U.S. patent application number 11/654513 was filed with the patent office on 2007-05-24 for high tenacity polyethylene-2, 6-naphthalate fibers.
This patent application is currently assigned to HYOSUNG CORPORATION. Invention is credited to Yun-Hyuk Bang, Ik-Hyeon Kwon, Deuk-Jin Lee, In-Ho Lee, Jong Lee.
Application Number | 20070116951 11/654513 |
Document ID | / |
Family ID | 36814461 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070116951 |
Kind Code |
A1 |
Kwon; Ik-Hyeon ; et
al. |
May 24, 2007 |
High tenacity polyethylene-2, 6-naphthalate fibers
Abstract
The present invention relates to a high strength
polyethylene-2,6-naphthalate fiber produced by a method comprising
controlling the stress-strain curve and fine structure of an
undrawn yarn such that the drawability of the undrawn yarn in a
drawing step is improved. The industrial
polyethylene-2,6-naphthalate fiber with high strength according to
the present invention shows high strength and low shrinkage, and a
treated cord formed from this fiber has improved dimensional
stability and high strength, such that it can be advantageously
employed as a fibrous reinforcement material of rubber products
such as tires.
Inventors: |
Kwon; Ik-Hyeon; (Seoul,
KR) ; Bang; Yun-Hyuk; (Kyonggi-do, KR) ; Lee;
Jong; (Seoul, KR) ; Lee; Deuk-Jin; (Seoul,
KR) ; Lee; In-Ho; (Seoul, KR) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
HYOSUNG CORPORATION
Kyonggi-Do
KR
|
Family ID: |
36814461 |
Appl. No.: |
11/654513 |
Filed: |
January 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10481475 |
Dec 18, 2003 |
|
|
|
11654513 |
Jan 18, 2007 |
|
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Current U.S.
Class: |
428/375 |
Current CPC
Class: |
B60C 9/08 20130101; B60C
9/04 20130101; B60C 9/02 20130101; B60C 9/0042 20130101; D01F 6/62
20130101; Y10T 428/2933 20150115 |
Class at
Publication: |
428/375 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2003 |
KR |
KR10-2003-0058347 |
Aug 23, 2003 |
KR |
KR10-2003-0058348 |
Oct 24, 2003 |
KR |
PCT/KR03/02252 |
Claims
1-10. (canceled)
11. A process for producing polyethylene naphthalate fiber
comprising the steps of: (a) extruding a polymer containing more
than 85 mol % of ethylene 2,6-naphthalate units and having an
intrinsic viscosity of 0.80-1.2, through a spinneret at a spinning
draft ratio from 20 to 200 at a temperature of 290-330.degree. C.
to form a molten spun yarn; (b) passing the molten spun yarn
through a retarded cooling zone and then quenching and solidifying
the spun yarn; (c) withdrawing the solidified yarn at a speed that
the undrawn yarn has a birefringence of 0.001-0.015 and shows a
stress-strain curve in which the yarn is elongated by less than 10%
and has an initial modulus of 10-50 g/d, when subjected to an
initial stress of 0.3 g/d, and it is elongated by at least 200%
when subjected to a stress greater than the initial stress but
smaller than 1.0 g/d; and (d) subjecting the withdrawn yarn to
multi-stage drawing to a total draw ratio of at least 4.0.
12. The process of claim 11, wherein the polymer used in the step
(a) is a solid state-polymerized polyethylene-2,6-naphthalate chip
containing 30-70 ppm of manganese metal and 150-300 ppm of antimony
metal.
13. The process of claim 12, wherein the chip further comprises a
phosphorus component in an amount such that the
manganese/phosphorus weight ratio is 2.0 or below.
14. The process of claim 11, wherein the solidification zone in
step (b) comprises a heating zone having a length of 200 to 700 mm
and is maintained at a temperature of 300 to 400.degree. C., and a
cooling zone disposed just below the heating zone.
15. A polyethylene naphthalate fiber obtained by the process
according to claim 11, wherein the polyethylene naphthalate fiber
has (1) an intrinsic viscosity of 0.6 to 0.9, (2) a tenacity of at
least 8.5 g/d, (3) an elongation of at least 6%, (4) a
birefringence of at least 0.35, (5) a density of 1.355 to 1.375,
and (5) a shrinkage of 1 to 4%.
Description
TECHNICAL FIELD
[0001] The present invention relates to a high strength
polyethylene-2,6-naphthalate fiber produced by a method comprising
controlling the stress-strain curve and fine structure of an
undrawn yarn such that the drawability of the undrawn yarn in a
drawing step is improved. The industrial yarn produced by the
present invention provides a treated cord having improved
dimensional stability and high strength.
[0002] Moreover, the present invention provides a dipped cord for
tire cords, which is characterized by having the following physical
properties and by showing a stress-strain curve wherein the undrawn
yarn is elongated by less than 2% and has an initial modulus of
50-250 g/d, when subjected to an initial stress of 1.0 g/d, and it
is elongated by at most 15% when subjected to a stress greater than
the initial stress but smaller than 6.0 g/d: (1) a tenacity of at
least 6.5 g/d, (2) an elongation of at least 6%, (3) an adhesion
with rubber of at least 10 kg, (4) a fatigue resistance of at least
90%, and (5) 2,000-8,000 denier.
[0003] Furthermore, the present invention provides a high
performance radial tire whose carcass ply contains this dipped
cord.
