U.S. patent application number 09/362377 was filed with the patent office on 2001-11-15 for polyester multifilamentary yarn for tire cords, dipped cord and production thereof.
Invention is credited to KIM, GI WOONG, KIM, SUNG JOONG, LEE, SEUNG OH.
Application Number | 20010039988 09/362377 |
Document ID | / |
Family ID | 23425872 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010039988 |
Kind Code |
A1 |
KIM, SUNG JOONG ; et
al. |
November 15, 2001 |
POLYESTER MULTIFILAMENTARY YARN FOR TIRE CORDS, DIPPED CORD AND
PRODUCTION THEREOF
Abstract
Disclosed are polyester multi-filamentary yarn useful as a
reinforcement for tires and a dipped cord formed therefrom. The
polyester multi-filamentary yarn comprises at least 90 mol % of
polyethylene terephthalate and has an intrinsic viscosity of
0.70.about.1.2 and a tenacity of 5.5.about.8.5 g/d with an
intermediate elongation difference (E1-E0) between intermediate
elongations E0 and E1 amounting to 6% or greater. The polyester
dipped cord is produced by subjecting at least two strands of
polyester multi-filamentary yarn to first twisting and second
twisting, the polyester multi-filamentary yarn comprising 90 mole %
of polyethylene terephthalate; forming the strands into a fabric;
and treating the fabric with blocked isocyanate and resorcinol
formaldehyde latex (RFL), wherein the cord satisfies the following
characteristics: a) a tenacity of 5.0 g/d or greater, b) a
dimensional stability index (E.sub.4.5+SR) of less than 7.0%, c) a
breaking elongation of 9% or greater, and d) an intermediate
elongation difference (E1-E0) of 3% or less. Showing a harmony of
high elastic modulus and low shrinkage, the filamentary yarn and
dipped cords are superior in dimensional stability and fatigue
resistance, so they can be used as reinforcements for rubber
composites such as tires.
Inventors: |
KIM, SUNG JOONG;
(KYUNGSANGBUK-DO, KR) ; KIM, GI WOONG;
(KYUNGSANGBUK-DO, KR) ; LEE, SEUNG OH;
(KYUNGSANGBUK-DO, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
23425872 |
Appl. No.: |
09/362377 |
Filed: |
July 28, 1999 |
Current U.S.
Class: |
152/556 ;
428/364; 428/375 |
Current CPC
Class: |
Y10T 428/2969 20150115;
Y10T 428/2933 20150115; D02G 3/02 20130101; D02G 3/48 20130101;
B60C 9/0042 20130101; Y10T 428/2913 20150115 |
Class at
Publication: |
152/556 ;
428/364; 428/375 |
International
Class: |
D02G 003/00; B60C
009/00 |
Claims
What is claimed is:
1. A process for producing polyester filamentary yarn for tire
cords from a polyester resin, comprising the steps of: melting at a
temperature of 290.degree. C. or below a polyester resin comprising
at least 90 mol % of polyethylene terephthalate with an intrinsic
viscosity of 0.7.about.1.2: filtering the molten resin for a
filtering retention time of 10 min or below; spinning the filtered,
molten resin by extrusion through a nozzle which has 250.about.500
holes, each ranging, in diameter, from 0.5 to 1.2 mm with a
length/diameter ratio from 2 to 5; primarily quenching the extruded
yarn at a temperature of 100.about.195.degree. C. in a zone of 50
mm or more distance directly below the nozzle; secondarily
quenching the yarn with quench air at its glass transition
temperature (Tg) or below; taking off the yarn at a spinning stress
of 0.3 g/d or greater; drawing the taken-off yarn at a total draw
ratio of 1.3 or greater; and thermally treating the yarn at a
temperature of 150.about.230.degree. C.
2. A process as set forth in claim 1, wherein the polyester resin
has an intrinsic viscosity of 0.7.about.0.9.
3. A process as set forth in claim 1, wherein the polyester resin
is melted at a temperature less than 288.degree. C.
4. A process as set forth in claim 3, wherein the polyester resin
is melted at a temperature of 285.about.288.degree. C.
5. A process as set forth in claim 1, wherein the spinning step is
conducted in the manner of 2 Cop winding after 4 ends spinning and
the nozzle contains 120.about.250 holes per one end.
6. A process as set forth in claim 1, wherein the spinning step is
conducted in the manner of 2 Cop winding after 2 ends spinning and
the nozzle contains 250.about.400 holes per one end.
7. A process as set forth in claim 1, wherein each of the holes
ranges, in diameter, from 0.8 to 1.0 mm and, in length/diameter,
from 3 to 5.
8. A process as set forth in claim 1, wherein the primarily
quenching step is conducted in a quenching zone extending from a 50
mm-distant point to a 250 mm-distant point from the nozzle.
9. A process as set forth in claim 8, wherein the primarily
quenching step is conducted in a quenching zone extending from a 50
mm-distant point to a 150 mm-distant point from the nozzle.
10. A process as set forth in claim 1, wherein the primarily
quenching step is conducted at a temperature of
100.about.180.degree. C.
11. A process as set forth in claim 10, wherein the primarily
quenching step is conducted at a temperature of
100.about.150.degree. C.
12. A process as set forth in claim 1, wherein the secondarily
quenching air is maintained at a temperature of 40.about.50.degree.
C.
13. A process as set forth in claim 1, wherein the taking off step
is conducted at a spinning stress of 0.5.about.0.9 g/d.
14. A process as set forth in claim 1, wherein the taking off step
is conducted at a winding speed of 2,500 m/min or greater.
15. A process as set forth in claim 14, wherein the taking off step
is conducted at a winding speed of 2,700.about.3,500m/min.
