Note: Descriptions are shown in the official language in which they were submitted.
CA 02548207 2006-06-02
DESCRIPTION
REINFORCING CORD FOR RUBBER REINFORCEMENT
AND RUBBER PRODUCT INCLUDING THE SAME
Technical Field
The present invention relates to a reinforcing cord for rubber
reinforcement and a rubber product reinforced with a reinforcing cord for
rubber reinforcement.
Background Art
Reinforcing fibers such as glass fibers and aramid fibers have been
used as reinforcing materials for rubber products such as rubber belts, tires,
etc. However, these rubber products are subjected to bending stress
repeatedly and thereby the performance thereof tends to deteriorate due to
bending fatigue. This tends to cause separation between reinforcing fibers
and a rubber matrix, or deterioration in strength due to fraying of the
reinforcing fibers. On the other hand, a toothed rubber belt that is used for
a camshaft drive of an internal-combustion engine of an automobile requires
high dimensional stability in order to maintain appropriate timing.
Furthermore, rubber belts that are used for not only the camshaft drive but
also an auxiliary drive of, for instance, an injection pump, and power
transmission in an industrial machine are required to have high elasticity
and high strength to bear a high load.
Under such circumstances, new materials have been studied as
reinforcing fibers for rubber belts. Recently, for instance, polyarylate
fibers
also have been proposed (see JP 2003-294086 A).
As described above, the reinforcing cord for rubber reinforcement is
required to have high strength, high elasticity, flexibility in bending, wear
resistance, etc. In the conventional cords, however, it was difficult to
achieve
a balance between the strength and the flexibility For example, when
polyarylate fibers are used as reinforcing fibers, a cord with high strength
and high elasticity can be obtained. In this cord, however, bending fatigue
tends to occur and thereby the strength thereof tends to deteriorate, which
has been a problem.
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Disclosure of Invention
With such a situation in mind, the present invention is intended to
provide a reinforcing cord for rubber reinforcement having high strength,
elasticity, and bending fatigue resistance, and a rubber product including the
same.
In order to achieve the above-mentioned object, the present inventors
made studies. As a result, they found out that an effect that was more
prominent than that they had expected was acquired by combining
polyarylate fibers and glass fibers in a specific arrangement. Based on this
new knowledge, the present invention described below was achieved.
The reinforcing cord for rubber reinforcement of the present invention
is a reinforcing cord for rubber reinforcement that includes reinforcing
fibers.
The reinforcing fibers include polyarylate fibers and a plurality of outer
strands that are arranged around the polyarylate fibers. The outer strands
include fibers other than polyarylate fibers. In this specification, the term
"strand" implies those obtained by bundling a plurality of filament fibers
without twisting them, those obtained by bundling and twisting a plurality of
filament fibers, those obtained by bundling a plurality of strands without
twisting them, and those obtained by bundling and twisting a plurality of
strands.
A rubber product of the present invention includes the reinforcing
cord for rubber reinforcement of the present invention described above.
According to the present invention, a reinforcing cord for rubber
reinforcement can be obtained that has high strength, elasticity, and bending
fatigue resistance and is excellent in dimensional stability. Particularly,
when a polyarylate fiber strand and glass fiber strands are combined in a
specific arrangement, a reinforcing cord for rubber reinforcement can be
obtained that has considerably high bending fatigue resistance. The rubber
product of the present invention includes the above-mentioned cord and
therefore has high strength, elasticity, and bending fatigue resistance and is
excellent in dimensional stability.
Brief Description of Drawings
FIG. 1 is a cross-sectional view that schematically shows an example
of the reinforcing cord for rubber reinforcement of the present invention.
FIG. 2 is a schematic view showing a bending test method employed
in Example.
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Description of the Invention
Embodiments of the present invention are described below.
Embodiment 1
In Embodiment 1, the description is directed to a reinforcing cord for
rubber reinforcement of the present invention. A reinforcing cord for rubber
reinforcement of the present invention includes reinforcing fibers. The
reinforcing fibers include polyarylate fibers and a plurality of strands
(outer
strands) that are arranged around the polyarylate fibers. The outer strands
include fibers (hereinafter may be referred to as "second fibers" in some
cases)
other than polyarylate fibers.
