Note: Descriptions are shown in the official language in which they were submitted.
309
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The present invention relates to porous threads,
a method of producing them and their use, in particular,
as a support substance for active ingredients.
It has already been known for a long time to
produce porous threads. In many cases, these threads
are designated as foam threads.
A large number of methods for obtaining threads
having a porous structure is already known. Thus, East
German Patent No. 103 375 describes a method in which a
pol~vmer melt consisting of one or more components,
preferably components which are incompatible with each
other, is extruded with the additon of physical and/or
chemical blowing agents through one or more rows of holes
in spinnerets with round, round and hollow or profiled
and hollow spinneret holes. These threads can be de-
posited so as to form non-woven fabrics by suitable
processing.
The threads with cavities known hitherto have
various disadvantages, ~d several methods thus lead to
threads which only have cavities in the interior and which
have a completely closed surface or possible a surface
having slight permeability. Other threads whose surfaces
exhibit opening are, however, produced with a surface
which lS rough, thus rendering them unsuitable for many
uses.
There is thus a need for improved methods of
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productio~ l partioular to provide methods by which the
spiIming composition to be extruded can be produced
simply and which operate without complicated spinning
baths. There is also a need for improved threads which
are porous, having openings on their surface but neverthe-
less have a smooth surface structure,
An object of the invention is therefore to provide
a method by which polymers can be shaped in a simple
manner in an extrudable spinning composition and which
simultaneously allows extrusion and allows the extruded
material to be solidified without complicated spinning
techniques and spinning baths having to be used.
Another object of the invention is to provide a method
which ailows threads having adjustable porosity to be
obtained merely by varying the operating parameters.
An object of the invention is also to provide porous
threads which have a desirable open surface relative
to the known foam threads. A further object of the
invention is to provide threads which can be used in the
textile field as well as in industrial and other spheres
and which are particularly suitable as a support substrate
for certain active ingredients.
According to the presen-t invention there is provided
a method of producing porous threads in which a
homogeneous mixture is extruded, the homogeneous mixture
comprisiIlg at least two oomponents, of which one oompon-
ent is a fusible polymer and the other component is a
liquid which is inert towards the polymer as ~erein-
after defined), the two components forming a binary
system, which llas, in the liquid sta-te, a region in which
the components are completely miscible and a rsgion in
which there is a discontinuity in, the homogeneous mixture
being extruded at a temperature above the critical
temperature of the binary system in to a bath containing
said other inert liquid component of the homogeneous
mixture and which is at a temperature below said critical
temperature, and the thread structure so formed is
solidified.
The fibre structure formed can be washed out using
a solvent after solidification, acetone being particularly
useful for this purpose.
It is advantageous if an air gap is included
between the outlet surface of the extrusion tool and the
surface of the bath. This air gap can be heated.
It is also possible to extrude the homogeneous
mixture directly into the bath.
A bath having a staggered temperature is used in
$ a particular embodiment of the me-thod according to the
invention. In that embodimen~ the bath can comprise
one or more parts which have a temperature gradient in
such a way tha-t the temperature increases continuously
_5
from the begining of the spinning bath to th~ outlet
end. `
It is also possible to use two or more separate
baths which each have a different temperature.
It has proved advantageous if the bath is at a
temperature which i8 at least 100C lower than the
critical temperature of the binary composition used.
Homogeneous mixtures of from 10 to 90/0 by weight of poly-
mer and from 90 to 10 ~ by weight of inert liquid can
be extruded according to the invention.
The homogeneous mixture can also initially be
extruded into a spinning tube connected upstream of the
bath and filledwith the bath liquid.
Polypropylene is preferably used as polymer and
NN-bis-(2-hydro~yethyl)-hexadecylamine is preferably used
as inert liquid.
The two components, namely the molten polymer and
the inert liquid, are preferably mixed continuously prior
to extrusion, in which process it is advantageous for
mixing only to ta~e place immediately prior to e~trusion.
The mixture can still be homogenised prior to extrusion.
