Rubber article reinforced with fibers embedded therein

A rubber having a fiber reinforcement embedded thereon. The reinforcement comprises a cylindrically braided cords by more than four and even numbered yarns and a center cord provided in a hollow part of it. The twist multiplier K is set lesser than 350, the twist multiplier K being expressed ##EQU1## where T is a number of twists per 10 cm and D is a total denier.

BACKGROUND OF THE INVENTION 
The present invention relates to a fiber reinforced rubber, particularly, a 
reinforcement embedded in a rubber. 
Since high plessley, high elasticity, high dimensional stability, and high 
adhesive strength has been required for rubbers such as a belt, a tire, 
and a hose, a reinforcing cord constructed by fibers or a reinforcing 
canvas is embedded in a rubber. Generally, a cord of twisted yarns is used 
for the reinforcement. The yarn may be all twisted, only half of them 
twisted, or lang lay. The yarns, all of them twisted, are most popular for 
reinforcement for a rubber. 
However, in a rubber reinforced by a twisted yarn, for example, an 
industrial belt such as a transmission belt and a conveyor belt, 
maintainability of plessley and maintainability of modulus of elasticity 
are lowered due to a twisted yarn twisted many times. This shows that 
maintainability of plessley and maintainability of modulus of elasticity 
decrease after a certain number of twists. 
A rubber reinforced by nontwisted yarn has been known to solve the above 
problems (maintainability of plessley and maintainability of modulus of 
elasticity). Although maintainability of plessley and maintainability of 
modulus of elasticity decrease when the number of twists of a yarn is 
large, high maintainability of plessley and maintainability of modulus of 
elasticity can be obtained when the number of twists of a yarn is small, 
so to speak less twisted. Therefore, a yarn loosely twisted at the optimum 
maintainability of plessley and maintainability of modulus of elasticity 
is considered suitable for a rubber. 
However, since a rubber reinforced by nontwisted yarn or less twisted yarn 
possesses disadvantages such as poor dimensional stability and its section 
is easily deformed to an external stress, destruction of filament is 
easily caused at a contacting surface to the reinforcement. 
A braided cord has been made for various purposes. Since the dimensional 
stability is especially high due to its structural characteristics in the 
cylindrically braided cord, more than four and even numbered cords are 
braided to form a hollow part, the dimensional stability of a rubber is 
improved and maintainability of plessley and maintainability of modulus of 
elasticity of a reinforcement are also kept high if a cylindrically 
braided cord is used for a reinforcement of a rubber. 
SUMMARY OF THE INVENTION 
The object of the present invention is to improve the dimensional stability 
of a rubber, besides improvement of maintainability of plessley and 
maintainability of modulus of elasticity, by providing a nontwisted yarn 
or less twisted yarn in a center hollow part of a cylindrically braided 
cord. 
In order to achieve the above object, a reinforcement embedded in a rubber 
is constructed by a cylindrically braided cord, which is braided in a 
cylindrical configuration by more than four and even numbered yarns, and a 
center cord provided inside the hollow. Also, the twist multiplier is set 
less than 350. The twist multiplier K is obtained by the following 
equation where T is the number of twists per 10 cm and D is the total 
denier

