U.S. patent application number 10/509116 was filed with the patent office on 2005-08-04 for coated optical fibre unit and methods of manufacturing coated optical fibre units.
Invention is credited to Ceschiat, Davide, Davies, Martin Vincent, Pike, Roger John, Pizzorno, Massimo, Sutehall, Ralph.
Application Number | 20050169588 10/509116 |
Document ID | / |
Family ID | 28459574 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050169588 |
Kind Code |
A1 |
Sutehall, Ralph ; et
al. |
August 4, 2005 |
Coated optical fibre unit and methods of manufacturing coated
optical fibre units
Abstract
An optical fibre unit having a sheath and a plurality of optical
fibre elements loosely housed in the sheath. The sheath is coated
with particles of an adherence reducing substance and has a radial
thickness that is not substantially greater than 0.3 mm. The
coating of adherence reducing particles is applied as a liquid
coating. The liquid coating is a dispersion of the particles and
heat is applied to evaporate the liquid content of the liquid
coating to produce a dry coating of particles on the sheath.
Inventors: |
Sutehall, Ralph; (Hamphire,
GB) ; Davies, Martin Vincent; (Hampshire, GB)
; Pike, Roger John; (Hampshire, GB) ; Ceschiat,
Davide; (Milano, IT) ; Pizzorno, Massimo;
(Milano, IT) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
28459574 |
Appl. No.: |
10/509116 |
Filed: |
September 28, 2004 |
PCT Filed: |
March 13, 2003 |
PCT NO: |
PCT/GB03/01064 |
Current U.S.
Class: |
385/109 ;
264/1.28; 264/1.29 |
Current CPC
Class: |
G02B 6/4485 20130101;
Y10T 428/2924 20150115; G02B 6/4438 20130101 |
Class at
Publication: |
385/109 ;
264/001.28; 264/001.29 |
International
Class: |
G02B 006/44; B29D
011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2002 |
EP |
02252345.0 |
Claims
What is claimed is:
1. An optical fibre unit comprising a sheath and a plurality of
optical fibre elements loosely housed in said sheath, said sheath
having a coating of adherence reducing material particles and a
radial thickness not substantially greater than 0.3 mm.
2. The optical fibre unit as claimed in claim 1, wherein said
sheath has a radial thickness substantially not greater than 0.2
mm.
3. The optical fibre unit as claimed in claim 2, wherein said
sheath has a radial thickness substantially in the range of 0.05 to
1.5 mm.
4. The optical fibre unit as claimed in claim 1, wherein said
adherence reducing material is graphite.
5. The optical fibre unit as claimed in claim 1, wherein said
sheath is made of a low smoke zero halogen material.
6. The optical fibre unit as claimed in claim 1, wherein said
particles have a nominal diameter not substantially greater than 8
microns.
7. The optical fibre unit as claimed in claim 6, wherein said
particles have a mean nominal diameter not substantially greater
than 2 microns.
8. The optical fibre unit as claimed in claim 1, wherein said
sheath has twelve optical fibre elements loosely housed
therein.
9. The optical fibre unit as claimed in claim 1, wherein said
sheath has a nominal outside diameter of 1.3 mm.
10. The optical fibre element as claimed in claim 1, wherein said
sheath has a nominal inside diameter of 1.1 mm.
11. A method of coating an optical fibre unit that comprises a
polymeric sheath and a plurality of optical fibre elements loosely
housed in said sheath, said method comprising applying a liquid
coating comprising a dispersion of adherence reducing material
particles to said sheath and applying heat to the optical fibre
unit to produce a dry coating of said particles on said sheath.
12. The method as claimed in claim 11, wherein said liquid coating
is applied to the polymeric sheath at room temperature.
13. The method as claimed in claim 11, wherein said liquid coating
comprises graphite particles and water.
14. The method as claimed in claim 13, wherein said heat applied to
said optical fibre unit evaporates the water content of said liquid
coating.
15. The method as claimed in any one of claims claim 11, wherein
said particles have a nominal diameter not substantially greater
than 8 microns.
16. The method as claimed in claim 15, wherein said particles have
a mean nominal diameter not substantially greater than 2
microns.
17. The method as claimed in claim 11, wherein said heat is applied
such that the temperature of said sheath does not exceed the
softening temperature of polymeric material forming the polymeric
sheath.