16. A process as set forth in claim 1, wherein the drawing step is
conducted at a drawing temperature of 120.degree. C. or below.
17. A process as set forth in claim 16, wherein the drawing step is
conducted at a drawing temperature of 70.about.120.degree.
18. A process as set forth in claim 1, wherein the thermally
treating step is carried out at a temperature of
150.about.180.degree. C.
19. A process as set forth in claim 1, wherein the thermally
treating step is carried out while relaxation is provided at
quantity of 2% or greater.
20. Polyester filamentary yarn for tire cords, which comprises at
least 90 mol % of polyethylene terephthalate and has an intrinsic
viscosity of 0.70.about.1.2 and a tenacity of 5.5.about.6.5 g/d
with an intermediate elongation difference (E1-E0) between
intermediate elongations E0 and E1 amounting to 6% or greater,
wherein the intermediate elongation E0 is the elongation under a
load of 4.5 g/d and the intermediate elongation E1 is the
elongation under a load of 4.5 g/d after conducting a thermal
treatment at 177.degree. C. for 10 min under a load of 0.01
g/d.
21. Polyester filamentary yarn as set forth in claim 20, wherein
the tenacity ranges from 5.5 to 7.5 g/d.
22. Polyester filamentary yarn as set forth in claim 20, wherein
the intermediate elongation difference E1-E0 is in a range of
6.about.15%.
23. Polyester filamentary yarn as set forth in claim 22, wherein
the intermediate elongation difference E1-E0 is in a range of
6.about.10%.
24. Polyester filamentary yarn as set forth in claim 20, 20 wherein
the yarn has an amorphous orientation function (fa) of 0.65 or
greater.
25. Polyester filamentary yarn as set forth in claim 20, wherein
the yarn has a terminal modulus of 15 g/d or below.
26. A polyester dipped cord, which is produced by subjecting at
least two strands of polyester multi-filamentary yarn to first
twisting and second twisting, said polyester multi-filamentary yarn
comprising 90 mol % of polyethylene terephthalate; forming the
strands into a fabric; and treating the fabric with blocked
isocyanate and resorcinol formaldehyde latex (RFL), wherein the
cord satisfies the following characteristics: a) a tenacity of 5.0
g/d or greater, b) a dimensional stability index (E.sub.4.5 +SR) of
Less than 7.0%, c) a breaking elongation of 9% or greater, and d)
an intermediate elongation difference (E1-0) of 3% or less, wherein
the intermediate elongation E0 is the is elongation under a load of
4.5 g/d and the intermediate elongation E1 is the elongation under
a load of 4.5 g/d after conducting a thermal treatment at
177.degree. C. for 10 min under a load of 0.01 g/d.
27. A polyester dipped cord as set forth in claim 26, wherein the
tenacity ranges from 5.5 to 7.5 g/d.
28. A polyester dipped cord as set forth in claim 26, wherein the
dimensional stability index is in a level of 6% or less.
29. A polyester dipped cord as set forth in claim 28, wherein the
breaking elongation is in a level of 15.about.18%.
30. A polyester dipped cord as set forth in claim 26, wherein the
intermediate elongation difference E1-E0 is in a level of 2% or
less.
31. A polyester dipped cord as set forth in claim 30, the
intermediate elongation difference E1-E0 is in a level of 1% or
less.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an industrial polyester
multifilamentary yarn of high modulus and low shrinkage, as a
reinforcement for tires, and a dipped cord formed therefrom. More
particularly, the present invention relates to a polyester
multifilamentary yarn which retains superior dimensional stability
and fatigue resistance even at high temperatures and a dipped cord
formed therefrom. Also, the present invention is concerned with a
method for producing such a polyester multifilamentary yarn and a
dipped cord.
[0003] 2. Description of the Prior Art
[0004] One of the typical functional uses which fibers have is to
reinforce rubber composites, such as tires. Examples of the fibers
useful as such a reinforcement include nylon, polyester, rayon,
etc. Of them, polyester fibers contain benzene rings in their
molecular structure, exhibiting a rigid property. Accordingly, tire
cords produced from polyester yarns shows high elastic modulus and
few flat spots with superiority in fatigue resistance, creep
resistance and endurance. By virtue of these high physical
properties, polyester is extensively used as a reinforcement for
rubber composites, especially tires.
[0005] In spite of these advantages, conventional polyester tire
cords suffer from a significant disadvantage of reducing the side
wall indentation of monoply radial tires. Also, industrial
polyester yarns are required to improve in dimensional stability in
order to replace the rayon fibers which have been applied for
radial tires. In this regard, recent research has been directed to
the development of polyester fibers which have high strength and
elastic modulus in the same level as that of rayon fibers.
[0006] Techniques for increasing thermal stability in polyester
fibers are found in, for example, U.S. Pat. Nos. 4,101,525 and
4,195,025 (both to Davis et al.) which disclose a polyester tire
cord produced by drawing highly oriented undrawn yarn in a
high-speed spinning process under a steaming condition to give
highly oriented drawn yarn, especially multi-drawn yarn containing
at least 85 mol % of polyethylene terephthalate, which ranges, in
denier per filament, from 1 to 20 and, in work loss at 150.degree.
C., from 0.004 to 0.02 lb.multidot.in, and dipping the multi-drawn
yarn in a rubber solution.
[0007] Another prior art relating to a tire cord can be acquired
from Japanese Pat. Laid-Open No. Sho. 61-12952 which discloses a
process for producing a tire cord, comprising the steps of spinning
a polyester having an intrinsic viscosity of 1.0, a diethylene
glycol content of 1.0 mol %, a carboxyl group content of 10
eq/10.sup.6 g at a spinning speed of 2,000.about.2,500 m/min to
obtain undrawn yarn, drawing the undrawn yarn at about 160.degree.
