Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to the methods of
manufacturing polyoxymethylene filaments, and, more particular-
ly, of high-strength low-shrinkage polyoxymethylene filaments.
These filaments can be widely used in the production
of fishing nets and tawls, of filtering cloth, of enyineering
rubber articles, cord, etc., since they offer a whole series
of valuable properties. Thus, among their properties is the
one of being hydrophobic or water-repellent, which means that
their strength is unaffected by moisture, they are proof to
the action of alkali, as well as of numerous organic solvents
at a temperature up to 100C, they are likewise proof to the
action of sea water and are biologically stable. Polyoxymethyl-
ene filaments also offer high tensile strength, resistance to
rubbing, fatigue strength and elasticity. .
Furthermore, polyoxymethylene filaments and yarn can
be widely used in the production of numerous textile articles,
, e.g. in the form of texturized or bulk yarn.
; There already exists a number of methods of manufact~-
,:~
ing polyoxymethylene filaments from melted polyoxymethylene by
moulding a ~ilament with .~ubsequent drawing.
The high viscosity of the melt and the high crystalliza-
tion rate of polyoxymethylene are reflected in the specific
features of its processing into filaments. The relatively low
temperature viscosity factor of the melt and the relatively low
thermal stability of the melt of polyoxymethylene would not
permit to considerably reduce the viscosity of the melt by in-
creasing the temperature of the melt. Particular difficulties
i are encountered at processing of polyoxymethylene with a high
molecular weight, which is the one generally used for manufactur-
ing polyoxymethylene filaments with high physical and mechanical
properties, such as elasticity, fatigue strength, etc. It is
this high viscosity of the melt of polyoxymethylene, particularly,
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of polyoxymethylene with a high molecular weight, which dooms
the rate of extrusion of the filaments to be substantially
lower than that of extrusion of filaments of other materials,
usually attained in the art of making man-made fibre.
There is known a method of manufacturing polyoxy-
methylene filaments, wherein, in order to step up the extruding
speed (and, consequent'y, the winding speed) there is effected
"cooling" of the jets of the melt, leaving the orifices of the
extrusion nozzle, at a temperature from 170C to 240C (see
,~ 10 Japanese Patent No. 3486, issued March 1, 1966, inventors
Hajanamy Hirosy, Inoue Takie~y, et al, Cl. 42D22). From the
described examples of this method it can be seen that raising
the temperature of the air in the vicinity of the extrusion
nozzle from normal to 190C enables one to step up the extruding
speed from 160 m/min to 670 m/min. However, the ratio of sub-
sequent drawing of the filament thus obtained at a temperature
~ of 150C does not exceed 7:1, and, consequently, the strength
q of this filament is but 67.5 grams per tex with elongation at
rupture about 20 per cent
There is known another method of manufacturing poly-
oxymethylene filaments from melted stabilized homo- and co-
polymers of formaldehyde or else of its cyclic trimer - trioxane -
with cyclic esters, e g. ethylene oxide, 1,3 dioxolane, etc.
~see British Patent No. 995,848, Cl. D 01 f, D 06 m, C 08 g).
~ Stabilizing additives are included in a quantity, for example,
;; of 0.1 to 3.0 per cent of the weight of the polymer. To reduce
,.!
the viscosity of the melt there is sometimes added into the
stabilized polymer a certain quantity of a plastifier. To mould
polyoxymethylene filaments, the said homo- or co-polymers are
subjected to melting at a temperature from 170C to 230~C and
at the same temperature the melted poly~er is forced through
the orifices of an extrusion nozzle. The jets of the melt,
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leaving the orifice, are cooled in the ambient air. After
the cooling, the moulded filament is subjected to drawing. sy
drawing the moulded filament at a rate of 10.2 m/min and
temperature from 120~C to 150C, e.g. 134C, the dra~t, for
example, being 9.05 : 1, there is obtained a filament with the
strength not in excess of 54.9 grams per tex. In order to step
up the strength of the filament, it is subjected to a repeated
drawing at a rate of 10.5 m/min at a temperature from 150C to
160C, the draft being from 1.05 : 1 to 2 : 1. As a result,
the strength is increased to 89.1 grams per tex.