BACKGROUND ART
[0004] Polyethylene-2,6-naphthalates have higher glass transition
temperature, crystallization temperature, melting temperature and
melting viscosity, than polyethylene terephthalates, due to their
bulky naphthalate units. Thus, to enhance their spinnability upon
spinning, i.e., to reduce the melting viscosity of their melt upon
spinning, they have been spun at a temperature higher than the
spinning temperature (310 to 320.degree. C.) of polyethylene
terephthalates.
[0005] However, since the spinning at high temperature causes the
thermal decomposition of the melt, resulting in a deterioration in
drawing workability of the melt and a significant reduction in
intrinsic viscosity of the melt, it is difficult to produce a high
strength yarn from polyethylene-2,6-naphthalate (see, Japanese
patent laid-open publication Nos. Sho 72-35318, 73-64222 and
75-16739).
[0006] Japanese Patent No. 2945130 describes a method of producing
polyethylene-2,6-naphthalate fibers with high strength and modulus
by controlling the spinning speed and spinning draft ratio and
changing the drawing temperature, instead of increasing the
spinning temperature. In this method, however, it is difficult to
achieve uniform spinning, and also it is difficult to perform
normal drawing because the temperature of first-stage drawing is
higher than 150.degree. C. and thus yarn width is increased.
[0007] It is generally well known in the production field of
industrial polyethylene-2,6-naphthalate yarns that at high
intrinsic viscosity (I.V.), preferably an intrinsic viscosity
(I.V.) of 0.8-1.2, and a low spinning speed of 200-1,000 m/sec, the
improvement of tenacity of yarns resulting from high drawing ratio
can be achieved only when the uniformity in fineness and
orientation between undrawn yarn filaments is increased.
[0008] In a theoretical consideration on this fact, the tenacity of
a final drawn yarn can be increased only when spinning tensile is
increased in the production of an industrial polyester yarn, such
that orientation of an undrawn yarn and formation of tie chains
connecting crystals with each other. To obtain a drawn yarn having
a more increased tenacity, it is necessary to ensure the fine
structure of an undrawn yarn which can be drawn at high draw
ratio.
DISCLOSURE OF INVENTION
[0009] From this viewpoint, the present invention comprises
controlling the stress-strain curve and fine structure of an
undrawn yarn such that the drawability of the undrawn yarn in a
drawing step can be increased.
[0010] Therefore, the present invention relates to a high strength
polyethylene naphthalate fiber produced by a method comprising
controlling the stress-strain curve and fine structure of an
undrawn yarn to increase the drawability of the undrawn yarn in a
drawing step, and an object of the present invention is to provide
a high strength polyethylene-2,6-naphthalate fiber with excellent
physical properties, which is produced by a method wherein the
drawability of an undrawn yarn in a drawing step is maximized by
withdrawing the undrawn yarn in such a speed that the undrawn yarn
has a birefringence of 0.001-0.015 and shows a stress-strain curve
wherein the undrawn yarn is elongated by less than 10% and has an
initial modulus of 10-50 g/d, when subjected to an initial stress
of 0.3 g/d, and it is elongated by at least 200%, when subjected to
a stress greater than the initial stress but smaller than 1.0
g/d.
[0011] Another object of the present invention is to provide a high
strength polyethylene naphthalate fiber useful for the production
of tire cords having excellent dimensional stability and high
strength.
[0012] The present invention provides a producing method of an
industrial polyethylene-2,6-naphthalate multifilament fiber, which
comprises the steps of: (A) extruding a polymer at a temperature of
290-330.degree. C. to form a molten spun yarn, the polymer
containing more than 85 mol % of ethylene terephthalate units and
having an intrinsic viscosity of 0.80-1.2; (B) passing the molten
spun yarn through a retarded cooling zone and then quenching and
solidifying the spun yarn; (C) withdrawing the solidified yarn in
such a speed that the undrawn yarn has a birefringence of
0.001-0.015 and shows a stress-strain curve wherein the undrawn
yarn is elongated by less than 10% and has an initial modulus of
10-50 g/d, when subjected to an initial stress of 0.3 g/d, and it
is elongated by at least 200% subjected to a stress greater than
the initial stress but smaller than 1.0 g/d; (D) subjecting the
withdrawn yarn to multi-stage drawing at a total draw ratio of
4.0.
[0013] The polyethylene-2,6-naphthalate polymer which is used in
the present invention contains at least 85 mol % of
ethylene-2,6-naphthalate units. Preferably, the
polyethylene-2,6-naphthalate polymer is composed essentially of
polyethylene-2,6-naphthalate units.
[0014] Alternatively, the polyethylene-2,6-naphthalate may
incorporate, as copolymer units, minor amounts of units derived
from one or more ester-forming ingredients other than ethylene
glycol and 2,6-naphthalene dicarboxylic acid or its derivatives.
Examples of other ester-forming ingredients which may be
copolymerized with the polyethylene terephthalate units include
glycols such as 1,3-propanediol, 1,4-butanediol and 1,6-hexanediol,
etc., and dicarboxylic acids such as terephthalic acid, isophthalic
acid, hexahydroterephthalic acid, stilbene dicarboxylic acid,
bibenzoic acid, adipic acid, sebacic acid and azelaic acid,
etc.