A pin mixer is particularly suitable for mixing purposes.
- ~ According to another aspect of the present invention
there is provided porous threads comprisi~g a s~thetic
polymer having from 10 to 90~0 by volume of pores which
COmmUniGate with each other and a smooth surface structure
haviIlg open pores, wherein the proporSion of openings
in the surfnce thereof amounts to from 10 to 90%,
Preferably the apparent density of the threads lies
between about 10 to 90~ of the actual density of the
polymer used.
The threads can be used as a support substrate, io e.
the threads can be impregnated with specific substances
which are given off at a subsequent moment. They can
also be used as insulating material.
It is possible to use, in particular, fibre-forming
macromolecular substances which are known per se,
particularly synthetic polymers which are obtained, for
example, by polymerisation, polyaddition or polyconden-
sation, for carrying out the method according to theinvention and for the production of threads according
to the invention. The polymer must be fusible, i.e.,
it must be able to pass into the liquid state without
decomposing and form a binary system with a liquid which
is inert towards it, which system having a range of com-
plete miscibility in the liquid state and also a range in
the liquid state with mixing gaps.
Systems of this type have a phase diagram for the
liquid state of, for example, the type shown for the
aniline/hexane system on page 724 of the Text Book of
physical Chemis-try by S. Glasstone, Macmillian and Co
Ltd, St, ~artins~ Street, London, 1953. Thisdiagram
indicates complete miscibility for the two components
above -the arched curve. Two liquid phases are in
equilibriu~ with each other beneath the curve~
It is not absolutely essential for carrying out
the invention for each of the two components in thetwo-
phase range still to exhibit considerably solubility
relative to the other components, as is the case in the -
above-mentioned graph. In many cases, it is sufficient
to have marginal solubility in the liquid two-phase
domain. It is however important for the two components
in the liquid state to form two liquid phases next to
each other. In this respect, the systems which can be
used according to the invention differ from those systems
in which the dissolved polymer is precipitated directly
as a solid when the temperature is lower without firstly
passing through the liquid state during the cooling
treatment.
Conventional fusible polymers can be used within
the scope of the invention, such as, for example the
polymers obtained by polymerisation, such as, polyethylene,
i polypropylene, polyvinylchloride, polyacrylates, poly
caprolactam as well as corresponding copoly~ers among
others; polycondensation polymers, such as, polyethylene
terephthalate, polybutylene terephthalate, polyamide
09
~),6 polyphenylene oxide, and poly addi-tion polymers,
such as, polyurethanes and polyureas.
All tho6e liquids which form a binary system
of the above-mentioned type with the polymer in the
liquid state are basically suitable as inert liquid
within the scope of the invention. By the phrase "inert
towards the polymer" as used herein, is meant that the
liquid does not cause considerable decomposition of the
polymer within a short period or does not react with
the polymer itself.
Although the above-mentioned phase diagram of the
state of the aniline/hexane sysb~mshows the ratios for a
binary mixture which consists of two uniform substances
which are themselves essentially pure, the term binary
system should not be appled strictly, in the context of
the invention, to mixtures of only two pure uniform
substances. The average skilled man knows that a polymer
substance is composed of a plurality of molecules of
differing molecular weight, and these polymers with
a corresponding molecular weight distribution are there-
fore to be considered within the scope of the invention
as one component, and the same applies to mixed poly-
- ~ mers. Under certain circumstances, polymer mixtures
can even behave as a uniform component and form a single
phase mixture with an inert solvent and separate only into
two liquid phases below a critical -temperature. It
is preferable, however, to use only one polymer~ The
liquid need not necessarily be completely pure and
represent a completely uniform substance~ In many cases,
it does not matter if relatively small quantities of
impurities and possibly also proportions of homo-
geneous c~mpounds of the type which are necessitated by
industrial production are added.
In order to carry out the method in practice, a homo~
geneous mixture is produced from the two components at
the required temperatures~ This can be effected by
- mixing the inert liquids with the comminuted polymer
heating it to suitable temperatures, ensuring that
mixing is sufficiently thorough.
