub.2 of the propylene random copolymer
accordingly is preferably from 1.5 to 3.0 g/10 min.
[0051] The propylene random copolymer used for the production of
the inventive polymer film preferably has a molecular weight
distribution with a polydispersity M.sub.w/M.sub.n from 2 to 7,
preferably from 4 to 6.
[0052] It is further preferred that the polymer used for the
production of the inventive cast film after visbreaking has a shear
thinning index SHI of 3 to 5, further preferred of 3.5 to 4.5.
[0053] The propylene random copolymers used for the production of
the inventive film which may be obtained according to the process
described below usually have a high degree of isotacticity measured
in accordance to the FTIR-method, due to the catalyst systems
(single-site or Ziegler-Natta) used for polymerisation.
[0054] Preferably, the propylene polymer has a degree of
isotacticity as determined from FTIR (as described in: T. Sundell,
H. Fagerholm & H. Crozier, Isotacticity determination of
polypropylene using FT-Raman spectroscopy, Polymer 37, 1996,
3227-31) of 90% or more, more preferably of 95% or more and most
preferably of 98% or more.
[0055] Further, before the production of the inventive film by
using propylene random copolymer conventional additives may be
added to the copolymer in small amounts.
[0056] The copolymer may contain commonly used additives like:
[0057] phenolic antioxidants like 2,6-di-tert.buty-4-methylphenol
(CAS 128-37-0, BHT);
Pentaerithrityl-tetrakis(3-(3',5'-di-tert.butyl-4-hydroxyphenyl)-pr-
opionate) (CAS 6683-19-8, Irganox 1010);
Octadecyl-3-(3',5'-di-tert.butyl-4-hydroxyphenyl)-propionate) (CAS
2082-79-3, Irganox 1076), [0058] phosphorus-containing antioxidants
like Tris(2,4-di-tert.butylphenyl)-phosphite (CAS 31570-04-4,
Irgafos 168);
Bis(2,4-di-tert.butylphenyl)-pentaerithrityl-di-phosphite (CAS
26741-53-7, Ultranox 626) [0059] C-radical scavengers like
5,7-di-tert.butyl-(3-(3,4-di-methylphenyl)3H-benzofuran-2-one (CAS
181314-48-7, HP 136) [0060] acid scavengers like Calcium stearate
(CAS 1592-23-0); Zinc stearate (CAS 557-05-1); Hydrotalcite (CAS
11097-59-9) [0061] UV-stabilisers like
Bis-(2,2,6,6-tetramethyl-4-piperidyl)-sebacate (CAS 52829-07-9,
Tinuvin 770); 2-hydroxy-4-n-octoxy-benzophenone (CAS 1843-05-6,
Cimassorb 81) [0062] antistatic agents like glycerol-monostearate
(CAS 97593-29-8) [0063] nucleating agents like sodium benzoate (CAS
532-32-1); 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (CAS
135861-56-2, Millad 3988) [0064] slip agents like erucamide (CAS
112-84-5); oleamide (CAS 301-02-0) [0065] antiblocking agents like
natural or synthetic silica (CAS 7631-86-9) in quantities of
100-10.000 ppm for each single component.
[0066] The propylene random copolymer used for the inventive films
in all of the above-described embodiments is preferably produced in
a process for preparing a propylene random comonomer comprising
polymerisation of propylene with a comonomer, said comonomer being
ethylene or an .alpha.-olefin comprising at least four carbon
atoms, in the presence of a catalyst in a multistage process
comprising polymerisation of propylene with a comonomer in a first
reaction zone including at least one slurry reactor to give a first
polymerisation product, transferring said first product to a second
reaction zone including at least one gas phase reactor and
polymerisation of propylene with a comonomer in said gas phase
reactor in the presence of said first polymerisation product,
wherein the temperature in the gas phase reactor is higher than
that in the slurry reactor.
[0067] With this process it is possible to produce propylene random
copolymers with a tailored ethylene distribution and hence to
fine-tune the properties of the produced polymer. Thus, by the
inventive process the properties of the polymer can be adopted in
particular for film applications so that polymers are obtained with
excellent properties for this kind of application.
[0068] Further, it is an advantage of this process that due to the
tailored comonomer distribution polymers with a low degree of
xylene solubles (XS) content are obtained. Thus, problems in the
process which can be caused by polymers with higher XS content are
avoided.
[0069] Preferably, in the process the temperature in the gas phase
reactor is at least 5.degree. C., preferably at least 10.degree. C.
and most preferably at least 15.degree. C. higher than that in the
slurry reactor.
