Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1151022
This invention relates to a method for manufacturing
a steel cord for use in reinforcing rubber articles, such as
tires and more particularly to a method for manufacturing a
steel cord having excellent fatigue resistance and corrosion
resistance.
Recently, radial tires using steel cords as belt
material or carcass material have been developed. The wear
resistance of tires has been found to be remarkably improved
as well as tread rubber quality. Thus, the life of tires has
been considerably extended. As the steel cord for such tires,
steel cords of so-called twisted in multiple structure prepared
by twisting at least a few strands which are in turn made by
twisting at least two filaments, are widely used for high pro-
ductivity.
However, such steel cords have the problem of fatigue
due to fretting, because the individual filaments are in point
contact with one another. Thus, there is a risk that tires
formed with these cords lose their usefulness due to the
fatigue of the steel cord before the tires have completely worn
out.
Consequently, a steel cord where the individual fila-
ments thereof are in linear contact with one another, for
example, a steel cord of twisted layer structure, has been pro-
posed to improve the fatigue resistance of the steel cord.
However, it is known that the tires having steel
cords have the disadvantage that, when the tires are scarred on
their surfaces, the steel cords are susceptible to rusting due
to, for example, rain water entering through the scars. Alter-
natively the gas
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generated during rubber vulcanization or water vapor vaporized
from the water present in the rubber caused by heat generation
during driving, can corrode the steel cords at the inside
clearances in the steel cord even without any scarring.
To overcome the aforesaid disadvantages it has been
proposed to modify the quality of the plating material, apply
a resin coating to steel cord, or apply a rustproof agent
thereto (Japanese Patent Publication No. 3121/78, etc.). How-
ever, these procedures are not satisfactory because inter alia
the adhesion of the cords to rubber presents a problem.
It is also known to fill the clearances between the
individual cords with unvulcanized rubber by winding filaments
around injection-molded rubber, as in Japanese Utility Model
Publication No. 40188/72. This procedure has the disadvantage
that the manufacturing steps are so complicated that productiv-
ity is reduced. With steel cords of twisted layer or simple
twisted structure where the filaments are in linear contact
with each other, it is hard to fill the clearances with rubber
according to such a procedure as above, and since the filaments
are in linear contact with one another, it is hard to permeate
the rubber even to the inside of cord in the calendering step.
Thus steel cords of excellent fatigue resistance and at the
same time corrosion resistance have not yet been obtained.
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According to the present invention there is provided
a method for manufacturing a steel cord having excellent fati-
gue resistance and corrosion resistance, in which a steel cord
formed of a plurality of steel filaments at least outermost
layer filaments of which are in linear contact with one another,
is treated with a rubber solution obtained by dissolving an un-
vulcanized rubber in a solvent having a compatibility with rub-
ber at a consistency of 1-20~ before rubberizing by calendering.
The present invention will be illustrated by way of
the accompanying drawings in which:
Figs. 1 and 2 are cross-sections of a steel cord to
be used in accordance with one embodiment of the present inven-
tion and formed of a plurality of steel filaments, the filaments
at least in the outermost layer being in linear contact with
one another;
Fig. 3 is a schematic view of the process according to
one embodiment of the present invention; and
Fig. 4 is a graph of strength retainability against
a number of bendings of various steel cards.
2Q The surface of the steel filament can be subjected to
the necessary treatment for adhesion to rubber. For example,
the surface can be plated by brass or zinc or by these metals
also containing nickel or cobalt, or by a ternary alloy of
copper-cobalt-zinc.
The unvulcanized rubber to be used in the method of
the present invention may be natural rubber or synthetic rubber
such as synthetic polyisoprene rubber, polybutadiene rubber, or
styrene-butadiene rubber, but preferably is the same type of rub-
ber as that of the coating rubber. Particularly preferable are
natural rubber and synthetic polyisoprene rubber.
The solvent having a compatibility with the rubber used
in the method of the present invention is preferably in~ustrial
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grade gasoline Nos. 1-4, alcohol and ether, and more preferably
rubber gasoline of industrial grade gasoline No. 2.
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1151022
The concentration of the rubber dipping solution used
in the process of the present invention is 1-20%, preferably
1-15%. Below 1%, an insufficient amount of rubber is deposited
in the inside clearances in the steel cord, whereas above 20%,
the rubber permeates to the inside of the steel cord with great
difficulty. Thus, either case is not preferable.
In the present invention, the rubber dipping solution
may be admixed, if necessary, with an antioxidant, filler,
vulcanizing agent, vulcanization promotor, vulcanization pro-
moting additive, etc., as used in the rubber industry.