C., thermally treating the yarn at 210.about.240.degree. C., and
dipping the yarn in an ordinary rubber solution. In this process,
the temperature just below a spinning nozzle ranges from 100 to
450.degree. C. The tire cord thus produced is, however, poor in
physical properties. For instance, the tire cord ranges, in
absorption peak temperature in amorphous portions, from 148 to
154.degree. C. and, in dry shrinkage, from 3.3 to 5% with a
tenacity of at least 7.0 g/d.
[0008] Focusing on high tenacity and low shrinkage, as introduced
above, the research which was made on the development of the
filamentary yarn for tire cords provided methods in which undrawn
yarn with a high quantity of orientation and crystallinity is
produced through spinning at a high stress and endowed with high
tenacity and low shrinkage properties through drawing at a high
draw ratio.
[0009] The yarns produced by the high-speed spinning or drawing
according to the prior arts are improved in fatigue resistance, but
problematic in that the molecular chain lengths in amorphous
portions are non-uniform and extend. As a result, relaxed molecular
chains coexist, giving rise to a great loss in tenacity. Thus, the
yarns suffer from significant disadvantages of being poor in
drawability owing to a large difference in physical properties
between inner and outer layers of the yarn and of exhibiting a
great variation in physical properties owing to defects in their
micro structure. Moreover, the yarns produced from a highly viscous
polymer with an intrinsic viscosity of 1.0 or more show a limit of
low shrinkage. Yarns which are drawn with a high orientation in
advance of undergoing a tire cord conversion process have a
definite two-phase structure of crystalline and amorphous portions.
Where the highly oriented yarns are subjected to a thermal
treatment by dipping in a rubber solution, deterioration is brought
about in the crystalline portion with aggravation in the
non-uniformity of the molecular chain, leading to a lowering of
strength. As for polyester multi-filamentary yarn, it is highly apt
to be damaged because it undergoes a series of after treatment
processes. For example, at least two strands of the drawn yarn
primarily obtained are subjecting to first and second twisting and
formed into a fabric, after which the fabric is dipped in a rubber
solution and incorporated into a rubber matrix of a tire, and
during these processes, the yarn may be changed in physical
properties and undergoes breaking of molecular chains.
SUMMARY OF THE INVENTION
[0010] Knowledge of the fact that, in order to use drawn polyester
filamentary yarn in tire cords, it is important to allow the drawn
yarn to have a uniform structure of molecular chains and the
balance of high elastic modulus and low shrinkage than to provide
the drawn yarn with high tenacity and low shrinkage because the
drawn yarn experiences serious alteration in physical properties
and molecular structure, leads to the present invention.
[0011] Therefore, it is an object of the present invention to
overcome the above problems encountered in prior arts and to
provide polyester multi-filamentary yarn for tire cords, which
retains excellent thermal stability and fatigue resistance even
after thermal aging.
[0012] It is another object of the present invention to provide
tire cords formed from such polyester multi-filamentary yarn.
[0013] It is a further object of the present invention to provide a
method for making such polyester multi-filamentary yarn for tire
cords.
[0014] In order to approach the above objects, first, when making
drawn yarn, factors causative of non-uniformity in the molecular
chain structure of the yarn must be excluded to as much extent as
possible and the balance of high elastic modulus and low shrinkage
is provided for the yarn. Next, the drawn yarn is allowed to
undergo a uniform structural change in the course of the dipping
process and even under the strict conditions of tire manufacturing
processes, so that the resulting dipped tire cords are deformed as
little as possible under a high temperature condition of the tires,
i.e. tire rotation while the car is driving. Consequently, the
tires are superb in endurability.
[0015] In other words, the factors which cause non-uniformity in
the molecular chain of the yarn are minimized during the producing
processes of the drawn yarn while the parameters which are involved
in the structural change of the molecular chains of the drawn yarn
and dipped tire cords are controlled in the dipping process and
tire-manufacturing processes.
[0016] There are many factors which are causative of non-uniformity
in the molecular chains of polyester yarn. For instance, in the
course from the melting of a polyester resin to the step just
before the extrusion of the molten polyester from nozzles, the
intrinsic viscosity and melting temperature of the polyester resin
have an influence on the molecular weight distribution of the
molten polymer, together with the retention time which it takes for
the molten polymer to flow to the nozzles. Upon extrusion of the
molten polymer from the nozzle, the number and the diameter of the
nozzles play an important role in determining the uniformity of the
resulting yarn. In the processes after the extrusion, such as a
quenching process and a winding process, quenching temperatures and
winding speeds cause a structural change in both of the inner and
outer layers of the yarn extruded from the nozzles (hereinafter
referred to as "extruded yarn"), thereby bringing about a
significant effect in the molecular chains of the inner and outer
layers. During the drawing of the extruded yarn by taking up, the
causative factors included the orientation and breakage of the
molecular chain. Upon thermal treatment, the relaxation extent of
the molecular chain is taken into account. Hence, the formation of
a uniform structure in the molecular chain is affected by a variety
of factors which are distributed in various process steps from
polymer melting through melt spinning, quenching (quenching
temperature), and drawing to thermal treatment. Since the factors
are interconnective to each other, an appropriate combination of
the factors is necessary to produce the drawn yarn which has a
uniform structure of the molecular chain.