[0015] The polyethylene naphthalate chip which is used in the
present invention may be preferably prepared by melt-mixing
naphthalene-2,6-dimethylcarboxylate (NDC) with ethylene glycol in a
weight ratio ranging from 1.6 to 2.3 at 190.degree. C., and
subjecting the molten mixture to transesterification at
190-240.degree. C. for about 2-3 hours and polycondensation at
280-300.degree. C. for about 2-3 hours to form a raw chip having an
intrinsic viscosity of about 0.42-0.70, and then subjecting the raw
chip to solid state polymerization at a temperature of
225-260.degree. C. in vacuum in such a manner as to have an
intrinsic viscosity of 0.80-1.20 and a moisture content of less
than 30 ppm.
[0016] In the transesterification, the ester-interchange catalyst,
such as manganese acetate, calcium acetate, magnesium acetate,
cobaltous acetate, and the like, may be added as a catalyst in such
an amount that the amount of manganese metal remaining in the final
polymer is in the range of 30 to 70 ppm. When the amount of the
remaining manganese metal is less than 30 ppm, the reaction rate
becomes too slow, while if the amount is more than 70 ppm, the
excessive amount of manganese metal acts as a foreign substance to
induces undesirable effects in solid state polymerization and
spinning.
[0017] In the polycondensation, the polymerization catalyst, such
as antimony acetate, antimony trioxide, titanium alkoxides,
germanium dioxide, stannous alkoxides, and the like, may be added
as a polymerization catalyst in such an amount that the amount of
antimony metal remaining in the final polymer is in the range of
150 to 300 ppm. When the amount of the remaining antimony metal is
less than 150 ppm, the polymerization rate becomes slow to cause in
a reduction in polymerization efficiency, while if the amount is
more than 300 ppm, the excessive amount of antimony metal acts as a
foreign substance to induce undesirable problems during spinning
and drawing. In addition, a phosphorus-based thermal stabilizer,
like phosphorous compound, such as phosphoric acid, trimethyl
phosphate, triethyl phosphate, trinonyl phosphate, trimethyl
phosphonoacetate, and the like, may be added in such an amount that
the amount of phosphorus element remaining in the final polymer is
in the range of 35 to 45 ppm, and that the manganese/phosphorus
content ratio is less than 2.0. If the manganese/phosphorus content
ratio is more than 2.0, excessive oxidation occurs during solid
state polymerization, giving a spun yarn having poor
properties.
[0018] The polyethylene naphthalate chip thus obtained is spun into
a fiber according to the method of the present invention. FIG. 1
schematically shows a producing process of a polyethylene
naphthalate fiber according to one preferred embodiment of the
present invention.
[0019] In the step (A) of the inventive method for the production
of the polyethylene naphthalate fiber, the polyethylene naphthalate
chip is melt-spun through a pack 1 and nozzles 2 at a spinning
draft ratio (the linear velocity on a first withdrawing roller/the
linear velocity in the nozzles) of 20-200 at a relatively low
temperature of 290-320.degree. C. in order to prevent its viscosity
decrease caused by thermal decomposition and hydrolysis. If the
spinning draft ratio is below 20, the uniformity of the filament
cross-section will be reduced to remarkably deteriorate the drawing
workability of the polymer, whereas if it exceeds 200, filament
breakage occurs during spinning, making it difficult to produce a
normal yarn.
[0020] In the step (B), the molten spun yarn 4 formed in the step
(A) is quenched by passing it through a cooling zone 3. If
necessary, a heating unit may be disposed over a section (i.e.,
hood length L) from just below the nozzles 2 to the start point of
the cooling zone 3.
[0021] This section is called the retarded cooling zone or the
heating zone, and has a 300 to 250 mm length and is maintained at a
temperature of 250 to 400.degree. C.
[0022] In the cooling zone 3, a quenching method which is selected
from open quenching, circular closed quenching, radial outflow
quenching and the like depending on a blowing method of cooling air
can be applied. Then, the solidified yarn 4 from the cooling zone 3
may be oiled to 0.5-1.0% by an oil-feeding unit 5.
[0023] In the step (C), the undrawn yarn is withdrawn in such a
speed that the undrawn yarn has a birefringence of 0.001-0.015 and
shows a stress-strain curve wherein, at an initial stress of 0.3
g/d, the undrawn yarn is elongated by less than 10% and has an
initial modulus of 10-50 g/d, and at a stress greater than the
initial stress but smaller than 1.0 g/d, it is elongated by at
least 200%. A preferred speed at which the undrawn yarn is
withdrawn is 200-1,000 min/minute.
[0024] In the present invention, the stress-strain curve and
birefringence of the undrawn yarn are used as factors of
controlling the fine structure of the undrawn yarn.
[0025] Particularly, the present invention is characterized in that
the undrawn yarn shows a stress-strain curve wherein the undrawn
yarn is elongated by less than 10% and has an initial modulus of
10-50 g/d when subjected to an initial stress of 0.3 g/d, and it is
elongated by at least 200% when subjected to a stress greater than
the initial stress but smaller than 1.0 g/d.
[0026] The undrawn yarn having such a stress-strain curve can show
maximized drawability in a subsequent drawing process.
[0027] Moreover, in the present invention, the birefringence of the
undrawn yarn is used as a factor of controlling the fine structure
of the undrawn yarn together with this stress-strain curve.