The polyarylate fibers are wholly aromatic polyester fibers. They
can be obtained through polycondensation of dihydric phenol (for example,
bisphenol A) and aromatic dicarboxylic acid (for example, phthalic acid or
isophthalic acid).
Preferably, the second fibers are fibers whose flexibility in bending is
higher than that of the polyarylate fibers. Examples of the second fibers to
be used herein include glass fibers, polyparaphenylene benzobisoxazole fibers,
carbon fibers, aramid fibers such as polyparaphenylene terephthalamide
fibers, and mixed fibers thereof. Preferably, the outer strands are formed of
at least one type of fibers selected from glass fibers, polyparaphenylene
benzobisoxazole fibers, carbon fibers, and aramid fibers (preferably
polyparaphenylene terephthalamide fibers, this also applies to the following).
It is particularly preferable that the outer strands be formed of glass fibers
or
aramid fibers.
When the ratio of the polyarylate fibers in the reinforcing fibers
becomes higher, the elastic modulus and dimensional stability improve, but
the dynamic flexibility deteriorates. On the other hand, when the ratio
becomes lower, the elastic modulus and dimensional stability deteriorate.
Accordingly, it is preferable that the ratio of the polyarylate fibers to the
whole reinforcing fibers be in the range of 20 vol.% to 80 vol.% (preferably
30
vol.% to 70 vol.%).
In the reinforcing cord for rubber reinforcement of the present
invention, it is preferable that the above-mentioned polyarylate fibers form a
strand of polyarylate fibers. In this case, the reinforcing cord for rubber
reinforcement includes a core strand of polyarylate fibers and a plurality of
outer strands that are arranged around the core strand. Preferably, the core
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strand is formed substantially of polyarylate fibers. Typically, the core
strand is formed of polyarylate fibers alone.
In the cord of the present invention, it is particularly preferable that
polyarylate fibers (preferably a strand of polyarylate fibers) with a high
elastic modulus be arranged near the center of the cord, while outer strands
that are excellent in flexibility and wear resistance be arranged around the
polyarylate fibers. The characteristics of the polyarylate fibers arranged
near the center of the cord allow the cord to have high strength and a high
elastic modulus as well as excellent dimensional stability The outer strands
may be formed of fibers (for example, glass fibers) whose elastic modulus is
lower than that of the polyarylate fibers. When such outer strands are used,
a reinforcing cord for rubber reinforcement can be obtained that has high
strength, elasticity, and bending fatigue resistance.
The diameter, elastic modulus, etc. of the polyarylate fibers are not
particularly limited. They are selected according to the characteristics that
are required for the reinforcing cord. For instance, polyarylate fibers may be
used that have a density of approximately 1.2 g/cm3 to 2.0 g/cm3.
Furthermore, polyarylate fibers with an elastic modulus (Young's modulus) of
approximately 70 GPa to 120 GPa also may be used.
The polyarylate fibers may be those that have not been twisted nor
been treated. They, however, may be those to which an adhesive has been
applied or those that have been twisted in order to improve the adhesiveness
or to prevent them from fraying. The adhesive is not particularly limited
but can be an epoxy compound, an isocyanate compound, a treatment
solution (hereinafter may be referred to as a "RFL treatment solution") that
contains rubber latex and the initial condensate of resorcin and formaldehyde
as its main components, etc. The number of twists of the polyarylate fibers
(the core strand) is not particularly limited. It generally is preferably 8.0
times/25 mm or less, for example, in the range of 0.5 to 5.0 times/25 mm.
When the polyarylate fibers are to be twisted, it is preferable that they be
twisted after the treatment solution is applied thereto. When the treatment
solution is applied to them after they are twisted, the strand of the
polyarylate fibers may tend to fray in some cases.
The thickness of the outer strands as well as the number and
diameter of the fibers of each outer strand are not particularly limited. They
are selected according to the characteristics that are required for the
reinforcing cord. Furthermore, the number of the outer strands that are
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arranged around the polyarylate fibers is usually approximately 3 to 20.