[0017] Fundamentally, in order to attain a uniform structure in the
molecular chain, the processing conditions at the process steps
which are important for the uniformity of the molecular chain are
set in such a manner that the occurrence of the non-uniformity is
minimized. For instance, it is preferable to minimize the retention
time in the melting and filtering steps of a polymer. The
non-uniformity due to a sudden change in a quenching step after
spinning can be significantly reduced by converting the sudden
change into a gradual one. Where the non-uniformity of the
molecular chain is due to drawing, it can be solved by conducting
the drawing process at a low draw ratio. In addition, a thermal
treatment stabilizes the molecular chain.
[0018] Accordingly, the present invention can be attained by
satisfying the conditions of the problematic process steps
simultaneously.
[0019] In accordance with an aspect of the present invention, there
is provided a process for producing polyester filamentary yarn from
a polyester resin which comprises at least 90 mol % of polyethylene
terephthalate with an intrinsic viscosity of 0.7.about.1.2,
comprising the steps of: melting the polyester resin at a
temperature of 290.degree. C. or below; filtering the molten resin
for a filtering retention time of 10 min or below;
extrusion-spinning the filtered, molten resin through a nozzle
which has 250.about.500 holes, each ranging, in diameter from 0.5
to 1.2 mm with a length/diameter ratio from 2 to 5; primarily
quenching the extruded yarn at a temperature of
100.about.195.degree. C. in a zone of 50 mm or more distance
directly below the nozzle; secondarily quenching the yarn with
quench air at its glass transition temperature (Tg) or below;
taking off the yarn at a spinning stress of 0.3 g/d or greater; and
drawing the taken-off yarn at a total draw ratio of 1.3 or greater
and thermally treating the yarn at a temperature of
150.about.230.degree. C.
[0020] The term "filtering retention time" as used herein means the
time it takes for the molten resin to travel from the screw end of
the extruder to the holes of the nozzle.
[0021] In accordance with another aspect of the present invention,
there is provided polyester filamentary yarn for tire cords, which
comprises at least 90 mol % of polyethylene terephthalate and has
an intrinsic viscosity of 0.70.about.1.2 and a tenacity of
5.5.about.8.5 g/d with an intermediate elongation difference
(E1-E0) between intermediate elongations E0 and E1 amounting to 6%
or greater. The intermediate elongation E0 is the elongation under
a load of 4.5 g/d while the intermediate elongation E1 is the
elongation under a load of 4.5 g/d after conducting a thermal
treatment at 177 C. for 10 min under a load of 0.01 g/d. The yarn
preferably has an amorphous orientation function of 0.65 or greater
and a terminal modulus of 15 g/d or below.
[0022] In accordance with a further aspect of the present
invention, there is provided a polyester dipped cord which is
produced by twisting the polyester filament yarn in at least two
strands, forming the strands into a fabric, and treating the fabric
with blocked isocyanate and resorcinol formaldehyde latex (RFL),
wherein the cord satisfies the following characteristics:
[0023] i) a tenacity of 5.0 g/d or greater,
[0024] ii) a dimensional stability index (E.sub.4.5+SR) of less
than 7.0%,
[0025] iii) a breaking elongation of 9% or greater,
[0026] iv) an intermediate elongation difference (E1-E0) of 3% or
less.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The present invention pertains to polyester filamentary yarn
for tire cords, which is uniform in molecular chain and has a
harmony of high elastic modulus and low shrinkage with superiority
in dimensional stability and fatigue resistance. Suitable for the
production of the polyester filamentary yarn according to the
present invention is a polyester resin which contains at least 90
mol % of polyethylene terephthalate and has an intrinsic viscosity
of 0.7.about.1.2 and preferably 0.7.about.0.9.
[0028] This resin was melted, filtered and spun by extrusion
through a nozzle. The melting of the polyester resin is conducted
at a temperature of less than 290.degree. C., preferably at a
temperature less than 288.degree. C. and more preferably at a
temperature of 285.about.288.degree. C. During the filtration, the
molten resin is treated for a filtering retention time of 10 min or
less, preferably 8 min or less. As for the nozzle, it has
250.about.500 holes, each ranging, in hole diameter, from 0.5 to
1.2 mm with a hole length/hole diameter ratio from 2 to 5.
[0029] Next, the extruded yarn is subjected to a primary quenching
process in which the yarn passes through a quenching zone of 50 mm
or more distance directly below the nozzle, maintained at a
temperature of 100.about.195.degree. C., so that the undrawn yarn
is allowed to have a spinning stress of 0.3 g/d or higher.
[0030] Subsequently, a secondary quenching process is conducted, in
which the extruded yarn is solidified by quenching with quench air
at the polymer's glass transition temperature or less.
[0031] Thereafter, the undrawn yarn is drawn at a temperature
between the Tg and the crystallization temperature of the
polymer.
[0032] Finally, the drawn yarn is thermally treated at a
temperature of 150.about.230.degree. C.
[0033] The polyester filamentary yarn of the present invention
preferably comprises polyethylene terephthalate at a content of 90
mol % and more preferably 95 mol %. Correspondingly, other
copolyesters than polyethylene terephthalate may be contained at an
amount of 10 mol % or less and preferably 5 mol % or less.
[0034] In addition to polyethylene terephthalate, useful
copolyesters in the present invention may be produced from glycols,
such as diethyl glycol, trimethylene glycol, tetramethylene glycol
and hexamethylene glycol, and dicarboxylic acids, such as
isophthalic acid, hexadihydroterephthalic acid, adipic acid,
cebasic acid and azellaic acid.
[0035] The polyester filamentary yarn of the present invention
usually has a fineness of 3.about.5 deniers per filament, but these
values can be varied in a wide range as is apparent to the skilled
in this art.
