U.S. patent application number 10/363972 was filed with the patent office on 2005-07-28 for controlled rheology polypropylene heterophasic copolymers.
Invention is credited to Albe, Lisa K., Vandeurzen, Phillppe.
Application Number | 20050163949 10/363972 |
Document ID | / |
Family ID | 8171991 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050163949 |
Kind Code |
A1 |
Vandeurzen, Phillppe ; et
al. |
July 28, 2005 |
Controlled rheology polypropylene heterophasic copolymers
Abstract
This invention relates to the use of a cyclic ketone peroxide of
half-life time larger than one second at a temperature of
225.degree. C., for producing a controlled rheology polypropylene
heterophasic copolymer of melt index MI2 larger than 15 g/10 min,
having simultaneously a very high impact resistance and a high
flexural modulus.
Inventors: |
Vandeurzen, Phillppe;
(Lennik, BE) ; Albe, Lisa K.; (Houston,
TX) |
Correspondence
Address: |
David J Alexander
Fina Technology Inc
PO Box 674412
Houston
TX
77267-4412
US
|
Family ID: |
8171991 |
Appl. No.: |
10/363972 |
Filed: |
February 10, 2005 |
PCT Filed: |
September 7, 2001 |
PCT NO: |
PCT/EP01/10350 |
Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
C08F 2810/10 20130101;
C08F 8/50 20130101; Y02W 30/62 20150501; Y02W 30/706 20150501; C08J
2323/14 20130101; C08K 5/14 20130101; C08F 2800/20 20130101; Y10T
428/1352 20150115; C08J 11/22 20130101; C08F 8/50 20130101; C08F
210/06 20130101; C08F 210/06 20130101; C08F 210/02 20130101; C08K
5/14 20130101; C08L 23/14 20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2000 |
EP |
00203099.7 |
Claims
1. A polymer composition produced by the process of degrading a
polypropylene (co)polymer with a cyclic ketone peroxide, said
polymer composition characterized by an Izod notched impact
strength for melt flow indices greater than 15 g/10 min that is at
least 50% higher than the Izod notched impact strength for melt
flow indices greater than 15 g/10 min of a comparative polymer
composition produced by degrading said propylene (co)polymer with a
linear peroxide under the same conditions of degrading.
2. The polymer composition of claim 1 produced by degrading a
polypropylene (co)polymer that looses its impact strength when the
melt flow index reaches a threshold value that increases with
decreasing extrusion temperature.
3. The polymer composition of claim 1 produced by degrading said
polypropylene (co)polymer in the presence of a cyclic ketone
peroxide having at least two peroxide groups.
4. The polymer composition of claim 3 produced by degrading said
propylene (co)polymer with
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
5. The polymer composition of claim 3 wherein the propylene
(co)polymer is degraded by extrusion at a temperature of from
160.degree. C. to less than 200.degree. C.
6. The polymer composition of claim 1 produced by degrading a
polypropylene heterophasic copolymer, containing from 5 to 20 wt %
of ethylene.
7. The polymer composition of claim 6 produced by degrading a
polypropylene heterophasic copolymer containing from 9 to 15 wt %
of ethylene.
8. The polymer composition of claim 6 produced by degrading a
copolymer that looses its impact strength when the melt flow index
reaches a threshold value that increases with increasing amount of
ethylene.
9. The polymer composition of claim 1 characterized by an Izod
notched impact strength that is at least twice that of the Izod
notched impact strength of said comparative polymer
composition.
10. The polymer composition of claim 1 characterized by a flexural
modulus that is at least 30 Mpa higher than the flexural modulus of
said comparative polymer composition.
11. A method of degrading a polypropylene (co)polymer which
comprises extruding said polypropylene (co)polymer with a cyclic
ketone peroxide to form a solid product of said polypropylene
(co)polymer having a melt index greater than 15 g/10 min with an
Izod notched impact strength that is at least 50% higher and a
flexural modulus that is at least 30 Mpa higher than the Izod
notched impact strength and flexural modulus of a corresponding
polypropylene (co)polymer degraded with a linear peroxide under
similar conditions.
12. The method of claim 11 wherein said extrusion is carried out at
an extrusion temperature of 200.degree. C. or less.
13. The method of claim 11 wherein said cyclic ketone peroxide has
a half-life of more than one second at a temperature of 225.degree.
C.