Like the outer strands, the strands that are arranged near the
periphery of the cord are required to ease the compressive stress and tensile
stress that are caused when the cord is bent. Preferable strands that satisfy
such requirements are glass fiber strands and aramid fiber strands. When
the glass fiber strands that contain glass fibers as their main fibers (at
least
50 vol.%, preferably at least 60 vol.%, for example, 100 vol.%) are arranged
around a core strand formed of polyarylate fibers, a reinforcing cord for
rubber reinforcement can be obtained that has particularly high strength,
elasticity, and bending fatigue resistance. Moreover, when glass fiber
strands are used as the outer strands, a reinforcing cord can be obtained that
adheres strongly to the rubber in which it is to be embedded. For the glass
fibers, E-glass filaments or high-strength glass filaments are used
preferably,
for example. Strands with a thickness of approximately 20 to 480 tex, each
of which is obtained by bundling and primarily twisting approximately 200 to
2400 glass filaments with a diameter of 7 to 9 Vim, are used preferably as the
glass fiber strands.
The outer strands may be primarily twisted. When the outer
strands that are arranged near the periphery of the cord are twisted
(primarily twisted), the bending fatigue resistance of the cord can be
improved. The number of twists is not particularly limited. Preferably, it is
approximately 0.25 to 5.0 times/25 mm.
Furthermore, the plurality of outer strands may be wound spirally
(i.e. may be finally twisted) with the polyarylate fibers used as a core. The
number of twists of the final twist can be approximately 0.5 to 10 times/25
mm, for example. In the case where the outer strands are primarily twisted
and are finally twisted, the direction of the final twist may be identical to
the
direction of the primary twist or may be different from it. When the final
twist and the primary twist are carried out in the same direction, a cord with
particularly high flexibility in bending can be obtained. In addition, high
dimensional stability is obtained when the final twist and the primary twist
are carried out in different directions from each other.
With respect to the reinforcing cord for rubber reinforcement of the
present invention, it is preferable that the surface thereof be coated with a
coating film containing rubber. Usually, the coating film is selected
according to the rubber (matrix rubber) in which the cord is to be embedded.
The method of forming the coating film is not particularly limited and a
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well-known method therefore can be used. For instance, after a treatment
solution containing rubber is applied to the cord, it is heat-treated or is
dried
and thereby a coating film can be formed. The treatment solution to be used
herein can be the RFL treatment solution, for example. Examples of the
rubber latex to be used for the RFL treatment solution include an
acrylic-rubber-based latex, a urethane-based latex, a
chlorosulfonated-polyethylene-based latex, denatured latexes thereof,
mixtures thereof, etc.
The peripheries of the fiber strands and the periphery of the cord may
be coated with coating films whose materials are different from each other.
For example, in order to improve the adhesiveness between the matrix rubber
of a rubber product and the cord of the present invention, the periphery of
the
cord may be subjected to an overcoating treatment. The overcoating
treatment can be carried out using a treatment solution containing a
crosslinker and rubber such as hydrogenated nitrile rubber, chlorosulfonated
polyethylene rubber (CSM), chloroprene rubber, crude rubber, or urethane
rubber, for example. Usually, the rubber to be used for the overcoating
treatment is selected according to the type of the matrix rubber. The
amount of the overcoat is not particularly limited. For example, it may be in
the range of 2.0 to 10.0 parts by mass with respect to 100 parts by mass of
the
cord obtained before the overcoating treatment.
FIG. 1 shows a cross-sectional view of a preferable example of the
reinforcing cord for rubber reinforcement of the present invention. A cord 10
shown in FIG. 1 includes: polyarylate fibers (a core strand) 11 arranged in
the
center of the cord 10~ a plurality of outer strands 12 arranged around the
polyarylate fibers 11~ and a coating film 13 (hatching thereof is omitted)
with
which both the polyarylate fibers 11 and the outer strands 12 are coated.
The plurality of outer strands 12 are wound spirally around the polyarylate
fibers 11. The coating film 13 contains rubber.
A method of producing the cord 10 is described below. The outer
strands 12 each can be formed by bundling fibers. A coating film may be
formed around the polyarylate fibers (the core strand) and/or the outer
strands by carrying out a treatment, for example, a RFL treatment as
required. Furthermore, the polyarylate fibers (the core strand) and/or the
outer strands may be twisted as required. Moreover, a plurality of strands
may be twisted to form one strand as required.