18. The method as in claimed in claim 17, wherein the temperature
of said sheath is at least 10.degree. C. lower than the softening
temperature of the polymeric material.
19. The method as claimed in claim 11, wherein said heat applying
step comprises passing the optical fibre unit through a plurality
of drying chambers.
20. The method as claimed in claim 19, wherein as the optical fibre
unit passes through each said drying chamber, substantially the
same amount of heat is applied to the optical fibre unit.
21. The method as claimed in claim 19, wherein said optical fibre
unit passes more than once through at least one of said drying
chambers.
22. The method as claimed in claim 19, wherein the direction of
movement of the optical fibre unit is different when passing
through one of said drying chambers to the direction of movement
when passing through one or more of the other drying chambers.
23. The method as claimed in claim 19, wherein said drying chambers
each have a length, said length being not substantially greater
than 0.35 mm.
24. The method as claimed in claim 11, further comprising applying
a surfactant to assist in the application of said liquid coating to
said sheath.
25. The method as claimed in claim 11, wherein said liquid coating
is applied to said sheath by passing said optical fibre unit
through a vessel containing said liquid coating.
26. The method as claimed in claim 25, further comprising applying
a surfactant to assist in the application of said liquid coating to
said sheath wherein said surfactant is contained in said
vessel.
27. The method as claimed in claim 11, wherein said optical fibre
unit moves substantially continuously at a speed of approximately
40 m/min during said liquid coating and heat applying steps.
28. An installation comprising a conduit and at least one optical
fibre unit as claimed in claim 1, said at least one optical fibre
unit being installed in said conduit by blowing the optical fibre
unit along said conduit.
29. An optical fibre unit for blown fibre installation, said
optical fibre unit comprising a sheath and a plurality of optical
fibre elements loosely housed in said sheath, said sheath having an
outer surface coated with adherence reducing material particles and
a radial thickness not substantially greater than 0.3 mm.
30. A method of coating an optical fibre unit for blown fibre
installation that comprises a polymeric sheath and a plurality of
optical fibre elements loosely housed in said sheath, which sheath
has a radial thickness not substantially greater than 0.3 mm, said
method comprising applying a liquid coating comprising a dispersion
of adherence reducing material particles to an outer surface of
said sheath and applying heat to the optical fibre unit to produce
a dry coating of said particles on said sheath.
31. An optical fibre unit for blown fibre installation, said
optical fibre unit comprising: a sheath defined by a generally
tubular wall, said wall having a radially outermost surface and a
radially innermost surface and a radial thickness not substantially
greater than 0.3 mm; a plurality of optical fibres loosely housed
in said sheath; and a coating adhered to said radially outermost
surface of said wall, said coating comprising adherence reducing
particles.
32. A method of coating an optical fibre unit for blown fibre
installation, said method comprising the steps of: forming a sheath
around a plurality of optical fibre elements such that said optical
fibre elements are loosely housed by the sheath, said sheath
comprising a generally tubular wall having a radially outer surface
and a radially inner surface and a radial thickness not
substantially greater than 0.3 mm; applying a liquid coating
comprising a dispersion of adherence reducing particles to said
radially outer surface; and passing the optical fibre unit through
a heated environment to dry said liquid coating to provide a dry
coating of said adherence reducing particles adhering to said
radially outer surface.
33. An installation comprising a conduit and at least one optical
fibre unit coated by the method of claim 11, said at least one
optical fibre being installed in said conduit by blowing the
optical fibre unit along said conduit.
34. The method as claimed in claim 19, wherein said drying chambers
each have a length, said length being not greater than
approximately 0.31 mm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to optical fibre units
comprising a thin-walled sheath and methods of manufacturing such
optical fibre units. The invention is particularly directed to
optical fibre units to be installed by blown fibre techniques.
BACKGROUND ART
[0002] EP A 0 108 590 discloses a method of installing optical
fibre units along a previously installed conduit or duct by drag
forces generated by a gaseous flow blown along the duct.
[0003] Generally speaking, it is desirable to increase the
distances over which optical fibre units can be blown, as otherwise
it can be necessary to install separate lengths of optical fibre
unit, which then have to be spliced together. Splicing involves
expense and time as it will often require the digging of holes in a
pavement (sidewalk) or roadway in order to gain access to the
ducting and then breaking into the ducting before the splice can be
made.