[0028] Particularly, in the present invention, the stress-strain
curve and birefringence of the undrawn yarn must satisfy the range
as described above such that the excellent drawability of the
undrawn yarn in a drawing process can be ensured. If the
birefringence of the undrawn yarn is lower than 0.001, the
crystallization speed of the undrawn yarn becomes too slow in the
drawing step so that the sufficient formation of tie chains between
crystals cannot be induced. If the birefringence is higher than
0.015, the crystallization speed becomes too fast in the drawing
process to lower the drawability of the undrawn yarn, making it
difficult to produce a high strength yarn.
[0029] In the step (D) of the inventive method, the yarn passed
through the first drawing roller 6 is passed through a series of
drawing rollers 7, 8, 9 and 10 by a multi-stage drawing process so
that it is drawn to a total draw ratio of at least 4.0, and
preferably 4.5-6.5, to form a final drawn yarn 11.
[0030] Making the interval between the nozzle unit and the upper
end of the cooling zone as narrow as possible in spinning is
advantageous in obtaining a final drawn yarn having high strength.
However, either if the interval between the lower end of the nozzle
unit and the lower end of the heating unit is shorter than 50 mm
(substantially 100 mm since about 50 mm-long spinning block is
disposed just below the nozzle unit and a 50 mm-long heating unit
is used), or the interval between the lower end of the heating unit
and the upper end of the cooling unit is out of a range of 50 to
150 mm, a significant non-uniformity in the undrawn yarn will occur
to make it impossible to obtain a drawn yarn having sufficient
physical properties.
[0031] The drawn polyethylene naphthalate fiber produced by the
inventive method has an intrinsic viscosity of 0.60-0.90, a
tenacity of at least 8.5 g/d, an elongation of at least 6.0%, a
birefringence of at least 0.35, a density of 1.355-1.375, a melting
point of 270-285.degree. C., and a shrinkage of 1-4%.
[0032] In the present invention, the high strength polyethylene
fiber meeting the above-described physical properties is twisted
with a twisting machine to form a raw cord, and then, woven and
dipped in a dipping solution, thereby giving a dipped polyethylene
naphthalate cord.
[0033] Hereinafter, twisting, weaving and dipping processes
according to the present invention will be described in further
detail.
[0034] In a more detailed description of the twisting process of
the present invention, the drawn polyethylene naphthalate yarn
produced by the method as described above is twisted with a direct
twisting machine where false-twist and ply-twist are conducted at
the same time. This gives a raw cord for tire cords. This raw cord
is produced by plying and cabling two strands of the polyethylene
naphthalate yarn for tire cords, in which the plying and cabling
generally have the same twist number, or if necessary, different
twist numbers.
[0035] An important result in the present invention is that the
strength and elongation, elongation at load and fatigue resistance,
etc. of a cord depend on the twist number of the polyethylene
terephthalate yarn. Generally, as the number of twists is
increased, the tenacity of the cord is decreased and the elongation
at load and elongation at break of the cord are increased. The
fatigue resistance of the cord shows a tendency to increase as the
twist number is increased. In the present invention, the
polyethylene naphthalate tire cord is produced to a twist number of
250 (cabling)/250 (plying) TPM to 500 (cabling)/500 (plying) TPM.
The reason why the cabling and plying have the same twist number is
because the resulting tire cord is easily maintained at a linear
shape to exhibit its physical properties at the maximum, without
showing revolutions or twists. If the twist number is smaller than
250/250 TPM, the elongation at break of the raw cord can be
reduced, resulting in a decrease in its fatigue resistance, whereas
if the twist number is higher than 500/500 TPM, a great reduction
in tenacity of the raw cord will occur, making it unsuitable for
tire cords.
[0036] In the present invention, the cabling and plying may also be
performed to different twist numbers, if necessary. In this case, a
raw cord is produced in such a manner that the cabling is performed
to a twist number of 350-500 TPM, and the plying, at 300-500 TMP.
The reason why the cabling and plying are performed to different
twist numbers is because, within a range of physical properties,
the lower the twist number, the lower the twisting costs, resulting
in economic advantages. As a constant of evaluating such a twist,
there is proposed a twist constant in the relevant field of the
art.
[0037] The raw cord produced is woven with a weaving machine, and
the resulting woven fabric is dipped in a dipping solution and
cured. This gives a dipped cord for tire cords having a resin layer
attached to the surface of the raw cord.
[0038] In a more detailed description of the dipping process of the
present invention, dipping is accomplished by impregnating the
surface of the fiber with a resin layer, called
resorcinol-formaline-latex (RFL). This dipping is carried out in
order to overcome the intrinsic shortcoming of the insufficient
adhesion to rubber of a fiber for tire cords. A conventional rayon
fiber or nylon is subjected to a one-bath dipping, but in the case
of a PET fiber, its surface is first activated and then treated
with adhesives (two-bath dipping), since the reactive groups of the
PET fiber are smaller than the rayon or nylon fiber. The
polyethylene naphthalate yarn is subjected to the two-bath dipping
using a dipping bath known for tire cords.
[0039] The dipped cord produced by the above method has the
following physical properties, and shows a stress-strain curve
wherein the cord is elongated by less than 2% and has an initial
modulus of 50-250 g/d, when subjected to an initial stress of 1.0
g/d, and it is elongated by at most 15% when subjected to a stress
greater than the initial stress but lower than 6.0 g/d: (1) a
tenacity of at least 6.5 g/d, (2) an elongation of at least 6%, (3)
an adhesion with rubber of at least 10 kg, (4) a fatigue resistance
of at least 90%, (5) a total denier of 2,000-8,000, (6) a twist
constant of 0.50-0.85, and (7) E.sup.2.25 (elongation at 2.25
g/dl)+FS (free shrinkage) of less than 5.5%.
