U.S. patent application number 14/345973 was filed with the patent office on 2014-08-14 for aramid fiber cord and method for manufacturing the same.
This patent application is currently assigned to KOLON INDUSTRIES, INC.. The applicant listed for this patent is KOLON INDUSTRIES, INC. Invention is credited to Ok Wha Jeon, Min Ho Lee.
Application Number | 20140223879 14/345973 |
Document ID | / |
Family ID | 47996601 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140223879 |
Kind Code |
A1 |
Lee; Min Ho ; et
al. |
August 14, 2014 |
ARAMID FIBER CORD AND METHOD FOR MANUFACTURING THE SAME
Abstract
The present invention relates to an aramid fiber cord which has
high strength as well as good disk fatigue property such that, when
it is used as a tire reinforcement, the degradation of its physical
properties and the degradation of its adhesion strength with
respect to a rubber after long and high speed driving can be
minimized, and to a method for manufacturing the same. The aramid
fiber cord of the present invention comprises an aramid cabled
yarn; and an adhesive coated on an outer surface of the aramid
cabled yarn, wherein penetration rate of the adhesive into the
aramid cabled yarn is 3.5 to 9%.
Inventors: |
Lee; Min Ho; (Gongju-si,
KR) ; Jeon; Ok Wha; (Daegu, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOLON INDUSTRIES, INC |
Gwacheon-si, Gyeonggi-do |
|
KR |
|
|
Assignee: |
KOLON INDUSTRIES, INC.
Gwacheon-si, Gyeonggi-do
KR
|
Family ID: |
47996601 |
Appl. No.: |
14/345973 |
Filed: |
September 26, 2012 |
PCT Filed: |
September 26, 2012 |
PCT NO: |
PCT/KR2012/007734 |
371 Date: |
March 20, 2014 |
Current U.S.
Class: |
57/241 ; 57/255;
57/292 |
Current CPC
Class: |
D02G 3/36 20130101; D06M
2101/36 20130101; D06M 15/693 20130101; D02G 3/02 20130101; D10B
2331/021 20130101; B60C 9/0042 20130101; B60C 2009/0092 20130101;
D06M 15/41 20130101; D02G 3/48 20130101 |
Class at
Publication: |
57/241 ; 57/255;
57/292 |
International
Class: |
D02G 3/48 20060101
D02G003/48; D02G 3/02 20060101 D02G003/02; D02G 3/36 20060101
D02G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2011 |
KR |
10-2011-0099479 |
Claims
1. An aramid fiber cord comprising: an aramid cabled yarn; and an
adhesive coated on an outer surface of the aramid cabled yarn,
wherein penetration rate of the adhesive into the aramid cabled
yarn is 3.5 to 9%.
2. The aramid fiber cord of claim 1, wherein the aramid fiber cord
has strength at 3% elongation of 6.3 to 8 g/d.
3. The aramid fiber cord of claim 1, wherein the aramid fiber cord
has tenacity retention rate of 95% or more after a disc fatigue
test performed according to JIS-L 1017 method of Japanese Standard
Association.
4. The aramid fiber cord of claim 1, wherein the adhesive is a
resorcinol-formaldehyde-latex adhesive.
5. The aramid fiber cord of claim 1, wherein the aramid cabled yarn
comprises at least 2 plies of aramid single yarns
secondarily-twisted together at a first twist number, and each of
the aramid single yarns is an aramid multifilament
primarily-twisted at a second twist number.
6. The aramid fiber cord of claim 5, wherein each of the first and
second twist numbers is 200 to 600 TPM.
7. The aramid fiber cord of claim 1, wherein the penetration rate
of the adhesive into the aramid cabled yarn is 5 to 7%.
8. A method for manufacturing an aramid fiber cord, the method
comprising: preparing an aramid cabled yarn; and dipping the aramid
cabled yarn into an adhesive solution, wherein a tension of 0.2 to
5 kg/cord is applied to the aramid cabled yarn when the aramid
cabled yarn is dipped into the adhesive solution.