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Preferred embodiment will be described below with reference to accompanying 
drawings. 
FIG. 3 illustrates a toothed belt A as a fiber reinforced rubber. The 
toothed belt A comprises a belt base 4 having an stretching rubber ply 1 
and a plurality of teeth 3 formed over one side thereon (underside of the 
belt base in FIG. 3) and made of the same material, a rubber, as the 
stretching rubber ply 1 (only two teeth are shown in FIG. 3). A fiber 
reinforcement 2 is embedded on the stretching rubber ply 1 of the belt 
base 4. A canvas layer 5 is adhered to a surface of teeth 3 of the belt 
base 4. 
The reinforcement 2, as enlargely shown in FIGS. 1 and 2, is constructed by 
both cylindrically braided cords 7 of more than four and even numbered 
yarns 6 (four yarns in the present embodiment) having a hollow part 8 and 
a center cord 9 provided inside a hollow part 8 of the cylindrically 
braided cord 7. The present invention is characterized in that the center 
cord 9 is constructed by nontwisted yarn or loosely twisted yarn having 
the twist multiplier K lesser than 350, the twist multiplier K being 
expressed by the following equation where T is the number of twists per 10 
cm and D is the total denier 
##EQU3## 
The yarn 6 may be an inorganic fiber, an organic fiber, or a metallic 
fiber. Further, a spun yarn of a short or long staple fiber or combination 
of those can be used for the yarn 6 depending on the required performance 
of the toothed belt A. A long staple fiber having high plessley and 
modulus of elasticity is preferred. When a combination yarn is used for 
the yarn 6, at least one of the yarn needs to be high plessley and high 
modulus of elasticity. 
Also, the number of yarns 6 forming a cylindrically braided cord 7 can be 
any even numbers if it is more than 4. In order to make a cord of 
cylindrical configuration, more than four and even numbered yarns are 
required. A symmetric hollow part 8 cannot be formed with the odd numbered 
yarns. Also, the total denier of the yarn 6 and the denier of the 
monofilament are selected according to the required performance of the 
toothed belt A. The center cord 9 is composed of the same or different 
fibers of the above yarn 6 depending on the usage and object of the cord. 
Since both maintainability of plessley and maintainability of modulus of 
elasticity are high wherein K=1.about.350, as shown in data in FIG. 4, the 
twist multiplier K is set lesser than 350, the twist multiplier K being 
expressed by the following equation where T is the number of twists per 10 
cm and D is the total denier 
##EQU4## 
The twisting direction of the center cord 9 and the twisting method (all 
yarns are twisted, half of yarns are twisted, or lang lay) is not limited 
to specific types. 
The cylindrically braided cord 7 go through adhesive process, which the 
cord is soaked into adhesive combined with epoxy resin, isocyanate 
compound, ethylene urea compound, and resorcin formalin latex (RFL), etc. 
and stretching process before it is embedded in the stretching rubber ply 
1. Dipping process is preferable for the adhesive process in order to soak 
adhesive evenly from surface to inside of it. 
The result of an elongation test is carried out, comparing the above 
constructed toothed belt A with a comparable example. 
Construction of Toothed Belt A According to the Present Invention 
Four 330 de of nylon fibers are used for the cylindrically braided cord 7, 
having three simply arranged 1500 de (the number of total denier is 4500 
de) Kevlar (product of DuPont) composed of aramid fibers used for a center 
cord 9 constructing a reinforcement 2. 
The cylindrically braided cord 7 is dipped into the isoayanate compound so 
as to form a sub-coat ply, then it is dipped into the adhesive combination 
liquid of resorcin formalin latex (RFL) so as to form a second-coat ply; 
further, it is dipped into chloroprene rubber so as to form a top-coat 
ply, and finally a stretching process is carried out with 1 g/de tension. 
The toothed belt A wherein the reinforcement 2 composed of a plurality of 
the cylindrically braided cords 7 having center cords 9 provided in the 
center hollow parts 8 are embedded on the belt base 4 is obtained in the 
following steps: a plurality of cylindrically braided cords 7 finished the 
stretching process is put spirally on the stretching rubber ply 1 of the 
chloroprene rubber, and the teeth 3 of the chloroprene rubber is formed on 
it so that the cylindrically braided cord 7 is embedded thereon, 
thereafter, the nylon cloth 5 is adhered to the surface of teeth 3 and the 
rubber is cured. The adhesive is soaked evenly from the surface to the 
inside of the cylindrically braided yarn 7 during the adhesive process. 
Toothed Belt of Comparable Example 
Three 1500 de (total denier is 4500) Kevlar (product of DuPont) of aramid 
fibers are used for the center cord 9. Other features are the same as the 
belt of the present invention. 
Test on Elongation 
The test was carried out by the system shown in FIG. 5, where the toothed 
belt A is wound around two pulleys (50 mm in diameter) and a predetermined 
tension is applied to the toothed belt A by a weight 11. 
The test data is shown in FIG. 6. From this test data, the elongation of 
the present invention is 0.015 mm and the elongation of the comparable 
example is 0.035 mm wherein the load 300 kgf is applied, which is more 
than double of the present invention. This shows that the present 
embodiment is superior in the dimensional stability. The difference 
results from that the center cord 9 provided in the hollow part 8 of the 
cylindrically braided cord 7 is composed of three simply arranged yarns, 
although the center cord 9 is composed of three yarns, all twisted yarns. 
As shown above, in the present invention, the reinforcement 2 embedded in 
the belt body 4 is constructed by providing the center cord 9 having the 
twist multiplier K lesser than 350 in the hollow part 8 of the 
cylindrically braided cord 7 braided by more than four and even numbered 
yarns 6. The twist multiplier being expressed by the equation 
##EQU5## 
where K is the twist multiplier, T is the number of twists per 10 cm, and 
D is the total denier. The twisting characteristic of the center cord 9 
improves maintainability of plessley and maintainability of modulus of 
elasticity. Also, the structural characteristic of the cylindrically 
braided cord 7 covers the deforms of a twisted yarn to the external stress 
and improves the dimensional stability of the toothed belt A. 
In the present embodiment, the flex rigidity of the toothed belt A (the 
cylindrically braided cord 7) is regulated by selecting the material and 
thickness of the center cord 9 according to the object and the usage. 
Moreover, in the present embodiment, the toothed belt A is shown for a 
rubber. However, the belt is not limited to the toothed belt A, but covers 
an industrial belt such as a conveyor belt and a transmission belt like a 
flat belt and a ribbed belt. The present invention also can be applied to 
rubbers other than belts, for example, to tires and hoses.