Next, the outer strands 12 are arranged around the polyarylate fibers
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11. This process can be carried out using a guide that has a center guide
hole and a plurality of peripheral guide holes arranged on a circle that
shares
its center with the center guide hole, for example. One polyarylate fiber 11
or a plurality of polyarylate fibers 11 that have not been twisted or have
been
primarily twisted are allowed to pass through the center guide hole, while the
outer strands 12 are allowed to pass through the plurality of peripheral guide
holes. Furthermore, when the guide is not used, a tension that is at least 1.2
times the tension that is applied to the peripheral fibers may be applied to
the center fibers. When a higher tension than the tension that is applied to
the peripheral fibers is applied to the center fibers, the arrangement of the
center fibers is facilitated and thereby the same effect as that obtained when
the guide is used is obtained. The outer strands 12 are primarily twisted as
required. The devices for doubling and twisting the strands are not
particularly limited. For example, a ring twisting frame, a flyer twisting
frame, or a twisting machine can be used.
Finally, the coating film 13 is formed so as to coat the whole of the
polyarylate fibers 11 and the outer strands 12. Thus, the cord 10 is
produced.
The cord of the present invention may be used independently (as a
rope structure). Furthermore, the cord of the present invention may be used
in a bamboo-blind-like structure, i.e., a structure in which a plurality of
cords
are arranged in the form of a sheet and are attached to each other loosely.
Embodiment 2
In Embodiment 2, the description is directed to a rubber product of
the present invention. The rubber product of the present invention includes
at least one reinforcing cord for rubber reinforcement described in
Embodiment 1. This reinforcing cord for rubber reinforcement may be a
rope structure. Furthermore, a plurality of reinforcing cords for rubber
reinforcement may be arranged and embedded in the shape of a sheet.
The rubber product of the present invention is not particularly
limited as long as it is a rubber product reinforced effectively with the
reinforcing cord for rubber reinforcement. Typical examples of the rubber
product of the present invention include rubber belts such as a toothed belt
and a move belt, and a rubber crawler.
In the rubber product of the present invention, the ratio of the
reinforcing cord for rubber reinforcement to the rubber product is
approximately 10 to 70 wt.%, for example.
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EXAMPLE
Hereinafter, the present invention is described further in detail using
examples. In the examples, reinforcing cords for rubber reinforcement of the
present invention and comparative examples were produced, and then the
characteristics thereof were evaluated.
Sample 1
A reinforcing cord for rubber reinforcement of the present invention
was produced by the following method. First, a resorcinol-formaldehyde
condensate (with a solid content of 8 wt.%), vinyl pyridine-styrene-butadiene
latex (with a solid content of 40 wt.%), and CSM (with a solid content of 40
wt.%) were mixed together in such a manner as to have a solid content mass
ratio of 2 : 13 : 6. Thus, a RFL treatment solution was prepared. This RFL
treatment solution was applied to a strand (with a diameter of approximately
0.8 mm~ a non-twisted product) formed of polyarylate fibers (with an elastic
modulus of 106 GPa and a density of approximately 1.41 g/cm3~ Uectran
(Trade Name) manufactured by KURARAY CO., LTD.). Thereafter, this
was heat-treated (at 180°C for 120 seconds) to be dried. Thus, a core
strand
(the amount of RFL that had adhered thereto: 20 wt.%) that had been
subjected to the RFL treatment was obtained.
On the other hand, a bundle of 600 glass fibers (with a diameter of 9
Vim, an elastic modulus of 70 GPa, and a density of approximately 2.5 g/cm3~
E Glass manufactured by Nippon Sheet Glass Co., Ltd.) that had been
aligned with one another was impregnated with a RFL treatment solution.
Thereafter, this was heat-treated (at 180°C for 120 seconds) to be
dried.
Then, it was primarily twisted in the S direction at a rate of 2.0 times/25
mm.
Thus, a glass fiber strand (the amount of RFL that had adhered thereto: 20
wt.%) of approximately 100 tex was obtained.
Next, nine glass fiber strands were arranged around the core strand
that had been subjected to the RFL treatment, in such a manner as to be
arranged as shown in FIG. 1. This was finally twisted in the Z direction at a
rate of 2.0 times/25 mm. Thus, a cord 1A was obtained. The diameter of
the cord 1A was approximately 1.20 mm. The ratio of the sectional area of
the polyarylate fibers to that of the whole fibers was 45%.
