Note: Descriptions are shown in the official language in which they were submitted.
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WATER BLOCKING COMPONENTS FOR FIBER OPTIC CABLES
The present invention relates to fiber optic cables
and, more particularly, to water blocking components of
fiber optic cables.
Fiber optic cables include optical fibers which
transmit information in cable television, computer, power,
and telephone systems. A fiber optic cable may be installed
in an environment where the cable is exposed to water. The
migration of water in a fiber optic cable is a problem which
1o may occur where the cable jacket has been cut or otherwise
breached and water enters the cable. The migration of water
in a cable may cause the flooding of a cable passageway or
enclosure, and/or it may negatively affect the performance
of the optical fibers. For example, fiber optic cables of
the slotted rod or loose tube types present potential water
migration paths.
To block the flow of water in a cable, known fiber
optic cables may include hardened resin walls, a hard to
remove flooding or filling compound, or a more craft-
2o friendly, dry water absorbent chemical. US-A-4381140
discloses a slotted core type fiber optic cable wherein
optical fibers are fixed to the slotted core by hardened
walls of polyurethane resin that define solid barriers
against the migration of water. This solution to the water
migration problem is disadvantageous because it makes the
cable heavy and stiff. An additional disadvantage is that,
upon bending of the cable, stress may flow from the slotted
core to the hardened polyurethane and thence to the optical
fibers therein, whereby the optical fibers may experience
3o breakage, macrobending, or microbending.
As noted above, flooding or filling compounds may be
used to block the flow of water in a fiber optic cable. US-
A-4752113 and US-A-4701015 disclose slotted rod type cables
that include a hard to remove polybutylene flooding compound
or jelly. Loosely applied damp-proof powder is disposed
between spaced masses of the jelly. This solution to the
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problem of water migration is disadvantageous because the
jelly is hard to remove. An additional disadvantage is that
the application of loose powder and spaced masses of jelly
hinder manufacturing processes and result in high production
costs. Moreover, the jelly is expensive and it makes the
cable heavy and difficult to route through cable
passageways. Further, the damp-proof powder is subject to a
variable distribution in the grooves of the slotted rod
which may leave sections of the cable unprotected from water
1o migration.
As noted above, a dry water absorbent chemical is more
craft-friendly than hardened resin walls or a hard to remove
and messy flooding or filling compound. A typical water
absorbent chemical includes a polymer chain with reaction
sites that react with water, thereby transforming the water
absorbent chemical into an expanded mass of viscous gel.
The viscous gel acts as a physical barrier to the migration
of water. The water absorbent chemical is typically
impregnated in a yarn or a non-woven tape. Such water
2o blocking tapes and yarns may be disadvantageous because,
rather than being generally distributed in a slotted core
groove, the water absorbent chemical is localized within the
immediate area of tape or yarn, e.g., in a small cross
sectional area of the groove. As described in more detail
below, the localized distribution of the water absorbent
chemical may limit the water blocking effectiveness of the
tape or yarn.
For example, the water blocking effectiveness of
conventional water absorptive tapes may be limited in
3o slotted rod type cables. US-A-5179611 discloses a slotted
rod type fiber optic cable that includes a dry water
absorptive tape wrapped around the slotted rod. Prior art
described therein is a water absorbent tape placed between
optical fiber ribbons located in a groove of the slotted
rod. The prior art solution to the water blocking problem
is stated to be cumbersome and time-consuming, resulting in
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a lowering of the production efficiency of the fiber optic
cable. The tape disclosed in US-A-5179611 is a non-woven
fabric, a paper or other sheet-like object, which is
topically coated or impregnated with a combination of a
thermoplastic elastomer binding agent, and a water
absorptive resin combined with a water soluble resin.
However, the water absorptive tape localizes the water
absorbent chemical in the area surrounding the slotted core)
which may negatively affect the water blocking effectiveness
1o of the tape. For example, upon gelation of the water
absorbent chemical, the gel may not extend to radially inner
interstices of the grooves.
