Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2000-12-15
2002-12-31
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S367000, C428S368000, C428S375000, C428S378000, C428S372000, C428S364000, C428S408000
Reexamination Certificate
active
06500531
ABSTRACT:
TECHNICAL FIELD
This invention relates to a rubber reinforcing cord suitably used as a reinforcing material of various rubber materials such as tires, belt and hoses, and also to a fiber reinforced rubber material reinforced by said rubber reinforcing cord.
BACKGROUND ART
Fiber reinforced rubber materials reinforced by rubber reinforcing cords are widely used as rubber materials such as tires, belts, hoses, etc. In general, in these rubber materials, a matrix containing a rubber is reinforced by a cord obtained by coating a twisted reinforcing fiber bundle with an adhesive to form the surface layer of the bundle.
Carbon fibers have high strength and high elastic modulus and also have excellent heat resistance and water resistance, but are poor in the fatigue resistance against such deformation as elongation and compression deformation and bending deformation. So, it has been considered that a fiber reinforced rubber material reinforced by a rubber reinforcing cord formed by carbon fibers is poor in durability.
As attempts to solve the problem, JP, 60-181369, A discloses a method of depositing a mixture consisting of an epoxy compound and a rubber latex on a carbon fiber bundle, and JP, 63-6165, A discloses a method of depositing a mixture consisting of a phenol derivative and a rubber latex on a carbon fiber bundle.
However, even these methods cannot satisfy the fatigue resistance required for such rubber materials as tires, belts and hoses, and any rubber reinforcing cord formed by carbon fibers having sufficient fatigue resistance has not be obtained yet.
DISCLOSURE OF THE INVENTION
To solve the above problem, this invention has the following constitution: A rubber reinforcing cord, characterized in that a carbon fiber bundle having a breaking extension of 1.7% or more is impregnated with a resin composition containing a rubber latex, and that the initial gradient (dM/dy) at y=0 of the bending load M—deflection y curve of the cord is 1000 N/m or less.
To solve the above problem, this invention also has the following constitution: A substantially twist-less rubber reinforcing cord, characterized in that a carbon fiber bundle having a breaking extension of 1.7% or more is impregnated with a resin composition containing a rubber latex, and that the number of twist of the cord is 10 per meter or less.
THE BEST MODE FOR CARRYING OUT THE INVENTION
The inventors found that a rubber enforcing cord, characterized in that a carbon fiber bundle having a breaking extension of more than a certain value is impregnated with a resin composition containing a rubber latex, and that the initial gradient of the bending load-deflection curve of the cord is less than a certain value or that the number of twist of the cord is less than a certain value can exhibit excellent fatigue resistance unexpectedly, to solve the above problems all at once.
In this invention, it is necessary that the breaking extension of the carbon fiber bundle is 1.7% or more. Preferable is 1.8% or more, and more preferable is 1.9% or more. If the breaking extension is less than 1.7%, the cord is likely to be broken when the rubber material is excessively deformed by an external force, and cannot be used for such applications as tires and belts.
In this invention, it is desirable that the rubber reinforcing cord is 1000 N/m or less or less in the initial gradient of the bending load-deflection curve used as an indicator of flexibility. Preferable is 900 N/m or less, and more preferable is 800 N/m. If the initial gradient is more than 1000 N/m, the cord is low in flexibility, and is likely to have stress concentration caused when the rubber material is repetitively deformed, and is insufficient in fatigue resistance.
In this invention, it is preferable that the rubber reinforcing cord is 10 per meter or less in the number of twist. Preferable are 7 per meter or less, and more preferable are 5 per meter or less. If the number of twist is more than 10 per meter, the abrasion between single fibers is likely to be caused in the cord when the rubber material is repetitively deformed, and the fatigue resistance may become insufficient.
The carbon fiber bundle used in this invention has a tensile strength of 4000 Mpa or more. Preferable is 4400 Mpa or more, and more preferable is 4800 Mpa or more. If the tensile strength is less than 4000 Mpa, the cord is likely to be broken when the rubber material is excessively loaded, and cannot be used for such applications as tires and belts.
It is desirable that the carbon fiber bundle used in this invention has 4000 or 20000 single fibers. A preferable range is 6000 to 18000, and a more preferable range is 8000 to 16000. If the number of single fibers is less than 4000, the reinforcing effect by the cord is insufficient, and the dimensional stability of the rubber material may become insufficient. If more than 20000, it can happen that the cord contains portions not impregnated with the resin composition, and that the rubber material becomes insufficient in fatigue resistance.
It is desirable that the carbon fiber bundle used in this invention is substantially circular in the cross sectional form of each single fiber. If the cross sectional form of each single fiber is not substantially circular and is of any other form such as ellipse, broad bean or three lobes, the abrasion between single fibers makes the cord likely to be broken, and the rubber material may become insufficient in fatigue resistance.
“Being substantially circular” in the above description means that the deformation degree of the section defined by ratio (=R/r) of the radius (R) of the circumscribed circle of the section of the single fiber to the radius (r) of the inscribed circle is in a range of 1 to 1.1.
In this invention, in order to prevent the breaking of the cord or the separation at the cord-rubber interface due to the abrasion between single fibers caused when the rubber material is repetitively deformed, and also in order to improve the fatigue resistance, it is necessary that the carbon fiber bundle is impregnated with a resin composition containing a rubber latex as an essential ingredient.
In general, a rubber latex has a high polymer stably dispersed in water. So, for preventing the voids that impair the fatigue resistance of the cord, it is preferable that the water contained in the cord is removed by heating and drying after the carbon fiber bundle has been impregnated with a resin composition containing a rubber latex.
It is desirable that the resin composition content after drying is 20 to 50 wt % based on 100 wt % of the carbon fiber bundle. A preferable range is 25 to 45 wt %, and a more preferable range is 30 to 40 wt %. If the content is less than 20 wt %, the impregnation of the resin composition into the center portion of the fibre bundle becomes insufficient and the prevention of abrasion between single fibers may become imperfect, and the fatigue resistance of the cord may become insufficient. If more than 50 wt %, the heat resistance, water resistance and solvent resistance of the cord may become insufficient.
In this invention, the elastic modulus of the dried film of the rubber latex at 25° C. (G′) should be 0.4 MPa or less, preferably, 0.3 MPa or less, more preferably 0.2 MPa or less. If it is more than 0.4 MPa, the fatigue resistance of the fiber reinforced rubber material becomes insufficient.
Examples of the rubber latex are acrylate-butadiene rubber latexes, acrylonitrile-butadiene rubber latex, isoprene rubber latex, urethane rubber latex, chloroprene rubber latex, styrene-butadiene rubber latex, natural rubber latex, and vinylpyridine-styrene-butadiene rubber latex. Among them, vinylpyridine-styrene-butadiene rubber latex, styrene-butadiene rubber latex and acrylonitrile-butadiene rubber latex are especially effective for improving the fatigue resistance.
It is desirable that the rubber latex (including that of RFL) content is 40 to 80 wt % based on 100 wt % of the resin composition after drying. A preferable range is 45 to 75 wt %, and a more preferable range is 50
Kishi Hajime
Kondo Haruhiko
Manabe Takao
Dixon Merrick
Toray Industries Inc.
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