[0036] Where the polyester filamentary yarn of the present
invention is incorporated as a reinforcing fiber into a rubber
composite such as a tire, the yarn allows the rubber composite to
show excellent dimensional stability and toughness. Therefore, the
polyester filamentary yarn can efficiently replace the rayon fibers
which have recently been used in monoply radial tires. Further, it
is expected that the polyester filamentary yarn of the present
invention will meet the requirements for a further improvement in
the dimensional stability of polyester.
[0037] First, when a cord is excessively shrunk during a curing
process, a remarkable reduction is brought about in the elastic
modulus of the cord. Second, the shrinkage of the cord is closely
concerned with the uniformity of the tire. In practice,
accordingly, the comparison of elastic modulus at high temperatures
with dry shrinkage is regarded as very important in tire cords. An
intermediate elongation E.sub.4.5 (an elongation under a load of
4.5 g/d) and an E.sub.4.5 growth after the free shrinkage (aging)
at a certain sulfurizing temperature are used as measures of
compliance. Of the factors to determine the controllability of
tires, the elastic modulus at high temperatures is one of the most
important parameters.
[0038] The polyester multi-filamentary yarn of the present
invention consists typically of 200.about.500 continuous filaments
with a fineness of 3.about.5 deniers per filament, but these values
may vary in a large range.
[0039] When being applied for dipped cords, the multi-filamentary
yarn of the present invention is comparable with rayon, which is
usually used as a reinforce material of tires. Particularly, the
multi-filamentary yarn of the present invention is useful as an
industrial fiber by virtue of its high tenacity and toughness even
in a high temperature condition of 100.degree. C. or greater and
low shrinkage.
[0040] Suitable as the starting material for the production of the
multi-filamentary yarn of the present invention is a polyester
which has an intrinsic viscosity (.eta.) of 0.7.about.1.2 and
preferably 0.7.about.0.9. The intrinsic viscosity may be calculated
from the following equation by determining the relative viscosity
(.eta..sub.r) of a solution of 8 g of a sample in 100 ml of
ortho-chlorophenol at 25.degree. C., using an Oswald viscometer. 1
= 0.042 r + 0.2634 r = t .times. d t 0 .times. d 0
[0041] wherein
[0042] t=dropping time of solution (sec),
[0043] t.sub.0=dropping time of ortho-chlorophenol (sec)
[0044] d=density of solution (g/cm.sup.3) and
[0045] d.sub.0=density of ortho-chlorophenol (g/cm.sup.3).
[0046] Since the polymerization quantity of a polymer, if it is a
kind of a molecular weight, has the same concept as intrinsic
viscosity, the polymerization quantity is closely connected with
the conformational stability and fatigue resistance of the polymer.
In detail, the lower the molecular weight of a polymer is, the more
advantageous the polymer is in terms of conformational stability.
On the other hand, as a polymer has a higher molecular weight, the
polymer is more advantageous in fatigue resistance. In the present
invention, an excellent conformational stability is secured by use
of a polymer which has a relatively low intrinsic viscosity ranging
from 0.7 to 1.2. Simultaneously, the degradation in fatigue
resistance was minimized by spinning the polymer at such a
temperature of 288.degree. C. or less and particularly,
285.about.288.degree. C. as to prevent the reduction of its
molecular weight.
[0047] The spinning nozzle useful in the present invention has
250.about.500 holes, in total, each of which has a diameter of
0.5.about.1.2 mm and preferably 0.8.about.1.0 mm and a
length/diameter ratio of 2.about.5 and preferably 3.about.5. Where
a spinning process is carried out in the manner of 2Cop winding
after 4 ends spinning, the number of holes preferably ranges from
120 to 250 per one end. In this case, doubling is conducted after
quenching. For the one-shot spinning in which 2Cop winding is
performed after 2ends spinning, 250.about.450 holes preferably
exist in one nozzle.
[0048] In order to obtain highly oriented, undrawn yarn, it is
important to raise the spinning stress of the undrawn yarn to 0.3
g/d or higher. This is affected by the magnitude of the tension
which the extruded yarn undergoes upon reaching the glass
transition temperature by cooling with quench air. In turn, the
magnitude of tension depends on the spinning speed, the discharge
quantity of per opening, the temperature of the atmosphere just
below the nozzle, and the temperature of the quench air.
[0049] Hence, the tension of the undrawn yarn is determined in the
point where the extruded yarn from the spinneret reaches a
temperature below the glass transition temperature by cooling with
quench air. In the present invention, there is provided a technique
of heightening the spinning speed to increase the speed of tensile
deformation of the extruded yarn in addition to raising the
spinning stress even at the same spinning speed by controlling the
temperature of the atmosphere just below the nozzle. In addition to
minimizing the frequency of cut or broken fibers, this technique
allows the raising of the spinning stress of the undrawn yarn,
leading to the production of highly oriented, undrawn yarn.
[0050] In accordance with the present invention, the extruded yarn
is primarily cooled in a quenching zone of 50 mm or more distance
directly below the nozzle, preferably in a quenching zone extending
from a 50 mm-distant point to a 250 mm-distant point from the
nozzle, more preferably from a 50 mm-distant point to a 150
mm-distant point, which is maintained at a temperature of
100.about.95.degree. C., preferably 100.about.180.degree. C. and
more preferably 100.about.150.degree. C.
[0051] Typically, a shroud which heats the atmosphere just below
the nozzle to the nozzle temperature or higher is set to reduce the
orientation quantity of the undrawn yarn, so as to achieve high
draw ratios at which the undrawn yarn is drawn to produce yarn of
high tenacity. However, the resulting yarn suffers from high
thermal shrinkage. If the spinning is conducted at a high speed
while keeping the shroud at high temperatures in order to improve
the dimensional stability, a steep deformational gradient is
brought about in the polymer, frequently causing fiber to be cut or
broken and giving rise to a sudden decrease in the production
efficiency.
