U.S. patent application number 10/815955 was filed with the patent office on 2005-06-02 for crosslinked polyvinyl alcohol fiber and method for producing the same.
This patent application is currently assigned to HYOSUNG Corporation. Invention is credited to Choi, Soo-Myung, Kim, Hak-Sung, Kwon, Ik-Hyeon, Oh, In-Seok, Park, Seong-Ho.
Application Number | 20050118419 10/815955 |
Document ID | / |
Family ID | 34511179 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050118419 |
Kind Code |
A1 |
Kwon, Ik-Hyeon ; et
al. |
June 2, 2005 |
Crosslinked polyvinyl alcohol fiber and method for producing the
same
Abstract
The present invention relates to crosslinked polyvinyl alcohol
raw cord 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, 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.
Inventors: |
Kwon, Ik-Hyeon; (Seoul,
KR) ; Choi, Soo-Myung; (Kyonggi-do, KR) ;
Park, Seong-Ho; (Kyonggi-do, KR) ; Kim, Hak-Sung;
(Kyonggi-do, KR) ; Oh, In-Seok; (Kyonggi-do,
KR) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
HYOSUNG Corporation
Kyonggi-do
KR
|
Family ID: |
34511179 |
Appl. No.: |
10/815955 |
Filed: |
April 2, 2004 |
Current U.S.
Class: |
428/364 |
Current CPC
Class: |
D06B 23/042 20130101;
Y10T 428/2913 20150115; D01F 6/14 20130101; D06M 2101/24 20130101;
D02G 3/48 20130101; D06M 13/123 20130101; D06M 2200/12
20130101 |
Class at
Publication: |
428/364 |
International
Class: |
D02G 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2003 |
KR |
10-2003-0084832 |
Claims
What is claimed is:
1. 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.
2. A crosslinker-introducing apparatus comprising: a bobbin for
crosslinking comprising a first bobbin and a second bobbin, the
first bobbin having a hollow formed therein, a plurality of
through-holes formed on the circumferential surface of the first
bobbin to provide a cylindrical bobbin axis on which a raw cord is
wound, and a coupling protrusion formed at one end of the bobbin
axis, the second bobbin having a hollow formed therein, a plurality
of through-holes formed on the circumferential surface of the
second bobbin to provide a cylindrical bobbin axis on which the PVA
raw cord is wound, and a coupling groove formed at one end of the
bobbin axis, the shape of the coupling groove corresponding to the
coupling protrusion and being coupled with the coupling protrusion;
a first bobbin wheel which is coupled to the other end of the first
bobbin axis and serves to prevent the separation of the wound PVA
raw cord and to close the hollow of the bobbin for crosslinking; a
second bobbin wheel which is coupled to the other end of the second
bobbin axis and serves to prevent the separation of the wound PVA
raw cord, the second bobbin wheel having a crosslinker-feeding
pipeline attached thereto, the crosslinker-feeding pipeline serving
to feed a crosslinker into the inside of the hollow of the bobbin
for crosslinking by pressurization or depressurization; 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.
3. 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 of claim 2 in an aqueous crosslinking solution containing
an aromatic aldehyde compound and an acid catalyst while adding
alcohol to the aqueous crosslinker solution.
4. The crosslinked raw cord of claim 3, wherein the alcohol added
to the aqueous crosslinking solution in the step (C) is
methanol.
5. The crosslinked raw cord of claim 3, wherein the content of the
alcohol added to the aqueous crosslinking solution in the step (C)
is 1-30 wt %.
6. The crosslinked raw cord of claim 3, wherein the content of the
aromatic aldehyde compound crosslinked to the raw cord in the step
(C) is 0.1-5.0 wt %.
7. The crosslinked raw cord of claim 3, wherein the aromatic
aldehyde crosslinked to the raw cord in the step (C) is
terephthaldicarboxaldehyde (TDA).
8. The crosslinked raw cord of claim 3, wherein the acid catalyst
used in the step (c) is acetic acid.
9. A treated cord for tire cords, which is produced by treating the
crosslinked raw cord of claims 1 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.degree. C.; and (4) a fatigue resistance
of at least 80%.
10. A treated cord for tire cords, which is produced by treating
the crosslinked raw cord of claims 3 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.degree. C.; and (4) a fatigue resistance
of at least 80%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Background of the Related Art
[0004] 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.
[0005] 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.
[0006] Till now, various methods for producing a high-strength PVA
fiber were proposed.
[0007] U.S. Pat. No. 4,440,711 discloses a method for preparing a
high-strength PVA fiber using a gel spinning technique (U.S. Pat.
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.
[0008] Furthermore, a technology on method for producing PVA fiber
having more excellent physical properties using this gel spinning
technique was also known.
[0009] 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.
[0010] 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.degree. 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.
[0011] 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.degree. 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.
[0012] 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.
[0013] 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.degree. C., a problem
occurs.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.degree. 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 Oc.
[0018] 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
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] Preferably, the alcohol added to the aqueous crosslinking
solution in the step (C) is methanol.
[0025] Preferably, the content of the alcohol added to the aqueous
crosslinking solution in the step (C) is 1-30 wt %.