9. The method of claim 8, wherein the preparing the aramid cabled
yarn comprises: primarily-twisting aramid multifilament at a first
twist number to prepare an aramid single yarn; and
secondarily-twisting two plies of the aramid single yarns together
at a second twist number.
10. The method of claim 9, wherein each of the first and second
twist numbers is 200 to 600 TPM.
11. The method of claim 8, further comprising: drying the aramid
cabled yarn containing the adhesive solution after the dipping;
heat-treating the dried aramid cabled yarn.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aramid fiber cord and a
method for manufacturing the same, and more particularly, to an
aramid fiber cord which has high strength as well as good disk
fatigue property such that, when it is used as a tire
reinforcement, the degradation of its physical properties after
long and high speed driving can be minimized, and to a method for
manufacturing the same.
BACKGROUND ART
[0002] A fiber cord, particularly a fiber cord treated with an
adhesive, are widely used as a reinforcement for the rubber
products such as tires, conveyor belts, V-belts, hoses and so on.
The fiber cord may be made of nylon fibers, polyester fibers, rayon
fibers and the likes. Among the important methods for improving the
performance of the final rubber products is to improve the physical
properties of the fiber cords which are used as the reinforcements
therefor.
[0003] A nylon fiber having high elongation and tenacity is
generally used for the tires of the heavy-duty trucks imposing
heavy load and the cars running the road of rough surface such as
an unpaved road. Since the nylon fiber has low modulus, however, it
is not proper for the tires of the racing cars running at high
speed and the sedan which requires good riding quality.
[0004] A polyester fiber has better dimensional stability and price
competitiveness than a nylon fiber, and thus the use thereof in the
field of a tire cord is increasing. However, its heat resistance
and adhesion strength with respect to a rubber are too low to be
used for a tire of a car running at high speed.
[0005] A rayon fiber, a regenerated cellulose fiber, exhibits
excellent tenacity retention rate and dimensional stability at high
temperature. Since the tenacity of the rayon fiber is remarkably
lowered by moisture, however, it is required to exhaustively manage
the moisture when a tire is manufactured. Further drawback to it is
lower tenacity compared to the price than those of other
fibers.
[0006] In lots of applications such as heavy vehicles, racing cars,
aircrafts, agricultural vehicles and so on, a fiber cord for a tire
enforcement is required to have much higher strength and modulus
than those obtainable from a polyester or nylon fiber. It is an
aromatic polyamide fiber, also known as an aramid fiber, that can
provide such high strength and modulus.
[0007] However, since the aramid fiber has an inherent property of
high modulus, the fiber cord manufactured using the same generally
has very low fatigue resistance. If a fiber cord having such low
fatigue resistance is used as a tire enforcement, lots of problems
as described below would occur.
[0008] When a car is driven, the temperature of the tire normally
rises due to the friction. Particularly, during a high speed
driving, the tire is maintained at high temperature and high
pressure for a long period of time, and thus the fiber cord for the
tire enforcement is exposed to the fatigue conditions of high
temperature and high pressure. If the fatigue resistance of the
fiber cord is low, the physical properties thereof, especially
tenacity, are rapidly degraded due to the repetitive
stretching/shrinkage, and thus the driving performance of the tire
might be significantly degraded. Further, in serious cases, the
tire may burst during driving.
DISCLOSURE
[0009] [Technical Problem]
[0010] Therefore, the present invention is directed to an aramid
fiber cord and a method for manufacturing the same capable of
preventing these limitations and drawbacks of the related art.
[0011] An aspect of the present invention is to provide an aramid
fiber cord which has high strength as well as good disk fatigue
property such that, when it is used as a tire reinforcement, the
degradation of its physical properties after long and high speed
driving can be minimized.
[0012] The other aspect of the present invention is to provide a
method for manufacturing an aramid fiber cord which has high
strength as well as good disk fatigue property such that, when it
is used as a tire reinforcement, the degradation of its physical
properties after long and high speed driving can be minimized.