Another suitable method involves bringing the two
components to the required temperature separately and
mixing the two components together continuously in the
desired proportion just before extrusion. This mixing
can be carried out in a pin mixer which is advantageously
arranged between themetering pumps for the individual
components and the spinning pump. Subsequent homogen-
isation may be advisable.
- ~ In many cases, it is advisable to aerate the
homogeneous mixture by applying a suitable vacuum before
extrusion.
The ratio of the polymer to inert liquid in the
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spinlling compositioIl can be varied within wide limits.
The interllal pore volume and also the surface texture
as well as the number of open pores on the surl'aces of the
hollow threads obtained, can be controlled to a large
èxtent by adjusting the ratio of polymer to inert liquid.
Porous threads which are suitable for a very wide range
of applications can thus be obtained.
It is generally sufficient for the temperature of
the homogeneous mixture prior to extrusion to lie only a
few degrees above the critical temperature or above the
disintegration temperature, depending on the respective
composition.
Interesting effects with regard to the texture
of the threads obtained can however also be achieved by
increasing the difference between the temperature of
the homogeneous mixture to be e~truded and the critical
temperature.
The homogeneous spinning composition is then
extruded into a bath containing the inert liquid of the
extruded component mixture and having a temperature below
the critical temperature. The bath preferably consists
completely or mainly oY the inert liquid which is also
- $ present in the extruded mixture. The temperature of
the bath lies below the critical temperature of the
mixture used, i.e. below the temperature above which the
two components can be mixed together completely homo-
V3~)9
genevusly. The teloperature of the bath preferably liesat least 100C below the critical temperature O:e -the
mixture used.
The temperature can also be sufficiently low to
progress in the range in which a solid phase occurs
according to the phase diagram relatingto the binary
system.
Once the temperature of the bath is sufficiently
high that it continues progressing in the liquid two
phase region, then it is necessary to solidify the thread
structure formed as soon as possible, which can be ef-
fected by reducing the temperature accordingly after a
certain interval inside the bath.
It is imp~rtant for the extruded mixture still
to be single-phase before it enters the bath, i.e. for
substantially no further disintegration into two phases~
to take place.
It has proven advantageous to arrange in front,
upstream end of the bath in certain cases a spinning tube
which is also filled with the bath liquid and the end
of which is submerged in the spinning bath. The spin-
ning tube can have a conventional spinning funnel at its
inlet opening, and the tube can be curved at its lower
end ~n order to make it easier to take off the thread
through the bath.
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The spinning tube can be filled by means of a
level container surrounding the spinning tube as a result
of overflow into the spimIing tube. In order to lill
the spinning tube completely and to maintain the level in
5 it, it is necessary to supply more bath liquid to this
level container from a main reservoir than flows out
through the spinning tube. The excess bath liquid can
be recirculated via a secondoverflow on the level cont-
ainer into the main reservoir. The main reservoir and
10 level container can be controlled thermostatically.
Once it has passed from the spinning bath, the
thread can be washed out with a suitable extraction agent.
A number of solvents such as, for example, acetone, cyclo--
hexanone and ethanol as well as mixtures of these liquids,
15 are suitable for extraction~
In some cases, it is not necessary to wash out
the thread, particularly when the actual inert liquid
s used is to impart to the thread extra properties which
are designed for its subsequent application or is even to
20 perform a function. Thus, for example, it is possible
to use liquids which exert an anti-static effect on the
thread or which act as lubricants. It has proven advant-
ageous for a number of applications to maintain an air
gap between the outlet surface of the extrustion tool,
25 i.e. the outlet surface, for example, of a corresponding
~ f~
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thread noz~le and the surface of thc bath. By varyiIlg
the air gap, it is possible to influence the structure
of the thread o'btained, and in particular, it surface.