The water blocking effectiveness of a water absorbent
powder may be limited by a non-uniform distribution of the
powder in the cable. US-A-4401366 discloses a slotted rod
type cable wherein each groove of the slotted rod includes
optical waveguides and a mixture of a hydrophilic powder and
a hydrophobic powder. The hydrophilic powder is a high
molecular weight polyacrylamide powder, and the hydrophobic
zo powder is a calcium carbonate powder, the particles of which
are coated with stearic acid. The polyacrylamide powder is
designed to prevent the optical waveguides from being
subjected to compression by ice in the grooves, whereby
attenuation in the waveguides is not increased. The powdery
mixture is disadvantageous because it may create
microbending, it is expensive, and it is subject to movement
in the grooves along the cable length. This results in a
variable distribution of the powders along the cable length,
whereby, upon gelation of the water absorbent chemical,
3o sections of the grooves may not be protected from the
migration of water.
In view of the foregoing, the localized distributions
of water absorbent tapes, and the variable distribution of
water absorbent powders, may not be effective to block the
flow of water in slotted core cables because, even though
the water absorbent chemicals may swell, nevertheless water
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migration paths may exist in unprotected areas of the
grooves. As a further illustration, US-A-4596443 discloses
a water detection system including a slotted rod type fiber
optic cable having a slot with a signaling optical conductor
herein. The signaling optical conductor is located in a
particular groove of the slotted rod, which groove includes
a wave-shaped pattern and a significant quantity of
localized water swellable material. When water enters the
particular groove, the water swellable material may swell
1o thereby forcing the wave shaped pattern into pressing
engagement with the signaling conductor. The signaling
conductor is deformed whereby it experiences a detectable
increase in attenuation that indicates that water has
penetrated into the groove. This arrangement is
disadvantageous because a significant amount of water
swellable material is required to support the forcing
function of the wave pattern, i.e., beyond that which is
needed to block the flow of water. Moreover, water may
migrate through the cable without contacting the localized
2o water swellable material.
As noted above, water blocking yarns localize the water
absorbent chemical and may have limited water blocking
effectiveness. For example, fibrous braids restrict water
absorbent chemicals to a sparse cross sectional area which
may cause potential leak paths. US-A-4703998 discloses a
slotted rod type fiber optic cable having optical fibers
disposed in respective grooves of the slotted rod. Each
optical fiber includes a water absorbent yarn wrapped
therearound. A disadvantage of this solution is that, since
3o the fibrous braid occupies only a sparse cross sectional
area of the groove, the fibrous braid restricts the
distribution of the water absorbent chemical to the small
cross sectional area thereof. The localized distribution of
the water absorbent chemical in the grooves limits the water
blocking effectiveness of the fibrous braids.
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Obiects of the Invention
In view of the foregoing, it is an object of the
present invention to provide a fiber optic cable comprising
a slotted rod having at least one groove, the groove
including at least one optical fiber, the cable further
including a water blocking component disposed in one of the
grooves, the water blocking component comprising a foamed
substrate which defines a profile, at least portions of the
1o profile comprise a stabilized water absorbent entity for
effective water blocking in the groove.
It is another object of the present invention to
provide a loose tube fiber optic cable having at least one
tube including at least one optical fiber therein, and
a water blocking component disposed adjacent to the at least
one tube, the water blocking component comprising a plastic
substrate which defines a profile, at least portions of the
profile comprising a stabilized water absorbent layer for
blocking water adjacent the tube, the water absorbent layer
comprising a mixture of a water absorbent substance and an
adhesive substance, wherein the adhesive substance
stabilizing the position of the water absorbent substance on
the profile.
It is a further object of the present invention to
z5 provide a fiber optic cable having at least one optical
fiber and a water blocking component, wherein the water
blocking component comprising a plastic material that
defines a non-porous profile, at least portions of the
profile comprising a stabilized water absorbent entity
3o thereon for effective water blocking.
It is another object of the present invention to
provide a method of installing a water absorbent component
in a cable core, comprising the steps of passing a water
blocking component in the form of a plastic substrate having
35 a stable water absorbent layer thereon through a rotatable
stranding device and stranding the water blocking component
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into a cable core. The water blocking component may be
stranded into a groove of a slotted rod, or stranded with
buffer tubes into a loose tube cable core.
brief Description of the Drawings
Figure 1 is an isometric view of a fiber optic cable
according to an embodiment of the present invention.