[0070] In the process the comonomer content of the product produced
in the gas phase reactor may be lower, equal to or higher than that
of the product produced in the slurry reactor.
[0071] Of course, due to the multistage nature of the inventive
process both products after being produced are inseparably mixed
with each other. The properties of the product produced in the gas
phase reactors such as its ethylene content may nevertheless be
determined by considering the corresponding values for the slurry
reactor product and the final polymer and taking into account the
production split.
[0072] Preferably, in the process the comonomer content of the
product produced in the gas phase reactor is the same or higher
than that of the product produced in the slurry reactor and
particularly preferred the comonomer content of the product
produced in the gas phase reactor is higher than that of the
product produced in the slurry reactor.
[0073] Preferably, the comonomer content of the product produced in
the gas phase reactor is at least 0.75 mol % (corresponding to 0.5
wt. % for ethylene as a comonomer), more preferably at least 1.5
mol % (corresponding to 1 wt. % for ethylene as a comonomer) higher
than that of the product produced in the slurry reactor.
[0074] Further preferred, the comonomer used in the process and
hence contained in the obtained polymer is ethylene.
Propylene-ethylene random copolymers are particularly suited for
film applications.
[0075] In the process it is further preferred that the ethylene
content of the product produced in the slurry reactor is from 3 to
6 wt. %, more preferably from 3 to 4 wt. %.
[0076] Further preferred, the ethylene content of the product
produced in the gas phase reactor is from 3 to 10 wt. %, more
preferably from 4 to 8 wt. %.
[0077] "Slurry reactor" designates any reactor such as a continuous
or simple batch stirred tank reactor or loop reactor operating in
bulk or slurry, including supercritical conditions, in which the
polymer forms in particulate form.
[0078] Preferably, the slurry reactor is operated as a bulk
reactor. "Bulk" means a polymerisation in a reaction medium
comprising at least 60 wt. % monomer.
[0079] Preferably, the bulk reactor is a loop reactor.
[0080] Further preferred, in the process the temperature in the
slurry reactor is 65.degree. C. or more, more preferably 70.degree.
C. or more.
[0081] Still further preferred, the temperature in the gas phase
reactor is 80.degree. C. or more, more preferably 85.degree. C. or
more.
[0082] In each of the different reactors--slurry reactor and gas
phase reactor--a part of the final propylene random copolymer is
produced. This production split between the reactors may be
adjusted according to the desired properties of the produced
copolymer.
[0083] It is preferred that the production split between the slurry
reactor and the gas phase reactor is from 10:90 to 70:30, more
preferred from 20:80 to 65:35 and most preferred from 40:60 to
60:40.
[0084] All catalysts suitable for the polymerisation of propylene
with ethylene or an .alpha.-olefin such as single-site catalysts
and Ziegler-Natta catalysts can be used. If single side catalysts
are used, those described in WO 95/12627 and WO 00/34341 are
preferred.
[0085] In a preferred embodiment of the process, a Ziegler-Natta
type catalyst system comprising a catalyst component (comprising
also vinyl-modified catalyst component), a cocatalyst component and
an external electron donor is used. Such catalyst systems are
described in, for example, U.S. Pat. No. 5,234,879, WO 92/19653, WO
92/19658 and WO 99/33843 and systems comprising vinyl-modified
catalyst components in WO 99/24478 and WO 99/24479. The content of
these documents is herein included by reference.
[0086] Generally, the external donors are silane based donors
having the formula (I) R.sub.nR'.sub.mSi(R''O).sub.4-n-m (I)
wherein R and R' can be the same or different and stand for linear,
branched or cyclic aliphatic or aromatic group; R'' is methyl or
ethyl; n is an integer 0 to 3; m is an integer 0 to 3; and n+m is 1
to 3.
[0087] The aliphatic groups in the meanings of R and R' can be
saturated or unsaturated.
[0088] Preferably, R and R' are linear C.sub.1 to C.sub.12
hydrocarbons which include methyl, ethyl, propyl, butyl, octyl and
decanyl. As examples of suitable saturated branched C.sub.1-8 alkyl
groups, the following can be mentioned: isopropyl, isobutyl,
isopentyl, tert.-butyl, tert.-amyl and neopentyl. Cyclic aliphatic
groups containing 4 to 8 carbon atoms comprise e.g. cyclopentyl,
cyclohexyl, methylcyclopentyl and cycloheptyl.
[0089] According to the present invention the donors used can be
strongly coordinating donors which form relatively strong complexes
with catalyst surface, mainly with MgCl.sub.2 surface in the
presence of aluminium alkyl and TiCl.sub.4.
