Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
1999-06-14
2001-02-06
Stryjewski, William (Department: 3741)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S902000
Reexamination Certificate
active
06182433
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a steel cord for the reinforcement of rubber articles, and more particularly to a steel cord usable as a reinforcing member in a belt layer for tuck and bus radial tire (TBR).
2. Description of Related Art
As a steel cord for the reinforcement of a belt in TBR, there has hitherto been used a steel cord of three-layer a structure consisting of a core formed by twisting plural steel filaments and two sheaths formed by twisting steel filaments around the core in two layers. Recently, to reduce the weight and simplify the structure in the belt of TBR, there is widely been used a steel cord of two-layer structure consisting of a core and a single sheath.
Among steel cords of two-layer structure, a steel cord having a core wherein plural steel filaments are arranged in line without twisting is known to have the following merits.
(1) The steel cord can be produced at a single twisting step, so that the economic situation is excellent.
(2) Such steel cords are arranged side by side in a belt layer of a tire to extend in a direction of a line connecting the centers of the core filaments in the cord (hereinafter referred to as a core parallel direction) within a plane of the belt layer. As a result the tire having an excellent steering stability is obtained without damaging ride comfort and the like. Also, the thickness of the belt layer can be thinned, so that tire weight can be reduced.
For example, there are disclosed the following techniques with respect to steel cords for the reinforcement of rubber article having a two-layer structure consisting of a core formed by arranging plural core filaments (M filaments) in parallel to each other without twisting and a single sheath formed by twisting plural sheath filaments (N filaments) around the core (hereinafter referred to as M parallel+N structure).
In JP-A-9-158065 is disclosed a steel cord of M parallel+N structure consisting of a core formed by arranging plural core filaments side by side without twisting and a sheath formed by circumscribing plural sheath filaments with the core filaments and twisting the sheath filaments around the core, and having an elliptical shape at its section.
In JP-A-9-156314 is disclosed a steel cord of 2 parallel+N structure (N=5-8) consisting of a core formed by arranging two core filaments of same diameter side by side without twisting and a sheath formed by helically winding 5-8 sheath filaments, each having a diameter corresponding to 0.8-1.2 times the diameter of the core filament, around the core close thereto at a pitch corresponding to 40-60 times the diameter of the sheath filament while forming a gap between the sheath filaments, and having substantially an elliptical shape at its sectional profile.
However, the conventional steel cords of M parallel+N structure have the following problems.
(1) Since the difference in load bearing between the core filament and the sheath filament is large, the efficiency of developing strength and durability are poor.
(2) The core filaments are easy to cross to each other.
(3) Since an internal distorsion remains between the core and the sheath, when a rubberized sheet containing a plurality of such steel cords arranged side by side is cut, it is easy to cause warping at a cut end portion of the sheet. Therefore, the handling of the cut sheet is poor in the production of the tire.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to solve the aforementioned problems and to provide steel cords for the reinforcement of rubber articles wherein cross portions of the core filaments hardly exist in the steel cord of M parallel+N structure and the residual internal distorsion is small and the efficiency of developing the strength and the durability are excellent.
The inventors have made various studies in order to solve the above problems and have found that the above object can be attained by rationalizing a filament diameter and a ratio of twisting pitch in a steel cord for the reinforcement of rubber article having 2 parallel+7 structure or 2 parallel+8 structure and as a result the invention has been accomplished.
According to a first aspect of the invention, there is the provision of a steel cord for the reinforcement of rubber article consisting of a core formed by arranging two straight core filaments having a diameter dc side by side in a longitudinal direction without twisting and a sheath formed by twisting seven sheath filaments having a diameter ds around the core, and having a flat profile at its section, wherein the diameter dc of the core filament is within a range of 0.30-0.38 mm, and the diameter ds of the sheath filament is not more than dc+0.03 mm but not less than dc−0.03 mm, and a twisting pitch P of the sheath filament is not less than 50 times the diameter dc of the core filament but not more than 120 times the diameter ds of the sheath filament.
In preferable embodiments of the first aspect of the invention, the diameter dc of the core filament is within a range of 0.32-0.36 mm, and the diameter ds of the sheath filament is not more than dc+0.03 mm but not less than dc−0.01 mm, and the twisting pitch P is not less than 60 times the diameter dc of the core filament but not more than 90 times the diameter ds of the sheath filament.
According to a second aspect of the invention, there is the provision of a steel cord for the reinforcement of rubber article consisting of a core formed by arranging two straight core filaments having a diameter dc side by side in a longitudinal direction without twisting and a sheath formed by twisting eight sheath filaments having a diameter ds around the core, and having a flat profile at its section, wherein the diameter dc of the core filament is within a range of 0.30-0.38 mm, and the diameter ds of the sheath filament is not more than dc−0.01 mm but not less than dc−0.05 mm, and a twisting pitch P of the sheath filament is not less than 50 times the diameter dc of the core filament but not more than 120 times the diameter ds of the sheath filament.
In preferable embodiments of the second aspect of the invention, the diameter dc of the core filament is within a range of 0.32-0.36 mm, and the diameter ds of the sheath filament is not more than dc−0.01 mm but not less than dc−0.03 mm, and the twisting pitch P is not less than 60 times the diameter dc of the core filament but not more than 90 times the diameter ds of the sheath filament.
REFERENCES:
patent: 4609024 (1986-09-01), Yatsunami et al.
patent: 5765355 (1998-06-01), Yanagisawa et al.
patent: 5802829 (1998-09-01), Yamanaka
patent: 0 399 795 (1990-11-01), None
patent: 9-158065 (1997-06-01), None
patent: 9-156314 (1997-06-01), None
Bridgestone Corporation
Stryjewski William
Sughrue Mion Zinn Macpeak & Seas, PLLC
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