Note: Descriptions are shown in the official language in which they were submitted.
23~7~
Stabilized polyolefins
This invention relates to polyolefins stabilized with
special phosphorous acid esters~
Organic poiymers such as polyolefins are subjected to
thermal and oxidative degradation and decomposition by
light. Numerous stabilizers are known for the various
polymers. Their effectiveness depends both on the causes
of decomposition and on the nature of the stabilized
polymer. Some compounds which are effective long term
antioxidants are relatively ineffective in processing
operations such as extrusion, in which the heat to which
the polymers are subjected is relatively high for a short
period.
A combination of various stabilizers is generally used for
obtaining sufficient stabilization of a polymer because
the presence of only one stabilizer does not ensure
sufficient protection against the various possible causes
of damage to the polymer. Thus DE-OS 28 56 801, for
example, describes alkylated 2,2'-~isphenylene-phosphites
which ara capable of stabilizing polymers against
processing conditions. The disadvantage of stabilizing
with these phosphates, however, is their insufficient long
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term stabilizing effect (see Comparison Example), which
necessitates the addition of further stabilizers.
European Patent Application 395 030 describes certain
organic phosphites which are suitable for stabilizing
polyolefins still containing residues of a Ziegler
catalyst, but even with these phosphites only insufficient
long term stability of the polyolefins i5 achieved.
It has now surprisingly been found that by using special
phosphorous acid esters of bisphenols, good processing
stability is obtained and the long term stability of the
resulting polyolefins is excellent and greatly improved
compared with that obtained with bisphenylene phosphites.
As a result, polyolefins which have been stabilized
according to the invention are also very durable in the
absence of co-stabilizers such as diphenolic antioxidants.
The present invention therefore relates to polyolefins
stabilized against processing and against long term
deterioration, containing from 0.01 to 5% by weight of
phosphorous acid esters corresponding to the following
general formula
OH
/ \
O O
R2~Y~R2
E~l R
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wherein
~1 stands for hydrogen or a C~-C18-alkyl, C5-C7-
cycloalkyl, C7-C10-aralkyl or C6-C10-aryl group,
R2 stands for a Cl-C8-alkyl, C5-C7-cycloalkyl, benzyl,
~-methylbenzyl or ~,~-dimethylbenzyl group and
Y stands for sulphur or for CHR3 in which R3 stands
for hydrogen, a Cl-C4-alkyl or a C5-C7-cycloalkyl
group.
In the above formula, Rl preferably stands for a straight
chained or branched alkyl group having 1 to 8 carbon
atoms, for example methyl, ethyl, isopropyl or tertiary
butyl, most preferably methyl or tertiary butyl~
R2 preferably stands for a branched alkyl group having 3
to 8 carbon atoms, e.g. isopropyl, isobutyl or tert.-
butyl, cyclohexyl, benzyl, ~-methylbenzyl, ~ dimethyl
benzyl or ~-methylcyclohexyl. Cyclohexyl, isopropyl,
ben~yl, ~-methylbenzyl and ~ dimethylbenzyl are
particularly preferred.
Y preferably stands for sulphur or the methylene group,
most preferably the methylene group.
The phosphorous acid esters used according to the
invention are known and are prepared by known methods;
see in this connection European Patent Application
No. 9115.
The phosphorous acid esters (stabilizers) according to
the invention are preferably used in guantities ,of from
Le A 28 156 4
17~
0.05 to 2% by weight, most preferably from 0.1 to 1% by
weight, based on the polyolefins to be stabilized.
The following are mentioned as preferred polyolefins which
can be stabilized with the phosphorous acid esters
according to the invention: Polyethylene, polypropylene,
polybutene-l, polypentene-l, polymethyl-pentene-1,
polyisoprene, polybutadiene and mixtures of the above-
mentioned polyolefins. Also to be mentioned are copolymers
of polyolefins, such as propylene-butene-l copolymers,
propylene-isobutylene copolymers, ethylene-butene-l
copolymers, ethylene-propylene copolymers and tertiary
polymers of ethylena and propylene with a diene such as
hexadiene, cyclopentadiene or ethylene norbornene.
The stabilized polyolefins according to the invention may,
of course, also contain other, conventional additives,
such as W absorbents and light protective agents, metal
inactivators, other phosphites, compounds which destroy
peroxides, nucleating agents, plasticizers, lubricants,
emulsifiers, fillers, carbon black, kaolin, talc, glass
fibres, pigments, optical brightening agents, flame-
protective agents, antistatic agents and other anti-
oxidants.