[0004] Many factors affect the distance over which an optical fibre
unit can be blown. Two known factors are friction between the
sheath and the ducting and the build-up of static charges that tend
to cause the sheath to adhere to the ducting.
[0005] EP A 0 108 590 discloses the possibility of blowing
compounds in liquid or powder form along the ducting prior to, or
during, installation in order to provide lubrication for the
optical fibre unit and suggests powdered talc as a suitable
lubricant. GB-A-2 156 837 is also concerned with optical fibre
units to be installed by blown fibre installation techniques. This
document discloses incorporating an adherence reducing substance in
the ducting and/or the sheath of the optical fibre unit. The
example given is of an extruded polyethylene conduit to which is
added less than 3% by volume of a compound commercially available
from BXL Plastics Ltd of Grangemouth, Stirlingshire, United
Kingdom. The compound is known as PZ 146 and comprises a slip
agent, an anti-block agent, an anti-static agent and an
antioxidant. The slip agent and anti-static agent of PZ 146 are
such that they migrate to the surface of the conduit to reduce
friction and improve the dissipation of static electric charges
generated during installation of the optical fibre unit. There is
no specific disclosure of a particular adherence reducing substance
incorporated in a sheath. The document also mentions the
possibility of coating a sheath with an adherence reducing
substance, but provides no disclosure of how this is done or of
suitable coating materials.
[0006] Other factors that affect the distances over which optical
fibre units can be blown are the weight of the unit, the difference
between the outside diameter of the unit and the internal diameter
of the ducting and the stiffness of the optical fibre unit.
[0007] Hitherto, commercially available optical fibre units (2, 4
and 8 fibre units) have relied on a tight package construction to
provide the rigidity necessary to permit blowing. The tight resin
sheath for the fibres is typically imbedded with glass beads that
serve to reduce the friction between the sheath and the
ducting.
[0008] One approach to increasing the potential blowing distances
of these constructions would be to reduce the overall diameter of
the package. However, this would reduce the number of optical
fibres that could be included in the package. An alternative
approach would be to reduce the thickness of the optical fibre
cable sheath. However, if the sheath thickness is reduced, the
inclusion of lubricating additives or glass beads in the sheath
material is problematical and conventional coating processes are
unsuitable for coating a thin-walled sheath.
SUMMARY OF THE INVENTION
[0009] An aspect of the invention provides an optical fibre unit
comprising a sheath and a plurality of optical fibre elements
loosely housed in said sheath, said sheath having a coating of
adherence reducing material particles and a radial thickness not
substantially greater than 0.3 mm.
[0010] Preferably said adherence reducing material is graphite.
[0011] Another aspect of the invention provides an installation
comprising a conduit and at least one optical fibre unit as
described in either of the last two preceding paragraphs, the or
each said optical fibre unit having been installed in said conduit
by blowing the optical fibre unit along said conduit.
[0012] Another aspect of the invention provides a method of coating
an optical fibre unit that comprises a polymeric sheath and a
plurality of optical fibre elements loosely housed in said sheath,
said method comprising applying a liquid coating comprising a
dispersion of adherence reducing material particles to said sheath
and applying heat to the optical fibre unit to produce a dry
coating of said particles on said sheath.
[0013] Preferably, the liquid coating is applied to the polymeric
sheath at room temperature.
[0014] Preferably, the liquid coating comprises graphite particles
and water.
[0015] Another aspect of the invention provides an installation
comprising a conduit and at least one optical fibre unit
manufactured according to the method described in any one of the
last three preceding paragraphs, the or each said conduit having
been installed by blowing the optical fibre unit along the
conduit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order that the invention may be well understood, some
embodiments, which are given by way of example only, will now be
described with reference to the drawings, in which:
[0017] FIG. 1 is a schematic cross-sectional view of an optical
fibre unit according to the invention;
[0018] FIG. 2 is a side view of apparatus for coating the sheath of
the optical fibre unit of FIG. 1; and
[0019] FIG. 3 is an enlarged view of a dipping bath of the
apparatus of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring to FIG. 1, an optical fibre unit 10 comprises a
thin-walled sheath 12 and a plurality of optical fibre elements 14.
