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Description  |
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FIELD OF THE INVENTION
The present invention relates to a process for the manufacture of fibrils
of short length as well as to devices which are particularly suitable for
carrying it out.
BACKGROUND OF THE INVENTION
It is well known to produce continuous fibrillated structures or rovings by
suddenly releasing the pressure acting on a two-phase liquid mixture which
is based on molten polymer and solvent and which is at a high pressure and
a high temperature. These continuous, fibrillated structures are, however,
very difficult to process directly, mainly because of their extremely high
volume and the rate at which they are produced. For this reason, in order
to economically process the continuous, fibrillated structures, they are
first subjected to a shredding treatment which reduces their dimensions
but which has a detrimental effect on their physical properties and which
necessitates tying up a large amount of capital and consuming a great deal
of energy.
This is why attempts have been made to develop processes which lead
directly to the formation of fibrils of short length when the pressure
acting on the above-mentioned mixtures is released suddenly.
Thus, in Belgian Pat. No. 787,032, filed Aug. 1, 1972, which corresponds to
U.S. patent application Ser. No. 277,033, assigned to the same assignee as
the present application, filed Aug. 1, 1972, entitled "Fabrication of
Discontinuous Fibrils", which is hereby incorporated by reference, there
is described a process for the direct manufacture of short fibrils in
which the two-phase liquid mixture is dispersed in an added fluid at the
exact instant when the pressure acting on it is released suddenly.
According to Belgian Pat. No. 787,033, filed Aug. 1, 1972, which
corresponds to U.S. patent application Ser. No. 277,032, assigned to the
same assignee as the present application, filed Aug. 1, 1972, entitled
"Process for the Manufacture of Discontinuous Fibrils", which is hereby
incorporated by reference, a similar result is achieved when the
fibrillated structure formed by suddenly releasing the pressure acting on
the two-phase liquid mixture is shredded at the very instant when it is
formed, by means of a transverse stream of fluid.
Although these processes very considerably improve the technique for the
manufacture of discontinuous fibrils, they nevertheless still possess some
disadvantages, the main one of which is that they require the use of very
large amounts of added fluid in order to produce adequate shredding.
Consequently, there have been continuing investigations for the purpose of
developing a process for the direct manufacture of short fibrils, which no
longer requires an added fluid to be supplied.
Thus, in Belgian Pat. No. 811,780, filed Mar. 1, 1974, which corresponds
to U.S. patent application Ser. No. 450,475, assigned to the same assignee
as the present application, filed Mar. 12, 1974, entitled "Process for the
Manufacture of Discontinuous Fibrils", which is hereby incorporated by
reference, there is described a process for the manufacture of short
fibrils which consists of pulverizing mechanically the ejection cone which
forms at the outlet of the orifice by means of which the pressure is
suddenly released. This technique, however, involves the use of mechanical
devices, such as rotary blades revolving at very high speed and at a very
short distance from the pressure release orifice. The result of this is
that, although this technique enables good results to be achieved, it is
very delicate to carry out, requiring special drive means, and can involve
stoppages due to mechanical failure.
SUMMARY OF THE INVENTION
It would consequently appear that, hitherto, despite the considerable
progress already achieved, no one has yet succeeded in developing a
reliable process, which does not require any added fluid, for the direct
production of short fibrils by suddenly releasing the pressure acting on
two-phase liquid mixtures of molten polymers and solvents. Accordingly, it
is an object of the present invention to provide an improved process for
directly producing short fibrils by suddenly releasing the pressure acting
on a two-phase liquid mixture of molten polymer and solvent. Another
object of the present invention is to provide such a process which does
not require any added fluid and which is reliable. A further object of the
present invention is to provide a process which no longer possesses the
above-mentioned disadvantages of the prior processes and which is
characterized by extremely great economy in the means which have to be
employed.
A still further object of the present invention is to provide devices for
performing the method of the present invention.