[0090] Typically, this kind of donors have the structure of the
general formula (II): R'''.sub.nSi(OMe).sub.4-n (II) wherein R'''
is a branched aliphatic or cyclic or aromatic group and n is 1 or
2, preferably 2 [Harkonen et al., Macromol. Chem. 192 (1991)
2857-2863].
[0091] In particular, the external donor is selected from the group
consisting of dicyclopentyl dimethoxysilane, diisopropyl
dimethoxysilane, di-isobutyl dimethoxysilane and di-t-butyl
dimethoxysilane, most preferably dicyclopentyl dimethoxysilane (D
donor).
[0092] Optionally, the main polymerisation stages may be preceded
by prepolymerisation in which up to 10 wt. %, preferably 0.1 to 10
wt. %, and most preferred from 0.5. to 5 wt. % of the total amount
of the polymer is produced.
[0093] In the following the invention is further illustrated by
means of examples with reference to the enclosed Figures.
[0094] FIG. 1 shows a TREF fractogram of the propylene/ethylene
random copolymer according to Example 1 having an overall ethylene
content of 3.3 wt. % and the corresponding loop product showing the
ethylene comonomer distribution in the polymer.
[0095] FIG. 2 shows a TREF fractogram showing the continuous TREF
functions ("TREF curves") of the propylene/ethylene random
copolymer according to example 2 and comparative example 2 having
an overall ethylene content of around 5 wt. % (5.1 and 4.7,
respectively) showing the bimodal ethylene comonomer distribution
in the polymer of example 2. The continuous TREF curves were
calculated from the data shown in FIG. 3.
[0096] FIG. 3 shows TREF fractograms of the propylene/ethylene
random copolymer according to example 2 and comparative example 2
having an overall ethylene content of around 5 wt. % (5.1 and 4.7,
respectively).
[0097] FIG. 4 shows the melting curve of propylene/ethylene random
copolymer according to Example 3 having an overall ethylene content
of 6 wt. %.
[0098] FIG. 5 shows the tensile modulus values of the inventive
copolymers as a function of the total ethylene content.
EXAMPLES
1) Measuring Methods
a) TREF-Method:
[0099] Fractionation of the polypropylene samples was achieved by
using analytical TREF. The TREF profiles were generated using a
home made instrument, which is similar to a published design (Wild,
L., Trends Polym Sci. 1993, 1, 50).
[0100] The sample was dissolved in xylene (2 to 4 mg/ml) at
130.degree. C. and injected into the column at 130.degree. C., and
the latter was then cooled to 20.degree. C. at a rate of 1.5 K/h.
The column was subsequently eluted with 1,2,4-trichlorobenzene
(TCB) at a flow rate of 0.5 ml/min while the temperature was
increased from 20.degree. C. to 130.degree. C. over 4.5 h. The
output, detected with an i.r. detector operating at a wavelength of
3.41 .mu.m, was presented as a fractogram normalised to constant
area.
b) Xylene Solubles (XS):
[0101] For the determination of the xylene solubles fraction, 2.0 g
of polymer is desolved in 250 ml p-xylene at 135.degree. C. under
agitation. After 30.+-.2 min the solution is allowed to cool for 15
min at ambient temperature and then allowed to settle for 30 min at
25.+-.0.5.degree. C. The solution is filtered with filter paper
into two 100 ml flasks.
[0102] The solution from the first 100 ml vessel is evaporated in
nitrogen flow and the residue is dried under vacuum at 90.degree.
C. until constant weight is reached. The xylene soluble fraction is
calculated using the following equation:
XS%=(100m.sub.1v.sub.0)/(m.sub.0v.sub.1) wherein m.sub.0=initial
polymer amount (g), m.sub.1=weight of residue (g), v.sub.0=initial
volume (ml), v.sub.1=volume of analysed sample (ml). c)
M.sub.w/M.sub.n
[0103] M.sub.w/M.sub.n was determined using gel permeation
chromatography (GPC) at 130.degree. C. As an eluent,
1,2,4-trichlorobenzene (TCB) was used.
d) Melt Flow Rate (MFR)
[0104] MFR.sub.2 was measured according to ISO 1133 at 230.degree.
C. and a load of 2.16 kg.
e) Thermal Properties
[0105] Melting temperature T.sub.m determined according to ISO
3146, crystallisation temperature T.sub.cr, and the degree of
crystallinity were measured with a Mettler TA820 differential
scanning calorimetry (DSC) on 3.+-.0.5 mg samples. Both
crystallisation and melting curves were obtained during 10.degree.
