BACKGROUND OF THE INVENTION
Field of the Invention
-
The present invention relates to
crosslinked polyvinyl alcohol fiber and method for
producing the same, and more particularly, to
crosslinked polyvinyl alcohol fiber, in which PVA
resin having a degree of polymerization of more than
1,000 and a degree of saponification of more than 97.0
mol% is dissolved in dimethyl sulfoxide (hereinafter,
referred to as DMSO), the solution is subjected to dry
and wet gel spinning using methanol as a coagulation
solution, drawn and thermally treated, the resulting
polyvinyl alcohol drawn yarn with 500-3,000 deniers is
twisted to produce a cabling yarn, the cabling yarn is
plied into a 2-ply or 3-ply yarn to produce a raw
cord, the raw cord is wound on a bobbin for crosslinking
and crosslinked in an aqueous crosslinking solution
containing an aromatic aldehyde compound and an
acid catalyst. Moreover, the present invention relates
to a crosslinker-introducing apparatus, which is
used in the above method and can effectively induce
the crosslinking reaction of the wound raw cord.
Background of the Related Art
-
A polyvinyl alcohol fiber (hereinafter, referred
to as PVA) shows superior strength and modulus
to general purpose fibers, such as polyamide, polyester,
and polyacrylonitrile fibers, and is very excellent
in particularly adhesion, water dispersibility,
alkaline resistance and chemical resistance. Thus, it
is used as materials of various industrial fields.
-
Recently, PVA is also used as a reinforcement
material for concrete, cement, rubber, plastic
and the like, and studied and developed as a material
with high applicability to new fields.
-
Till now, various methods for producing a
high-strength PVA fiber were proposed.
-
US Patent No. 4,440,711 discloses a method
for preparing a high-strength PVA fiber using a gel
spinning technique (US patent No. 4,698,194) in which
high-molecular weight polyethylene as a raw material
is drawn to high draw ratio to produce the high-strength
fiber. The gel spinning technique is a general
method for producing the high-strength fiber, in
which a polymer compound is mixed with solvent to prepare
a uniform solution, and then, the solution is
drawn to high draw ratio while suitably adjusting
phase separation and gelling occurring in a spinning
process.
-
Furthermore, a technology on method for
producing PVA fiber having more excellent physical
properties using this gel spinning technique was also
known.
-
Japanese patent laid-open publication No.
Heisei 7-109616 discloses a method for producing a PVA
multifilament fiber with a tensile strength of at
least 22 g/denier, an initial modulus of at least 440
g/denier and a yarn CV of less than 5%, in which dry
and wet spinning processes are performed using a spinneret
with an orifice diameter of 0.1-1 mm and an orifice
length-to-diameter (L/D) ratio of 3-20.
-
However, although the PVA fiber produced by
this method has excellent mechanical properties, the
PVA resin is dissolved in hot water with a high temperature
above 100 °C or has reduced mechanical properties,
due to the hydrophilicity of PVA resin itself.
Thus, it has many limitations for use in applications,
such as tire cords which have the biggest market among
the industrial fibers.
-
Although a very small amount of water is
present in the inside of a tire, excess water can flow
into the tire when the tire gets damaged. Also, when
the tire temperature is increased to 130 °C as a result
of high-speed running of automobile, the water is
thermally hydrated to cause damages to the PVA fiber,
so that the stability of automobiles is endangered.
Thus, the PVA fiber according to the prior art could
not be used as a tire reinforcement material without
anxiety.
-
Also, since the high crystallinity of the
PVA fiber results in a reduction in fatigue resistance
when it is used for tire cords, this problem needs to
be solved.
-
To improve hot water resistance and fatigue
resistance, various methods were developed in which
PVA with a high degree of polymerization is spun,
thermally drawn to high draw ratio, thermally treated,
acetalized and crosslinked by an acid catalyst. However,
it is difficult to use the PVA fibers as filaments
for industrial purpose. And, when the PVA resin
produced by such methods is used in hot water above
130 °C, a problem occurs.
-
Particularly in the crosslinking technology
proposed in the prior art, a crosslinker is added to a
spinning dope before a drawing process or during an
extraction or oil-treating process.
-
Korean patent registration No. 210727 discloses
a method for producing a polyvinyl alcohol fiber
with excellent hot water resistance, in which a
yarn containing an acetal compound of aliphatic dialdehyde
as a crosslinker is prepared, subjected to dry
heat drawing and crosslinked by an acid.