The use of plastifiers in certain cases involves the
necessity of resorting to additional labour-consuming operations
in removing the plastifier. On the other hand, the presen~e of
the plastifier in a final filamen~ considerably affects its
physical and mechanical properties.
To obtain filaments of a sufficiently high strength by
the last-described method, the moulded filament is d~awrl not in
a single stag~, but in two stages, which also complicates thc
technology. Besides, this drawing is effected at a relatively
low 5peed, which lowers the productivity of the equipment.
Furthermore, the cooling of the jets leaving the nozzle
in the ambient air would not permit to mould the filaments at
high speeds, which becomes particularly apparent when polyoxy-
methylene of a high molecular weight is processed.
It is an object of the present invention to develop a
method of manufacturing polyoxymethylene filaments, which should
provide for obtaining polyoxymethylene filaments with high
physical and mechanical properties.
It is another object of the present invention to
simplify the technology of the manufacturing process.
With these and other objects in vie~, the present in-
vention resides in a method of manufacturing polyoxymethylene
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filaments, wherein polyoxymethylene having a molecular weight
within a range from 30,000 to 100,000 and including stabilizing
additives in a quantity from 0.1 to 3.0 per cent of the weight
of said polyoxymethylene is thermall~ treated at a temperature
within a range from 100C to 150C and pressure from 1 to 100
mmHg to a constant weight; said thermally treated polyoxymethylen~?
is subjected to meltin~ at a temperature within a range from 170C
to 230C, the thus obtained melt is forced through the orifices
of an extrusion nozzle; the jets of said melt, leaving the
orifices of the extrusion nozzle are cooled to a temperature
within a range from 70C to 169~C; after said cooling the
moulded filaments obtained are subjected to drawing at a tempera-
ture within a range from 120C to 165C to a length exceeding the
: initial length from seven to fourteen times.
For the filament-forming polyoxymethylene there are
used either homo- or co-polymers of formaldehyde or else of its
cyclic trimer - trioxane - with cyclic esters of a yeneral
formula, for example CH2 - O
CH2 - ( OCH2 ) n
where "n" is an integer within a range from 0 to 2. The weight
content of the second co-monomer in the co-polymer may vary
within a range from 0.5 to 10 per cent, depe-~ding on the destina-
tion of the'filaments to be manufactured.
The molecular weight (Mw) of the polyoxymethylene used
may vary from 30,000 to 100,000 and is calculated from the
formula: [~] = K.MW where [~] is the characteristic viscosity
of solution of polyoxymethylene in dimethylformamide, measured
at 150~C - 0.5C on Ostwald-Pinkevich viscosimeter, K equals 4.4
4.4 10 4 and ~ equals 0.66.
It is not advisable to use polyoxymethylene with a
molecular weight below 30,000, since the strength of filaments
produced from such a polymer is insufficient. On the other hand,
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when polyoxymethylene with a molecular weight in excess of
100,000 is used, there are encountered certain techn~logical
, ~ .
difficulties on account of the high viscosity of the melt.
An increased content of the second co-monomer in the
co-polymer leads to a lower melting point of the co-polymer, and,
consequently, to a reduced thermal strength of the filament.
To step up the thermal stability of polyoxymethylene,
, there are introduced thereinto stabilizing additives in a
, quantity from 0.1 to 3.0 per cent of the weight of the mass
of polyoxymethylene. For the stabilizers can be used, for
instance, a system of two components including an antioxidant
and an acceptor of formaldehyde. Among the antioxidants are
such substances as bis-phenols, e.g. 2,2'-methylene bis-(4-
methyl-6-tertiary butyl-phenol), 4,4'-butylidene bis-(6-tertiary-
butyl-4-methyl-phenol), while among the acceptors are polyamides,
polyurethanes, compositions containing tertiary amînes and
i final amide groups, for example, dicyanamide ~cyanguanidine).
~ The properties of the filament are to a great extent
; dependent on the initial raw materials and the techno~ogical
conditions of their manufacture.
Stabilized polyoxymethylene may contain up to 0.2 per
cent by weight of equilibrium moisture (water). m e presence
of the moisture (water) in the polymer adversely affects the
moulding and drawing operations and the quality of the filaments.