[0052] After completion of the primary cooling process, the
filamentary yarn is subjected to a secondary cooling treatment with
quench air. The cooling is preferably carried out at a temperature
of 20.degree. C. to the glass transition temperature of the polymer
and preferably 40.about.50.degree. C. In the temperature range, the
temperature difference the inner and outer layers of the filament
at the solidification point can be reduced. Accordingly, a tenacity
reduction attributable to the structural difference between the
inner and outer layers of the filament can be minimized. In
addition, alleviating the deformational gradient of the polymer
improves its spinning property, so that the molten polymer shot
from the nozzle by spinning under a high stress condition has an
alleviated deformational gradient, thereby minimizing the
non-uniformity of physical properties and the occurrence of broken
filaments.
[0053] If non-uniformity happens in the filament upon quenching, a
significant decrease in the tenacity of the yarn is caused after
drawing, making it virtually impossible to achieve an excellent
dimensional stability as well as high tenacity by use of low
viscosity polymers.
[0054] In the present invention, the undrawn yarn thus obtained is
wound in such a manner that the yarn has a spinning stress of 0.3
g/d or greater and more preferably 0.5.about.0.8 g/d. The winding
is conducted at a speed of 2,500 m/min or higher and more
preferably 2,700.about.3,500 m/min. Subsequently, the wound yarn is
drawn at a low draw ratio and at a temperature ranging from the
glass transition temperature to the crystallization temperature of
the undrawn yarn.
[0055] A multi-step drawing process is preferably used in the
present invention. Since the crystallization temperature of a
highly oriented undrawn yarn produced by a high-speed spinning
process is usually lower by 10.degree. C. or more than that of an
undrawn yarn obtained by a low-speed spinning process, the drawing
temperature is preferably adjusted to a range of 120.degree. C. or
below, more preferably 70.about.120.degree. C. and most preferably
70.about.100.degree. C. For example, if the drawing temperature
exceeds 120.degree. C., fine crystals are already formed before the
orientation of the molecular chains, degrading the drawability of
the yarn and, in an extreme case, breaking the molecular chains. On
the other hand, if the drawing is conducted at a temperature less
than 70.degree. C., the molecular chains lose their mobility so
that the drawing efficiency is lowered. with the aim of providing
the yarn with a tenacity of at least 5.0 g/d, the total ratio is
controlled to be in the range of 1.3:1.about.2.0:1 and preferably
1.3:1.about.1.6:1. For example, where the total draw ratio is below
1.3:1, the resulting fiber is poor in tenacity. On the other hand,
if the ratio is over 2.0:1, high modulus values and low shrinkage
cannot be attained with a high percentage in tenacity
reduction.
[0056] As for the multi-step drawing process, the drawing is
preferably conducted so as to achieve about 70% or less of the
total draw ratio in the first drawing zone. For example, if more
than 70% of the total draw ratio is accomplished in the first
drawing zone, the period of time which it takes for the tangled
molecular chains to attain a fibrillar structure is so short that
parts of the molecular chains still remain tangled. Serving as a
structural defect, the tangled molecular chains gives rise to an
increase in thermal shrinkage.
[0057] In the present invention, advantage is taken of the
characteristic properties of the highly oriented undrawn yarn
produced by the high-speed spinning process, e.g., the properties
in which the undrawn yarn is transformed into a liquid-like form
rather than undergoes shrinkage when it is thermally treated under
a specific condition after the drawing, so as to greatly decrease
the shrinkage of the dipped cord.
[0058] The elongation and shrinkage behavior upon heat application
can be thought to result from the difference of elongation power
due to the crystallization of the oriented amorphous molecular
chains. Accordingly, the present invention utilizes the mechanism
of the elongation and shrinkage behavior in minimizing the
shrinkage.
[0059] The intensive and thorough research, repeated by the present
inventors, resulted in the finding that, in order to maximize the
water-like elongation behavior, crystallization by heat should not
occur during the drawing. To this end, the drawing is conducted at
a temperature lower than the crystallization temperature of the
undrawn yarn and at a low draw ratio. In the case that
crystallization by heat occurs, in advance, in the drawing process,
the oriented amorphous portions are transformed into crystalline
portions and therefore, the elongation transformation which usually
occurs as the oriented amorphous portions are changed to oriented
crystals no longer occurs. There occurs only the shrinkage behavior
ascribed to the disorientation of the amorphous molecular chains
which are present in the amorphous portions, leading to an increase
of dry shrinkage.
[0060] A characteristic of the present invention is to thermally
treat the drawn yarn. Because the yarn whose orientation is almost
completely finished is subjected to thermal treatment, the
structure of the yarn is dependent greatly on the temperature. The
thermal treatment is carried out at a temperature of
150.about.230.degree. C. and preferably 150.about.180.degree. C.
For example, if the temperature is higher than 210.degree. C.,
there exists a clear discrimination between the amorphous portions
and the crystalline portions, so that the orientation quantity of
the crystalline portions is extremely increased while the amorphous
portions are decreased. As a result, the degradation of physical
properties due to abnormal crystal growth cannot be minimized in a
subsequent dipping process. Upon the thermal treatment, the yarn
may be relaxed at a quantity of 2% or greater.
[0061] In general, the undrawn yarn attains the characteristic
properties of the finally produced yarn as a consequence of the
crystallization and orientation of molecular chains when the undraw
yarn undergoes a drawing process. The orientation in the course of
the drawing takes place in both of the crystalline and amorphous
portions and the drawing tension of the amorphous portions are
higher than that of the crystalline portions.
