Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Moldinq com~Qsitions based on polyethylene havinq an
averaqe molecular wei~ht of at least 500 r 000 g~mol
The present invention relates to molding composition~ of
polyethylene having an average molecular weight of at
least 500,000 g/mol, preferably at least 1 x 10~ g/mol,
which are stabilized against the effects of weathering,
in particular against degradation by the action of heak
and lightO The novel molding compo~itions contain
sterically hindered amines and copper phthalocyanine as
stabilizers.
As the degree of polymerization increases, a number of
industrially important properties of polyethylene are
improved considerably. Thus, the notched impact strength
increases, the heat distortion point and tear strength at
elevated temperature increase and the resistance to
stress corrosion is increased. The high resis~ance to
wear, the low coefficient of friction compared with othPr
materials, the excellent toughness properties and the
remarkable resistance to numerous chemicals are further-
more to be emphasized. The industrial properties men
tioned are particularly pronounced in the case of ultra-
high molecular weight polyethylene, PE-UHMW, which has an
average molecular weight of at least 2.5 x 106 g~mol to
about 1 x 107 gJmol.
Like all polymers, high molecular weight polyethylen2 is
chemically changed by heat and light and oxidation
effects associated therewith, with the consequence that
its mechanical properties are noticeably impaired.
Polyethylene, including the high molecular weight types,
must therefore be protected from the action of heat and
o~ygen. If the polyolefins are to be used in the open,
protection against sunlight is also necessary, the W
content of sunlight damaginy the plastic with the assis-
tance of atmospheric oxygen~ The polyolefins are there-
fore stabilized by addition of antioxidants and if
appropriate other additives which suppress photo-
oxidation.
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A large number of addi~ives which protect the pol~mer
against oxidation during storage, against oxidation and
heat during processing and against the surface oxidation
caused by light and elevated temperature during use over
long periods of time have been developed over the years.
Representatives of the following groups of substances
have proved particularly suitable for light stabilization
of polyolefins for external use: sterically hindered
mono-, di- or trihydric phenols, sterically hindered
bisphenols and trisphenols; sterically hindered, pre-
dominantly aromatic, secondary amines; mercaptans,
thioethers and disulfides; derivatives of phosphorous
acid and of dithiophosphoric acid; and carbon black; and
the following are used specifically for protection
against W radiation: o-hydroxybenzophenones;
2-(o-hydroxyphenyl)-benzotriazoles; phenyl salicylates;
and cinnamic acid derivatives.
Apart from individual substances, combinations of two or
more compounds also have a distinctly light-stabilizing
influence. An example which may be mentioned is the use
of a mixture of 2,6-di-(tert -butyl)-4-methylphenol and
glycerol monostearate as a light stabilizer.
The life of polyolefins is not increased to an unlimited
length of time by addition of light stabilizers; in
general, it is increased three-fold in comparison with
non-stabilized material, a period of time which does not
always meet economic and industrial requirements. Efforts
are therefore being made to develop novel, more effective
stabilizers or to increase the effectiveness of known
stabilizers by combination with other substances, w~ich
do not themsel~es have to be light or W ~tabilizers.
In connection with high molecular weight polyethylene in
particular, attempts are moreover being made to use
additives which are already effective in amounts which do
not lead to an impairment of the material properties of
the polymer.
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The objec~ was therefore to develop compositions of high
molecular weight polyethylene which have the excellent
physical and chemical properties of the base material and
at the same tLme are largely insensitive, and insensitive
over long periods of time, ~o weathering influences.
This object is achieved by molding compositions of
polyethylene having an average molecular weight, measured
by viscometry, of at least 500,000 g/mol, preferably at
least 1 x lo6 y/mol, which contain, in each case based on
the molding composition, 0.05 to 0.5 ~ by weight of a
sterically hindered amine and 0.1 to 0.5 ~ by weight of
copper phthalocyanine, and if appropriate other customary
additives.
Surprisingly, the light-stabilizing action of sterically
hindered amines is increased significantly by copper
phthalocyanine. It is particularly remarkable that the
copper compound by itself has no influence on ~he
behavior of polyethylene in visible light or under W
radiation. It is furthermore to be emphasized that the
physical properties of polyethylene are not Lmpaired by
the additives.
The preparation of polyethylene having an average mole-
cular weight, measured by viscometry, of at least
500,000 g/mol, preferably at least 1 x 106 g/mol to
1 x 107 g/mol, is known. It can be carried out by various
processes. A proven process, which is carried out under
low pressure using a mixed catalyst of titanium(III~
halides and organoaluminum compounds, is described in
DE-B 23 61 508. Other processes, which are also carried
out under low pressures, use, for example, chromium oxide
catalysts.