An increased content of water leads to formation of hubhles of
steam in the jets of the melt, leaving the orifices of the
extrusion nozzle, which might result in breakage of the jets
in the moulding operation, or else in breakage of the filament
during subsequent drawing.
Under the herein disclosed conditions of thermal
treatment of the initial mass of polyoxymethylene to a constant
weight, i.e. at a temperature from 100C to 150C and pressure
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from 1 to 100 mm mercury, it has been quite unexpectedly found
that the loss of weight by the pol~,ler substantially exceeds
the content therein of the equilibrium water. It has also been
found that the strength of the filament produced from the poly-
mer subjected to this thermal treatment is enhanced. In the
process of thermal treatment water and other volatile compounds
are removed from the polymer. Volatile components may comprise
on th~ one hand, formaldehyde which remains in the mass (block)
~ ~o~o~
of polymer granules after gr~nul~ting lt at a polymer manufactur-
ing plant, and, on the other hand, formaldehyde which breaksaway (separates) from the unstable portion of the macromolecules
of polyoxymethylene while heating the latter. Besides, it is
not altogether improbable that under the above conditions there
~; are partially removed the stabilizing additives which had been
introduced earlier.
The presence of volatile components in the mass of
polyoxymethylene likewise adversely affects the processing
properties of the polymer, as it is the case with water. The
presence of volatile components in the mass of polyoxy.nethylene,
on the one hand, influences the permissible range of melting
temperatures. With a high content of volatile substances there
might appear in the melt an amount of bubbles which is greater,
the higher this melting temperature. Consequently, with a
reduced content of volatile substances in the mass of polyoxy-
methylene, which is attained by the above described preliminary
thermal treatment, it is fairly permissible to raise the melting
temperature. The smaller the content of volatile substances in
the melt of polyoxymethylene, the smaller is the degree of
their evolution from the jets of the melt, leaving the orifices
of the extrusion nozzle, and, consequently, the smaller is the
probability of jet breakage. -
The Table hereinbelow contains data on the amount of -
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volatile substar,ces removed from the st~bilized co-polymer of
trioxane and 1,3 dioxolane (the latter contained in a quantity
of 4 per cent by weight), as well as on the amount of water
left in the co-polymer, depending on the therlllal treatment
conditions.
Residual Amount Residual Amount of
Content of Vola- Content Volatile
Tem of Water tile Sub- of Water Substances
P in Speci- stances in Speci- removed
C men, % by removed men, % by from
weight from weight Specimen,
Specimen, % by weight
_ _ % bY weiqht _ __ _
Thermal treatment in Thermal treatment ln Vacuum,
Air under Normal with Pressure from 1 to 5 mm
Pressure mercurv
0.12 - 0.12
100 0.04 0.16 traces 0.26
140 0.02 0.42 d.t.o. 0.62
20155 traces0.55 d.t.o. 0.70
. . _ . _ _ _
It can be seen from the above data that th~ amourlt of
removed volatile substances grows with the increase of the
temperature of the treatment and with the reduction of the
pressure, whereas the water content is practically unaffected
by these conditions. The water content was determined by a
method based on reduction of iodine in tlle presence of water
by sulphur dioxide, known as the Fischer method (see "Control
over production of chemical fibre", "Khimiya" Publishers,
Moscow, 1967, p. 293). The amount of the removed volatile sub-
stances was determined as the difference between the weight ofthe specimen prior to and after the thermal treatment.
Moulding of the filaments is effected by melting the
stabilized polyoxymethylene which had been subjected to the
thermal treatment, forcing the melt through the orifices of
an extrusion nozzle and cooling down the jets of the melt,
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leaving the orifices of the nozzle. The meltin~ temperature
c~n be in the ranye from 170~C to 230~C depending on the
nature of the polyoxymethylene being processed, on its molecular
weight and the time of its existence in the melted state,
determined by the capacity of the equipment used. The cooling
~ down of the jets of the melt in the vicinity of the nozzle is
; effected at a temperature from ~G~C to 169C. Under the herein
disclosed "mild" cooling conditions, the general molecular
orientatios~ of the composition is effected and, consequently,
the drawing ab;lity of the moulded filaments is stepped up
(the draft can be increased), as compared with the drawing
ability of filaments moulded at a lower cooling temperature,
e.g. at 20C. The phenomenon of reduction of general molecular
orientation at processing of polyoxymethylene of d high mole-
cular weight, as high as 50,000 to 100,000, is particularly
pronounced. Filaments moulded at higher cooling temperatures
and subjected to greater draft offer better physical and
mechanical properties.