[0040] In another aspect, the present invention provides a
pneumatic radial tire having improved dimensional stability and
fatigue resistance and an aspect ratio of less than 0.65, in which
a carcass ply of the tire comprises the dipped cord produced by the
method as described above and having excellent physical properties
at high temperature, improved dimensional stability and high
strength, the dipped cord showing a stress-strain curve wherein the
cord is elongated by less than 2% and has an initial modulus of
50-250 g/d when subjected to an initial stress of 1.0 g/d, and is
elongated by at most 15% when subjected to a stress greater than
the initial stress but lower than 6.0 g/d.
[0041] Particularly, according to the present invention, the dipped
polyethylene naphthalate cord which is used in the carcass ply must
have an elongation of less than 2% at a stress of less than 1.0
g/d. If the elongation is higher than 2%, a remarkable reduction in
handing stability resulting from the severe deformation of the
carcass layer will be caused. Furthermore, the dipped cord
according to the present invention must show a stress-strain curve
wherein the dipped cord is elongated by at most 15% when subjected
to a stress greater than 1.0 g/d but smaller than 6.0 g/d. If this
elongation is higher than 15%, the deformation of the carcass will
be easily caused, leading to a reduction in inner pressure
resistance of the carcass as a pressure container.
[0042] Concretely, a tire as shown in FIG. 3 is produced. More
concretely, a carcass cord 13 made of the dipped polyethylene
naphthalate cord produced by the present invention has a total
denier of 2,000 d-8,000 d. A carcass ply 12 comprises at least one
layer of the tire cord 13 for carcass ply reinforcement. The
reinforcement density of the dipped cord in the carcass ply is
preferably 15-35 EPI. If the reinforcement density is lower than 15
EPI, the mechanical properties of the carcass ply will be lowered
rapidly, whereas if it exceeds 35 EPI, disadvantages with respect
to economic efficiency will be caused.
[0043] The carcass ply 12 with a ply turn-up 14 comprises carcass
cords, preferably in one or two layers. The carcass cord 13 for
reinforcement is oriented at an angle of 85-90.degree. with respect
to the circumferential direction of a tire 11. In the shown
embodiment, the reinforcing carcass cord 13 is oriented at an angle
of 90.degree. with respect to the circumferential direction of the
tire. The ply turn-up 14 preferably has a width of about 40-80%
relative to the maximum section width of the tire. If the ply
turn-up has a width of less than 40% relative to the maximum
section width, its effect of supplementing the rigidity of tire
sidewalls will be excessively reduced, whereas if is higher than
80%, an excessive increase in rigidity of the tire sidewalls will
be caused, resulting in an adverse effect on ride comfort.
[0044] Hereinafter, the tire shown in FIG. 3 will be described in
more detail.
[0045] A bead region 15 of the tire 11 has a non-expandable annular
bead core 16. This bead core is preferably made of a continuously
wound single-filament steel wire. In a preferred embodiment, a
high-strength steel wire with a diameter of 0.95-1.00 mm is formed
into a 4.times.4 structure or a 4.times.5 structure.
[0046] In a preferred embodiment of the present invention, the bead
region has a bead filler 17. The bead filler needs to have a
hardness higher than a certain level, and preferably a shore A
hardness of 40.
[0047] In the present invention, the tire 11 is reinforced with a
structure of a belt 18 and a cap ply 19 at its crown portion. The
belt structure 18 comprises two cut belt plies 20. A cord 21 of the
belt plies 20 is oriented at about 20.degree. with respect to the
circumferential direction of the tire. The cord 21 of the belt
plies is disposed in the opposite direction to a cord 22 of another
ply. However, the belt 18 may comprise an optional number of plies,
and preferably can be disposed at an angle range of 16-24.degree..
The belt 18 acts to provide lateral rigidity so as to minimize the
rising of a tread 23 from the road surface during the running of
the tire. The cords 21 and 22 of the belt 18 are made of steel
cords in a 2+2 structure, but may also have other structures. The
upper portion of the belt 18 is reinforced with a cap ply 21 and an
edge ply 24. A cap ply cord 25 within the cap ply 19 is disposed in
the parallel direction to the circumferential direction of the tire
and serves to inhibit a change in size by high-speed running of the
tire. Also the cap ply cord 25 is made of a material having high
shrinkage stress at high temperature. Although one layer of the cap
ply 19 and one layer of the edge ply 21 may be used, one or two
layer of the cap ply and one or two layers of the edge ply are
preferably used.
[0048] Moreover, the drawn yarn produced by the present invention
can be converted into a treated cord by a conventional method.
[0049] For example, two strands of the drawn yarn with a 1,500
denier are plied and cabled to 390 TPM (the standard twist number
of a general polyethylene-2,6-naphthalate treated cord) to form a
cord yarn. Then, the cord yarn is dipped with adhesive solution
(isocynate+epoxy or PCP resin+REL (resorcinol-formaline-latex)) in
a first dipping tank, and then, dried and stretched in a drying
zone at a temperature of 130-180.degree. C. for 150-200 seconds at
a stretch ratio of 1.0-4.0%. Then, the dried cord is stretched and
heat-set in a hot stretching zone at a temperature of
200-245.degree. C. for 45-80 seconds at a stretch ratio of 0-6.0%.