[0013] Additional aspects and features of the present invention
will be set forth in part in the description which follows and in
part will become apparent to those having ordinary skill in the art
upon examination of the following or may be learned from practice
of the invention. The objectives and other advantages of the
invention may be realized and attained by the structure
particularly pointed out in the written description and claims.
[0014] [Technical Solution]
[0015] In accordance with the aspect of the present invention,
there is provided an aramid fiber cord comprising: an aramid cabled
yarn; and an adhesive coated on an outer surface of the aramid
cabled yarn, wherein penetration rate of the adhesive into the
aramid cabled yarn is 3.5 to 9%.
[0016] In accordance with the other aspect of the present
invention, there is provided a method for manufacturing an aramid
fiber cord, the method comprising: preparing an aramid cabled yarn;
and dipping the aramid cabled yarn in an adhesive solution, wherein
a tension of 0.2 to 5 kg/cord is applied to the aramid cabled yarn
when the aramid cabled yarn is dipped in the adhesive solution.
[0017] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
[0018] [Advantageous Effect]
[0019] The aramid fiber cord of the present invention satisfies the
strength generally required of the tire cord for heavy vehicles,
racing cars, aircrafts, agricultural vehicles and so on and, at the
same time, has excellent disc fatigue properties. Thus, if the
aramid fiber cord of the present invention is used as a tire
enforcement, the degradation of its physical properties after long
and high speed driving can be minimized
DESCRIPTION OF DRAWINGS
[0020] The accompanying drawing, which is included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrates embodiment of
the invention and together with the description serves to explain
the principle of the invention.
[0021] FIG. 1 schematically shows a system for manufacturing an
aramid fiber cord according to one embodiment of the present
invention.
MODE FOR INVENTION
[0022] The embodiments of the present invention are provided merely
to make the invention become better understood and does not
restrict the scope of the invention thereto. Those skilled in the
art will appreciate that various modifications and alternatives are
possible, without departing from the scope and spirit of the
invention.
[0023] The term `multifilament` as used herein refers to a bundle
of monofilaments formed by coagulating the spinning dope extruded
through a spinneret.
[0024] The term `single yarn` as used herein refers to a ply of
yarn prepared by twisting a multifilament in a certain direction,
and the twist of the single yarn is referred to as `primary
twist.`
[0025] The term `cabled yarn` as used herein refers to a yarn
prepared by twisting at least 2 single yarns together in a certain
direction, which is also called `raw cord.`The twist of the cabled
yarn is referred to as `secondary twist.`
[0026] Generally, the primary twist provides a yarn with a twist in
counterclockwise direction (Z-twist) and the secondary twist
provides a yarn with a twist in clockwise direction (S-twist).
[0027] The term `twist number` as used herein refers to the number
of twist per 1 m, and the measure of the twist number is TPM (Twist
Per Meter).
[0028] The term `fiber cord` as used herein generally refers to a
cabled yarn containing an adhesive so that it can be embedded to a
rubber product at firsthand, which is also called `dipped cord.`
The "fiber cord" also include an adhesive-impregnated fabric made
by weaving a fabric with the cabled yarns and then dipping the
fabric into an adhesive solution.
[0029] The term `penetration rate of an adhesive into a cabled
yarn` as used herein is defined by the formula as below:
P=[(A1-A2)/A1].times.100(%)
[0030] wherein P is the penetration ratio of the adhesive into the
cabled yarn, A1 is the area of the first polygon formed by
connecting the peripheral monofilaments in a cross section of the
fiber cord perpendicular with the longitudinal direction of the
fiber cord, and A2 is the area of the second polygon formed by
connecting the monofilaments in the cross section of the fiber
cord, which are in contact with the adhesive only partially.
[0031] The term `tenacity at 3% elongation` as used herein refers
to the tenacity corresponding to the elongation of 3% in the
elongation-load graph of the cabled yarn containing the
adhesive.
[0032] The term `strength at 3% elongation` as used herein refers
to the `tenacity at 3% elongation` divided by the fineness of the
aramid fiber cord.