Figure 2 is a cross sectional view of the fiber optic
cable of Figure 1 taken along line 2-2.
1o Figure 3 is a cross sectional view of a fiber optic
cable according to a second embodiment of the present
invention.
Figure 4 is a quarter section of a fiber optic cable
according to a third embodiment of the present invention.
Figure 5 is a cross sectional view of an extrusion head
for use in the making of water blocking components in
accordance with the present invention.
Figure 6 is a part sectional view of a stranding device
for use in the manufacture of fiber optic cables according
2o to the present invention.
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Detailed Description of the Invention
In achieving the foregoing objects, the present
invention provides water blocking components for blocking
the flow of water in fiber optic cables and methods of
making the components. Each water blocking component
includes a respective substrate that includes a water
absorbent entity. In an embodiment of the present
invention, the substrate is a rod formed of a plastic
polymeric material, and the water absorbent entity is a
io water absorbent layer. The water absorbent layer is a
mixture of a water absorbent substance and an adhesive
substance. The cross sectional profiles of water blocking
components distribute the water absorbent substance, and the
adhesive substance stabilizes the position of the water
is absorbent substance, thereby advantageously controlling the
location and distribution of the water blocking substance
and avoiding undesirable localization and variable
distribution of the water blocking substance. Additionally,
the bulk of the rods themselves substantially fill the
2o grooves and thereby effectuate a water blocking function. A
method of making the water blocking components includes the
application of a water absorbent layer to a rod as a thin
surface treatment, i.e., it is not impregnated into the rod
but, rather, it is adhered to the smooth, non-porous
25 surfaces of the rod. The rod may be formed of a foamed or a
non-foamed plastic.
Referring to Figures 1 and 2, a fiber optic cable 10
according to an embodiment of the present invention will be
described. Fiber optic cable 10 includes a slotted rod 12
3o with a central dielectric strength member 11 and buffer
tubes 13 disposed in helical or SZ-shaped grooves 25.
Slotted rod 12 includes ribs 12a that distribute radially
applied crushing loads from one side of cable 10 to another
while avoiding the application of crushing loads to buffer
35 tubes 13 and thereby protecting optical fibers in ribbon
stacks 14. A slotted rod suitable for use in the present
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invention is disclosed in commonly assigned patent US-A-
4784461, which patent is hereby incorporated by reference in
its entirety. Buffer tubes 13 may be surrounded by a water
swellable material 16 comprising a conventional water
blocking substance within grooves 25 (Figure 1).
Slotted rod 12 may be surrounded by a conventional
water blocking tape 18. Tape 18 typically comprises a
substrate, e.g. a non-woven tape, which is impregnated with
a conventional water swellable material. Tape 18 also
1o performs the function of holding buffer tubes 13 in grooves
25. Surrounding tape 18 is a metallic tape 20 which may
include corrugations and longitudinally overlapping edges.
A ripcord 19 may be disposed along the inner or outer
surface of tape 20. An outer jacket 21 surrounds metallic
tape 20, and jacket 21 may bond with tape 20 during
extrusion of jacket 21 around tape 20.
Water blocking components according to the present
invention will now be described. Where the fiber count of
fiber optic cable 10 does not require all of grooves 25 to
2o contain buffer tubes and/or optical fiber ribbons; water
blocking components according to the present invention, used
as filler rods, may be placed in the non-fiber containing
grooves 25 to prevent the migration of water therein. For
example, water blocking components 31,35 are disposed in
respective grooves 25 and include respective substrates, for
example, rods 32,36. At least portions of rods 32,36 are
treated with a water absorbent entity in the form of a water
absorbent layer 60, as further described below.
As shown in Figure 3, water blocking components
3o according to the present invention may be installed in a
slotted core type fiber optic cable 40. Fiber optic cable
40 includes a slotted rod 43 with a central member 44 and
slots 45 having optical fiber ribbons 42 therein. A
conventional water absorbent tape 47 surrounds slotted rod
43, and a jacket 48 surrounds water absorbent tape 47.
Water blocking components 51,55 are disposed in respective
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slots 43 and include respective substrates, for example,
rods 52,56. At least portions of water blocking components
51,55 are treated with a water absorbent layer 60.