Next, the resulting cord is dipped with adhesive solution (RFL) in
a second dipping tank, followed by drying at a temperature of
120-180.degree. C. for 90-120 seconds. The dried cord is heat-set
at a temperature of 200-245.degree. C. and a stretch ratio of -4.0
to 4.0%, thereby producing a dipped cord.
[0050] The treated cord (1500 denier, two strands twisted to 390
TPM) has a good dimensional stability, represented by the sum of
E.sup.2.25 (elongation at 2.25 g/d load) and FS (free shrinkage)
being less than 5.5%, and a tenacity of at least 6.8 g/d.
[0051] As described above, the treated cord produced using the
polyethylene-2,6-naphthalate fiber with high modulus and low
shrinkage has improved dimensional stability and high strength, and
thus, can be advantageously employed as a fibrous reinforcement
material of rubber products such as tires and industrial belts, and
other industrial applications.
BRIEF DESCRIPTION OF DRAWINGS
[0052] FIG. 1 schematically illustrates a process for the
production of a polyethylene-2,6-naphthalate fiber according to the
present;
[0053] FIG. 2 shows a stress-strain curve of an undrawn yarn formed
in the present invention; and
[0054] FIG. 3 schematically shows the structure of an automobile
tire comprising high strength polyethylene naphthalate dipped tire
according to the present invention.
[0055] TABLE-US-00001 11: tire 12: carcass layer 13: carcass
layer-reinforcing cord 14: ply turn-up 15: bead region 16: bead
core 17: bead filler 18: belt structure 19: cap ply 20: belt ply
21, 22: belt cord 23: tread 24: edge ply 25: cap ply cord
BEST MODE FOR CARRYING OUT THE INVENTION
[0056] The following Examples are given for the purpose of
illustration only, and are not intended to limit the scope of the
invention. In the Examples and Comparative Examples, the
characteristics of the yarns and treated cords produced were
evaluated in accordance with the following methods.
[0057] (1) Intrinsic Viscosity (I.V.)
[0058] 0.1 g of a sample was dissolved in a mixture of phenol and
1,1,2,3-tetrachloroethane (60/40 by weight) to a concentration of
0.4 g/100 ml. The solution was put in Ubbelohde viscometer and kept
in a 30.degree. C. water bath for 10 minutes. The flow time of the
solution as well as that of the solvent were measured and RV and IV
values were calculated based on the following formulae: R.V.=flow
time of the solution/flow time of the solvent (1)
I.V.=1/4.times.(R.V.-1)/C+3/4.times.(ln R.V./C) (2)
[0059] Wherein, C is the sample concentration (g/100 ml).
[0060] (2) Tenacity and Elongation
[0061] The tenacity and elongation of a sample was determined in
accordance with ASTMD 885 at a sample length of 250 mm, a tensile
speed of 300 mm/min. and 20 turns/m under a standard atmosphere
(20.degree. C., 65% relative humidity), using Instron 5565 (Instron
Co., Ltd, USA).
[0062] (3) Density
[0063] The density (.rho.) of a sample was determined using a
xylene/carbon tetrachloride density gradient column at 23.degree.
C. The gradient column was prepared and calibrated according to
ASTM D 1505 at a density range of 1.34 to 1.41 g/cm.sup.3.
[0064] (4) Shrinkage
[0065] A sample was kept under a standard atmosphere (20.degree.
C., 65% relative humidity) for 24 hours and then its length
(L.sub.0) at 0.1 g/d load was measured. Alternatively, a sample was
kept in a dry oven of 150.degree. C. under a non-tension condition
for 30 minutes and left outdoors for 4 hours, and then its length
(L) at 0.1 g/d load was measured. Shrinkage (%) was calculated form
the following formula: .DELTA.S=(L.sub.0-L)/L.sub.0.times.100
(3)
[0066] (5) Elongation at Specific Load
[0067] As an elongation at specific load, the elongation at 4.5 g/d
load was measured on the S-S tenacity and elongation curve for and
original yarn sample, and the elongation at 2.25 g/d load, for a
treated cord sample.
[0068] (6) Dimensional Stability
[0069] The dimensional stability (%) of a treated cord, which is
related to the tire sidewall indentations (SWI) and tire handling
properties, is determined by the modulus at a given shrinkage, and
the sum E.sub.2.25 (elongation at 2.25 g/d load)+FS (free
shrinkage) is a good indicator of the dimensional stability for a
treated cord processed under a particular heat-treatment condition,
and the lower the sum, the better the dimensional stability.
[0070] (7) Birefringence
[0071] The birefringence of a sample was determined using a
polarizing light microscope equipped with a Berek compensator.
[0072] (8) Melting Point
[0073] A sample was powdered, and 2 mg of the sample powder was put
in a pan and sealed. Then, the sample was heated at a rate of
20.degree. C. per 1 minute from room temperature to 290.degree. C.
using Perkin-Elmer DSC under a nitrogen atmosphere and the
temperature at the maximum heat-absorption peak was set as the
melting point.
[0074] (9) Fatigue Resistance
[0075] Samples were subjected a fatigue test using a Goodrich disc
fatigue tester which is conventionally used for the fatigue test
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%
compression. After the fatigue test, the samples were dipped 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 using a conventional tensile
strength tester by the above-described measurement method (2),
after drying at 107.degree. C. for 2 hours.