Additional objects and advantages of the present invention will be set
forth in part in the description which follows and in part will be obvious
from the description or can be learned by practice of the invention. The
objects and advantages are achieved by means of the methods,
instrumentalities and combinations particularly pointed out in the
appended claims.
To achieve the foregoing objects and in accordance with its purpose, as
embodied and broadly described, the present invention provides a process
for the manufacture of fibrils of short length by suddenly releasing the
pressure acting on a two-phase liquid mixture of molten polymer and
solvent and which is at a high pressure and a high temperature, by
ejecting the mixture through a pressure release orifice to vaporize the
solvent instantaneously and solidify the polymer, and in which the flow
path of the two-phase liquid mixture is perturbed at the instant when it
enters the pressure release orifice.
As used herein, the term "fibrils of short length" means elongated
fibrillated structures consisting of very fine filaments, of a thickness
of the order of a micron, connected to one another to form a
three-dimensional network. The general shape of these fibrils, which have
a flocculent appearance, is oblong. Their length varies approximately from
0.5 mm to 5 cm and their diameter varies approximately from 0.01 mm to 5
mm. The specific surface area of these products is very high; it is
greater than 1 m.sup.2 /g and in many cases greater than 10 m.sup.2 /g.
These fibrils are an excellent starting material for the production of
non-woven textiles and synthetic papers, by the usual methods.
As used herein, the expression "two-phase liquid mixture of molten polymer
and solvent" is defined below.
When a very high pressure is applied to a mixture of polymer and a suitable
solvent, which possesses a suitable concentration of polymer and which is
at a temperature above the melting point of the polymer, it is found that
the mixture is in the form of a single homogeneous liquid phase. If,
thereafter, the pressure is gradually reduced, while keeping all the other
conditions the same, it is found that, from a certain pressure which
varies depending on the particular cases, the homogeneous liquid phase
becomes cloudy due to the appearance of a system consisting of two liquid
phases comprising a continuous polymerrich liquid phase in which droplets
of a polymer-depleted liquid phase are dispersed. This system consisting
of two liquid phases is the "two-phase liquid mixture" referred to above.
The value of the pressure at which this phenomenon of two liquid phases
appears can easily be determined experimentally for various values of
temperature and polymer concentration. In order to obtain high quality
structures by means of the sudden release of pressure, it is advisable to
employ mixtures which are in the two-phase state.
In a further aspect of the present invention, a device is provided for the
manufacture of fibrils of short length by suddenly releasing the pressure
acting on a two-phase liquid mixture of molten polymer and solvent which
comprises a spinneret containing a perturbation chamber having at least
one supply orifice for receiving the two-phase liquid mixture and a
pressure release orifice opposite the supply orifice.
It is to be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory, but are not
restrictive of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate, diagrammatically and in cross
section, examples of the presently preferred embodiments of the devices
according to the invention for practicing the method of the invention and
together with the description serve to explain the principles of the
invention.
Of the drawings:
FIG. 1 is a view of a complete device which is suitable for carrying out
the process according to the invention;
FIGS. 2 to 7 shows alternate embodiments of the terminal part of the device
according to FIG. 1;
FIG. 8 shows an alternate embodiment of a device which makes use of several
perturbation chambers arranged in series;
FIG. 9 is a view of a device which makes use of a metal gauze;
FIG. 10 is a view of a device possessing two supply orifices;
FIG. 11 is a cross-sectional view along the axis A--A' of FIG. 10;
FIG. 12 is a view of an alternate embodiment of the device according to
FIG. 10; and
FIG. 13 is a view of an alternate embodiment of a spinneret according to
the invention, which makes it possible to form a continuous film of
lubricant on the wall of the pressure release orifice.
DETAILED DESCRIPTION OF THE INVENTION
The polymer or polymers present in the two-phase liquid mixture which is
subjected to the sudden release of pressure can be any polymer(s)
whatsoever provided that it can lead to the formation of two-phase liquid
mixtures in the presence of suitable solvents.