The sheath 12 has a coating 16 in the form of adherence reducing
substance, preferably comprising ultra fine graphite particles.
[0021] In a preferred embodiment, the coating 16 comprises graphite
particles having a nominal diameter of 1 to 2 microns with a
maximum value of 8 microns.
[0022] Alternatively, other adherence reducing materials can be
used, such as molybdenum disulfide of polytetrafluoroethylene
(PTFE) particles.
[0023] The thin-walled sheath 12 has a radial thickness of not more
than about 0.3 mm, preferably of not more than about 0.2 mm. A
thickness not lower than about 0.05 mm is preferred and most
preferably said thickness is in the region of 0.05 to 0.15 mm. In a
preferred embodiment the sheath has an outside diameter of 1.35
mm+/-0.05 mm and an inside diameter of 1.1 mm+/-0.05 mm. The sheath
may be made from a polymeric composition including a polymeric
material and optionally an inert filler. The polymeric material can
be for instance a polyolefin, such as polyethylene, polypropylene,
ethylene-propylene copolymer, ethylene-vinylacetate copolymers
(EVA) or polyvinyl chloride (PVC). Inorganic fillers which can
generally be used are hydroxides, hydrated oxides, salts or
hydrated salts of-metals, in particular of calcium, magnesium, or
aluminium, also in admixture with other inorganic fillers such as
silicates. The amount of inorganic filler may vary for instance
from about 40% to about 90% by weight of the total weight of the
polymeric composition. Conventional additives such as stabilizers,
antioxidants, processing agents and coupling agents can be
incorporated into the polymeric composition.
[0024] The sheath is preferably made of PVC or more preferably of a
low smoke zero halogen polymeric compositions (LSOH). Suitable LSOH
polymeric compositions typically comprise a polyolefin material
(e.g. EVA or mixtures of EVA and polyethylene) and an inorganic
filler (e.g. aluminium hydroxide), typically in an amount of about
50-70% by weight of the total composition.
[0025] In the preferred embodiment there are twelve optical fibres
14 contained in the sheath 12. The optical fibres 14 may be
single-mode fibres, multi-mode fibres, dispersion shifted (DS)
fibres, non-zero dispersion (NZD) fibres, or fibres with a large
effective area and the like, depending on the application
requirements of the optical fibre unit 10. If desired, some of the
optical fibres 14 housed inside the sheath can be replaced by
non-transmitting glass fibres in order to maintain an optimum fibre
count within the sheath. The optical fibre elements 12 may be laid
up in parallel formation or stranded around each other in SZ
formation.
[0026] The sheath 12 may contain water blocking means, e.g. in the
form of a grease like or oily filler such as, for instance, a
silicon oil based filling composition. Alternatively the water
blocking means can be in the form of water swellable powder
compositions, for instance a mixture of polyacrylate particles and
talc particles, as described in International Patent Application WO
00/58768.
[0027] The optical fibre unit is typically blown through a conduit,
e.g. of polymeric material, such as polyethylene, particularly high
density PE. Optionally, a low friction liner (e.g. silicon) is
disposed within the bore.
[0028] The internal diameter of the conduit is typically of about 3
to 4 mm, e.g. about 3.5 mm. Accordingly, a plurality of optical
fibre elements (e.g. three) can be blown through said conduit using
conventional blowing techniques.
[0029] Referring to FIGS. 2 and 3, an apparatus 50 for applying the
coating 16 to the sheath 12 comprises an unwinding device 52 on
which is mounted a coil 54 of uncoated optical fibre unit 10.
Optical fibre unit 10 is led from the coil 54 to a dipping bath 56
via a drive belt 58. The drive belt 58 is arranged to provide a
controlled unwinding tension, e.g. of about 200 g.
[0030] As best seen in FIG. 3, the dipping bath 56 comprises a
vessel 60 containing a liquid dispersion 62 of the adhesion
reducing coating material. The optical fibre unit 10 is directed
into the vessel 60 via a guide roller 64 and passes under a
relatively larger diameter pulley 66 that is partially submerged in
the liquid 62 so that the optical fibre unit 10 is constrained to
pass through the liquid. The liquid coating is applied onto the
polymeric sheath at room, or ambient, temperature, i.e. at a
temperature lower than 40.degree. C., typically between 15.degree.
and 30.degree..