Next, an overcoat treatment solution whose components are indicated
in Table 1 below was applied to the cord 1A, which then was dried. Thus, a
cord 1B was obtained. The amount of the solid content of the overcoat
treatment solution that had adhered to the cord 1B was 5 wt.%. The linear
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density (the weight (g) per length of 1000 m) of the cord 1B was 1580 tex
(g/1000 m). With respect to the cord 1B thus obtained, the tensile strength
and the elongation (%) at rupture were measured. The tensile strength
(initial) per cord 1B was 1250 N/cord, while the elongation at rupture was
3.2%.
Table 1
Com onents Ratio (Parts b Mass)
CSM (Trade Name: TS-340, manufactured
by Tosoh
Corporation chlorine content: 43 wt.%, 5.25
sulfur content:
1.1 wt.%)
P-dinitrosobenzene 2.25
Carbon Black 3.0
Mixed Solvent of Xylene and Trichlorethylene
(Mass Ratio between Xylene and Trichlorethylene85.0
=
1.5 : 1.0)
In addition, two rubber sheets (with a width of 10 mm, a length of 300
mm, and a thickness of 1 mm) were prepared that contained the components
indicated in Table 2 below.
Table 2
Com onents Ratio (Parts b Mass)
Hydrogenated Acrylonitrile-Butadiene Rubber100
(Zetpol 2020, manufactured by ZEON CORPORATION)
Zinc Oxide, Grade 1 5
Stearic Acid 1.0
HAF Carbon 60
Trioct 1 Trimellitate 10
4,4-(a,a-dimeth lbenz 1)di henylamine 1.5
2-mercaptobenzimidazole Zinc Salt 1.5
Sulfur 0.5
Tetrameth lthiuramsulfide 1.5
Cyclohexyl-Benzothiazylsulfenamide 1.0
One cord 1B with a length of 300 mm was placed on one rubber sheet
and the other rubber sheet was placed thereon. This was pressed from the
upper and lower sides thereof at 150°C for 20 minutes to be cured. Thus
a
belt-shaped specimen was produced.
Next, with respect to this specimen, a bending test was carried out
with a bending tester 20 shown in FIG. 2. The bending tester 20 was
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provided with one flat pulley 21 having a diameter of 25 mm, a motor (not
shown in FIG. 2), and four guide pulleys 22. First, the specimen 23
produced as above was placed on the five pulleys. Then a weight was
attached to one end 23a of the specimen 23 to apply an initial tension of 9.8
N
to the specimen 23. In this state, the other end 23b of the specimen 23 was
reciprocated 10000 times for a distance of 10 cm in the directions indicated
with a double-headed arrow in FIG. 2. Thus the specimen 23 was bended
repeatedly around the flat pulley 21. The bending test was carried out at
room temperature. After the specimen 23 was subjected to the bending test
as described above, the tensile strength of the specimen was measured.
Then the tensile-strength retention rate (%) of the specimen after the bending
test was determined, with the tensile strength of the specimen before the
bending test being taken as 100%. The higher the tensile-strength retention
rate, the better the bending fatigue resistance. The specimen of Sample 1
had a tensile-strength retention rate of 85%.
Sample 2
Sample 2 is different from Sample 1 in that the core strand was
primarily twisted. In this case, a RFL treatment solution was applied to the
polyarylate fiber strand used in Sample 1. Thereafter, it was primarily
twisted at a rate of 2.0 times/25 mm, which further was heat-treated. Thus,
a core strand was produced. Then a cord 2A was produced by the same
method as that employed for producing the cord 1A of Sample 1 except that
the core strand obtained above was used.
The cord 2A thus obtained was subjected to the overcoating treatment
by the same method as in the case of Sample 1. Thus, a cord 2B was
obtained. The tensile strength and the elongation (%) at rupture of this cord
2B were measured. The tensile strength (initial) per cord 2B was 1200
N/cord, while the elongation at rupture was 3.0%.
Furthermore, using the cord 2B, a specimen for the bending test was
produced in the same manner as in the case of Sample 1 and was subjected to
the bending test. Then the tensile-strength retention rate (%) of the
specimen after the bending test was determined.