[0062] According to the method of the present invention, there can
be produced filamentary yarn which has an intrinsic viscosity of
0.70.about.1.2 and preferably 0.7.about.0.9, a tenacity of
5.5.about.8.5 g/d and more preferably 5.5.about.7.5 g/d with an
intermediate elongation difference (E1-E0 ) between intermediate
elongations E0 and E1 amounting to 6% or greater, preferably
6.about.15% and more preferably 6.about.10%.
[0063] Because of the interconnection among the above properties,
the filamentary yarn must satisfy all of the properties in order to
afford a tire cord which exhibits the desirable characteristics. In
particular, the intermediate elongation difference (E1 -E0), which
is one of the most important indexes to inform the uniformity of
the molecular chains during the production of the drawn yarn, must
be in a range of 6% or greater with which the molecular chains
continue to be uniformly changed in subsequent dipping and
tire-manufacturing processes. In this range, the molecular chain
structure of the drawn yarn is converted into a uniform one in the
dipping process which is executed at a high temperature under a
tension condition. If the difference E1-E0 is less than 6%,
non-uniformity may be brought about in the molecular chain
structure when the dipping process is carried cut at a high
temperature under a high tension condition.
[0064] As high as 0.65 in the amorphous orientation function (fa)
of the yarn allows the yarn to be improved in tenacity in the
dipping process. More preferably, the yarn has an amorphous
orientation degree (fa) of 0.65.about.0.8. In addition, in order to
bring about a more uniform molecular chain in the yarn in the
dipping process, it is preferable to set the terminal modulus of
the yarn in a range of 15 g/d or below.
[0065] Most of the accumulated stresses in the yarn are attributed
to the heat which is used in the drawing and thermal treatment. In
order to reduce such stresses, the orientation quantity of the
amorphous portion was decreased to 0.6 as disclosed in U.S. Pat.
Nos. 4,101,515 and 4,195,052. Even in this case, however,
constrained amorphous molecular chains cannot be sufficiently
released owing to the folded molecular chains on the crystal
surface and a large amount of defects on the crystal interface, and
it is not easy to obtain high elastic properties due to the
decrease of the proportion of tie molecules.
[0066] The filaments according to the present invention are twisted
in more than two strands on the basis of a fineness of
1,000.about.2,000 deniers and formed into a fabric, after which the
fabric is dipped in a conventional adhesive solution such as RFL
(resorcinol-formaldehyde-latex- ). After being dried, the dipped
fabric is thermally treated at a certain temperature under a
tension condition, followed by normalizing the fabric to give
dipped cord cloth. The term "dipped cord" as used herein means the
warp cord constituting the dipped cord cloth. In the dipped cord
cloth, the weft serves only to secure the distance between the warp
cords. Therefore, the characteristics of dipped cord cloth are
represented mainly by those of the warp cord. The same is true of
the present invention.
[0067] The tire cord which is obtained by use of the filament of
the present invention has a dimensional stability index of 7 % or
less and preferably 6%, a tenacity of 5.0 g/d or greater and
preferably 5.5.about.7.5 g/d, and a breaking elongation of 9% or
more, and more preferably 15.about.20% with the intermediate
elongation difference E1-E0 amounting to 3% or less, preferably 2%
or less and more preferably 1% or less.
[0068] As retaining excellent dimensional stability and fatigue
resistance even under a high temperature condition, the dipped cord
of the present invention can be applied for rubber composites, such
as tires.
[0069] The physical properties described above were measured
according to the following methods:
[0070] tenacity and elongation: samples 250 mm long were tested at
a tensile speed of 300 mm/min under the atmospheric conditions of
25.degree. C. and 65% RH by use of a low-speed elongation type
tensile strength tester, commercially available from Instron Co.,
Ltd., in accordance with JIS-L 1017 (1983).
[0071] intermediate elongation of yarn (E.sub.4.5): the elongation
value at a load of 4.5 g/d on an elongation load curve obtained by
use of the tensile strength tester in accordance with JIS-L 1017.
E0 is an intermediate elongation under a load of 4.5 g/d while E1
is an intermediate elongation under a load of 4.5 g/d after a
thermal treatment for 10 min at 177.degree. C. under a load of 0.01
g/d.
[0072] intermediate elongation growth: E1-E0.
[0073] intermediate elongation of dipped cord and its growth: the
same procedure as in the yarn was repeated.
[0074] terminal modulus of yarn: on a tenacity-elongation curve,
the increase of the tenacity (.DELTA.T(g/d)) between a braking
elongation (E(%)) and a certain point (E-2.4) is obtained. A
terminal modulus is calculated from the following equation. 2
Terminal Modulus ( Mt ) = T 2.4 .times. 10 - 2 ( g / d )
[0075] dry shrinkage of cord (SR): the value calculated from the
following equation wherein I.sub.cwas the length of the cord fabric
measured under a dead weight load of 20 g after it was placed at
25.degree. C., 65% RH for more than 24 hours and I.sub.1 was the
length after it was placed in an oven at 150.degree. C. for 30 min
under a dead weight load of 20 g. 3 SR ( % ) = l 0 - l 1 l 0
.times. 100
[0076] thermal stability index: the intermediate elongation plus
the dry shrinkage of cord.
[0077] amorphous orientation function (fa) calculated from the
following equation (1): 4 fa = n - x c f c n c ( 1 - x c ) na ( 1
)
[0078] where
[0079] .DELTA.n.sub.c=intrinsic birefringence of crystal
(0.220)
[0080] .DELTA.n.sub.a=intrinsic birefringence of amorphous (0.275).