[0033] Hereinafter, an embodiment of the method of the invention
for manufacturing an aramid fiber cord will be described in detail
with reference to the accompanying drawings.
[0034] FIG. 1 schematically shows a system for manufacturing an
aramid fiber cord according to one embodiment of the present
invention.
[0035] First, a multifilament is formed by dissolving an aromatic
polyamide, e.g., poly(paraphenylene terephthalamide) (PPD-T),
having inherent viscosity (I.V.) of 5.0 to 7.0 in a concentrated
sulfuric acid solvent to prepare a spinning dope, spinning the
spinning dope through a spinneret 100, and then allowing the dope
to pass through an air gap and a coagulation bath 200 sequentially
to coagulate it.
[0036] When the dope extruded from the spinneret 100 passes through
the coagulating solution, the sulfuric acid is removed from the
dope thereby forming the multifilament. If the sulfuric acid
existing at the outer side of the dope is rapidly removed, the
surface becomes coagulated before the sulfuric acid existing at the
inner side gets out of it, thereby causing the degradation of the
uniformity of the multifilament. Therefore, it is desirable to add
sulfuric acid to the coagulation solution to prevent the sulfuric
acid at the outer side of the dope from getting out of it
rapidly.
[0037] Then, the sulfuric acid remaining in the multifilament thus
obtained is removed. Although most of the sulfuric acid used for
preparing the spinning dope is removed when the dope passes through
the coagulation bath 200, it is possible that it is not completely
removed and some of them remains. Further, if sulfuric acid is
added to the coagulating solution in the coagulation bath 200 to
enable the sulfuric acid in the dope to uniformly get out of it, it
is more than likely that there is sulfuric acid remaining in the
multifilament. Since the sulfuric acid remaining in the
multifilament, even if the amount thereof is so small, reversely
affects the quality of the aramid fiber, it is important to
completely remove the sulfuric acid from the multifilament. The
sulfuric acid remaining in the multifilament can be removed
therefrom by washing it with water or mixture solution of water and
alkali solution.
[0038] The washing process may be a multistep process. For example,
the first washing of the multifilament having sulfuric acid is
performed in the first washing bath 300 containing 0.3 to 1.3%
aqueous caustic solution, and then the second washing thereof is
performed in the second washing bath 400 containing 0.01 to 0.1%
aqueous caustic solution. The first and second washing rolls 310,
410 are provided in the first and second washing baths 300, 400
respectively to move the multifilament.
[0039] Subsequently, a drying process is carried out in the drying
unit 500 to remove the moisture remaining on the multifilament. The
moisture content of the filament can be controlled during the
drying process by adjusting the time for which the filament keeps
in contact with the drying roll 510 in the drying unit 500 or by
adjusting the temperature of the drying roll 510.
[0040] The dried multifilament is heat-treated in the heat
treatment unit 600 having a plurality of heat treatment roll 610 so
as to complete the aramid multifilament.
[0041] The aramid multifilament of the present invention has
strength of 10 to 25 g/d, modulus of 400 to 750 g/d, and elongation
at break of 2 to 6%. The aramid multifilament of the present
invention has total fineness of 800 to 10,000 denier, and may
comprise 500 to 1,200 monofilaments. The fineness of the
monofilament is desirably 1 to 2 denier.
[0042] The aramid multifilament thus prepared is twisted by means
of a twister to prepare an aramid single yarn. Then, 2 plies of the
aramid single yarns are twisted together to prepare an aramid
cabled yarn. According to one embodiment of the present invention,
the aramid single yarn is prepared by twisting the multifilament in
counterclockwise direction (Z-direction) at the first twist number,
and the aramid cabled yarn is prepared by twisting 2 plies of the
aramid singles yarns together in clockwise direction (S-direction)
at the second twist number.