-
Korean patent laid-open publication No. 96-41438
discloses a method for producing a polyvinyl alcohol
fiber with excellent hot water resistance, in
which a yarn containing an ammonium sulfate
crosslinker is subjected to dry heat drawing and then
crosslinked.
-
As described above, in the crosslinking
technologies proposed till now, the crosslinker is
added to the spinning dope before the drawing process
or in the extraction or oil-treating process. In such
prior crosslinking methods, when subjected to thermal
drawing at a high temperature above 200 °C, the
crosslinker contained in the PVA undrawn yarn cause
crosslinking reaction to reduce drawability, or the
crosslinker with low boiling point is volatilized to
reduce crosslinking efficiency. Thus, the crosslinker
hardly has a hot water resistance above 130 °C.
-
Furthermore, the crosslinking treatment
methods as described above have a problem in that,
since crosslinking treatment is performed by simply
dipping a bobbin wound with a undrawn yarn into the
crosslinker, a portion of the undrawn yarn wound inside
the bobbin is not impregnated with the
crosslinker, and thus, incompletely crosslinked, or
the outer side of the undrawn yarn wound on the bobbin
is crosslinked at a significantly different level from
the inside of the undrawn yarn.
SUMMARY OF THE INVENTION
-
An object of the present invention is to
provide a crosslinked polyvinyl alcohol fiber, in
which a polyvinyl alcohol drawn yarn with 500-3,000
deniers is twisted to form a cabling yarn, the cabling
yarn is plied into a 2-ply or 3-ply yarn to prepare a
raw cord, the raw cord wound on a bobbin for
crosslinking reaction is crosslinked in an aqueous
crosslinking solution containing an aromatic aldehyde
compound and an acid catalyst.
-
Another object of the present invention is
to provide a crosslinker-introducing apparatus, which
is used in the above inventive method and allows the
polyvinyl alcohol fiber to have excellent hot water
resistance and high strength.
-
To accomplish the above objects, according
to one aspect of the present invention, there is provided
a crosslinked raw cord which is produced by a
method comprising the steps of: (A) spinning polyvinyl
alcohol having a degree of polymerization of 1,000-7,000
according to a dry and wet spinning technique or
a wet spinning technique, drawing the undrawn yarn to
high draw ratio, and thermally treating the drawn
yarn; (B) twisting the polyvinyl alcohol drawn yarn to
prepare a cabling yarn, and plying the cabling yarn
into a 2-ply or 3-ply yarn to produce a raw cord; and
(C) crosslinking the raw cord by dipping it into the
crosslinker.
-
To accomplish the above objects, according
to one aspect of the present invention, there is provided
a crosslinker-introducing apparatus comprising a
cylindrical bobbin which has a hollow formed therein,
a plurality of through-holes formed on the circumferential
surface and on which a raw cord is wound and a
closed container which is charged with the crosslinker
and provided in such a manner that the bobbin for
crosslinking is dipped in the crosslinker.
-
To accomplish the above objects, according
to one aspect of the present invention, there is provided
a crosslinked raw cord which is produced by a
method comprising the steps of: (A) dissolving polyvinyl
alcohol having a degree of polymerization of
1,000-7,000 and a degree of saponification of more
than 97.0 mol% in dimethyl sulfoxide, spinning the solution
according to a dry and wet spinning technique
or a wet spinning technique, drawing the undrawn yarn
to high draw ratio, and thermally treating the drawn
yarn; (B) twisting the polyvinyl alcohol drawn
yarn to prepare a cabling yarn, and plying the cabling
yarn into a 2-ply or 3-ply yarn to produce a raw cord;
and (C) crosslinking the raw cord using the
crosslinker-introducing apparatus described above in
an aqueous crosslinking solution containing an aromatic
aldehyde compound and an acid catalyst while
adding alcohol to the aqueous crosslinker solution.
-
Preferably, the alcohol added to the aqueous
crosslinking solution in the step (C) is methanol.
-
Preferably, the content of the alcohol
added to the aqueous crosslinking solution in the step
(C) is 1-30 wt%.
-
Preferably, the content of the aromatic aldehyde
compound crosslinked to the raw cord in the
step (C) is 0.1-5.0 wt%.
-
Preferably, the aromatic aldehyde
crosslinked to the raw cord in the step (C) is
terephthaldicarboxaldehyde (TDA).