14. The method of claim 11 wherein said cyclic ketone peroxide has
a half-life of from two to 10 seconds at a temperature of
225.degree. C.
15. The method of claim 11 wherein said extrusion is carried out at
a temperature of from 160.degree. C. to less than 200.degree.
C.
16. The method of claim 15, wherein the polypropylene (co)polymer
is a polypropylene heterophasic copolymer containing from 5 to 20
wt % of ethylene.
17. The method of claim 11 wherein said polypropylene (co)polymer
is a polypropylene heterophasic copolymer containing ethylene in an
amount within the range of 9-15 wt %.
18. The method of claim 17 wherein said polypropylene heterophasic
copolymer contains from 11 to 14 wt % ethylene.
19. The method of claim 11 wherein the extrusion temperature is
within the range of 160-190.degree. C.
20. The method of claim 11 wherein said cyclic ketone peroxide is
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
Description
[0001] The present invention relates to polypropylene heterophasic
copolymers modified with cyclic ketone peroxides in order to better
control their impact strength.
[0002] Several processes for increasing the impact strength of
polypropylene (co)polymers are known in the art, for example, by
modifying said (co)polymers with elastomeric modifiers or with
peroxides.
[0003] Where elastomeric modifier is used to modify the
(co)polymers, it can be added in either of the following ways:
[0004] reactor polymerisation of polypropylene heterophasic
copolymers. These polypropylene heterophasic copolymers exhibit
typical heterophasic morphology consisting of ethylene propylene
bipolymer spherical domains dispersed in a semi-crystalline
polypropylene matrix. This material consists generally of three
components: a polypropylene homopolymer, a rubbery ethylene
propylene bipolymer and a crystalline ethylene-rich ethylene
propylene bipolymer. The amount and properties of the three
component material are controlled by the process conditions. The
mechanical properties of the final product are influenced for
example by:
[0005] 1. the molecular weight, molecular weight distribution and
tacticity of the propylene homopolymer matrix;
[0006] 2. the molecular weight and molecular weight distribution of
the ethylene propylene rubber phase;
[0007] 3. the ethylene/propylene ratio of the ethylene propylene
rubber phase;
[0008] 4. the content and dispersion of the optional ethylene rich
ethylene propylene bipolymer;
[0009] 5. the size and distribution of the rubber phase
domains;
[0010] 6. the melt viscosity ratio of the propylene matrix and
rubber phase components.
[0011] Melt blending polypropylene (co)polymers with elastomeric
modifiers to prepare polypropylene heterophasic copolymers.
Elastomers such as ethylene propylene rubber (EPR) or ethylene
propylene diene monomer (EPDM) provide improved impact behaviour.
The impact resistance of these compositions depends upon the
content, the composition and the morphology of the elastomeric
modifier.
[0012] Both methods have been described for example in:
Polypropylene, structure, blends and composites. Volume
2--Copolymers and blends. Edited by J. Karger-Kocsis, Published in
1995 by Chapman .sctn. Hall.
[0013] WO-95/11938 discloses a process of modifying (co)polymers by
contacting them with a peroxide compound containing an activated
unsaturated group and an acid group in the presence of a polymer
reinforcing material, or prior to the addition of a polymer
reinforcing material. The primary object of that invention was to
modify (co)polymers in order to introduce an adhesion promoting
functional group and to improve their properties. The resulting
modified (co)polymers have improved impact strength, flexural
strength, tensile strength and elongation at break, increased melt
flow index and the other properties equal those of the unmodified
impact (co)polymers.
[0014] WO-97/49759 discloses a process for enhancing the melt
strength of a propylene (co)polymer by the steps of:
[0015] mixing an initiator with the propylene (co)polymer at a
temperature below the decomposition temperature;
[0016] then heating the mixture above the initiator decomposition
temperature in order to decompose the initiator before the polymer
has melted and in order to react the radicals created by the
decomposition with the polymer.
[0017] WO-96/03444 discloses a process for modifying (co)polymers
by contacting these with an organic peroxide, some of said peroxide
being decomposed. Cyclic ketone peroxides have been found
particularly efficient in the modification processes. They have
been employed in the degradation of polyolefins, the cross-linking
of polyolefins, the dynamic cross-linking of blends of elastomers
and thermoplastic polymers, the grafting of monomers onto polymers,
or the functionalisation of polyolefins. The resulting modified
(co)polymers had a larger melt flow index, a lower weight average
molecular weight and a narrower molecular weight than the starting
(co)polymers, while keeping an adequate melt strength.