C./min cooling and heating scans between 30.degree. C. and
225.degree. C.
[0106] Melting and crystallisation temperatures were taken as the
peaks of endotherms and exotherms. The degree of crystallinity was
calculated by comparison with heat of fusion of a perfectly
crystalline polypropylene, i.e. 209 J/g.
f) Viscosity Function and Shear Thinning (SHI)
[0107] Viscosity measurements are made with a dynamic rheometer
(RDA-II QC).
[0108] The shear thinning index. SHI, is the most sensitive
parameter for obtaining information about the MMD of polypropylene.
SHI is calculated by dividing the Zero Shear Viscosity by a complex
viscosity value obtained at a certain constant shear stress value,
G*.
[0109] The Zero Shear Viscosity is defined as
.eta..sub.0=limG''/.omega.(.omega..fwdarw.0).
[0110] The abbreviation SHI.sub.(0/50) is the ratio between the
zero shear viscosity and the viscosity at a shear stress of 50 000
Pa.
2) Production of Copolymers and Properties Thereof
[0111] Continous multistage process was used to produce propylene
copolymers. The process comprised a prepolymerisation step, a loop
reactor and a fluidized bed gas phase reactor was used.
[0112] The catalyst used was highly active, stereospecific
transesterified MgCl.sub.2-supported Ziegler-Natta catalyst
prepared according to U.S. Pat. No. 5,234,879 at a titanization
temperature of 135.degree. C. The catalyst was contacted with a
co-catalyst (triethylaluminium, TEAL), and an external donor (donor
D, dicyclopentyl dimethoxysilane) with the Al/Ti ratio of 200 and
an Al/D ratio of 10, to yield a catalyst system.
[0113] The catalyst system and propylene were fed into the
prepolymerisation reactor which was operated at 30.degree. C. The
prepolymerised catalyst was used in the subsequent polymerisation
reactors.
[0114] Propylene, ethylene and hydrogen and the prepolymerised
catalyst were fed into the loop reactor which was operated as bulk
reactor at the temperatures as indicated in Table 1 and a pressure
of 55 bar.
[0115] Then, the polymer slurry stream was fed from the loop
reactor into the gas phase reactor which was operated at the
temperatures as indicated in Table 1 and a pressure of 20 bar. More
propylene, ethylene and hydrogen were fed into the gas phase
reactor to control the desired properties of the final polymer.
[0116] In the comparative examples 1 and 2 propylene random
copolymers were produced in the same manner as the inventive
polymers except that two loop reactors instead of one gas phase and
one loop reactor were used wherein the temperature in both loop
reactors was the same (67.degree. C.).
[0117] The split between loop/gas phase reactor or loop/loop
reactor (comparative examples) was 70/30 to 40/60. TABLE-US-00001
TABLE 1 Comparative Comparative Unit Example 1 Example 2 Example 3
Example 1 Example 2 Al/D mol/mol 10 10 10 10 10 Al/Ti mol/mol 200
200 200 200 200 Production 70:30 40:60 45:55 60:40 60:40 split
Loop:GPR/2nd loop) Loop Temperature .degree. C. 70 70 70 67 67
Ethylene wt. % 3.2 3.9 3.4 3.5 4.7 MFR.sub.2 g/10 min 1.5 1.5 1.5
1.5 1.5 GPR/2nd loop Temperature .degree. C. 85 85 85 67 67 Final
Product Ethylene wt. % 3.3 5.1 6.0 3.5 4.7 MFR.sub.2 g/10 min 1.3
1.3 1.5 1.5 1.5
a) Polymer Structure and Properties
[0118] The analytical results of the polymers of table 1 are
collected in table 2.
b) Ethylene Content and Distribution
[0119] Ethylene content in loop product varied between 3.2 and 3.9
wt. %. The final ethylene content was 3.3 wt. %, 5 wt. % to 6 wt.
%.