In general, any polymer(s) which can be spun can be used according to the
present invention.
By way of example, polyolefins, polyamides, thermoplastic polyesters,
polyurethanes, polycarbonates, vinyl polymers (such as polymers based on
vinyl chloride, vinyl acetate or vinylidene fluoride) and acrylic polymers
(such as polymers of acrylonitrile or methyl acrylate) may be used.
It is preferred, however, to use crystalline polymers, the degree of
crystallinity of which, measured by X-ray diffraction, is greater than
10%, and more preferably greater than 20%. In fact, the stretching which
the very fine filaments forming the fibrils undergo during the
instantaneous vaporization of the solvent, because of the sudden evolution
of solvent vapors, imparts an oriented structure to them when they are
made of a crystalline polymer, and consequently gives remarkably good
mechanical properties.
The best results are obtained starting from crystalline polyolefins. Among
the latter, those most used are polymers with a substantially linear
structure comprising at least 50 mol% of an alpha-olefin containing 2 to 6
carbon atoms. By way of examples, there may be used high density
polyethylene and isotactic polypropylene which are very readily available
commercially, as well as isotactic polybut-1-ene and isotactic
poly-4-methyl-pent-1-ene which are produced on a much smaller scale.
With regard to the solvent or solvents employed, it is preferable that they
should not dissolve the polymer under normal pressure and temperature
conditions (atmospheric pressure and 20.degree. C). Under these
conditions, they must not dissolve more than 50 g of polymer per liter,
and preferably not more than 10 g of polymer per liter.
In the second place, it is preferable that the boiling point of the solvent
or solvents should be below the temperature at which the polymer or
polymers can be plastically deformed; they must have a boiling point, at
normal pressure, more than 20.degree. C and preferably more than
40.degree. C below the plasticization temperature of the polymer or
polymers. Moreover, they must allow two-phase liquid mixtures, as defined
above, to form under temperature and pressure conditions which permit
instantaneous vaporization of the solvents and solidification of the
polymer.
To make matters easier, it is always preferable to use a common solvent
when several different polymers are employed.
Among the many solvents which can be used, there may be mentioned
especially aliphatic hydrocarbons (such as normal butane, normal pentane,
normal hexane, normal heptane and normal octane as well as their isomers),
cycloaliphatic hydrocarbons (such as cyclohexane and methylcyclohexane),
aromatic hydrocarbons (such as benzene, toluene and xylene), halogenated
alkanes (such as chloromethanes, chlorofluoromethanes, chloroethanes and
chlorofluoroethanes), alcohols, ketones, esters, amides, nitriles and
ethers.
When one or more polymers selected from the group consisting of the
crystalline polyolefins are employed, it is preferred to use a solvent
selected from the group consisting of aliphatic and cycloaliphatic
hydrocarbons containing 4 to 8 carbon atoms such as, for example, hexane
and cyclohexane of technical quality.
In the process according to the present invention, it is advisable to
choose the pressure of the mixture which is subjected to the sudden
release of pressure in such a way that it is in the form of a two-phase
liquid mixture. The same applies to the temperature and to the polymer
concentration.
It is generally preferred to work at a temperature of between 100.degree.
and 300.degree. C and more preferably between 125.degree. and 250.degree.
C.
The concentration of polymer is generally between 1 and 500 g per kg of
mixture. It is preferred to employ mixtures containing 10 to 300 g of
polymer per kg of solvent, and more preferably 50 to 200 g/kg.
In addition to the polymer and the solvent which, as has been stated, can
be individual components or can themselves consist of mixtures, the
two-phase liquid mixture can also contain customary additives for polymers
such as anti-oxidants, light-stabilizing agents, anti-static agents,
surface-active agents, strengthening agents, fillers, pigments, dyestuffs
and nucleation agents, provided that these additives do not have a
detrimental effect on the formation of the two-phase liquid mixture, the
instantaneous vaporization of the solvent and the solidification of the
polymer.
