Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2001-02-05
2004-09-21
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
Optical transmission cable
Loose tube type
C385S112000, C385S113000
Reexamination Certificate
active
06795625
ABSTRACT:
FIELD OF THE ART
This invention concerns an SZ-spiral-grooved spacer for optical fiber cable, an optical fiber cable that uses this spacer, and a method for producing this spacer, and in particular, concerns an SZ-spiral-grooved spacer, which is made thin in diameter as a result of the groove inclination at the inversion parts being restricted even though the minimum rib thickness is 1.0 mm or less.
BACKGROUND ART
The making of optical fiber cables thin in diameter, lightweight, and high in optical wiring density is being pursued to reduce cable prices and laying costs, and there have been stringent demands for making polyethylene (PE) spacers, which accommodate optical fibers, thin in diameter as well.
Meanwhile, with recent aerial optical fiber cables, intermediate post-branching performance of the optical fibers is being required in addition to high optical wiring densities, and this has lead to the frequent use of SZ-type optical fiber cables, which use a PE spacer (SZ spacer), having grooves that accommodate the optical fibers and are alternately inverted in spiraling direction in SZ-like manner, and with which a plurality of tape-form optical fibers are accommodated within each groove of the spacer.
In the case where a rigid optical tape is to be accommodated used in an SZ spacer, the dimensions of an accommodating groove must enable the securing of adequate space for allowing the twisting of the tape. Also, though the polyethylene resin that comprises the rib undergoes three-dimensional molding shrinkage (sum of the shrinkage due to recrystallization during solidification and volume shrinkage due to lowering of the resin temperature) in the process of extrusion molding, unlike in the case of a unidirectionally stranded spacer, with which there is no allowance for shrinkage of the ribs in the length direction, in the case of an SZ spacer, lengthwise shrinkage of the ribs is possible in the form of short-cutting the inversion curve at just the inversion part, and as a result, the ribs can collapse towards the inner side of the inversion curve.
This phenomenon becomes more prominent when the ribs are made thin in root thickness and, along with the abovementioned securing of groove space, this has been a factor that has hampered the making of SZ slots thin in diameter.
It is considered that besides the molding shrinkage of the resin, the collapsing of the ribs may be caused by the mutual pulling of the coating resins, due to differences in the drawdown of the resin, etc., in the process of performing extrusion coating from a nozzle.
In the case of an optical fiber cable that uses a thin-diameter SZ spacer, with which the minimum rib thickness at the root, etc. of the rib is thin, the inversion pitch must be made short in order to allow for extra lengths of optical fiber, and since the inclination angle of the groove at the inversion part thus becomes large, the transmission loss is increased inevitably.
An object of this invention is to provide an SZ-spiral-grooved spacer for optical fiber cable, with which the groove inclination at the inversion parts of the SZ spacer is restricted and is low in the increase of transmission loss, and an optical fiber cable that uses this spacer to realize the making of optical fiber cables thin in diameter.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, this invention provides in a polyethylene spacer for optical fiber cable, with which a thermoplastic resin, with compatibility with polyethylene, is applied as an intermediate coating layer onto the periphery of a central tensile member and with which a main coating, having continuous spiral grooves that are for accommodating optical fibers and are inverted periodically in direction along the length direction, is formed from polyethylene on the outer periphery of the abovementioned intermediate coating layer, a spacer such that the minimum rib thickness of the ribs that define the abovementioned spiral grooves is 1.0 mm or less and the groove inclination angle in the spacer cross section of the inversion parts is 18° or less.
This invention also provides in a polyethylene spacer for optical fiber cable, with which a main coating, having continuous spiral grooves that are for accommodating optical fibers and are inverted periodically in direction along the length direction, is formed from polyethylene on the outer periphery of a central tensile member, a spacer such that the minimum rib thickness of the ribs that define the abovementioned spiral grooves is 1.0 mm or less and the groove inclination angle in the spacer cross section of the inversion parts is 18 or less.
With the spacer of the above arrangement, the resin density of the portions substantially at the roots of the ribs that define the abovementioned spiral grooves may be made the smallest in comparison to the tip parts of the ribs and the central parts of the ribs.
With the spacer of the above arrangement, the average roughness of the groove bottoms of the abovementioned spiral grooves may be made 1.2 &mgr;m or less.
With the spacer of the above arrangement, the spiral progression angle (&bgr;), as determined by
tan&bgr;=(
d
×&pgr;×&thgr;/360)/
p
where d is the outer diameter, &thgr; is the spiral groove inversion angle, and p is the spiral groove inversion pitch, may be set in the range, 5 to 15°.
Also with the present invention, the spacer of the above arrangement may be used to accommodate a plurality of tape-form optical fibers in at least one or more spiral grooves to form an optical fiber cable.
Also with the present invention, the spacer of the above arrangement may be used to accommodate a single-core optical fiber in at least one or more spiral grooves to form an optical fiber cable.
Furthermore, the present invention provides in a method for producing a polyethylene spacer for optical fiber cable, with which a thermoplastic resin, with compatibility with polyethylene, is applied as an intermediate coating layer onto the periphery of a central tensile member and with which a polyethylene main spacer coating, having continuous spiral grooves that are for accommodating optical fibers and are inverted periodically in direction along the length direction, is formed on the outer periphery of the abovementioned intermediate coating layer, a production method wherein after the abovementioned main spacer coating spacer is applied, a cooling medium is blown, obliquely at a predetermined angle with respect to the running direction of the abovementioned spacer, onto the outer periphery of the abovementioned spacer.
This invention also provides in a method for producing a polyethylene spacer for optical fiber cable, with which a polyethylene main spacer coating, having continuous spiral grooves that are for accommodating optical fibers and are inverted periodically in direction along the length direction, is formed on the periphery of a central tensile member, a production method wherein after the abovementioned main spacer coating spacer is applied, a cooling medium is blown, obliquely at a predetermined angle with respect to the running direction of the abovementioned spacer, onto the outer periphery of the abovementioned spacer.
This invention also provides in a method for producing a polyethylene spacer for optical fiber cable, with which a polyethylene main spacer coating, having continuous spiral grooves that are for accommodating optical fibers and are inverted periodically in direction along the length direction, is formed on the outer periphery of a central tensile member, a production method wherein a reinforced fiber bundle, which comprises the abovementioned tensile member, is drawn upon being impregnated with an uncured thermosetting resin, then upon inserting this reinforced fiber bundle into a melt extrusion molding die, a polyethylene resin is extruded and coated onto the outer periphery, then after cooling the coated resin on the surface, the thermosetting resin in the interior is cured, and then after applying the abovementioned main spacer coating onto the outer periphery of
Ishii Toku
Ito Kenji
Watanabe Kazunori
Jordan and Hamburg LLP
Rahll Jerry T
Ube-Nitto Kasei Co., Ltd.
Ullah Akm Enayet
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