[0026] Preferably, the content of the aromatic aldehyde compound
crosslinked to the raw cord in the step (C) is 0.1-5.0 wt %.
[0027] Preferably, the aromatic aldehyde crosslinked to the raw
cord in the step (C) is terephthaldicarboxaldehyde (TDA).
[0028] Preferably, the acid catalyst is used in the crosslinking of
the raw cord in the step (C).
[0029] Preferably, the acid catalyst used in the step (c) is acetic
acid.
[0030] 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.degree. C.; and (4) a fatigue resistance of at least
80%.
[0031] 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.
[0032] Examples of this aromatic aldehyde compound include
terephthaldicarboxaldehyde (TDA), isophthaldicarboxaldehyde (IDA)
and naphthaldicarboxaldehyde (NDA), and a mixture of two or more
thereof.
[0033] As the aromatic aldehyde compound,
terephthaldicarboxaldehyde (TDA) is preferably used in the present
invention.
[0034] 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.
[0035] 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.degree. 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.
[0036] 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.degree. C. and a fatigue resistance of
at least 80%.
[0037] 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.
[0038] Hereinafter, the producing method of the PVA fiber will be
described in detail.
[0039] 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.
[0040] 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.
[0041] A coagulation bath has a temperature of -30 to 30.degree. C.
for possible spinning, and preferably -10 to 10.degree. C. for the
formation of uniform gel. If the temperature of the coagulation
bath is below -30.degree. C., PVA spinning dope may be frozen. If
the temperature of the coagulation bath is higher than 30.degree.
C., gel formation becomes impossible so that spinnability will be
reduced.
[0042] 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.
[0043] 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.degree. C., and preferably 160-230.degree. C. At a
heating temperature below 140.degree. C., molecular chains will not
sufficiently move to make the thermal drawing at high draw ratio
impossible, and above 250.degree. C., PVA is liable to be
decomposed to cause a reduction in physical properties.
[0044] 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.
[0045] To enhance hot water resistance and fatigue resistance, the
twisted PVA raw cord is crosslinked by the addition of a
crosslinker.
[0046] 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.
[0047] 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.degree. 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.degree. 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.
[0053] 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.
[0054] 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.
1 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
[0055] The solution prepared as described above is reacted at
25.degree. C. for 5 hours with stirring, and then added with the
following components.
2 VP-Latex of 40 wt % 300 weight part Pure water 129 weight part
Ammonia water of 28% 23.8 weight part
[0056] The solution containing the above components is aged at
25.degree. C. for 20 hours, and maintained at a solid concentration
of 19.05%.
[0057] 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.degree. C., and preferably
200-220.degree. 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.degree. C. such that the remaining
crosslinker can be reacted or volatilized to further improve
crosslinking efficiency.
[0058] Hereinafter, the bobbin for crosslinking used in the
crosslinking as described above, and the use state thereof, will be
described in brief.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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
[0063] FIG. 1 is a perspective diagram showing a bobbin for
crosslinking according to the present invention.
[0064] 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
[0065] 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.
[0066] (a) Tenacity (kgf) of PVA Cord
[0067] The tenacity of the filament is measured using low speed
elongation tester, and the filament is tested after being dried at
107.degree. C. for 2 hours. The filament is twisted by 80 TPM (80
turns/meter) and the length of the filament is 250 mm and the
elongation speed is 300 m/min.
[0068] (b) Hot Water Resistance (WTb, .degree. C.)
[0069] A twisted raw cord with 3,000 deniers is selected, cut into
a 4-cm size, and then applied with a load of 3 g/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.degree. C./minute.
[0070] (c) Fatigue Resistance
[0071] 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.degree. 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.degree. C. for 2 hours using a conventional tensile strength
tester by the above-described measurement method (a).
EXAMPLE 1
[0072] 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.degree. 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.degree.
C. at the first step and 220.degree. 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.degree. 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
[0073] 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
[0074] 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
[0075] 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.degree. C. and the results are
given in Table 1.
3 TABLE 1 Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex.
3 Ex. 4 Concentra- 2 2 2 -- 5 2 2 tion of TDA (wt %/ agueous
solution) Concentra- 10 10 15 -- 10 10 10 tion of Acetic acid (wt
%/ aqueous solution) Concentra- 10 5 10 -- -- 10 10 tion of
Methanol (wt %/ aqueous solution) Reaction 70 70 70 -- 70 70 30
temp. (.degree. C.) Reaction 60 60 60 -- 60 360 60 time (min)
Tensile 13.5 13.5 13.5 13.5 13.5 13.5 13.5 strength of drawn yarn
(g/d) Strength of 34 34 34 34 34 34 34 raw cord (k g f) Strength of
33.6 32.8 32.1 -- 21.2 28.2 33.4 treated raw cord (k g f) Strength
of 37.9 37.2 36.5 38 26.4 31.5 38.2 dipped cord (k g f) Fatigue 99
95 97 62 98 98 68 resistance (%) Hot water 172 167 172 107 170 171
108 resistance (.degree. C.)
[0076] 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.
* * * * *