-
Preferably, the acid catalyst is used in
the crosslinking of the raw cord in the step (C).
-
Preferably, the acid catalyst used in the
step (c) is acetic acid.
-
To accomplish the above objects, according
to one aspect of the present invention, there is provided
a treated cord for tire cords, which is produced
by treating the crosslinked raw cord described above
with a dipping solution (RFL) and has the following
physical properties: (1) a breaking load of 20.0-50.0
kgf; (2) a fineness of 1,000-6,000 deniers; (3) hot
water resistance of at least 130 °C; and (4) a fatigue
resistance of at least 80%.
-
The crosslinker which is used in the present
invention is preferably an aldehyde compound capable
of crosslinking with the hydroxy group of PVA,
and the aldehyde compound preferably has two or more
aldehyde groups in order to increase crosslinking efficiency.
The aldehyde compound is more preferably an
aromatic compound which infiltrates only into the non-crystalline
region of the fiber.
-
Examples of this aromatic aldehyde compound
include terephthaldicarboxaldehyde (TDA), isophthaldicarboxaldehyde
(IDA) and naphthaldicarboxaldehyde
(NDA), and a mixture of two or more thereof.
-
As the aromatic aldehyde compound,
terephthaldicarboxaldehyde (TDA) is preferably used in
the present invention.
-
It is the key technical point of the present
invention that the aromatic aldehyde capable of
infiltrating only into the non-crystalline region of
the drawn yarn is used as the crosslinker. Since the
aromatic aldehyde is mainly infiltrated only into the
non-crystalline region of the yarn, the tenacity of
the drawn yarn can be prevented from being reduced due
to the crosslinker.
-
The most important characteristic of the
present invention is a crosslinking process. In general
crosslinking, there is used a method wherein the
crosslinker is dissolved in an organic solvent in an
extraction process in order to infiltrate the
crosslinker into the inside of the fiber. However,
this crosslinker within the undrawn fiber causes a reduction
in drawability in a thermal drawing step at
high temperature above 200 °C, so that the drawn yarn
does not have sufficient hot water resistance and fatigue
resistance. The crosslinker used in the extraction
process makes organic solvent recovery difficult
and thus an entire process difficult.
-
For this reason, in the present invention,
in order to increase crosslinking efficiency and to
prevent fiber damage, the twisted PVA raw cord is
crosslinked after it is infiltrated with the
crosslinker. This gives a high-strength PVA fiber
having a hot water resistance above 130 °C and a fatigue
resistance of at least 80%.
-
A key technical point in the present invention
is that the raw cord is crosslinked in a
crosslinking solution containing an aromatic aldehyde
compound and an acid catalyst while adding alcohol to
the aqueous crosslinking solution. The addition of
alcohol to the crosslinking solution allows significant
prevention of reduction in tenacity.
-
Hereinafter, the producing method of the
PVA fiber will be described in detail.
-
PVA has a degree of polymerization of about
1,000-7,000, and preferably 1,500-4,000. At a degree
of polymerization lower than 1,000, it is difficult to
form it into fibers, and at a degree of polymerization
higher than 7,000, it has so high viscosity to reduce
spinning processability. Since the high-strength PVA
fibers which are mostly used in the industrial material
field need to have hot water resistance, PVA with
a saponification degree of more than 97.0 mol% is
used. As the organic solvent, ethylene glycol, glycerin,
and DMSO may be used, but DMSO is suitable for
its highest solubility for PVA. This DMSO is preferably
purified to a water content of less than several
tens ppm before use.
-
The concentration of the PVA dope is adjusted
such that its viscosity is preferably in a
range of 50-4,000 poise, and more preferably 500-3,000
poise in order to obtain excellent physical properties.
At a viscosity below 50 poise, it is difficult
to form the PVA dope into a fiber, and at a viscosity
above 4,000 poise, fiber spinnability is reduced.
-
A coagulation bath has a temperature of -30
to 30 °C for possible spinning, and preferably -10 to
10 °C for the formation of uniform gel. If the temperature
of the coagulation bath is below -30 °C, PVA
spinning dope may be frozen. If the temperature of
the coagulation bath is higher than 30 °C, gel formation
becomes impossible so that spinnability will be
reduced.