The cooling media can be air, an inert gas, e.g.
nitrogen, steam.
After the cooling the moulded filament is drawn at a
temperature from 120C to 165C to a length exceeding the initial
length 7 to 14 times. At temperatures below 120C it is not
possible to draw polyoxymethylene to a degree providing for
production of filaments with adequately high strength. This
fact is related to the high degree of crystallinity of polyoxy-
methylene, as well as to the large size of the above-molecular
structure. To break up this structure for drawing purposes, it
is essential that the filament should be heated up to a tempera-
ture not below 120C. As the temperature is raised above 145C -
150C, there takes place maximally complete breaking up of the
initial above-molecular structure, which simplifies the task of
its-re-arrangement and re-orientation, and, consequently, the
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attainable value of draft is sharply increased. Un~er these
conditions it becomes possible to draw the moulded filament to
a length exceeding the initial length from 9 to 14 times even
by single-stage drawing, which provides for high physical and
mechanical properties of the filament.
As the drawn polyoxymethylene filaments are worked
into various articles and during operation of these articles
under the action of elevated temperatures, there might be
developed within these filaments considerable internal stresses,
as high as 10 kg/mm . Thus, if the filament during its thermal
treatment is not tensioned, these internal stresses might lead
to shrinkage of the filament, and at the same time there might
take place reduction of the tensile strength and an increase of
,~ the value of elongation at rupture.
In order to reduce shrinkage of the produced filaments
at subsequent thermal treatment, as well as to maintain the
strength of the filaments after such subsequent thermal treat-
ment, it is advisable that the drawn polyoxymethylene filaments
be subjected to a thermal treatment at a temperature 2~C to 50C
above the temperature at which the filaments were drawn, with the
filaments being in a tensioned state. It is possible first to ,
~ tension the drawn filaments and then to subject them to the said
; thermal treatment.
As it has been already stated hereinabove, in the
, process of thermal treatment of a filament manufactured from
thermally pre-treated stabilized polyoxymethylene under the
above-specified conditions no reduction of the original strength
of the filament is encountered. However, in the process of
similar thermal treatment of a filament manufactured from the
same stabilized polyoxymethylene pre-treated under different
conditions, e.g. in open air at a temperature of 140C, the
filament has been found to lose its strength after the above-
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1046)372 ~ ~
specified thermal treatment thereof.
The herein disclosed method is simple technologically.
; It does not require any specific equipment. The method provides
for processing into filaments of polyoxymethylene of a high
molecular weight without the use of plastifiers (i.e. substances
reducing the viscosity of the melt of polyoxymethylene) the
addition of which brings about the necessity of carrying out an
additional operation connected with removal of these plastifiers
from the filament. Furthermore, a filament produced from ther-
mally pre-treated polyoxymethylene and moulded under the said
cooling conditions is characterized by low general molecular
orientation and a minimal content of gas-like impurities. There-
fore, it can be drawn under a given temperature duty even in a
single stage, with high draft and high drawing speeds (as high
as 100 mm/min) which further simplifies the technology and
increases the productivity of the equipment.
The herein disclosed method provides for manufacturing
polyoxymethylene filaments having high physical and mechanical
properties. The tensile strength of the filaments is within a
range from 70 to 100 grams per tex, with elongation at rupture
from 9 to 12 per cent, the initial modulus being from 1200 to
1800 kilograms per square millimeter. The filaments offer an
increased thermal stability and stability to the action of
acids, high fatigue stren~th and rubbing resistance. Moreover,
the herein disclosed method provides for reducing considerably
the degree of shrinkage of a drawn filament, due to the fila-
ment having been subjected to tensioning and thermal treatment.
The method of manufacturing polyoxymethylene filaments
is carried out as follows.