It has been f~lnd that the numberof open pores
can be reduced by extending the air gap and can be
increased by shortening it. The diameter o~ the pores
also decreases as the air gap increases,
The air gap can be heated, preferably to a
temperature above the critical temperatureof the extruded
mixture.
The air gap is generally at least 1 mm wide and
can assume a length of up to about 10 cm depending on the
operating conditions. It is important to prevent any
disintegration or at least any noticeable disintegration
into two liquid phases in the air gap before entry into
the bath . As stated, this can be c~ntrolled by the
shortness of the interval or by heating, but it is however
also possible to counteract premature disintegration by
increasing outlet speed at the nozzle.
In a particular embodiment of the method according
to the invention, however, the homogeneous mixture is
extruded directly into the bath, open pores having a
maximum diameter being formed at the surface.
;Owing to their particular surface structure and
the structure inside the threads, they are also eminently
3(~9
suitable as a substrate for certain substances. Thus,
tlle threads can be impregnated with anti-static agents
which are already in use as an iner-t liquid during the
spinning process or the agent can be introduced in-to the
thread strueture only subsequently by treating it9 for
example, by impregnation, after production of the thread.
In this way, it is possible to obtain compositions
having a long term effect, which slowly give off the
absorbed active ingredient again. Conversely, the threads
can also be used for the adsorption of substances.
The threads can also be used in a wide variety of
textile applications, for example,~they can be processed
into sheets, such as, woven or non-woven fabrics~
Another field of applieation is insulation, such as, for
example, thermal insulation and sound-proofing.
The pores in the threads aceording to the invention
can be of various shapes. Thus, they can be rounded or
elongated and can be interconneeted, in some cases by
small conneeting passages and in other cases due to them
passing directly into eaeh other. Even in threads which
have been obtained from mixtures having a polymer content
of about 30%~ the poly~er can be the matrix, in whieh the
individual pores are distrubted and form fairly discrete,
but intereonneeted eavities. Conversely, it is also
possible to produce structures in which the cavities
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form the ~atrix as wi-th non-woven fabrics and the poly-
mer substance is arranged in a almost fibrillar con-
figuration. The transitions between these two structures
are not strongly defined and are thus partly mixed. The
5 structural forms can also be influenced by other oper-
ating parameters such as, for example, take-off speed,
cooling speed, draft below the nazzle.
An apparatus which is suitable forthe production
of the threads according to the invention is illustrated
in more detail in the accompanying drawing.
The numeral 1 refers to a container which can be
thermostatically controlled, from which inert liquid is
metered by means of a double piston pump 3 and another
heater 4 into the mixer 8. The heater 2 provides
preliminary heating. Polypropylene passes from the chip
container 5 via an ex~ruder 6 and a gear pump 7 into the
mixer 8, from which a nozzle 10 is supplied via a gear
p~p 9. The issuing mass passes via an air gap into a
spinning tube 12 which is provided with a spinning
funnel 11 and is provided with inert liquid via a level
container 13 from the main reservoir 14. The spinning
tube has a curve at its lower end and the threads are
- ~ conveyed to a winder 16 af-ter leaving a bath 15.
;The invention is illustrated in more detail by
the following Example:
ll~V~309
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Polypropylene chips are melted in an~extruder
and metered into a pin mixer using a gear plmlp
Liquid NN-bis-(2-hydroxyethyl)-hexadcylamine
at a temperature of 40~ is simultaneously pumped from
a storage container which can be heated, via a double
piston pump into an electrically heated heater and is
conveyed from there into the mixer at a temperature o-f
about 150C. A pin ~xer is used a mixer.
After homogenisation of the two components, the
melt is pressed through a spinneret by a metering pump
and extruded into a spinning bath which consists of pure
NN-bis-(2-hydroxyethyl)-hexadecylamine and has a temp-
erature of 50C.
Once the thread has passed through the spinning
bath, having a length of 50 cm, the thread obtained is
extracted over ethanol and dried. A porous thread
having excellent properties and a particularly good
surface structure is obtained.
.~