~he molecular weights quantified above are understood as
being the values measured by viscometry. A method for
their measurement is described, for example, in
CZ-Chemietechnik 4 (1974), page 129 et seq.
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The molding composi~ions according to the invention
con~ain sterically hindered amine~ and copper phthalo-
cyanine as additivesO
The term sterically hindered amines is understood as
meaning compounds in which one or more space filling
organic radicals are bonded to their trivalent nitrogen
atom. ~hese are mainly aromatic and secondary amines.
Examples which may be men~ioned are N,N'-disubstituted
p-phenylenediamines, such as N,N'-diisopropyl-p-phenyl-
enediamine, N,N~-di-sec.-butyl-p phenylenediamine,
diphenylamine derivatives, such as N-phenyl-l-naphthyl-
amine, and aminophenol derivatives, such as 4-dodecanoyl-
aminophenol. Bis~2,2,6,6-~etramethyl-4-piperidyl) seba
cate has p~oved to be particularly suitable. The
sterically hindered amines are used in a concentration of
0.05 to 0.5 % by weight, in particular 0.1 to 0.3 % by
weight, based on the total weight oE khe molding
composition.
Copper phthalocyanine, which is employed as an organic
pigmenk, is obtained industrially from ph~halic acid
dinitrile and copper(I) chloride. It is added in the
commercially available form to the molding compositions
according to the invention. Taking into consideration the
material properties sought, the preparation and the
~5 processahility of the novel molding composition~, it is
advisable for the concentration of the copper compound to
be adjusted to values of 0.1 to 0.5 % by weight, prefer-
ably 0.2 to 0.35 % by weight, in each case based on the
total weight of the molding composition.
Apart from amines and copper phthalocyanine, the molding
compositions according to the invention can also contain
other customary additives, such as lubricants and proces-
sing stabilizers.
The stabiliæed molding compositions are prepared by
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homogeneous mixing of the starting materials in a mixer
and, depending on the molecular weight, by melting at
temperatures of 125 to 145C or b~ sintering at tempera-
tures of 180 to 250~C, in particular 200 to 230C. The
pressure during sintering is 3 to 5 MPa, in particular 3
to 4 MPa. Cooling after sintering is also carried out
under pressure, with 5 to 10 MPa, preferably 8 to 10 MPa,
having proved suitable. The sinteriny and coollng tLme
largely depend on the ~hickness of the material.
The novel molding compositions can be worked mechanic-
ally, for example drilledr milled and sawed, in the
customary manner; they can be shaped by compression
molding.
The invention is illustrated in more detail in the
following example, but is not limited to this e~odLment.
Example
The behavior of stabilized and non-stabilized poly-
ethylene under the weathering conditions prevailing in
Central Europe was investigated under natural conditions
in the open on test specimens which were stored on a test
stand at an angle of 45 in the south-westerly direction.
Samples were taken at fixed inter~als of time over a
period of 5 years.
The test specimens used were square sheets of 150 mm side
face and 1.5 mm thick (test sheets) obtained from pressed
sheets by hot ski~ing. The pressed sheets were produced
from pulverulent polyethylene having a molecular weight,
measured by viscometry, of 500,000 g/mol, which was
pressed by itself (sample 1) or after admixing of 0.15 ~
by weight (based on the mixture) of bis(2,2,6,6-tetra-
methyl-4-piperidyl) sebacate (sample 2) or 0.15 % by
weight of the sebacate and 0.3 % by weight of copper
phthalocyanine (in each case based on the mixture -
sample 3), to give sheets having the dimensions 800 mm x
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400 mm x 30 mmr which were first sin~ered at 180C under
a pressure of 3 MPa for 2 hours and then cooled under a
pressure of 8 MPa for 1.5 hours.
The mechanical properties of density, tear strength and
elongation at break from the stress-elongation diagram at
23 and 120C as well as wear and notched impact strength
were de~ermined on the samples exposed in the open. The
density and the strength properties were tested on test
specimens stamped out of the 1.5 mm thick sheets, while
the notched impact strength and wear samples were taken
by machining from the 20 mm sheets, from the weathered
side, in a sample thickness of 10 or 6.25 mm.
To evaluate the change in the pattern of properties under
natural clLmatic conditions, the stress and elonga~ion
properties of the test sheets at 23C were selected, and
the time taken for the original values to fall to 50 %
was determined.
The elongation at break of sample 1 had already reached
the value 0 after 3 months of external weathering and the
material had become embrittled. By addition o a light
stabilizer (sample 23, the strength properties had
improved under the climatic conditions of Central Europe
and the elongation at break fell to half the original
value after 9 months. Light stabilizer in combination
with copper phthalocyanine (sample 3) significantly
increases the resistance of high molecular weight poly-
ethylene to weathering influences. The elongation at
break dropped to 50 % of its original value only af er
3.5 years.
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