An initial mass of polyoxymethylene, e.g. in the form
of granules, containing stabilizing additives, is thermally pre-
treated on a standard equipment, e.g. in vacuum drum-type dryers
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at a temperature from lOO~C to 150C and pressure from 1 to 100
mm mercury to constant weight. The said thermal treatment may
be effected in an inert gas atmosphere, e.g. in a nitrogen
atmosphere. In this case the temperature of thermal pre-treatment
of polyoxymethylene may be stepped up to 160C to 165C and the
operation may be carried out under atmospheric pressure.
Thereafter the thermally pre-treated polyoxymethylene
is melted, preferably in an extrusion machine. The melting is
performed at a temperature from 170C to 230C, depending on
the chemical nature and molecular weight of the polyoxymethylene
used. The melting operation may be carried out either in air
or in an inert gas atmosphere, e.g. in a nitrogen atmosphere.
The temperature of melting depends on the nature of the poly-
oxymethylene used, on the atmosphere in which the melting is
performed, on the design of the equipment and may vary from
0.1 to 60 minutes.
The thus obtained polyoxymethylene melt is fed by a
metering pump to an extrusion nozzle having either one or
several orifices. Prior to being supplied to the nozzle, wherever
necessary, the melt may be filtered through metal filtering
screens, quartz sand or any other suitable filtering means.
The jets of the melt, leaving the orifices of the
extrusion nozzle, are cooled, e.g. in an atmosphere of air
heated to 70C - 169C. This may be performed in a closed
heated shaft, or else by directing a stream of heated gas, as
it is being generally done at the manufacturing of a majority
of known synthetic filaments produced by moulding from a polymer
melt.
The filament leaving the cooling zone has applied
thereon a lubricant, water or any other substance, depending
on the destination of the filament.
Then the filament is either wound into a package or
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else this stage is by-passed, and the filament is fed directly
into a drawing machine. In other words, the herein disclosed
method may be performed both in an intermittent and continuous
mode.
Drawing or drafting of the filament is effected in a
single stage at a temperature from 120C to 165C to a 7:1 to
14:1 draft. The drawing operation is performed by a commonly -~
known system including a feed roller and a drafting one, the
circumferential speed of the drafting roller being higher than
that of the feeding one. Heating of the filament is effected
intermediate of the rollers. The filament can be heated by
contact heaters of the "iron" type, or else by passing through
a heated tube (with either hot air or radiation heating),
alternatively, the filament may pass through a heat0d liquid.
The drawn filament, depending on its destination, may be
eithqr twisted or not twisted. The twisting may be performed
by any suitable known twisting mechanism, e.g. of the ring
twisting kind. It is also possible to cut the drawn filament
into staple fibre of a required length.
To obtain low-shrinkage polyoxymethylene filament,
the drawn filament is tensioned and thermally treated at a
temperature 2C to 50C above the drawing temperature. The
thermal treatment may be performed in a continuous "drawing-
cum-thermal treatment" process. In this case thermal treatment
of the filament may be effected by various existing systems
providing for tensioning the filament and heating it to required
parameters, e.g. a system including a pair of rollers inter-
mediate of which there is ensured a required tension and a
heater is provided. In a case of an intermittent process any
suitable technique may be used, e.g. thermal treatment of the
filament wound at a required tension on a rigid bobbin. The
thermal treatment of the filament may be performed in various
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~040372
atmospheres (gaseous or liquid) wherein no chemical dcstruct-
ion of polyoxymethylene takes place, or else in air. The time
and parameters of the thermal treatment of the filament are
defined by the requirements as to the value of permissible
shrinkage of final filaments.
For the present invention to be better understood,
there are described hereinbelow several examples.
Exam~le 1.
Granulated co-polymer of trioxane and 1,3-dioxolane
(the weight content of the latter being 4 per cent) with
additives: 2,2'-methylene bis-(4-methyl-6-terbutyl phenol) in a
quantity of 0.5 per cent by weight as the antioxidant and
formaldehyde-dicyanamide in a quantity of 0.5 per cent by
weight as the acceptor, with characteristic viscosity in
dimethylformamide equalling 0.56 is thermally treated at 100C
and pressure of 5 mm mercury, melted in an extrusion machine in
an air atmosphere at 190C, and the melt is forced by a metering
pump through an extrusion nozzle with a single orifice 1.2 mm in
diameter. The rate of feed of the melt is 5 gr/min. The jet of
the melt is cooled in a 0.5 m long tube. The temperature of the
air cooling the jet of the melt is 90C. The filament mou~ding
rate is 250 m/min.