[0076] (10) Adhesion
[0077] In order to measure initial adhesion to the rubber of a
dipped hybrid cord, a H-test was carried out. In the H-test, a both
ends of the dipped cord were impregnated into 9.5 mm rubber lumps,
the interval between the rubber lumps was maintained at 9 mm, and
the rubber lumps were pulled while measuring the maximum load at
which the separation of the cord from the rubber occurs, thereby
evaluating adhesion. Before evaluating the adhesion, samples were
vulcanized at 160.degree. C. for 20 minutes under a pressure 25
kg/cm.sup.2 to impart sufficient strength to the rubber. The rubber
used in the test had the following composition: 100 parts of
natural rubber, 3 parts of zinc oxide, 28.9 parts of carbon black,
2 parts of stearic acid, 7.0 parts of pine tar, 1.25 parts of MBTS,
3 parts of sulfur, 0.15 parts of diphenyl guanidine, and 1.0 part
of phenyl-beta-naphthylamine.
EXAMPLE 1
[0078] Solid state polymerization was conducted to produce a
polyethylene naphthalate chip having a manganese content of 40 ppm,
an antimony content of 220 ppm, an intrinsic viscosity (I.V.) of
0.95, a manganese/phosphorus content ratio of 1.8, and a moisture
content of 20 ppm. The produced chip was melt-spun by passing it
through an extender at 305.degree. C. at a discharge rate of 620
g/min and a spinning draft ratio of 40. At this time, the polymer
being melt-spun was mixed uniformly in a polymer transporting pipe
using a static mixer composed of three units. Then, the spun yarn
was solidified by passing successively it through a 40 cm-long
heating zone of a 370.degree. C. atmosphere temperature located
just below the nozzles, and a 500 mm-long cooling zone in which a
cooling air of 20.degree. C. was blown at a rate of 0.5 m/sec. The
solidified yarn was oiled and withdrawn at a rate of 380 m/min to
form an undrawn yarn, which was predrawn to the extent of 5%, and
then, drawn in two stages. The first stage drawing was performed at
a draw ratio of 6.0 at 168.degree. C., and the second stage
drawing, at a draw ratio of 1.1 at 173.degree. C. Then, the drawn
yarn was heat-set at 230.degree. C., relaxed to 2% and wound to
form a 1,500 denier final drawn yarn.
[0079] Two strands of the drawn yarn thus obtained was plied and
cabled to 390 turns/m to produce a cord yarn. The cord yarn was
dipped with an adhesive solution (PCR resin+RFL) in a dipping tank,
dried and stretched at 170.degree. C. for 150 seconds at a stretch
ratio of 4.0% in a cooling zone, heat-set and stretched at
220.degree. C. for 150 seconds in a hot stretching zone, dipped in
RFL, dried at a temperature of 170.degree. C. for 100 seconds, and
then, heat-set at 240.degree. C. for 40 seconds at a stretch ratio
of -1.0%, to give a treated cord.
[0080] The properties of the drawn yarn and the treated cord thus
obtained were measured and the results are given in Table 2.
EXAMPLE 2.about.4 AND COMPARATIVE EXAMPLE 1.about.4
[0081] Various drawn yarns and treated cords were produced in the
same manner as in Example 1 except that the intrinsic viscosity of
the chip, manganese/phosphorus content ratio, spinning temperature,
length or temperature of the heating zone, or birefringence of the
undrawn yarn was changed as given in Table 1.
[0082] The properties of the drawn yarn and the treated cord thus
obtained were measured and the results are given in Table 2.
TABLE-US-00002 TABLE 1 Undrawn yarn Heating zone Elongation at
Elongation at load Chip Mn/P Wt. Spin. temp. Length Temp. initial
load of 0.5 g/d after Item I.V. ratio (.degree. C.) Fineness (cm)
(.degree. C.) Birefringence of 0.3 g/d (%) 25% of elongation Ex. 1
0.93 1.8 316 6.0 40 370 0.007 5.0 220 Ex. 2 0.93 1.7 315 6.0 30 370
0.008 6.1 230 Ex. 3 0.93 1.7 315 6.0 30 390 0.010 7.2 235 Ex. 4
0.93 1.7 315 6.0 45 390 0.008 6.7 237 Comp. 0.91 1.7 315 6.0 45 310
0.012 11.2 187 Ex. 1 Comp. 1.02 1.7 320 6.0 45 370 0.015 11.5 178
Ex. 2 Comp. 0.93 1.7 315 6.0 60 410 0.005 12.6 176 Ex. 3 Comp. 0.93
2.1 315 6.0 45 410 0.008 13.1 161 Ex. 4
[0083] TABLE-US-00003 TABLE 2 Drawn yarn Treated cord Tenac- Mid-
Shrink- Tenac- Mid- Shrink- Fatigue Adhesion Birefrin- ity elong.