[0043] According to one embodiment of the present invention, the
first and second twist numbers are 200 to 600 TPM (Twist Per
Meter). If the twist number is less than 200 TPM, the strength of
the aramid cabled yarn is high, but the elongation at break of the
fiber cord made thereof is lowered and adhesion strength of the
fiber cord with respect to a rubber is degraded. On the other hand,
if the twist number is more than 600 TPM, the fiber cord made of
such aramid cabled yarn cannot satisfy the strength of such degree
as required in this art.
[0044] The aramid cabled yarn thus obtained is dipped into the
resorcinol-formaldehyde-latex (RFL) solution. 1-bath dipping or
2-bath dipping may be used. According to one embodiment of the
present invention, the RFL adhesive solution comprises 1.0 to 3.0
wt. % of resorcinol, 2.0 to 4.0 wt. % of formalin (37%), 0.5 to 1.5
wt. % of sodium hydroxide (10%), 35 to 55 wt. % of
styrene/butadiene/vinylpyridine (15/70/15) rubber (41%), and
water.
[0045] According to the present invention, a tension of 0.2 to 5
kg/cord is applied to the aramid cabled yarn when the aramid cabled
yarn is dipped into the adhesive solution. According to one
embodiment of the present invention, the tension may be controlled
by changing the ratio of the rotating speed of the rear roll to
that of the front roll in the dipping bath.
[0046] If the tension is less than 0.2 kg/cord, the penetration
ratio of the adhesive into the cabled yarn becomes more than 9%. If
the penetration ratio of the adhesive into the cabled yarn is more
than 9%, the strength of the aramid fiber cord is lowered and the
disc fatigue property of such degree as required in this art cannot
be satisfied. Further, due to the very characteristic of the cabled
yarn having twist, if the tension is less than 0.2 kg/cord, the
cabled yarn droops and leaves the roll, thereby adversely affecting
the processibility.
[0047] On the other hand, if the tension is more than 5 kg/cord,
the penetration ratio of the adhesive into the cabled yarn becomes
less than 3.5%. If the penetration ratio of the adhesive into the
cabled yarn is less than 3.5%, the adhesion strength with respect
to a rubber becomes low. Furthermore, if the high tension more than
5 kg/cord is applied, direct damages may be caused to the cabled
yarn and fiber cord, or the strength at 3% elongation becomes more
than 8 g/d thereby adversely affecting the fatigue properties.
Thus, the fatigue properties of the tire made of the fiber cord
thus obtained cannot satisfy such degree as required in this
art.
[0048] The aramid cabled yarn impregnated with the RFL solution
through the dipping process is dried at 105 to 200.degree. C. for
10 to 400 seconds and then heat-treated at 240 to 280 .degree. C.
for 10 to 400 seconds to complete an aramid fiber cord. The drying
process is to remove the moisture existing in the aramid cabled
yarn, and the heat treatment process is to activate the RFL
adhesive solution in the aramid cabled yarn so that the aramid
fiber cord is provided with the adhesion strength with respect to a
rubber.
[0049] If the drying time and heat treatment time are shorter than
the aforementioned ranges or the drying temperature and heat
treatment temperature are lower than the aforementioned ranges, the
adhesion strength of the aramid fiber cord with respect to a rubber
becomes low. On the other hand, if the drying time and heat
treatment time are longer than the aforementioned ranges or the
drying temperature and heat treatment temperature are higher than
the aforementioned ranges, the excessive heat makes the adhesion
strength of the aramid fiber cord with respect to a rubber lower,
and its physical properties such as strength, fatigue resistance
and so on are degraded.
[0050] The aramid fiber cord of the present invention made through
the aforementioned method has strength at 3% elongation of 6.3 to 8
g/d and tenacity retention rate of 95% or more after a disc fatigue
test performed according to JIS-L 1017 method of Japanese Standard
Association (JSA).
[0051] Furthermore, the aramid fiber cord of the present invention
has tenacity retention rate of 80% or more after a disc fatigue
test performed under the conditions severer than those of the JIS-L
1017 method of JSA in terms of stretching, contracting and time.