During the sudden pressure release procedure, the pressure of the two-phase
liquid mixture or mixtures is brought to a value close to atmospheric
pressure, and preferably to an absolute pressure of less than 3
kg/cm.sup.2, within a very short period of time, preferably less than 1
second. This release of pressure is achieved by passing the mixture
through a preferably cylindrical orifice, the diameter of which is between
0.1 and 3 mm and preferably between 0.5 and 1.5 mm, and the
length/diameter ratio of which is between 0.1 and 10 and preferably
between 0.5 and 2.
In the case where the orifice does not have a circular cross section, the
diameter which must be taken into consideration is the hydraulic diameter
of the orifice.
In accordance with the present invention, the flow of two-phase liquid
mixture which travels towards the inlet of the pressure release orifice is
perturbed just before entering therein. Since the continuous liquid phase
of the two-phase liquid mixture is the polymer-rich phase, the two-phase
liquid mixture possesses an extremely high viscosity. Because of this, it
is assumed that the mixture travels under conditions of laminar flow, with
the fluid streams having parallel trajectories. The effect of the
perturbation is to alter these conditions of flow just before the
two-phase liquid mixture enters the pressure release orifice. Of course,
this perturbation must be effected under conditions such that it has not
yet become damped at the instant when the two-phase liquid mixture enters
the pressure release orifice.
According to a preferred embodiment of the present invention, the flow path
of the two-phase liquid mixture is perturbed by deflecting, upstream from
the pressure release orifice, a part of the two-phase liquid mixture flow
subjected to the sudden release of pressure, and by guiding the deflected
part so that it enters the pressure release orifice in a direction which
makes an angle with the axis of the pressure release orifice.
The angle formed between the direction of the part of the flow which is
deflected to the greatest extent and the axis of the pressure release
orifice is preferably between 30.degree. and 135.degree.. The best results
are obtained when this angle is between 75.degree. and 120.degree.. In the
simplest embodiment, this angle has a value of 90.degree..
This deflection can be effected advantageously by passing the two-phase
liquid mixture subjected to the sudden release of pressure through a
perturbation chamber opening onto the pressure release orifice.
According to a variant of this embodiment, the two-phase liquid mixture
flow entering the perturbation chamber is divided, by means of a supply
orifice, into a plurality of flows.
This division of the two-phase liquid mixture flow can be effected by
increasing the number of orifices which supply the perturbation chamber,
or by interposing an element or a grid for dividing up the flow,
preferably a metal gauze, in the trajectory followed by this flow.
When a metal gauze is used, it can, for example, be positioned above the
supply orifice of the perturbation chamber, that is to say against the
upstream face of the partition in which this supply orifice is formed or
pierced. Preferably, however, the metal gauze is positioned in the
perturbation chamber, preferably against the partition possessing the
supply orifice. The metal gauze should preferably be positioned so as to
be perpendicular to the direction of the two-phase liquid mixture flow.
The mesh opening of the metal gauze must be at least 0.1 mm so as to avoid
any danger of choking and possible clogging. The size of the meshes of the
metal gauze can be as large as the size of the supply orifice and can even
exceed this value provided, of course, that at least one of its
constituent strands is opposite the supply orifice, that is to say on the
trajectory followed by the two-phase liquid mixture flow.
It is also possible to cause the two-phase liquid mixture flow to divide by
supplying the perturbation chamber via a plurality of supply orifices,
these orifices being formed or pierced in the upstream partition or walk
which defines the perturbation chamber. The axes of these orifices can be
parallel to one another or can be inclined relative to one another.
It is, however, very obvious that these two variants can be combined and
that it is possible advantageously to supply the perturbation chamber via
several orifices and moreover to equip this chamber with a metal gauze.
It can be valuable to provide a diverging component at the outlet of the
pressure release orifice in order to channel and guide the short fibrils
issuing from this orifice. It has been found that it is advisable,
however, for the angle of this diverging component to be at least
150.degree..