Water absorbent layers 60 comprise a mixture of an
adhesive substance and at least one water absorbent
substance. Water absorbent layers 60 are a surface
treatment on the respective rods which are preferably not
impregnated with the water absorbent substance. The water
absorbent substance may be, for example, commercially
io available potassium polyacrylate particles or sodium
polyacrylate particles, as disclosed in US-A-5684904, which
patent is incorporated by reference herein in its entirety.
The adhesive substance may be an elastomer, e.g. a latex
binder, as disclosed in US-A-5689601, a water soluble or
water absorptive resin as disclosed in US-A-5179611, or a
water soluble hot melt adhesive as disclosed in US-A-
5649041, which patents are incorporated by reference herein
in their respective entireties. Additionally, water
absorbent layer 60 may be a plastisol) an ultraviolet (UV)_
light curable resin, as described in US-A-5684904, which
patent is incorporated by reference herein in its entirety.
Moreover) water absorbent layers 60 may include a
mixture of two distinct water absorbent substances. One of
the water absorbent substances is characterized by a very
fast swell rate, i.e., it has a relatively lightly plastic
polymeric structure. The other superabsorbent substance is
characterized by a high gel strength, i.e., it has a
relatively highly plastic polymeric structure. Suitable
superabsorbent substances having a very fast swell rate are
3o made commercially available by Sumitomo Chemicals, e.g.
formulation No. J550, and by Chemdal Cabdry, e.g.
formulation Nos. 130 or 150. Suitable superabsorbent
substances having a high gel strength are made commercially
available by Stockhausen, e.g. formulation Nos. 85-13 or 88-
13 sieved. Furthermore, water absorbent layers 60 may
include an anti-freezing chemical that is effective to
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depress the freezing point of water. Anti-freeze chemicals
are disclosed in US-A-5410629, US-A-5321788, and US-A-
4401366, which patents are hereby incorporated by reference.
The cross sectional profiles of water blocking
components 31,35,51,55 permit a distribution of the water
absorbent substance in each quadrant of a respective groove,
and the adhesive substance stabilizes the position of the
water absorbent substance, thereby advantageously
establishing the water blocking effectiveness of components
31,35,51,55. For example, as shown by the distribution of
portions of layer 60 of rod 55 about reference axes X-X,Y-Y
(Figure 3), portions of layer 60 are stabilized in each
quadrant of groove 45 thereby avoiding undesirable
localization of the water absorbent substance. Under normal
1s operating conditions, vibration or bending of the cable will
not redistribute the water absorbent substance thereby
avoiding an undesirable variable distribution of the water
absorbent substance along the cable length. A stable
distribution of the water absorbent substance is thus
2o achieved, thereby establishing the water blocking
effectiveness of components 31,35,51,55. The stable
distribution of the water absorbent substance may extend in
each quadrant of the groove, symmetrically or
asymmetrically, and/or along the full length of the water
25 blocking component.
Additionally, the bulk of the rods themselves
substantially fill the grooves and thereby effectuate a
water blocking function. For example, the profile of rod 32
has a cross sectional shape that is complementary to the
3o cross sectional shape of the groove, but loosely fits in the
groove. The loose fit between layer 60 and the walls of the
groove permits easy relative movement between the rod and
the groove during cable bending, thereby avoiding undue
contributions to the stiffness of the cable. Alternatively,
35 a water blocking component, for example as shown by the
profile of rod 52 (Figure 3), may be sized so that water
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absorbent layer 60 more tightly fits, and may press against,
the walls of the groove.
The amount of surface area treated with the water
absorbent substance of layer 60 is an important factor
s because it bears on the degree of exposure of the water
absorbent substance to water in the groove. For example,
the profile of rod 35 includes a geometry that includes
angles which define a capacious surface area that maximizes
the degree of exposure of water absorbent layer 60 in each
1o quadrant of the groove. The circular profile of water
blocking component 55 likewise defines a capacious surface
area, and rod 56 thereof has the added advantage of being a
commercially available item from the Aeroquip Corporation.