[0018] WO-00/23434 discloses a composition comprising a cyclic
ketone peroxide and a phlegmatizer having a 95% boil-off point
falling in the range of 220-265.degree. C. Preferably, the peroxide
is a cyclic ethyl ketone peroxide and a single phlegmatiser is
used.
[0019] U.S. Pat. No. 4,707,524 discloses the use of peroxides that
do not decompose to tert-butyl alcohol and have a half-life in the
range of 1 to 10 hours at 128.degree. C. for controlling the
molecular weight and molecular weight distribution of
polypropylene.
[0020] WO-96/03397 discloses a transportable, storage stable ketone
peroxide composition which comprises 1 to 90 wt % of one or more
cyclic ketone peroxides and 10 to 99 wt % of one or more diluents
selected from the group consisting of liquid phlegmatisers for the
cyclic ketone peroxides, plasticisers, solid polymeric carriers,
inorganic supports, organic peroxides and mixtures thereof.
[0021] WO-96/20247 discloses cross-linked polymer compositions of
propylene-ethylene copolymer and ethylene-.alpha.-olefin copolymer
prepared by melting and kneading the constituents in the presence
of a radical forming agent, a cross-linking agent and eventually a
peroxide inhibitor. These compositions were characterised by a high
impact strength and a high flexural modulus.
[0022] EP-0,208,330 discloses a propylene polymer composition with
increased whitening resistance and increased impact strength,
obtained by addition of an ester, in the presence of a peroxide,
during extrusion.
[0023] None of these prior art documents discloses polypropylene
heterophasic copolymers having simultaneously a melt flow index MI2
larger than 15 g/10 min and increased impact strength, while
keeping adequate rigidity.
[0024] It is an aim of the present invention to provide
polypropylene heterophasic copolymers exhibiting simultaneously
high melt flow index and high impact strength.
[0025] It is another aim of the present invention to provide
polypropylene heterophasic copolymers with very high impact
resistance over a large range of temperatures.
[0026] It is a further aim of the present invention to obtain
polypropylene heterophasic copolymers with controlled rheology.
[0027] It is yet another aim of the present invention to obtain a
material with an optimal balance of stiffness, impact strength and
melt flow.
[0028] This invention discloses a polypropylene (co)polymer
degraded with a cyclic ketone peroxide characterised in that it
retains an Izod notched impact strength for melt flow indices
larger than 15 g/10 min that is at least 50% higher than that of a
polypropylene (co)polymer degraded with a linear peroxide under
similar conditions.
[0029] Preferably, the impact strength of the degraded
polypropylene (co)polymer of the present invention retains an Izod
notched impact strength that is twice as large as that of the prior
art resins.
[0030] This invention also discloses the use of cyclic ketone
peroxide, to degrade a polypropylene (co)polymer, for producing a
controlled rheology material of melt index MI2 larger than 15 g/10
min, said impact propylene copolymer having simultaneously an
impact resistance that is at least 50% higher and a flexural
modulus that is 30 Mpa higher than those of the polypropylene
(co)polymers degraded with linear peroxides under similar
conditions.
[0031] The half-life time of the cyclic ketone peroxides of the
present invention is typically longer than one second at a
temperature of 225.degree. C., preferably it is of from 2 to 10
seconds at a temperature of 225.degree. C., and most preferably, it
is about 4 seconds at a temperature of 225.degree. C.
[0032] The half-life time of peroxide is defined as the time
required to decompose one half of the molecules at a given
temperature, and thus a less reactive peroxide has a longer
half-life time. A longer half-life time has two favourable
consequences:
[0033] 1. the peroxide decomposes more slowly; there is thus more
time for mixing with the polymer melt in the extruder resulting in
a more homogeneous material;
[0034] 2. there is at any time a lower radical concentration,
reducing the probability of side reactions.
[0035] Reducing the extrusion temperature increases the half-life
time of the peroxide.
[0036] The melt index MI2 is measured using the method of standard
test ISO 1133 at 230.degree. C. and under a load of 2.16 kg, the
flexural modulus is measured using the method of standard test ISO
178 and the impact strength is the Izod notched impact strength
measured according to the methods of standard test ISO 180.