-
A method for producing a PVA fiber is performed
by a dry spinning technique, a wet spinning
technique, and a dry and wet spinning technique, but
in a method for producing a high-strength PVA fiber
where a drawing process with high draw ratio is required,
the dry and wet spinning technique is preferred.
For the production of a PVA filament, the
air-gap in the dry and wet spinning technique may be
5-200 mm, but for thermal drawing to high draw ratio,
a narrow air-gap of 5-50 mm is preferred. At an air-gap
below 5 mm, workability will be reduced. On the
other hand, at an air-gap above 200 mm, crystallinity
is greater than gelling to make the thermal drawing at
high draw ratio impossible, and also the fusion between
fibers on a nozzle section occurs to reduce productivity.
-
In the producing method of the high-strength
PVA fiber, the drawing process is very important
for high strength and improved hot water resistance.
Examples of a heating manner in the drawing
process include a hot air heating manner and a roller
heating manner. In the roller heating manner, a filament
is in contact with the roller surface such that
the fiber surface is liable to be damaged. Thus, the
hot air heating manner is more effective for the production
of the high-strength PVA fiber. The heating
temperature may be 140-250 °C, and preferably 160-230
°C. At a heating temperature below 140 °C, molecular
chains will not sufficiently move to make the thermal
drawing at high draw ratio impossible, and above 250
°C, PVA is liable to be decomposed to cause a reduction
in physical properties.
-
Furthermore, in the PVA fiber used as a
tire cord among industrial materials, high strength
and fatigue resistance are required. To meet such requirements,
a PVA drawn yarn is twisted to produce a
raw cord. In a general process for twisting synthetic
fibers, an increase in twist number will result in a
reduction in tenacity but an increase in fatigue resistance.
Thus, selecting suitable twist number according
to the purpose of use is very important. For
example, a tire cord used for carcass of a tire with
1500 d/2p is twisted to 300-500 TPM (turns per meter)
before use.
-
To enhance hot water resistance and fatigue
resistance, the twisted PVA raw cord is crosslinked by
the addition of a crosslinker.
-
To infiltrate the crosslinker only into the
non-crystalline region of the PVA fiber drawn to high
draw ratio, the aromatic aldehyde is used as the
crosslinker as described above.
-
The aromatic aldehyde compound, which is
used in the present invention, is preferably
terephthaldicarboxaldehyde (TDA). The crosslinking
compound is used at the amount of 0.1-5 wt% relative
to a fiber, and preferably 0.5-2.0 wt%. If it is used
at the amount of less than 0.1 wt%, an insufficient
heat water resistance below 130 °C will be caused, and
if it is used at the amount of more than 5.0 wt%, a
great reduction in tenacity will be caused to make the
use of the high-tenacity tire cord difficult.
-
To react the crosslinking compound with the
OH group of PVA, an acid catalyst is required in an
aqueous crosslinking solution. Although acids, such
as sulfuric acid or acetic acid, may be used as the
acid catalyst, the acetic acid is preferable in view
of reaction rate adjustment and stability. The acid
catalyst is preferably used at the amount of 5-30 wt%
relative to the aqueous crosslinking solution. If the
acid catalyst is used at less than 5 wt%, crosslinking
reaction will progress too slowly, and if it is used
at more than 30 wt%, it will be difficult to remove
the acid catalyst in a water-washing process after reaction.
-
It is a key technical point in the present
invention that crosslinking is performed with the addition
of alcohol to the aqueous crosslinking solution
containing the aromatic aldehyde compound and the acid
catalyst. The addition of alcohol to the crosslinking
solution allows significant prevention of a reduction
in tenacity after crosslinking.
-
Examples of preferred alcohols, which are
added to the aqueous crosslinking solution in the present
invention, include methanol, ethanol, propanol
and butanol. Methanol is more preferred. The alcohol
is added at the amount of 1-30 wt% relative to the
aqueous crosslinking solution. At less than 1 wt%, a
great reduction in tenacity will be caused during
crosslinking to make the use for the high-tenacity
tire cord difficult, and at more than 30 wt%, a cost
disadvantage will be caused and also crosslinking will
progress at a too slow rate.
-
Another key technical point in the present
invention is that a polyvinyl alcohol drawn yarn is
plied into a 2-ply or 3-ply yarn to produce a raw cord
wound on a bobbin for crosslinking, and then, the raw
cord wound on the bobbin for crosslinking is
crosslinked by dipping it into the crosslinking solution.