Finally, it has been found that it is preferable for the two-phase liquid
mixture to enter the perturbation chamber via one or more orifices, the
angle formed by the inlet walls of which is at most equal to 30.degree. or
at least equal to 150.degree..
The processes described above make it possible to produce fibrils of short
length directly and economically, but this is, however, frequently
accompanied by the undesirable formation of a relatively large number of
pellets, that is to say small dense particles having the structure of a
film or a skin, the largest dimension of which can be as much as and can
exceed 0.5 mm.
The presence of these pellets in the short fibrils thus produced proves
objectionable when these fibrils are being processed subsequently in order
to manufacture synthetic papers. It is found, in fact, that these pellets
are difficult to remove and that they are generally to be found, in the
papers produced, in the form of transparent specks or impurities which
have a detrimental effect on the pulp of the finished products.
In a preferred embodiment of the invention, it is possible substantially to
reduce the formation of pellets and even to eliminate it completely by
lubricating the wall of the pressure release orifice by means of a film of
a lubricant which is incompatible with the two-phase liquid mixture.
According to one embodiment of this aspect of the invention, it is possible
to coat the walls of the pressure release orifice with a thin skin of a
suitable lubricant such as, for example, a silicone.
However, the substantial improvement observed in this case from the point
of view of reducing the number of pellets is not permanent. It is noted,
in fact, that the number of pellets formed, which is markedly reduced when
the device is brought into use, tends to increase gradually as a function
of the period of time for which the device is used.
Consequently, according to a preferential embodiment, the walls of the
pressure release orifice are lubricated by means of the continuous flow,
formed at the inlet of the pressure release orifice, of a film of a liquid
lubricant which is incompatible with the two-phase liquid mixture.
By following this procedure, it has, in fact, been found that the decrease
in the number of pellets formed, or their elimination, is maintained with
the passage of time.
The liquid lubricant employed in the process according to this variant of
the present invention can be any liquid lubricant whatsoever, provided
that it is incompatible with the two-phase liquid mixture, that is to say,
provided that it forms a continuous phase which is distinct from this
mixture, and in particular, provided that it does not dissolve the polymer
present in this mixture. This lubricant is preferably raised to a
temperature close to the temperature of the two-phase liquid mixture
before being conveyed onto the wall of the pressure release orifice.
For reasons of simplicity and economy, however, the lubricant used
preferably is water which optionally contains a wetting agent. This type
of lubricant, in fact, enables excellent results to be achieved. Moreover,
the short fibrils thus produced are very easily suspended in water even
when the polymer of which they are made is hydrophobic. Finally, when the
fibrils are being produced, the water vaporizes and forms a sheath which
surrounds the flow of fibrils and prevents the latter from becoming struck
on the hot parts of the pressure release spinneret.
The liquid lubricant is introduced at a flow rate of between 30 and 250
liters/hour, and preferably between 40 and 150 liters/hour, when the
special devices described below are used, the pressure release orifice of
which has a diameter of the order of 1 mm.
In order to make it possible to carry out the process according to the
invention, several devices of a particular type have been produced and
these devices also form part of the present invention.
These devices or spinnerets differ mainly from those already known in that
they comprise a perturbation chamber possessing at least one supply
orifice and a pressure release orifice opposite the latter.
In the simplest embodiment of these devices, the supply orifice, which is
also cylindrical, and the pressure release orifice are coaxial and the
perturbation chamber possesses a symmetry of revolution about their common
axis.
According to a first variant, the perturbation chamber can be equipped with
a metal gauze or can be supplied via a plurality of supply orifices.
According to a second variant, the perturbation chamber can be surrounded
by a second chamber which is peripheral and which is connected to a source
of liquid lubricant which opens into the perturbation chamber via an
annular slit which surrounds the inlet of the pressure release orifice. In
this way, the peripheral chamber communicates with the perturbation
chamber so as continuously to direct a film of liquid lubricant onto the
wall of the pressure release orifice.