[0037] The process for preparing a controlled rheology
polypropylene heterophasic copolymer by degrading a polypropylene
with a cyclic ketone peroxide, comprises the steps of:
[0038] either
[0039] a) Reactor polymerising a polypropylene heterophasic
copolymer;
[0040] b) Extruding the polypropylene heterophasic copolymer of
step a), with said cyclic ketone peroxide and optionally with one
or more filler(s), in an extruder, at a temperature sufficient to
maintain the copolymer in the molten state;
[0041] Or
[0042] c) Extruding a polypropylene (co)polymer with said cyclic
ketone peroxides, and optionally, with one or more elastomeric
modifier(s) and/or one or more filler(s), in an extruder, at a
temperature sufficient to maintain the copolymer in the molten
state.
[0043] The specific group of cyclic ketone peroxide of half-life
time longer than one second at a temperature of 225.degree. C., can
be represented by either of the general formulae: 1
[0044] Wherein R.sub.1-R.sub.10 are independently selected from the
group consisting of hydrogen, C.sub.1-C.sub.20 alkyl,
C.sub.3-C.sub.20 cycloalkyl, C.sub.6-C.sub.20 aryl,
C.sub.7-C.sub.20 aralkyl, C.sub.7-C.sub.20 alkaryl, which groups
may include linear or branched alkyl moieties; and each of
R.sub.1-R.sub.10 may be optionally substituted with one or more
groups selected from hydroxy, C.sub.1-C.sub.20 alkoxy, linear or
branched C.sub.1-C.sub.20 alkyl, C.sub.6-C.sub.20 aryloxy, halogen,
ester carboxy, nitrile, and amino.
[0045] Preferably, the peroxide is a cyclic peroxide containing at
least two peroxide goups, and most preferably, it is
3,6,9-triethyl-3,6,9-trime- thyl-1,4,7-triperoxonane. The latter
molecule has three peroxide groups and a relatively small number of
carbon atoms and thus a level of active oxygen of the order of
18.16 wt %.
[0046] The treatment of a polypropylene with peroxide generally
produces a modified polymer by creation of functional groups.
Peroxide radicals can cause chain scission and/or cross-linking,
resulting in an increase of the melt flow index. It must be noted
however that increasing the degradation ratio causes a decrease of
the flexural modulus. The amount of peroxide necessary to carry out
the invention depends upon the chemical nature of the peroxide,
upon the starting melt flow index and upon the desired final melt
flow index: it is directly proportional to the final melt flow
index. Melt flow index of from 2 to 70 g/10 min have been obtained,
but the efforts of the present invention are focused on products
having a melt flow index larger than 15 g/10 min. The main
departure from the strength and stiffness behaviour of prior art
materials occurs for resins having a melt flow index above 15 g/10
min.
[0047] In a preferred embodiment of the present invention, the
polypropylene heterophasic copolymer is prepared by copolymerising
propylene with ethylene in the proportions of from 5 to 20 wt % of
ethylene and 95 to 80 wt % of propylene. The copolymerisation is
effected in two reactors as follows:
[0048] a) the catalyst and propylene are charged into a first loop
reactor equipped with a circulation pump, at a temperature of from
60 to 80.degree. C. and under a pressure of from 35 to 40 bars,
using the liquid monomer as a suspension vehicle, in order to
produce a homopolymer of propylene on the surface of the catalyst
grains;
[0049] b) the polymer-coated catalyst grains are transferred to one
or more secondary gas phase reactors with a fluidised bed and
ethylene is added in order to produce an ethylene-propylene
rubber.
[0050] The polypropylene heterophasic copolymer so obtained has a
typical heterophasic morphology consisting of ethylene-propylene
bipolymer spherical domains dispersed in a semi-crystalline
polypropylene matrix. These materials generally consist of three
components: a propylene homopolymer, a rubbery ethylene-propylene
bipolymer and a crystalline ethylene-rich ethylene-propylene
bipolymer. The amount and properties of the components are
controlled by the process conditions and the physical properties of
the resulting material are correlated to the nature and amount of
the three components. In the present invention, the preferred
amount of ethylene is of from 9 to 15 wt % and more preferably, it
is from 11 to 14 wt %.