-
To infiltrate the crosslinking compound
into the non-crystalline region of a PVA fiber having
high crystallinity, a method is used in which the reaction
solution is heated to 50 °C to increase the activity
of the crosslinking compound, and a reactor is
pressurized before use. Also, crosslinking time varies
depending on the crosslinking compound and conditions,
but is preferably longer than 30 minutes. However,
if the crosslinking is performed for too long
time, a great reduction in tenacity will be caused.
-
The crosslinked PVA raw cord is washed and
dried. To improve the adhesion to rubber, the dried
raw cord is dipped in a RFL solution, dried and thermally
treated. Concretely speaking, the dipping process
is achieved by impregnating the fiber surface with
a resin solution called resorcinol-formaline-latex
(RFL), and this dipping process is performed in order
to improve the problem of low adhesion to rubber of
the tire cord fiber.
-
The dipping solution, which is used for the
adhesion between the PVA raw cord and rubber in the
present invention, can be prepared by, for example,
the following method. The following preparation example
is given to more fully understand the present invention
and is not intended to limit the present invention.
Resorcinol of 29.4 wt% | 45.6 weight part |
Pure water | 255.5 weight part |
Formalin of 37% | 20 weight part |
Sodium Hydroxide of 10 wt% | 3.8 weight part |
-
The solution prepared as described above is
reacted at 25 °C for 5 hours with stirring, and then
added with the following components.
VP-Latex of 40 wt% | 300 weight part |
Pure water | 129 weight part |
Ammonia water of 28% | 23.8 weight part |
-
The solution containing the above components
is aged at 25 °C for 20 hours, and maintained at
a solid concentration of 19.05%.
-
In order to prevent the RFL solution from
infiltrating deeply into the inside of the fiber during
the RFL dipping process, the raw cord is stretched
to a stretch ratio of 0.5-3%, and a dip pick up (DPU)
of the RFL is 3.0-9.0 wt%. At a stretch ratio of less
than 0.5%, DPU will exceed 9 wt% so that the RFL solution
will be infiltrated deeply into the inside of the
staple fiber to reduce fatigue resistance. At a
stretch ratio of more than 3%, excessive tension will
be applied to the raw cord and thus will cause damages
to the raw cord. Thermal treatment should be performed
at a temperature of 170-230 °C, and preferably
200-220 °C where the movement of PVA molecules is the
best. By minimizing the tension applied to the fiber
to allow for the greatest possible movement of the PVA
molecules to maximize a heat treatment effect, the
production of a treated high-tenacity PVA cord becomes
possible. In a heat treatment process conducted after
dipping the raw cord in the RFL solution, it is important
that the dipped cord is maintained at a stretch
ratio of 0 to -5%. If the stretch ratio in the heat
treatment process is above 0%, when the dipped cord is
used in a tire cord requiring high fatigue resistance,
a cord cutting or separation phenomenon will occur
which is due to low fatigue resistance below 60% resulting
from the low elongation of the dipped cord.
On the other hand, at a stretch ratio below -5%, molecular
recrystallization in a vertical direction to
the fiber axis will occur due to excessive molecular
movement to cause a reduction in tenacity. If the
crosslinker is present within the fiber not having
been washed in the water-washing process after the
crosslinking process, it acts as an impurity in a
product where the PVA fiber was used. Thus, heat
treatment is performed above 200 °C such that the remaining
crosslinker can be reacted or volatilized to
further improve crosslinking efficiency.
-
Hereinafter, the bobbin for crosslinking
used in the crosslinking as described above, and the
use state thereof, will be described in brief.
-
FIG. 1 is a perspective diagram showing the
bobbin for crosslinking according to the present invention,
and FIG. 2 is a use state diagram showing the
use state of the bobbin for crosslinking according to
the present invention.
-
In the crosslinking as described above, a
bobbin for crosslinking 10 is provided. The bobbin
for crosslinking 10 comprises a first bobbin 10a forming
one portion of the crosslinking bobbin 10, and a
second bobbin 10b, which is detachably coupled to the
first bobbin 10a and forms the other portion of the
crosslinking bobbin 10. In the first and second bobbins
10a and 10b, hollows 16a and 16b are formed, respectively,
a plurality of through- holes 13a and 13b
are formed in the circumferential portion of the first
and second bobbins so that cylindrical bobbin axes 12a
and 12b on which a PVA raw cord is wound up are provided.