Thio compounds may also be added to the polyolefins, for
example those which produce a marked synergistic ef~ect,
such as dilauryl thiodipropionate and distearyl thiodipro-
pionate. These compounds are used at a concentration of
from 0.01 to 5% by weight, preferably from 0.05 to 2% by
weight, most preferably from 0.1 to 1% by weight, based on
the polyolefins to be stabilized.
The phosphorous acid esters to be used according to the
invention can easily be incorporated in the polyolefins by
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2 ~.3 i~
.
the usual methods at any phase during the preparation or
processing of the polyolefins.
Polyolefins which have been stabilized by the phosphorous
acid esters according to the invention are distinguished
by their only slight discolouration when processed at high
temperatures. The discolouration is only slight even if
the polyolefin is extruded several times. Polyolefins
which are particularly marked in this property are:
Polypropylene, polyethylene, polybutylene-l and the
various ethylene-propylene copolymers.
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~ ~ ~ 1 7 r~ ~
Examples
Example 1
Phosphorous acid ester of bis-(2-hydroxy-3-cyclohexyl-5-
methyl-phenyl)-methane:
O H
/ \
A mixture of 392 g ~1 mol) of bis-(2-hydroxy-3-cyclohexyl-
5-methyl-phenyl)-methane, 310 g (1 mol) of triphenyl-
phosphite and 18 g (1 mol) of water is heated to 180C
under nitrogen at normal pressure. The reaction mixture is
left to cool to 100C and is then heated from 100 to 200C
at 3333 Pa in 2.5 hours. 275 g of phenol distil over in
this process. ~n almost colourless, slowly crystallizing
product is left as residue (445 g).
Mp. 180-181~C (from toluene/hexane).
Exam~le 2
Phosphorous acid ester of bis-(2-hydroxy-3-styryl-5-
methyl-phenyl)-methane:
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2 0
~) H
/ \
O O
Ph ~J~Ph
A mixture of 218 g (0.5 mol) of bis-~2-hydroxy-3-styryl-5-
methyl-phenyl)-methane and 68.7 g (0.5 mol) of phosphorus
trichloride is heated to 60 70C in toluene for 3 hours.
9 g (0.5 mol) of water are then added and stirring is
continued for 3 hours at 90~C. After removal of the
solvent by distillation, 239 g of an almost colourless
resin is obtained as residue.
Mp. 214~C (from tvluene/hexane).
Test of processing stability of polypropylene:
lo Unstabilized polypropylene (e.g. Hostalen PPK 0160 F) is
homogenised with 0.15% of the stabilizer described in
Example 1 in a high speed mixer, extruded as a strand in a
single shaft extruder at 250C and granulated.
The granulate i5 passed through the extruder a further
four times. A sample of granulate is removed a~ter each
passage through the extruder and its melt index MVI-
230/2.16 (cm3jlO min) is determined according to
DIN 53 735. For this purpose, a sample of the granulate is
heated to 230 C and pushed with a force of 2.16 kilopond
through a nozzle having an opening of 2.095 mm. The volume
of sample pressed through the nozzle in 10 minutes is
measured.
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MVI-230C/2.16 tcm3/10 min]
Number of extrusions
1 2 3 4
Polypropylene unstabilized 22.3 121 - -
Irgaphos 168 (Ciba) 11~5 95.7 - -
Substance from Example 1 1.2 4.8 9.9 16.1
This shows that the substances according to the invention
have an excellent processing stabilizing effect as
indicated by the comparatively slight lowering of the
viscosity.
Oven ageing of polypropylene wafers containing phosphorous
acid ester:
Unstabilized polypropylene powder (e.g. Hostalen PPK
0160 F) is carefully mixed with 0.2% by weight of the
given stabilizer. In addition, samples containing 0.2% by
weight of the same stabilizer and 0.1% by weight of
distearyl-thiodipropionate are prepared. The mixed
material is then ground in a two-roller mill for 10
minutes at room temperature. The stabilized polypropylene
powder is then compressed in a hydraulic press under a
pressure of 200 bar at 180C for 10 minutes. The resulting
plates 0.1 mm in thickness are tested for their resistance
to accelerated ageing in an oven at 150C. As soon as the
platelets show the ~irst signs of friability, e.g. brown
edges, they are regarded as decomposed.
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2 ~ 7 c~ 1~
Hours until decomposition
unstabilized 6
Stabilizer from Example 1 240
Stabilizer from Example 1 ~
5 0.1% distearyl thiodipropionate330
Stabilizer from Example 2 280
Stabilizer from Example 2 +
0.1% of distearyl thiodipropionate 350
Comparison ExamPle
10 6,6'-Di-(tert~-butyl-4,4'- 40
dimethyl-2,2'-biphenylene)-
phosphite
(substance from Example 3 and
Claim 4 of DOS 2 856 801~
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