[0051] The polypropylene heterophasic copolymer is then extruded in
an extruder with a cyclic ketone peroxide and with one or more
optional fillers, such as glass fillers, talc, calcium carbonate or
clay minerals. The cyclic ketone peroxide has a half-life time
longer than one second at a temperature of 225.degree. C. The
extrusion is carried out at a temperature sufficient to maintain
the material in a molten state. In the examples carried out with
the preferred peroxide of the present invention, the extrusion
temperatures are from 160.degree. C. up to less than 200.degree.
C., preferably from 160 to 190.degree. C. The resin obtained after
degradation of the polypropylene (co)polymer at low temperature
exhibit an excellent impact performance. That result is totally
unexpected as it is generally known in the art to work at
temperatures higher than 200.degree. C. with long half-life time
peroxides, in order to compensate for their low reactivity level.
It must be noted in addition that the resins prepared according to
the present invention retain higher impact strength than prior art
resins, for extrusion temperatures higher than 200.degree. C.
[0052] The Izod notched impact strength of the final resin depends
upon the amount of ethylene present in the polypropylene
heterophasic copolymer: it increases with increasing amounts of
ethylene. The rigidity, on the contrary, decreases with increasing
amounts of ethylene, thereby imposing an upper limit to the amount
of ethylene incorporated into the copolymer.
[0053] It is further observed, that the final resins obtained
according to the present invention, when extruded at cold
temperature, retain an Izod notched impact strength at 23.degree.
C. above 40 kJ/m.sup.2, for melt flow indices ranging from 15 to 40
g/10 min and for an ethylene content of from 9 to 15 wt % in the
polypropylene heterophasic copolymer. For an ethylene content in
the polypropylene heterophasic copolymer larger than 12 wt % and an
extrusion temperature of at most 200.degree. C., the impact
strength of the compositions according to the present invention
remains above 40 kJ/m.sup.2 for melt flow indices up to 70 g/10
min. Throughout this disclosure, cold extrusion temperature is
understood as a temperature ranging from the temperature at which
all components are in the molten state up to a temperature of less
than 200.degree. C.
[0054] In addition, it is also observed that both the extrusion
temperature and the percentage of ethylene contained in the
polypropylene heterophasic copolymer have an influence on the
behaviour of the Izod notched impact strength as a function of melt
flow index. Decreasing the extrusion temperature or increasing the
amount of ethylene results in final resins that retain the impact
properties at values of the melt flow index larger than 40 g/10
min. It is thus possible, playing with these two parameters to
tailor the desired final resins.
[0055] The copolymers of the present invention are used in several
applications that require simultaneously a melt flow index larger
than 15 g/10 min, high impact strength and high flexural modulus
such as for example: crates, ice cream containers, yoghurt beakers,
storage bins, suitcases, lids, pails, technical parts, garden
articles, automotive parts, batteries, thin wall packaging, medical
waste containers and compounds. Compounds are particularly valuable
as they allow the production of articles with less or no
elastomeric modifiers thereby allowing reduction of cost and
processing time.
LIST OF FIGURES
[0056] FIG. 1 represents a plot of the Izod notched impact strength
at 23.degree. C., expressed in kJ/m.sup.2, as a function of the
melt flow index, expressed in g/10 min, for an ethylene content in
the polypropylene heterophasic copolymer of 11.3 wt % and for an
extrusion temperature of 200.degree. C.
[0057] FIG. 2 represents a plot of the Izod notched impact strength
at 23.degree. C., expressed in kJ/m.sup.2 as a function of the melt
flow index, expressed in g/10 min, for an ethylene content in the
polypropylene heterophasic copolymer of 11.3 wt % and for extrusion
temperatures of 160.degree. C. and of 200.degree. C.
[0058] FIG. 3 represents a plot of the Izod notched impact strength
at 23.degree. C., expressed in kJ/m.sup.2, as a function of the
melt flow index, expressed in g/10 min, for an ethylene content in
the polypropylene heterophasic copolymer of 13.2 wt % and for an
extrusion temperature of 200.degree. C.
[0059] FIG. 4 represents a plot of the Izod notched impact strength
at 10.degree. C., expressed in kJ/m.sup.2, as a function of the
melt flow index, expressed in g/10 min, for an ethylene content in
the polypropylene heterophasic copolymer of 13.2 wt % and for an
extrusion temperature of 200.degree. C.