Comparative Sample 1
First, 11 glass fiber strands produced for Sample 1 were bundled and
finally twisted. Then this was subjected to the overcoating treatment by the
same method as that employed for Sample 1. Thus a cord of Comparative
Sample 1 was produced. With respect to this cord, the initial tensile
CA 02548207 2006-06-02
strength and elongation (%) at rupture were measured. Furthermore, using
the cord of Comparative Sample 1, a specimen for the bending test was
produced in the same manner as in the case of Sample 1 and was subjected to
the bending test. Then the tensile-strength retention rate (%) of the
specimen after the bending test was determined.
Comparative Sample 2
First, 2 polyarylate fiber strands used in Sample 1 were prepared.
Each of them was subjected to the RFL treatment and then was primarily
twisted. Next, the two strands thus obtained were bundled and finally
twisted. Thus a cord was obtained and then was subjected to the
overcoating treatment by the same method as that employed for Sample 1.
Thus a cord of Comparative Sample 2 was produced. With respect to this
cord, the initial tensile strength and elongation (%) at rupture were
measured.
Furthermore, using the cord of Comparative Sample 2, a specimen for the
bending test was produced in the same manner as in the case of Sample 1
and was subjected to the bending test. Then the tensile-strength retention
rate (%) of the specimen after the bending test was determined.
Comparative Sample 3
First, polyarylate fibers and glass fibers used in Sample 1 were mixed
together without being separated into the core strand and the outer strands,
which then was twisted. The number of twists was set at 2.0 times/25 mm.
A cord thus obtained was subjected to the overcoating treatment by the same
method as that employed for Sample 1. Thus a cord of Comparative Sample
3 was produced. With respect to this cord, the initial tensile strength and
elongation (%) at rupture were measured. Furthermore, using the cord of
Comparative Sample 3, a specimen for the bending test was produced in the
same manner as in the case of Sample 1 and was subjected to the bending
test. Then the tensile-strength retention rate (%) of the specimen after the
bending test was determined.
Table 3 indicates evaluation results with respect to five types of
samples thus obtained.
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Table 3
Tensile-
Reinforcing Diam- LinearInitial Elonga-Strength
Fibers
eter DensityTensile tion Retention
of
Section[g/ Strengthat Rate
Center Peri heral[mm] 1000m][N/cord]Ruptureafter
p
[%] Bending
Part Part Test
[%]
Poly- g E-Glass
Sample arylateStrands 1.20 1580 1250 3.2 85
1
Fibers
Poly- g E-Glass
Sample arylateStrands 1-22 1580 1200 3.0 70
2
Fibers
Comparative11 E-
-
Glass 1.13 1440 890 3.5 51
Sample Strands
1
Comparative2 Poly-
ar3'late- 1.00 860 1020 2.9 45
Sample Fibers
2
ComparativePolyarylate
Fibers 1.28 1580 1100 3.4 65
and
Sample E-Glass
3 Fibers
As shown in Table 3, the cords in which only the polyarylate fibers or
glass fibers were used as reinforcing fibers had lower initial strength and
lower strength after the bending test. Furthermore, in Comparative Sample
3 in which glass fiber strands were not arranged to surround a polyarylate
fiber strand, the initial strength, elongation at rupture, and strength after
the bending test were insufficient. Particularly, in Comparative Sample 3,
the elongation at rupture was high. A cord with a high elongation at
rupture has a problem in that the dimensional stability thereof is lower, and
when it is used for a toothed belt, the tooth part thereof tends to be
damaged.
Hence, it is preferable that the elongation at rupture be as low as possible.
In Sample 2 in which the polyarylate fiber strand was primarily twisted, the
elongation at rupture was particularly low.
On the other hand, the reinforcing cord of the present invention in
which the glass fiber strands were arranged around the polyarylate fiber
strand had a high initial strength, a lower elongation at rupture, and a high
tensile-strength retention rate after the bending test. These values were
considerably higher than those of Comparative Sample 3 in which the
polyarylate fibers and the glass fibers were mixed simply together.
Industrial Applicability
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The present invention is applicable to a reinforcing cord for rubber
reinforcement that is suitable for reinforcing various rubber products.
Furthermore, the present invention is applicable to various rubber products
that are reinforced with a reinforcing cord for rubber reinforcement of the
present invention. For instance, the present invention is applicable to
rubber belts such as a toothed belt and a move belt, and rubber crawlers.
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