The moulded filament is drawn to a 10:1 draft at a
speed of 125 m/min over a 250 mm long "iron" at 150C. The
!, obtained filament has 72 grams per tex tensile strength and
elongation at rupture equalling 11.5%. The shrinkage of the
filament is 18~/o~ with 80% of the initial strength remaining
after the shrinkage.
After the drawing operation the filament is thermally
treated in air under a tension of 2 kilograms per square milli-
meter at 155C. for 30 minutes. After this treatment the
shrinkage value is 4%, with 95% of the initial strength rer"aining
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after the shrinkage.
Example 2.
Polyoxymethylene filaments are moulded and drawn, as
described above in Example 1, with a difference that the initial
mass of polyoxymethylene is thermally treated at 130C and
pressure of 10 mm mercury, the co-polymer is melted at 200C,
and the jet of the melt is cooled in air at a temperature of
70C.
The filament obtained features 75 gr/tex tensile
strength and 11.1% elongation at rupture. The shrinkage rate
of this filament is 17%, with 82% of the initial strength remain-
ing after the shrinkage. After the drawing operation the fila-
ment is thermally treated in a nitrogen atmosphere at 161~C under
6 kg/mm2 tension for 20 minutes. After this treatment the
shrinkage rate of the filament is 1%, with 96% of the initial
~trength remaining after the shrinkage.
ExamPle 3.
Polyoxymethylene filaments are moulded and drawn, as
described above in Example 1, with a difference that a co-
polymer of formaldehyde and 1,3-dioxolane is used, haviny
characteristic viscosity in dimethylformamide equalling 0.65,
the co-polymer is thermally treated at 150~C and 1 mm mercury
pressure, the co-polymer is melted at 185C, and the jet of
the melt is cooled in air at 140C in a 0.4 m long tube. The
moulded filament is drawn to a 12:1 draft a speed of 75 m/min
over a 400 mm long "iron".
The filament obtained has 86 gr/tex tensile strenyth
and 10% elongation at rupture. The shrinkage rate of this
filament is 15%, with 87% of the initial strength remaining
after the shrinkage.
After the drawing the filament is thermally treated at
170C in a nitrogen atmosphere under 10 kg/mm2 tension for 5
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minutes. Following this treatment the shrinkage is 0.5~0,
with 95% of the initial strength remaining after the shrin]c-
age.
Example 4.
A polyoxymethylene filament is moulded as described
above in Example 3, a difference being in that the co-polymer
is thermally treated at 140C and pressure of 95 mm mercury;
the co-polymer is melted at 180C; the jet of the melt is
cooled in air at 120~C.
The moulded filament is drawn to a 13.6:1 draft at a
speed of 25 m/min over a 1000 mm long "iron" at 158"C.
The filament obtained is characterized by 98 gr/tex
tensile strength and 9% elongation at rupture. The shrinkage
rate of the filament is 11%, with 90% of the initial strength
remaining after the shrinkage.
, After the drawing the filament is thermally treated at
150C under 0.2 kg/mm2 tension for 150 minutes. F'ollowing the
treatment, the shrinkage of the filament is 3%, with 9~'~O of
the initial strength remaining.
Example 5.
A polyoxymethylene filament is moulded and drawn, as
described abo~e in Example 1, with a difference that there is
used a copolymer of trioxane and a cyclic ester, i.e, ethylene
oxide (the weight content of the latter being 3 per cent), having
characteristic viscosity in dimethylformamide equalling 0.50;
the copolymer is thermally treated at 130C and pressure
equalling 50 mm mercury, the copolymer is melted at 170~C,
and the melt is forced through an extrusion nozzle having 24
orifices 0.40 mm in diameter. The rate of feed of the mel-c is
20 grams per minute. The jets of the melt are cooled in a 0.7 m
long tube with air at 100C. The filament moulding rate is
450 m/min.
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The filament obtained is characterized by 76 yr/tex
tensile strength and 14% elongation at rupture. The shrinkage
of this filament is 20%, with 75% of the initial strength
remaining after the shrinkage.
After the drawing the filament is thermally treated
in a nitrogen atmosphere at 152C under 4 kg/mm2 tension for
240 minutes.