In the inner end of the first and second bobbins
10a and 10b, a coupling protrusion 18a and a coupling
groove 18b are formed which correspond to each
other such that the second bobbin 10b is coupled to
the first bobbin 10a.
-
Herein, the first bobbin wheel 14a coupled
to the first bobbin 10a serves to close the hollow 16a
of the bobbin for crosslinking 10, and the second bobbin
wheel 14b coupled to the second bobbin 10b serves
to be connected with a crosslinker-feeding pipeline 30
in order to supply the crosslinker 2 into the inside
of the PVA raw cord 1 wound on a bobbin for crosslinking
10 through a hollow 16a and 16b formed in a bobbin
for crosslinking 10 by pressurizing or depressurizing
with supplying apparatus by which crosslinker 2 is
supplied in a specified pressure.
-
In the crosslinking step, the bobbin for
crosslinking 10 on which the PVA raw cord 1 was wound
is provided in such a manner that it is dipped in a
crosslinker 2 contained in a closed container 40
charged with the crosslinker 2. The crosslinker 2 is
pressurized or depressurized to a specified pressure
and supplied through a crosslinker-feeding pipeline
30. The supplied crosslinker is moved from inside to
outside of the wound PVA raw cord 1 through the
through- holes 13a and 13b formed in the respective
bobbin axes 12a and 12b or moved from the outside to
inside of the PVA raw cord 1, so that the inside and
outside of the PVA raw cord 1 wound on the crosslinking
bobbin 10 can be uniformly crosslinked.
BRIEF DESCRIPTION OF THE DRAWINGS
-
FIG. 1 is a perspective diagram showing a
bobbin for crosslinking according to the present invention.
-
FIG. 2 is a use state diagram showing a
crosslinker-introducing system using the bobbin for
crosslinking according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
-
Hereinafter, the present invention is described
in detail with referring to the following examples,
but it is to be understood that the examples
is solely for the purpose of illustration and do not
limit the scope of the present invention. In the following
examples, the estimating method and the measuring
method as following is used.
(a) tenacity(kgf) of PVA cord
-
The tenacity of the filament is measured
using low speed elongation tester, and the filament is
tested after being dried at 107 °C for 2 hours. The
filament is twisted by 80TPM(80turns/meter) and the
length of the filament is 250mm and the elongation
speed is 300m/min.
(b) hot water resistance(WTb, °C)
-
A twisted raw cord with 3,000 deniers is
selected, cut into a 4-cm size, and then applied with
a load of 3g/ply. The cord is dipped in water contained
in a glass container for pressurization, and
the temperature at which the fiber is broken is measured
while elevating the temperature at a rate of 2
°C/minute.
(c) fatigue resistance
-
Samples were subjected a fatigue test using
a Goodrich disc fatigue tester which is conventionally
used for the fatigue test of tire cords. Then, they
were measured for residual tenacity, and fatigue resistances
were compared. The fatigue test was conducted
under the following conditions: 120 °C, 2,500
rpm, and 10% and 18% compression. After the fatigue
test, the samples were submerged in tetrachloroethylene
solution to swell rubber, and then, a cord was
separated from the rubber and measured for residual
tenacity. This residual tenacity was measured after
drying at 107 °C for 2 hours using a conventional tensile
strength tester by the above-described measurement
method (a).
Example 1
-
PVA was used in a powder form with a degree
of saponification of 99.9 mol% and a degree of polymerization
of 2,000, and methyl alcohol and DMSO were
used in a purified solvent mixture form with a water
content of less than 100 ppm. To prepare the solvent
mixture, DMSO and methyl were mixed such that the content
of methyl alcohol content in the solvent was 5%
by volume. PVA was dissolved in the solvent mixture
such that it was 22 wt% relative to a PVA spinning
dope. Next, the PVA solution was produced into a PVA
fiber by a dry and wet spinning technique, using gel
spinning. In this spinning process, a circular nozzle
with a nozzle hole number of 500, a nozzle hole diameter
of 0.5 mm and a L/D ratio of 5 was used. Also,
air-gap was 50 mm, and methanol was used as a solvent
in a coagulation bath. At this time, the coagulation
bath was maintained at a solvent/methanol mixing ratio
of 20/80 and a temperature of 0 °C. After passing
through an extraction tank, the PVA fiber must be free
of the DMSO solvent. If the solvent remains in the
filament, it is discolored in a thermal drawing process
at high temperature to act as a main cause of deteriorating
the physical properties of the final filament.
