Note: Descriptions are shown in the official language in which they were submitted.
. '17~302~L3
PROCESS FOR THE MANUFACTURE OF POLYPROPYLENE FIRES
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The present invention relates to a process for the manufacture of
polypropylene fires having stretching properties at the outlet of the
die, greatly improved as regards to what is presently known in the art.
It is well-known that the polypropylene fires have many applications
for several years, for instance non-woven fabric, carpets and other
analogs.
In the usual processes for the manufacture of fires, polypropylene
is introduced in the melting stave in a sheet die having a high number of
orifices, generally between 2û00 and about 20,0D0. Polypropylene is
introduced into such a die in order to give it the form of a yarn. These
yarns are then stretched continuously in an horizontal oven at a temperature
comprised between 90 and 16DC. The stretching rates which are normally
used are usually comprised between 100 and 300%. It is also known in the
art that a low stretching rate will produce a fire having a high residual
elongation, but such a property leads to introduce in the horizontal oven
a yarn having a finer diameter in order to obtain the desired number of
denier. Therefore a more important stretching of the material must be
applied at the outlet of the sheet die.
The stretching properties of the yarns crossing these orifices depend
particularly on the nature of the polypropylene yarn in the melting stave,
and particularly on the dispersion of the molecular weight of this latter.
Moreover, the fires may be stretched upward or downward, in accordance
with the selected process, or still in accordance with the selected melt
spinning speed, the highest speeds being reached with downward stretching.
Presently, the polypropylene which are used in the manufacture of
fires do not present a sufficient elongation Al viscosity, that is to say,
a viscosity such that it is possible to form a yarn with the melt material
at a high speed, and such that it allows to suitably stretch this yarn in
order to obtain fires of 1.5 denier, in case of a upward stretching at a
speed of about ~Om/minute.
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In case of a downward stretching, the usual polypropylene do not
allow to reach high melt spinning speeds of about mounts
loin order to overcome these drawbacks, it has already been proposed
to introduce peroxides in polypropylene compositions. However, this
process did not lead to favorable results in case of upward stretching,
because the viscosity of the composition was too low to have a chance to
form a yarn. Moreover the material which contains these peroxides is
partially degraded, typically it has a high melt flow index and a very
low viscosity, these facts being not always very interesting for some fur-
then applications.
There is therefore a need for a process for the manufacture of polyp
propylene fires having improved stretching properties.
The first object of the invention is to overcome all these here above
mentioned drawbacks.
An object of the present invention is a process for the manufacture
of polypropylene fires which allows an easy extrusion of the yarns either
upward or downward, while obtaining fires having an acceptable residual
elongation.
A particular object of the present invention is a process for the
manufacture of polypropylene fires having low denier, generally comprised
between 5 and 1 denier.
The process of the present invention for the manufacture of polyp
propylene fires having improved stretching properties comprises the steps
which consist in introducing into polypropylene, from about 0.01 to about
0.5% by weight, based on polypropylene, of iris t3,5-di-t-butyl-4-hydroxy-
benzyl)isocyanurate, and in carrying out the extrusion at a temperature
comprised between 220C and awoke.
The polypropylene which is used in the process of the invention is
a propylene crystalline homopolymer, which may eventually contain nucleating
agents. Said crystalline polypropylene is generally obtained by polymerize-
lion in the presence of a stereo specific catalyst.
It has unexpectedly been noticed that if 1,3,5-triazine-2,4,G-t1H,3H.
triune, - 1,3,5 - iris -3,5 - bus t1.1-dimethylethyl)-4-hydroxyphenyl-
methyl, more commonly called tris(3,5-di-t-butyl-4-hydrDxy 3-isocyanu-
rate, is introduced in an amount from n.01 to 0,5% by weight, based on the
polypropylene weight, the elongation Al viscosity properties of the polymer
are greatly improved, the stretching of the extruded yarns being carried
out either upward or downward.
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However, it has been noted that the best results were obtained when
said compound was used in an amount comprised between about û.05 and 0.2%
by weight.
When amounts lower than 0.01% by weight are used, based on pulpier-
pylon, no significant effect is noted: on the other hand, the use of
amounts higher than 0.5~ by weight do not bring any additional benefit.
When the stretching of the extruded yarns have been carried out
upwards, we reached to form fire of 3 deniers having a residual elongation
as high as 25D%, and fires of 1.5 denier still having an elongation of 100%.
This fact it quite unexpected, if it is taken into account that this result
is obtained with orifices of the extrusion die having a L/D ratio of Z,
because with usual compositions, extruded on the same sheet dies, thus
having the same L/D ratio, many breaks of the yarn are obtained at such
a stretching.
Although we are not bound by the proposed theory, it may however be
supposed that the introduction of a compound such as trist3,5-di-t-butyl-4-
hydroxybenzyl~isocyanurate has an influence on the dispersion of the mole-
cuter weight of the polypropylene. Moreover, this compound allows to control
said dispersion by means of the temperature at which the polymer material,
which has to be treated, is introduced into the sheet die.
It has been noted that the process of the invention may be carried
out successfully if the polymer material is extruded in the sheet die at
a temperature comprised between about 220 and about 2B0C. More part-
ocularly, when the yarns are stretched upwards, the extrusion is carried
out at a temperature comprised between about 220 and about 250C, and
preferably between about 230 and about 25GC, while when the yarns are
stretched downwards, the extrusion is carried out at a temperature comprised
between about 220 and about 280C, and preferably between about 230C and
260C.
The low temperatures are generally used to manufacture fires of
high denier.
The following examples are given in order to better illustrate the
process of the present invention, but without limiting its scope.
Example 1
0.15 parts by weight of iris t3,5-di-t-butyl-4-hydroxyben~yl)isocyanu-
rate were introduced into 100 parts by weight of propylene homopolymer
having a melt flow index of US g~10 mix determined at 230C under a pressure
4. lo Lo
of 2.16 kg in accordance with the ASTM D 1Z3~ method.
The resulting blend was introduced into an extrusion sheet die at
a temperature of 23DC. The finest fires which have been obtained, had
3 deniers, with an upward stretching, at a speed of 50 minute: the fires
had a residual elongation of ODD%. The L/D ratio of the orifices of the
sheet of the die was 2.
By way of comparison, polypropylene containing D.D5% of a usual
peroxide, was extruded. With said polypropylene it has never been possible,
by means of an upward stretching, to obtain fires of 3 deniers.
Example 2
D.05 parts by weight of iris (3,5-di-t-butyl-4-hydroxybenzyl~isocya-
curate were introduced into ODD parts by weight of the polypropylene used
in Example 1.
The resulting blend was thereafter introduced into an extrusion sheet
die at a temperature of 25DC.
Fires of 3 deniers have been manufactured by upward stretching, at
a speed of Monet These fires had a residual elongation of 250%.
Fires of 1.5 denier having a residual elongation of ODD%
In the present example, it has been possible to manufacture finer
yarns at the end of the sheet die, that allow to use lower stretching rates
during the passage in the horizontal oven.
Thy L/D ratio of the orifice of the sheet of the die was 2. It has
also been observed 1 break/hour with the sheet die which has been employed.
This sheet die had 1~D,000 orifices.
Example 3
The same blend as defined in Example 2 was prepared. This blend was
thereafter extruded at a temperature of 260C in an extrusion sheet die
working with a downward stretching.
Fires of 1.5 denier were manufactured with a melt spinning speed of
about Monet
The number of breaks per hour had never exceed 3 with the sheet die employed.
This sheet die had 12,000 orifices.
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