Elong. age ity Elong. age E2.25 + resistance With rubber Item I.V.
gence Density (g/d) (%) (%) (%) (g/d) (%) (*) FS (%) (%) (kg)
Remark Ex. 1 0.78 0.452 1.360 9.7 3.0 9.5 1.9 7.1 2.3 2.0 4.3 93
13.4 Ex. 2 0.77 0.453 1.357 9.6 2.8 9.5 2.2 6.8 2.2 12.2 4.4 92
14.4 Ex. 3 0.77 0.454 1.360 9.7 2.7 9.5 2.2 6.9 2.2 2.3 4.5 94 13.9
Ex. 4 0.77 0.454 1.363 10.0 2.9 9.5 2.2 7.1 2.2 2.2 4.4 94 13.9
Comp 0.74 0.444 1.357 8.3 2.9 9.1 2.1 6.0 2.2 2.2 4.4 79 10.7 Ex. 1
Comp 0.81 0.455 1.365 9.2 3.2 8.8 2.2 Ex. 2 Comp. 0.77 0.450 1.360
9.3 2.9 9.5 2.2 6.6 2.2 2.2 4.4 77 10.3 Ex. 3 Comp 0.75 0.446 1.360
8.4 3.0 9.3 2.1 6.2 2.2 2.2 4.4 74 11.7 .box-solid. Ex. 4
.box-solid.: Poor appearance, : Very poor appearance and it was
impossible to prepare treated cord
EXAMPLE 5
[0084] In this example, a radial tire was manufactured using the
dipped polyethylene naphthalate cord produced by Example 4. This
radial tire had a carcass layer which has a ply turn-up extending
radially outward therefrom and comprises one or two layers of the
dipped polyethylene naphthalate cord produced by Example 4. This
carcass cord had a specification give in Table 3 below, and was
oriented at an angle of 90.degree. with respect to the
circumferential direction of the tire. The ply turn-up 14 had a
height of 40-80% relative to the maximum section height of the
tire. The bead portion 15 had the bead core 16 made of a high
strength steel wire with a 0.95-1.00 mm diameter in a 4.times.4
configuration, and the bead filler 17 with a shore A hardness of
more than 40. The upper portion of the belt 18 was reinforced with
a belt-reinforcing layer consisting of one layer of the cap ply 19
and one layer of the edge ply 24. A cap ply cord in the cap ply 19
was disposed parallel to the circumferential direction of the tire.
TABLE-US-00004 TABLE 3 Ex. 5 Comp. Ex. 5 Comp. Ex. 6 Carcass
Material PEN PET Rayon Specification 1500d/2 1500d/2 1650d/3
(d/twist yarn) EPI (ends/in) 24 25 25 Strength (kg) 23 22 26
Elastic 90 75 60 coefficient (g/d) Cap ply Material Nylon Nylon
Nylon Specification 1260d/2 1260d/2 1260d/2 (d/twist yarn) Strength
(kg) 24 24 35 Elastic 30 30 30 coefficient (g/d) Tire Aspect ratio
0.60 0.60 0.60 Number of 1 1 1 car cass layers Number of cap 1 1 1
ply layers
COMPARATIVE EXAMPLE 5-6
[0085] Tire was produced in the same manner as in Example 5 except
that material and specification of cord for tire was changed as
given in Table 3.
[0086] 235/45 R17 Y tires manufactured in Example 5 and Comparative
Examples 5 and 6 were mounted on 2000 cc cars and ran at 60 km/h,
while noise occurring in the cars was measured and noise in the
audio frequency range was expressed in dB. Handling stability and
ride comfort were rated at intervals of 5 points of 100 by skilled
drivers after running a predetermined course, and the results are
given in Table 4 below. Furthermore, the endurance of the tires was
measured according to a P-metric tire endurance test by running the
tires at 38.+-.3.degree. C., and 85%, 90% and 100% of a load marked
on tires, and a speed of 80 km/h, for 34 hours. In this endurance
measurement, if bead separation, cord cutting, belt separation and
the like could not found in any of portions, including treads,
sidewalls, carcass cords, inner liners, and beads, etc., the tire
was evaluated as "OK" TABLE-US-00005 TABLE 4 Item Ex. 5 Comp. Ex. 5
Comp. Ex. 6 Weight of 9.85 9.98 10.12 tire (kg) Ride comfort 100 90
95 Handling 100 95 95 stability Endurance OK OK OK Uniformity 100
95 97 Noise (dB) 61.4 64.5 63.2
[0087] From the test results in Table 4, it can be found that the
inventive tire (Example 5) has a lower weight than the tires of
Comparative Examples 5 and 6 having a PET or rayon cord at their
carcass, such that its rotation resistance can be reduced.
Moreover, it can be found that the inventive tire whose carcass
comprises the PEN cord produced by the present invention has
excellent ride comfort and handling stability, reduced noise, and
improved uniformity.
INDUSTRIAL APPLICABILITY
[0088] The present invention allows the production of the high
strength polyethylene naphthalate fiber by controlling the
stress-strain curve and fine structure of the undrawn yarn and thus
improving the drawability of the undrawn yarn in the drawing step.
The treated cord produced using this fiber has improved dimensional
stability and high strength, such that it can be advantageously
employed as a fibrous reinforcement material of rubber products
such as tires and industrial belts, and other industrial
applications.
[0089] According to the present invention, the high strength PEN
cord of the present invention is applied in a carcass layer of high
performance radial tires, and thus, satisfactory results with
respect to the endurance, ride comfort and handling stability of
tires can be obtained.
[0090] In addition, according to the present invention, the high
strength PEN fiber is applied, making it possible to reduce the
weight of tires.
[0091] While the present invention have been described in detail
with respect to the preferred embodiment, it is obvious to a person
skilled in the art that various changes and modifications can be
made therein without departing from the spirit and scope of the
present invention, and such changes and modifications should be
limited only by the scope of the appended claims.
* * * * *