Turning now to the drawings, as is apparent in FIGS. 1 to 7, a spinneret 1
made in accordance with the invention, possesses a pressure release
orifice 2 and a pre-(pressure release) device. This pre-(pressure release)
device, which consists, according to the embodiment represented, of a
partition 3 possessing a central orifice 4, is by no means indispensable.
Its role is to cause a pressure drop in the mixture of molten polymer and
solvent which is in the form of a single-phase liquid passing through the
spinneret, in order to bring about the formation of a two-phase liquid
mixture.
This method of working possesses certain advantages: firstly, it is simpler
to prepare a single-phase mixture, and secondly, the two-phase liquid
mixture is of more uniform quality.
However, this device can be dispensed with in the case where the spinneret
is supplied directly with a two-phase liquid mixture of polymer and
solvent.
The spinneret also comprises a perturbation chamber 5 defined especially by
the wall 20 possessing the pressure release orifice 2 and by a flat upper
wall 6 possessing the supply orifice 7 at its center. The supply and
pressure release orifices are opposite and coaxial. The perturbation
chamber is cylindrical with a circular cross section. The orifices are
positioned at the centers of the bases. The distance between the supply
and pressure release orifices (height) is generally less than 10 cm and
preferably less than 7.5 cm. Additional information on the subject of this
chamber will be provided later.
As FIGS. 2 to 7 show, the inlet and the outlet of the pressure release
orifice 2 can be given various profiles.
When the chamber 8 of the spinneret is supplied with a two-phase liquid
mixture of molten polymer and solvent, this mixture, because of the
alignment of the orifice 7 in the wall 6 and of the pressure release
orifice 2, flows through the perturbation chamber 5 along a preferential
central fluid stream 9 and along side streams 10, which, in the vicinity
of the pressure release orifice 2, are guided transversely relative to the
central stream by the walls of the perturbation chamber. The angle of
incidence of these side streams can be varied by altering the profile of
the wall 20 possessing the pressure release orifice 2, as is apparent in
FIGS. 2 to 7 where this wall is identified by 20a to 20f, respectively. It
is seen that the angle formed between the axis of the pressure release
orifice and the wall of the chamber in which this orifice is pierced or
formed determines the angle of incidence of the most eccentric side
streams which are those deflected to the greatest extent. This angle is
preferably between 30.degree. and 135.degree., the best results being
obtained when it is between 75.degree. and 120.degree.. In the simplest
embodiments, as seen in FIGS. 1, 3, 4, 7 and 8, it is equal to 90.degree..
Furthermore, it can also be advantageous to give the perturbation chamber
5 a profile, for example by removing sharp angles, as is shown especially
in FIG. 7, so that the trajectory of the side streams which are deflected
to the greatest extent and which travel in the vicinity of the wall is
tangential at every point to the wall. In this case, the speed of the part
of the flow which is deflected to the greatest extent is at a maximum.
It can also be advantageous to produce a spinneret like that represented in
FIG. 8, in which several perturbation chambers arranged in series are
provided.
It is moreover desirable that the perturbation chamber should fulfill
various criteria in order to optimize its effectiveness.
Thus it is obviously advisable for the perturbation chamber to have a
transverse dimension sufficient to form side streams which can perturb the
central stream at the inlet of the pressure release orifice 2.
For a similar reason, it is also advisable for the distance between the
orifices of the perturbation chamber (height of the chamber) also to be
greater than the diameter of the supply orifice. It is in fact obvious
that when the height of the perturbation chamber is too small, the
deflected side streams cannot be effectively guided transversely relative
to the central stream.
On the other hand, when the height of the perturbation chamber becomes too
great, the deflected transverse streams have a tendency to rejoin the
central stream and to become parallel to it again before reaching the
pressure release orifice. It has been found that the height which the
perturbation chamber can have is related to the diameter of this chamber.