Manufacturing aspects of rods 32,36,52,56 will now be
1s described. Rods 32,36,52,56 may be made with an extrusion
head (not shown) having a suitable extrusion profile. Rods
32,36,52,56 may be formed of a non-foamed polyethylene, or a
medium density polyethylene that is foamed 20~-30~ with a
physical or a chemical foaming agent. The post extrusion,
2o surface finish of the rods is such that it is smooth and
non-porous. Such rods exhibit suitable flexibility and are
not easily compressed. Alternatively, one or more of the
rods may be foamed to 30~-50~ or more to reduce costs,
increase flexibility, and/or to increase compressibility.
25 During manufacture of water blocking components
31,35,51,55 water absorbent layer 60 is applied as a thin
surface treatment, i.e.) it is not impregnated into the rods
but, rather, it is adhered to the smooth, non-porous
surfaces of the rods. For example, as shown in Figure 5, a
3o coating die 200 with an inlet port 202 is used to apply a
thin water absorbent layer 60 to rod 55. In this example,
water absorbent layer 60 is a compound of a water absorbent
substance and an adhesive substance which is fed under
pressure and heat through inlet port 202. Alternatively,
35 extrusion head 200 may be adapted to co-extrude the plastic
of rods 32,36,52,56 with respective water absorbent layers
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60. In either event, the water absorbent layer is cured
after extrusion whereby the position of the water absorbent
substance becomes stabilized.
An exemplary manufacturing operation for installing water
s blocking components 31,35,51,55 in a slotted rod will now be
described. A stranding device 300 (Figure 6) may be used to
install water blocking components 31,35,51,55 in respective
grooves 25,45 of fiber optic cables 10,40. Device 300 is
made and used generally in accordance with the stranding
1o devices described US-A-4154049 and/or US-A-4195468, which
are hereby incorporated by reference in their respective
entireties. Stranding device 300 includes a rotatable plate
301 mounted to a stationary plate 302 with thrust bearings
303. Rotatable plate 302 includes distribution holes 305,
15 guide members 306, and a central aperture 307. In the
exemplary manufacturing operation, during a manufacturing
step in the manufacture of fiber optic cable 40, slotted rod
43 (Figure 3) passes through central hole 307 as water
blocking component 55 is fed through distribution hole 30~
20 (Figure 6). Guide member 306 guides the component into
groove 45 and rotatable plate is free to rotate as component
55 is guided into the groove.
The present invention has thus been described with
reference to the foregoing embodiments, which embodiments
25 are intended to be illustrative of the inventive concepts
rather than limiting. Persons of skill in the art will
appreciate that variations and modifications of the
foregoing embodiments may be made without departing from the
scope of the appended claims. For example, although the
3o invention has been described with reference to slotted rod
type cables, water blocking components 31,35,51,55 of the
present invention may be used with other fiber optic cable
types as well. For example, water blocking component 55 may
be installed in a cable 70 (Figure 4) having a loose tube
35 type cable core, for example as disclosed in commonly
assigned co-pending Application No. 08/885,575 which is
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incorporated by reference herein in its entirety, whereby
water absorbent layer 60 is effective to block the flow of
water between buffer tubes 73. Water blocking component 55
may be stranded with buffer tubes 73 in a loose tube cable
manufacturing process, for example, as disclosed in US-A-
5283014) which patent is incorporated by reference herein.
Although rods 32,36,52,55 have been described with
particular reference to a medium density foamed
polyethylene, other densities may be used well. In
io addition, the rods may be formed of suitable alternative
materials, for example, foamed or non-foamed polypropylene,
polyurethane, elastomers, or polyvinylchloride.
Moreover, water absorbent layer 60 may be applied to
only pre-selected portions of the rods. For example, a side
of a rod that faces a water blocking tape may be left
untreated by water absorbent layer 60. Further, water
absorbent layer 60 may be applied intermittently in the form
of annular bands, or in the form of longitudinal or helical
stripes. A rod according to the present invention may have
2o a hollow portion. A water blocking component according to
the present invention may share the same groove with one or
more optical fibers. where it is not desirable to use a
water absorbent layer 60, water absorbent entities, for
example) in the form of yarns 62 (Figure 3) or a tape 64
(Figure 2) may be placed adjacent a rod to define a water
blocking component 37 or 57, respectively.
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