Accordingly, the aramid fiber cord of the present invention can be
used as a cord for a high performance tire
[0052] Hereinafter, the examples of the present invention and
comparative example will be described to explain the present
invention in detail. Since the following examples are provided only
for better understanding of the present invention, the scope of the
present invention should not be limited thereto.
Example 1
[0053] A spinning dope was prepared by dissolving
poly(paraphenylene terephthalamide) (PPD-T) having inherent
viscosity (I.V.) of 5.5 in a 100% concentrated sulfuric acid
solvent. A multifilament was formed by spinning the spinning dope
through a spinneret, and then allowing the dope to pass through an
air gap of 7 mm and a coagulation bath containing 13% sulfuric acid
aqueous solution sequentially to coagulate it.
[0054] To remove the sulfuric acid remaining in the aramid
multifilament, the first washing of the multifilament was performed
in the first washing bath containing 0.5% aqueous caustic solution,
and then the second washing was performed in the second washing
bath containing 0.05% aqueous caustic solution.
[0055] Subsequently, a drying process was carried out to remove the
moisture remaining in the aramid multifilament and the dried aramid
multifilament was heat-treated so that a final aramid multifilament
can be obtained.
[0056] The aramid multifilament was primarily twisted in
counterclockwise direction at 350 TPM by means of a Ring Type
Twister of Allma Co. to prepare an aramid single yarn, and then, 2
plies of the aramid single yarns were secondarily twisted together
in clockwise direction at 350 TPM to prepare an aramid cabled
yarn.
[0057] The aramid cabled yarn thus obtained was dipped into the
resorcinol-formaldehyde-latex (RFL) solution comprising 2.0 wt. %
of resorcinol, 3.2 wt. % of formalin (37%), 1.1 wt. % of sodium
hydroxide (10%), 43.9 wt. % of styrene/butadiene/vinylpyridine
(15/70/15) rubber (41%), and water. A tension applied to applied to
the aramid cabled yarn during the dipping process was adjusted to
0.5 kg/cord.
[0058] The aramid cabled yarn impregnated with the RFL solution
through the dipping process was dried at 150.degree. C. for 100
seconds and then heat-treated at 240.degree. C. for 100 seconds to
complete an aramid fiber cord.
Examples 2 & 3 and Comparative Example
[0059] Aramid fiber cords were made in the same manner as that of
the Example 1 except that the tension applied to the aramid cabled
yarn during the dipping process was adjusted in accordance with the
following Table 1.
TABLE-US-00001 TABLE 1 Ex. 2 Ex. 3 Comp. Ex. Tension applied during
Dipping 1 2 6 Process (kg/cord)
[0060] The aramid fiber cords finally obtained in the Examples 1 to
3 and Comparative Example were evaluated with respect to their
penetration rate of adhesive, strength at 3% elongation, breaking
strength, and disc fatigue property in accordance with the
following methods, and the results thereof are shown in the
following Table 2.
[0061] Penetration Rate of Adhesive into Cabled Yarn
[0062] The aramid fiber cord was fixed on a metal rack of
predetermined thickness and size, and then the portion of the
aramid fiber cord sticking out of the metal rack was cut out in the
direction perpendicular with the longitudinal direction thereof
with a sharp instrument. The area of the first polygon formed by
connecting the peripheral monofilaments in the cross section of the
fiber cord, and the area of the second polygon formed by connecting
the monofilaments in the cross section of the fiber cord, which are
in contact with the adhesive only partially, were measured
respectively by means of an optical microscope of 200
magnifications. Then, the penetration rate of the adhesive into the
cabled yarn was calculated in accordance with the following
formula:
P=[(A1-A2)/A1].times.100(%)
[0063] wherein P is the penetration ratio of the adhesive into the
cabled yarn, A1 is the area of the first polygon formed by
connecting the peripheral monofilaments in a cross section of the
fiber cord perpendicular with the longitudinal direction of the
fiber cord, and A2 is the area of the second polygon formed by
connecting the monofilaments in the cross section of the fiber
cord, which are in contact with the adhesive only partially.