In fact, in order to achieve maximum effectiveness, it is necessary for
the ratio of the height of this chamber (distance between orifices) to its
lateral dimension to be less than 5 and preferably less than 3.
Finally, it has been found that it is preferable for the diameter of the
supply orifice to be at least equal to half the diameter of the pressure
release orifice.
As is apparent in FIG. 9, the spinneret 1 for effecting sudden pressure
release can be equipped with a metal gauze 12 positioned in the
perturbation chamber 5. This perturbation chamber 5 is defined especially
by the wall 20g possessing the pressure release orifice 2 and by a flat
upper wall 6 possessing a supply orifice 7 at its center. The pressure
release orifice 2 and the supply orifice 7 are, in this particular case,
opposite and coaxial. The side wall 22 of the perturbation chamber 5 which
is cylindrical is defined by an annular ring 13. It should, however, be
noted that the perturbation chamber 5 can have some other shape and
especially that of a parallelepiped. The annular ring 13 fulfills a
two-fold function: firstly, this ring defines the height of the
perturbation chamber 5, and secondly, it holds the fine mesh gauze 12
located in the perturbation chamber in place against the wall 6 possessing
the supply orifice 7.
The spinnerets represented in FIGS. 10, 11 and 12 are of the same type as
that represented in FIG. 9, except that they do not possess any metal
gauze located in the perturbation chamber. Moreover, communication between
the supply chamber 8 and the perturbation chamber 5 is provided by two
supply orifices 7, the axes of which are inclined relative to one another
and which join up again to form a single orifice on the side of the supply
chamber. In these spinnerets, the annular ring 13 delimiting the
cylindrical side wall of the perturbation chamber 5 serves solely to
determine the height of this chamber.
As has been stated, the spinnerets represented in FIGS. 10, 11 and 12 could
also be provided with a metal gauze positioned in their perturbation
chamber and/or could be equipped with two or more orifices, the axes of
which would be parallel.
As is apparent especially in FIGS. 1, 2, 3, 4, 8 and 12, it is possible to
provide a diverging component 11 at the outlet of the pressure release
orifice, the angle of this diverging component being preferably greater
than 150.degree..
Finally, as is apparent in FIG. 13, the spinneret 1 which possesses a
pre-(pressure release) chamber 8, an orifice 7 for supplying the
perturbation chamber 5 and a pressure release orifice 2 can also be
equipped with a peripheral chamber 15 which surrounds the perturbation
chamber 5, the partition 14 separating these chambers being interrupted at
the inlet of the pressure release orifice 2 so as to form an annular slit
17 coaxial with the pressure release orifice. The peripheral chamber 15 is
also equipped with a connection 16 to enable it to be brought into
communication with a source of liquid lubricant.
The process according to the invention is moreover illustrated by the
practical embodiment examples which now follow. It is, however, to be
understood that these examples are given purely by way of illustration and
that they do not in any way limit the scope of the present invention.
It is possible, in particular, to produce other types of spinnerets and
especially spinnerets which make it possible to employ two-phase liquid
mixtures of different compositions.
EXAMPLE 1
A two-phase liquid mixture is produced by bringing a mixture comprising 15%
by weight of ELTEX A 1050 and 85% by weight of technical hexane to a
temperature of 195.degree. C and to a pressure of 63 kg/cm.sup.2. These
conditions correspond to the start of the appearance of two liquid phases.
ELTEX A 1050 is a high density polyethylene with a melt index of 5,
produced and sold by Solvay & Cie. of Brussels, Belgium.
The pressure acting on this mixture is released by passing the latter
through a spinneret possessing a perturbation chamber as represented in
FIG. 4 of the attached drawings and having the following geometric
characteristics:
a. ratio of the diameter of the perturbation chamber to the diameter of the
supply orifice 7 (not shown) equal to 16;
b. ratio of the height of the perturbation chamber to the diameter of the
supply orifice 7 equal to 5; | | |