[0060] FIG. 5 represents a plot of the Izod notched impact strength
at 23.degree. C., expressed in kJ/m.sup.2, as a function of the
melt flow index, expressed in g/10 min, for ethylene contents in
the polypropylene heterophasic copolymer of 11.3 and of 13.2 wt %,
and for an extrusion temperature of 200.degree. C.
EXAMPLE 1
[0061] Several samples have been prepared using as starting
material a polypropylene heterophasic copolymer having a melt flow
value MI2 of 2 g/10 min and an ethylene content of 11.3 wt %. The
polypropylene heterophasic copolymer has been extruded in a
single-screw Gloenco extruder, at a temperature of 200.degree. C.,
with various amounts of the cyclic peroxide
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane in a 41.3%
solution of Isopar M diluent and having 7.5 wt % of active oxygen,
in order to obtain the desired melt flow index for the finished
material. The formulation of these materials contains in addition
Irganox and Irgafos as antioxidants, 400 ppm of calcium stearate,
3500 ppm of talc and 2000 ppm of glycerol monostearate (GMS) as
antistatic agent. The data are summarised in Table I.
1 TABLE I Cyclic peroxide consumption (ppm) Final MFI (g/10') 350
7.2 700 12 900 24.7 1380 37.9 1810 56 2110 73.4
[0062] The flexural modulus has been measured at 23.degree. C.
using the method of standard test ISO 178 and the Izod notched
impact strength has been measured at 23.degree. C. using the method
of standard test ISO 180. The results are summarised in Table II
and in FIG. 1.
COMPARATIVE EXAMPLES
[0063] The same polypropylene heterophasic copolymer as that used
hereabove has been extruded with various amounts of
2,5-bis(tert-butylperoxy)-2,5-dimethylhexane sold by Akzo Nobel.
Chemicals B.V. under the trade-name Trigonox 101 under the same
conditions as in Example 1. The amounts of peroxide have been
adjusted in order to produce finished materials with comparable
melt flow indices of respectively 8, 12, 27.2, 38.2, 63.5 and 74,
as those of the samples according to the invention. The amounts of
peroxide consumed are respectively 250, 500, 800, 1060, 1390 and
1650 ppm. The flexural modulus and Izod notched impact strength are
also presented in Table II and FIG. 1 for comparison.
2 TABLE II Perox. 101* cycl* 101 cycl 101 cycl 101 cycl 101 cycl
101 cycl MFI 8 7.2 12 12 27.2 24.7 38.2 37.9 63.5 56 74 73.4 g/10'
Flex. 1160 1216 1050 1120 1040 1065 1000 1036 965 1000 945 995 Mod.
Mpa Izod 56.5 60.7 19 54 20.7 51 13.2 21.1 12.7 15.1 11.7 14.3
23.degree. C. kJ/m.sup.2 *101 = Trigonox 101 and cycl =
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
[0064] From Table II and FIG. 1, it appears that the material
produced according to the present invention has a flexural modulus
that is larger by about 40 MPa than that of the material produced
with Trigonox 101 for melt indices larger than 15 g/10 min.
[0065] From Table II and FIG. 1, it is observed that the Izod
notched impact strength at 23.degree. C., of the material produced
according to the present invention, quite unexpectedly does not
decrease sharply for a melt flow index larger than 15 g/10 min as
does the material prepared with Trigonox 101. It remains fairly
high up to a value of the melt index of about 40 g/10 min. Above
that value, it remains significantly higher than that of the
comparative samples.
EXAMPLE 2
[0066] The Izod notched impact strength has been measured, at the
temperatures 23, 10 and -20.degree. C., for melt indices of 12, 25
and 40, for extrusion temperatures of 160, 180 and 200.degree. C.
and for two peroxides. The controlled rheology polypropylene
heterophasic copolymer samples according to the present invention
have been prepared with an ethylene content of 11.3 wt % and with
the same cyclic ketone peroxide as that used in example 1. The
comparative examples have been prepared with the linear peroxide
sold by Akzo Nobel Chemicals B.V. under the name Trigonox 101. The
results are summarised in Table III and in FIG. 2.
3TABLE III Izod notched impact strength (kJ/m.sup.2) at 23.degree.
C., 10.degree. C. and -20.degree. C. Ex. T. = 200.degree. C. Ex. T.