Following this treatment the shrinkage is 5%, with
92% of the initial strength remaining.
ExamPle 6.
Polyoxymethylene filaments are moulded and drawn,
as described above in Example 5, with a difference that the
temperature of the air cooling the jets of the melt is 70C.
The moulded filament is drawn to a 7:1 draft at a
10 m/min speed over a 700 mrn long "iron" at 120C.
The filament obtained has 62 gr/tex tensile strength,
with 16% elongation at rupture. The shrinkage rate of this
filament is 25%, with 67% of the initial strength rernairling
after the shrinkage.
After the drawing the filament is thermally treated
in a nitrogen atmosphere at 150C under 8 kg/mm2 tension.
Following this treatment the shrinkage rate at 150~C
is 10%, with 85% of the initial strength remaining.
Exam~le 7.
A co-polymer of formaldehyde and 1,3-dioxolane (the
weight content of the latter being 5%) in a powder form is mixed
with stabilizing additives, viz. 2,2'-methylene bis-(4-mcthyl-
6-terbutyl phenol) in a quantity of 2.5% by weight as the anti-
oxidant and formaldehyde-dicyanamide in a quantity of 0.5% by
weight as the acceptor: the co-polymer is thermally treated,
as described above in Example 5 and melted at 170C. The co-
polymer used has characteristic viscosity of 0.42.
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The filament is moulded, as described hereinabove in
Example 6, and drawn to a 8:1 draft in a contactless 800 mm long
heater in an atmosphere of air heated to 130C at a speed of S0
m/min.
The filament obtained is characterized by 59 gr/tex
tensile strength and 20% elongation at rupture.
Example 8.
A granulated homo-polymer of formaldehyde, containing
0.5% by weight co-polymer based on hexamethylene diamine,
adipinic acid and caprolactam and 0.5% by weight dicyanamide,
having characteristic viscosity in dimethylformamide equalling
0.86, is thermally treated at 110C and 0.5 mm mercury pressure.
Then the polymer is melted in a nitrogen atmosphere at 210C,
and the melt thus obtained is forced through an extrusion nozzle
with 12 orifices 0.8 mm in diameter, the rate of feed of the
melt being 20 grams a minute. The jets of the melt are cooled
with nitrogen heated to 165C. The filament moulding spee~ iq
500 m/min.
The moulded filament is drawn to a 8:1 draft at a rate
of 15 m/min over a 700 mm long "iron" at 161C.
The filament obtained has 71 gr/tex tensile strength
and elongation at rupture equalling 12%.
,: ExamPle 9.
A polyoxymethylene filament is moulded, as described
above in Example 1, with a difference that the polyoxymethylene
is melted in a nitrogen atmosphere at 225C, and the melt thus
obtained is forced through an extrusion nozzle having 80 orifices
' 0.5 mm in diameter, the rate of feed of the melt being 150
gr/min. The temperature of the air cooling the jets of the
; 30 melt is 80C. The filament moulding speed is 300 m/min.
The moulded filament is drawn to a 9:1 draft over a
500 mm long "iron" at 150C.
1~4~)37Z
The filament obtained is characterized by 75 gr/tex
tensile strength and 13% elongation at rupture. The shrinkage
of this filament is 17%, with 82% of the initial strength
remaining after the shrinkage.
After the drawing the filament is thermally treated
in air at 157C under 8 kg/mm2 tension for 40 minutes.
Following this treatment the shrinkage rate of the
filament is 4%, with 92% of the initial strength remaining.
In the above examples the tensile strength was
determined on a pendulum-type rupturing machine, with filament
elongation rate being 500 mm/min. and clamping length being
250 mm.
The shrinkage rate of the filament is determined
from the ratio:
shrinkage rate equals Il 2 .100%, where
Il is the initial length of the specimen, equalling 250 mm;
I2 is the length of the specimen after the filament has
been heated slack to 150C in air for O.S hours.
The conservation of strength (rate of strength preserved)
after shrinkage of the filament is determined by the ratio:
p2 .100%, where
Pl is the strength of the initial filament (before the
heat treatment of the filament), in grams per tex, and
P2 is the preserved strength of the filament after its
shrinkage, in grams per tex.
' '
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