In the thermal drawing process, two-step hot
air heating was used in which the hot air heating temperature
was 200 °C at the first step and 220 °C at
the second step, and the draw ratio was adjusted such
that total draw ratio was 13.5. As a result, a high-strength
PVA fiber with a strength of 13.0 g/d and an
elongation of 7.0% was produced. This drawn yarn was
twisted to plying and cabling number of 300 TPM to
produce a raw cord yarn having a tenacity of 34 kgf.
The raw cord wound on a bobbin for crosslinking was
crosslinked by dipping it in terephthaldicarboxaldehyde
(TDA) as aromatic aldehyde through a crosslinker-introducing
apparatus capable of effectively inducing
crosslinking. In the crosslinking reaction, 2 wt% of
terephthaldicarboxaldehyde (TDA) and 10 wt% of acetic
acid were dissolved in water to prepare an aqueous
crosslinking solution, and 10 wt% of methanol was
added to the aqueous crosslinking solution, and then,
the raw cord wound on the bobbin for crosslinking was
crosslinked by dipping it in the aqueous crosslinking
solution at 70 °C for one hour and washed with water.
The crosslinked raw cord with tenacity of 33.6 kgf was
impregnated with a RFL solution to produce a treated
PVA cord. The treated PVA cord was measured for its
physical properties and the results are summarized in
Table 1 below.
Examples 2 and 3
-
The ratio between terephthaldicarboxaldehyde,
acetic acid and methanol was adjusted to a ratio
given in Table 1, and the resulting raw cord was
crosslinked and then measured for its physical properties,
including tenacity and fatigue resistance.
Comparative Examples 1 and 2
-
Comparative Example 1 is a non-crosslinked
case and the results are given in Table 1, and Comparative
Example 2 is a case where methanol was not
used in the aqueous crosslinking solution. The results
for Comparative Example 1 and 2 are given in Table
1.
Comparative Examples 3 and 4
-
In Comparative Example 3, crosslinking was
performed for 6 hours and the results are given in Table
1. In Comparative Example 4, crosslinking was
performed at 30 °C and the results are given in Table
1.
| Ex. 1 | Ex. 2 | Ex. 3 | Comp. Ex. 1 | Comp. Ex. 2 | Comp. Ex. 3 | Comp. Ex. 4 |
Concentration of TDA (wt %/aqueous solution) | 2 | 2 | 2 | - | 5 | 2 | 2 |
Concentration of Acetic acid (wt %/aqueous solution) | 10 | 10 | 15 | - | 10 | 10 | 10 |
Concentration of Methanol (wt %/aqueous solution) | 10 | 5 | 10 | - | - | 10 | 10 |
Reaction temp.(°C) | 70 | 70 | 70 | - | 70 | 70 | 30 |
Reaction time(min) | 60 | 60 | 60 | - | 60 | 360 | 60 |
Tensile strength of drawn yarn ( g / d ) | 13.5 | 13.5 | 13.5 | 13.5 | 13.5 | 13.5 | 13.5 |
Strength of raw cord ( k g f ) | 34 | 34 | 34 | 34 | 34 | 34 | 34 |
Strength of treated raw cord (k g f ) | 33.6 | 32.8 | 32.1 | - | 21.2 | 28.2 | 33.4 |
Strength of dipped cord ( k g f ) | 37.9 | 37.2 | 36.5 | 38 | 26.4 | 31.5 | 38.2 |
Fatigue resistance (%) | 99 | 95 | 97 | 62 | 98 | 98 | 68 |
Hot water resistance (°C) | 172 | 167 | 172 | 107 | 170 | 171 | 108 |
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As described above, the present invention
provides the crosslinked raw cord which is produced by
the method comprising the steps of: twisting a polyvinyl
alcohol drawn yarn with 500-3,000 deniers to prepare
a cabling yarn; plying the cabling yarn into a 2-ply
or 3-ply yarn to prepare a raw cord; winding the
raw cord on a bobbin for crosslinking; and crosslinking
the raw cord wound on the bobbin for crosslinking,
in an aqueous crosslinking solution containing an aromatic
aldehyde compound and an acid catalyst, while
adding alcohol to the aqueous crosslinking solution.
The crosslinked raw cord has excellent hot water resistance,
and thus, can be suitably used for tire
cords.