= 180.degree. C. Ex. T. = 160.degree. C. Peroxide MFI 23 10 -20 23
10 -20 23 10 -20 101 12 19 na 6 45* 13 6 47* 13 6 101 25 20 na 8
32** 10 6 24** 10 6 101 40 13 na 7 14 8 5 14 9 5 cyclic 12 54* na 7
51* 43* 6 52* 42* 7 cyclic 25 51* na 7 48* 13 6 46* 13 6 Cyclic 40
21 na 8 45* 11 6 45* 11 6 na: not available *no break **no break of
some samples
[0067] It can be concluded from these results that the material
prepared according to the present invention has an impact strength
that is superior to that of the comparative samples, in all cases.
The results are particularly remarkable at low extrusion
temperatures of 160 and 180.degree. C.
EXAMPLE 3
[0068] Controlled rheology resins were prepared based on the MI2=2
g/10 min (ISO 1133) reactor polymerised polypropylene heterophasic
copolymer with an ethylene content of 13.2%. Anti-oxidants, calcium
stearate (400 ppm), nucleation (talc 3500 ppm) and antistatic
agents (glycerol monostearate (GMS) 90% 2000 ppm) were added during
extrusion on a single screw Gloenco extruder. Two different
peroxide were used: 2,5-di-tert-butyl-2,5-dimethylhexyl peroxide
sold by Akzo Nobel Chemicals B.V. under the trade-name Trigonox 101
and 3,6,9-Triethyl-3,6,9-Trimethyl- -1,4,7-triperoxonane.
[0069] The degradation ratios were of 6, 12.5 and 20 and the
extrusion temperature was 200.degree. C. Melt flow index, flexural
modulus and Izod notched impact strength are reported in Table IV.
The Izod notched impact strength results are also summarised on
FIGS. 3, 4 and 5 for temperatures of +23.degree. C. and +10.degree.
C. respectively.
4TABLE 4 Tr. 101 cyclic Tr. 101 cyclic Tr. 101 Cyclic Tr. 101
Cyclic Property Start MFI 12 MFI 12 MFI 25 MFI 25 MFI 40 MFI 40 MFI
70 MFI 70 MFI (g/10 min) 2.4 11.3 11.3 24.3 23.0 39.0 39.2 70 70
Flexural Modulus 1130 1040 1035 990 995 925 980 (MPa) Izod Notched
+23.degree. C. 57.7* 49.4* 54.2* 43.1* 48.7* 14.5 41.7* 14 41
(kJ/m.sup.2) Izod Notched +10.degree. C. 50.1* 16.0 48.3** 10.3
27.4** 12.1 11.9 (kJ/m.sup.2) Izod Notched -20.degree. C. 7.5 6.4
6.6 5.6 6.2 5.7 4.9 (kJ/m.sup.2) *no-break **no-break of some
samples.
[0070] All the resins produced with both the linear and cyclic
peroxides at an extrusion temperature of 200.degree. C. and for
melt flow index of from 12 to 25 g/10 min show `no break` at room
temperature. This in contrast to the results obtained in the
previous example prepared by degrading a polypropylene heterophasic
copolymer with a lower ethylene content. A higher ethylene content
(13.2 vs. 11.3%) thus drastically improves the impact performance
of polypropylene heterophasic copolymers.
[0071] Changing the peroxide type from linear (Trigonox 101) to
cyclic improves the `no break` performance of the final resin with
a melt flow index of 70 g/10 min at a temperature of 23.degree.
C.
[0072] The resins having a melt flow index of 12 and of 25 g/10 min
produced with the cyclic ketone peroxide also show excellent impact
performance at a temperature of 10.degree. C.
[0073] From these examples, it can be concluded that the cyclic
ketone peroxide offers an important mechanical advantage over the
linear peroxide Trigonox 101.
[0074] It is possible to produce better flow materials that keep
their impact strength for a melt flow index as high 70 g/10 min and
show `no-break` from an Izod notched impact test at room
temperature. The materials also show a better impact performance at
other temperatures.
[0075] In almost all cases the flexural modulus is higher.
[0076] In conclusion, the resins produced according to the present
invention exhibit an improved balance of stiffness, impact,
strength and flow properties. The materials produced according to
the present invention are thus particularly useful for preparing
articles that require simultaneously high melt flow and good impact
strength. Indeed high melt flow material is easier and faster to
process, particularly in injection moulding, thus allowing shorter
cycle time and reduction of the walls' thickness while keeping an
acceptable stiffness and impact strength.
* * * * *