The birefringence (.DELTA.n) may be calculated from the following
equation (2) by measuring the retardation obtained from the
Interference fringe by the sample using a Berek compensator mounted
in a polarizing light microscope,
.DELTA.n=R/d (2)
[0081] where
[0082] d=thickness of sample (nm)
[0083] R=retardation (nm).
[0084] crystallinity (Xc): determined from the following equation
using the density (.rho.unit: g/cm.sup.3) of the yarn. 5 c = c - (
- a ) ( c - a )
[0085] where,
[0086] .rho.c (g/cm.sup.3)=1.445
[0087] .rho.a (g/cm.sup.3)=1.335
[0088] The density (.rho.) may be determined by measurements
according to density gradient column method using n-heptane and
carbon tetrachloride at 25 .degree. C.
[0089] spinning stress: measured between an oiling device and a
first godet roller with the aid of a tension meter.
A better understanding of the present invention may be obtained in
the light of the following examples which are set forth to
illustrate, but are not to be construed to limit the present
invention.
EXAMPLES 1 TO 5
Comparative Example 1 TO 4
[0090] Polyester chips with an intrinsic viscosity of 0.65, which
were prepared by solid polymerization, were melt-spun through a
spinneret which contained 300 holes (hole diameter 0.60 mm) under
the conditions indicated in Table 1, below. The molten resin were
filtering for filtering retention time of 8 min. A shroud 200 mm
long was placed immediately below the spinneret to provide various
temperature conditions as shown in Table 1. In a quenching zone,
solidification was performed with secondarily quenching air of
40.degree. C. which moved at a speed of 0.6 m/sec while the undrawn
yarn was taken off at a speed of 3,000 m/min. subsequently, the
undrawn yarn was drawn in a two-step drawing process at 80.degree.
C. and 100.degree. C. (total draw ratio 1.60 times) using a godet
roller. On the godet roller, the yarn was thermally treated at
various temperatures as indicated in Table 1. While being relaxed
at a quantity of 2%, the yarn 1,000 deniers in fineness was wound
on a winder.
[0091] The physical properties of the yarn obtained from each
example were shown in Table 2, below.
[0092] Two strands of the yarn obtained from each examples were
subjected to first twisting and second twisting, respectively, at
480 TPM and dipped in RFL at 245.degree. C. to give dipped cords.
The physical properties of the dipped cords are shown in Table 3,
below.
1TABLE 1 Primarily Thermally Intrin. Spinning quenching Spring of
treated Nos. of Viscos. Temp. Temp. undrawn Temp. Exemp. of Chips
(C.) (C.) yarn (g/d) (C.) Exmp. 1 0.75 282 100 0.35 190 Exmp. 2
0.75 282 190 0.32 190 Exmp. 3 0.85 284 150 0.42 200 Exmp. 4 0.85
284 195 0.40 200 Exmp. 5 0.95 288 150 0.55 200 C.Exmp. 1 0.70 295
250 0.25 230 C.Exmp. 2 0.95 300 250 0.34 230 C.Exmp. 3 0.95 300 320
0.32 230 C.Exmp. 4 1.10 305 320 0.41 230
[0093]
2TABLE 2 Amorph. Intermed. Break. Term. Orient. Intrin. Elong. Nos.
of Tenac. Elong. Modul. Degree Viscos. Growth Exmp. (g/d) (%) (g/d)
(fa) of yarn (%) Exmp. 1 5.8 15.8 2.5 0.81 0.71 11.8 Exmp. 2 5.8
15.5 2.0 0.78 0.70 13.2 Exmp. 3 7.0 16.0 12.0 0.75 0.82 10.5 Exmp.
4 7.0 16.0 10.8 0.69 0.82 8.1 Exmp. 5 7.0 15.8 12.9 0.75 0.92 6.9
C.Exmp. 1 5.4 12.9 26.6 0.62 0.64 4.2 C.Exmp. 2 6.8 12.2 32.0 0.64
0.88 5.7 C.Exmp. 3 6.9 12.5 32.8 0.64 0.88 5.3 C.Exmp. 4 7.5 12.3
34.9 0.63 0.95 4.8
[0094]
3TABLE 3 Physical Prop. of dipped Cords Intermed. Nos. of tenacity
Elong. Exmp. (g/d) E.sub.4.5 SR ES Growth (%) Remarks Exmp. 1 5.2
3.5 2.3 5.8 2.6 -- Exmp. 2 5.2 3.5 2.5 6.0 2.3 -- Exmp. 3 6.2 3.5
2.8 6.3 2.6 -- Exmp. 4 6.2 3.5 3.0 6.5 2.8 -- Exmp. 5 6.3 3.5 3.1
6.6 3.0 -- Exmp. 2 4.7 3.5 3.0 6.5 3.8 Greatly Exmp. 2 5.3 3.5 4.0
7.5 5.6 reduced Exmp. 3 5.5 3.5 4.0 7.5 5.3 yarn Exmp. 4 5.9 3.5
4.3 7.8 5.2 tenacity
[0095] Taken together, the data obtained in the examples and
comparative examples demonstrate that the filamentary yarn and
dipped cords of the present invention show a harmony of high
elastic modulus and low shrinkage in addition to being superior in
dimensional stability and fatigue resistance. Consequently, the
filamentary yarn and dipped cords of the present invention can be
used as reinforcements for rubber composites such as tires.
[0096] The present invention has been described in an illustrative
manner, and it is to be understood the terminology used is intended
to be in the nature of description rather than of limitation. Many
modifications and variations of the present invention are possible
in light of the above teachings. Therefore, it is to be understood
that within the scope of the appended claims, the invention may be
practiced otherwise than as specifically described.
* * * * *