Referring specifically to Fig. 3 a steel cord 1 is
unwound from feed roll 2 and dipped in a rubber dippinq solution
7 in a tank 6 passing around guide rolls 3, 4 and 5. The dip-
ped steel cord 1' is continuously rubberized by calender rolls
8. ~efore rubberizing the dipped steel cord 1', the cord can
be wound around a roll and stored.
In the foregoing manner, a steel cord having excellent
fatigue resistance and a corrosion resistance can be readily
and cheaply produced.
The present invention will be described in more detail
by way of the following Examples.
Example 1
Twisted layer structure steel cord of [(1 x 3 + 9 +
15) x 0.175 + 1 x 0.15] each filament of which is brass-plated,
as shown in Fig. 1, was used. Rubber solutions were prepared
by dissolving an unvulcanized rubber composition shown in
Table 1 in rubber gasoline to provide the concentrations there-
of of 5, 10 and 15%. Dipping time was 2 seconds each, and
after the dipping drying was carried out, and then the result-
ing dried steel cord was rubberized by calendering with the
unvulcanized rubber composition of Table 1 and finally said
rubberized steel cord was vulcanized.
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Table l
Natural rubber lO0 parts by weight
HAF carbon black 50 "
Aroma oil lO "
Stearic acid 3 "
N-phenyl-N'-isopropyl-p-phenylene-diamine l.0 "
N-oxydiethylene-2-benzothiazyl-sulphenamide 0.5 "
Cobalt stearate 4 "
Sulfur 2.5 "
The resulting steel cords were cut in the cross-
sectional direction by a diamond cutter, and the cross-section
was observed under a microscope to evaluate the permeation
degree of the rubber to the inside.
Then, the corrosion resistance of the steel cords
thus obtained was determined by a bending fatigue test in which
cotton was fixed to a predetermined position on the steel
cord under 10% load of cord strength at 80 runs/min. and about
l cc of water was injected into the cotton by a syringe every
24 hours. The results are shown in Table 2. For comparison,
the steel cords without treatment with the rubber solution were
similarly determined.
Table 2
Steel cord species State of rubber Number of bending
permeation till cord fracture
No dipping treatment ~ ly permeated 247,305
Treatment in 5% Completely 887,763
rubber permeated
Treatment in 10% Substantially com-
rubber solution pletely permeated 792,542
__ .......... _ .
Treatment in 15% Partially leaving 564,273
rubber solution vacant space
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It is clear from Table 2 that, in case of the steel
cords manufactured according to the present invention, the rub-
ber is permeated to the inside of the cords, and thus the
corrosion resistance and the fatigue resistance are improved
at least twice compared with those of the convention steel
cords.
Example 2
Simply twisted structure steel cords of (1 x 5 x 0.25)
each filament of which is brass-plated as shown in Fig. 2 was
used for evaluation in the same manner as in Example 1. The
results are shown in Table 3.
Table 3
Steel cord species State of rubber Number of bending
permeation till cord fracture
No dipping treatment Hardly permeated 11,927
Treatment in 5% Completely 20,173
rubber solution permeated
As is clear in Table 3, the steel cords of the pre-
sent invention have considerably improved corrosion resistance
and fatigue resistance.
Example 3
Twisted layer structure steel cords of [(1 x 3 + 9 +
15) x 0.175 + 1 x 0.15] each filament of which is brass-plated,
as used in Example 1, and twisted layer structure steel cords
of [(1 x 3 + 9 + 15) x 0.175 + 1 x 0.15] each filament of which
is plated by a ternary alloy of copper-cobalt-zinc (65/5/30 by
weight) were treated with 5% rubber solution and then rubber-
ized and finally vulcanized in the same manner as in Example 1.
The resulting rubberized steel cord layers were sampled as
pieces of 220 mm of length and 50 mm of width, and these
samples were subjected to a bending test under conditions of
5% NaCl spraying at a spray pressure of 1 kg/cm2 by a saline
water sprayer, a bath temperature of 40C, and a bending angle
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of 40 cpm. Then, the sample pieces were subjected to a draw-
ing test, and the bending fatigue resistance of the cords was
evaluated in terms of percent strength retainability on the
basis of the cord strength measured before the bending test.
The results were shown in Fig. 4. For comparison, two types
of the cords without the dipping treatment were also evaluated.
As clear from Fig. 4, the steel cords of the present
invention had a considerably improved fatigue resistance, and
particularly the fatigue resistance is synergistically improved
in the case of the ternary alloy-plated steel cord.