[0064] Strength at 3% Elongation
[0065] The tenacity corresponding to the 3% elongation in the
elongation-load graph obtained through the method for measuring the
strength of the aramid fiber cord was indentified, and then, the
identified tenacity was divided by the fineness of the aramid fiber
cord to obtain the strength at 3% elongation.
[0066] Breaking Strength
[0067] The breaking tenacity of the aramid fiber cord was measured
according to ASTM D-885 test method by applying the tensile
velocity of 300 m/min to the sample having the length of 250 mm
using the Instron Tester (Instron Engineering Corp., Canton,
Mass.). Then, the breaking tenacity so measured was divided by the
fineness of the aramid fiber cord to obtain the breaking strength
(g/d).
[0068] Disc Fatigue Property
[0069] The tenacity (i.e., tenacity before fatigue) of the aramid
fiber cord was measured, and then, the aramid fiber cord and a
rubber were vulcanized together to produce a sample. Then,
according to JIS-L 1017 method of Japanese Standard Association,
the fatigue was applied to the sample by means of the disc fatigue
tester by repeating the stretching and contracting steps within the
range of .+-.2% at 80.degree. C. for 8 hours while rotating the
sample at 2500 rpm. Further, to measure the fatigue property
thereof under the severer conditions, the fatigue was applied to
the sample by repeating the stretching and contracting steps within
the range of +3/-10% for 16 hours. Subsequently, the rubber was
removed from the sample and the tenacity after fatigue of the
aramid fiber cord was measured. The tenacity retention rate defined
as the following formula was calculated based on the tenacity
before fatigue and tenacity after fatigue:
Tenacity retention rate (%)=[Tenacity after fatigue (kgf)/Tenacity
before fatigue (kgf)].times.100
[0070] wherein the tenacities (kgf) before and after fatigue were
obtained respectively according to ASTM D-885 by applying the
tensile velocity of 300 m/min to the sample having the length of
250 mm using the Instron Tester (Instron Engineering Corp., Canton,
Mass.) and measuring the breaking tenacity of the aramid fiber
cord.
[0071] The strength and disc fatigue property of the aramid fiber
cords of the examples and comparative example as measured through
the aforementioned methods are shown in the following Table 2.
TABLE-US-00002 TABLE 2 Ex. 1 Ex. 2 Ex. 3 Comp. Ex. Penetration Rate
of Adhesive (%) 8.5 6.3 4.5 3.2 Strength at 3% Elongation (g/d) 7.4
7.0 7.7 8.5 Breaking Strength (g/d) 17.8 17.8 17.9 18.2 Tenacity
retention rate (%) 97.1 99.5 95.3 94.5 Tenacity retention rate 89.7
93.2 85.6 56.9 under severer conditions (%)
[0072] As shown in Table 2, in the comparative example where the
tension applied to the cabled yarn when it was dipped into the RFL
adhesive solution was more than 5 kg/cord, the strength at 3%
elongation was more than 8 g/d and the penetration rate of the
adhesive into the cabled yarn was less than 3.5%. Consequently,
although the tenacity degradation due to the penetration of the
adhesive solution was not caused, the disc fatigue property and the
tenacity retention rate after the severer conditions did not come
up to such degree as required in this art. Particularly, when the
disc fatigue property under the severer conditions was measured,
some samples thereof were broken.
[0073] Meanwhile, it is shown that the penetration rate of the
adhesive into the cabled yarn has a significant effect on the
`tenacity retention rate` and `tenacity retention rate under
severer conditions` of the aramid fiber cord while having little
effect on the breaking strength thereof. Particularly, in each of
the cases where the penetration rate of the adhesive is more than
7% (Ex. 1) or less than 5% (Ex. 3 and Comp. Ex.), the aramid fiber
cords satisfied neither the `tenacity retention rate` of 98% or
more nor the `tenacity retention rate under severer conditions` of
90% or more. Accordingly, from the test results as above, it might
be said that it is most desirable that the penetration rate of the
adhesive into the cabled yarn is 5 to 7%.
* * * * *