[0120] The difference in ethylene distributions of two high
ethylene content copolymers is clearly demonstrated in TREF curves
(FIGS. 2 and 3). TABLE-US-00002 TABLE 2 Analytical test results of
Cast film and Blow Moulding polymers Sample Comp. Comp. Pellets
Example 1 Example 2 Example 3 Example 4 Ex. 1 Ex. 2 MFR.sub.2 g/10
min 7.3* 7.9* 7.2* 1.4 8.0* 8.0* Ethene wt. % 3.3 5.1 6.0 5.8 3.2
4.7 mol. % 4.95 7.65 9.0 8.7 4.7 XS wt. % 5.7 9.1 11.1 6.0 11
elution .degree. C. 30.2 58.5 60.5 60.5 40.9 interval T.sub.m of PP
.degree. C. 142.8 137.2 137.6 139.2 142.0 136.2 Crystallinity %
39.3 32.7 29.9 28.9 34.1 RDA, Zero Pas 2500 2450 2720 24600 2420
viscosity SHI.sub.(0/50) Pa 3.9 3.8 3.7 6.7 3.7 *visbroken
c) Xylene Solubles (XS)
[0121] The content of xylene solubles (XS) was increased from 5.5
to 11 wt. %, when total ethylene content increased from 3.3 to 6
wt. %. Less sticky material (XS) was produced in GPR at a certain
comonomer content compared to loop (FIG. 4). By using the splitted
ethylene concept, where loop ethylene content was <4 wt. %, the
XS of the final product was much lower than that in high ethylene
products having the same final ethylene content, but being produced
with the same ethylene content in both reactors.
d) Melting Behaviour
[0122] Loop ethylene content determined the melting point of
product, and it was between 137 and 147.degree. C. in spite of
increased ethylene content in GPR.
[0123] The higher ethylene content in GPR was seen in broadening of
the melting range. The shape of DSC curve indicates low seal
initiation temperature and good sealing properties (FIG. 4).
3) Production of Film
[0124] For the production of the films according to the invention,
examples 4 and 5 the polymer according to example 2 was used and
for the production of the films of examples 6 and 7 the polymer of
example 3 was used.
[0125] For the production of the comparative films, polypropylene
copolymers RD226CF (PP random copolymer) and SD233CF (PP random
heterophasic copolymer) commercially available from Borealis were
used.
[0126] The following additives were added to the propylene random
copolymers used for the production of the films according to the
invention and to the polymers used for the production of the
comparative films before film production: TABLE-US-00003 Irganox
B215 1500 ppm (antioxidant mixture of Irganox 1010 and Irgafos
168)) Calcium stearate 1000 ppm (acid scavenger) Erucamide 1000 ppm
(slip agent) Oleamide 1000 ppm (slip agent) Syloblock 45 1800 ppm
(silica, antiblock agent)
[0127] Visbreaking has been done with Trigonox 101 (peroxide) for
examples according to the invention, Trigonox B for RD226CF
(comparative).
[0128] The films were produced on a single-screw extruder with a
screw diameter of 60 mm, using a multilayer feedblock and a slot
die of 6.6.times.800 mm in a cast-film setup with a melt
temperature at the die of 250.degree. C., a chill roll temperature
of 15.degree. C. and a counter-roll temperature of 25.degree. C.
The takeoff speed was adjusted such that the desired thickness of
30 and 50 .mu.m was achieved.
4) Testing Standards for Film Testing
[0129] The tensile modulus in machine direction MD, the yield
stress MD and elongation at break MD were determined according to
the tensile test DIN 53455.
[0130] The haze was determined according to ASTM D-1003-92.
[0131] The delta friction (1/4), i.e. the relative reduction the
static friction value (inside/inside) was calculated from friction
test DIN 53375.
[0132] Blooming was assessed qualitatively.
6) Film Properties
[0133] For the production of the films of examples 4 and 5 the
polymer according to example 2 was used and for the production of
the films of examples 6 and 7 the polymer of example 3 was used.
TABLE-US-00004 TABLE 3 Film properties Examples Comparative
Examples 4 5 6 7 3 4 5 Material # B5341 B5341 B5343 B5343 RD226CF
RD226CF SD233CF MFR.sub.2 g/10 min 8 8 8 8 8 8 8 Total C.sub.2 wt %
5.1 5.1 6.0 6.0 3.5 3.5 16 content T.sub.m (DSC) .degree. C. 137
137 138 138 142 142 143 Film thickness .mu.m 30 50 30 50 30 50 50
Tens. Modulus MPa 292 302 245 262 411 420 220 MD Yield stress MPa
1.95 1.88 6.1 4.5 4.4 15.5 9.7 MD Elong. Break % 706 718 697 708
675 702 775 MD Haze % 2.1 2.4 2.5 2.6 1.9 2.0 10.3 Delta friction %
50 n.d. 40 n.d. 30 n.d. 25 (1/4)* SIT** .degree. C. 104 n.d. 104
n.d. 114 114 n.d. Delta (T.sub.m - .degree. C. 33 n.d. 34 n.d. 28
28 n.d. SIT) Blooming*** -- none none none none strong strong light
*relative reduction of static friction value (inside/inside) from 1
to 4 days **sealing initiation temperature ***qualitative judgement
after 14 days at room temperature
* * * * *