[0031] A further guide roller 68 is positioned downstream of the
pulley 66 and arranged to guide the optical fibre unit 10 into a
felt 70 that serves to remove excess liquid from the optical fibre
unit.
[0032] A drying station 80 is situated downstream of the dipping
bath 56. The drying station 80 comprises a first oven 82 and a
second oven 84. Each oven comprises an elongate hollow body 83
through which the optical fibre unit can pass and a source of heat
86. In a preferred embodiment of the coating apparatus 50, the
source of heat is a hot air blower 86. A suitable blower for this
purpose is the Leister CH6065, which is rated at 3400 W. In the
preferred embodiment, the length of the elongate bodies is
approximately 0.3 m.
[0033] Respective guide pulleys 90,92 are provided adjacent the
ends of the ovens 82,84 and arranged such that the optical fibre
unit, having passed once through the lower oven 82 heading in the
downstream direction of the apparatus, is directed upwardly into
the upper oven 84 through which it passes heading in the upstream
direction of the machine before being fed downwardly from the exit
of the upper oven and into the lower oven 82 for a second pass
therethrough.
[0034] Each oven 82, 84 is provided with a means 98 for monitoring
the temperature within the oven. These monitoring means 98 include
a suitable temperature sensor (not shown) and a display for
displaying the sensed temperature. The temperature monitoring means
may comprise any suitable sensor, display and circuitry and the
like for conditioning the sensor signal as will all be well known
to those skilled in the art. Accordingly, no detailed description
of the temperature monitoring means will be supplied herein.
[0035] A winding device 110 is disposed downstream of the ovens 82,
84 to receive the coated optical fibre unit 10. The winding device
110 comprises a driven belt 112 that provides a controlled winding
tension, e.g. of about 200 g. The winding device 110 farther
comprises a suitable mounting for a spool onto which the coated
optical fibre unit 10 is coiled.
[0036] In order to manufacture an optical fibre unit 10, the
required number of optical fibre elements 14 are passed through an
extrusion cross-head and the thin-walled sheath 12 is extruded
around the fibre elements. On exiting the extruder, the sheath is
air-cooled and the optical fibre unit is coiled on a spool. The
equipment on which these processes are carried out is conventional
and known to those skilled in the art and will not therefore be
described in detail herein. The spool is later fitted onto the
unwinding device 52 of the coating apparatus 50 and an end of the
coil 54 of optical fibre unit is fed through the apparatus and onto
an empty spool fitted on the winding device 110.
[0037] In a preferred embodiment of the method of manufacture, the
vessel 60 is filled with a coating liquid 62 including ultra fine
dispersed graphite particles. A commercial product known as Aquadag
Dag .RTM. T144 made by Acheson Colloids Company of Prince Rock,
Plymouth 266351 USA is advantageously employed, which is a
concentrated dispersion of ultra fine graphite particles in water.
This material is thixotropic and is normally diluted using
distilled or soft mineral water in order to obtain a suitable
consistency. A surfactant, preferably of the non ionic type, is
preferably added to the liquid 62, e.g. in an amount of 0.5 to 5%
by weight, for increasing the wettability of the sheath material.
Preferably, the non ionic surfactant is an ethoxylated derivative
of a (C8-C12) alkylphenole. In the preferred embodiment, 1% by
weight of IGEPAL CO/620 (Rhone-Poulenc) was added.
[0038] The unwinding and winding devices 54, 110 are operated to
provide a line speed of 40 m/min. The ovens 82, 84 are set to a
temperature of 108.degree. C. After an initial phase of a run, in
order to maintain the 108.degree. set temperature, the heating
power supplied to the hot air blowers has to be increased to take
account of the evaporation of the water in the coating liquid
62.
[0039] Under the above process conditions, the temperature of the
sheath during its first pass through oven 82 is in the region of
38.degree. C. During the passage through the oven 84, the
temperature of the sheath increases to approximately 40.degree. C.
and during the second passage through the oven 82, the temperature
increases to approximately 57.degree. C.
[0040] On exiting the oven 82 after its second passage
therethrough, the liquid content of the liquid coating 62 has
evaporated leaving a uniform layer 16 of ultra fine graphite
particles on the sheath 12 to provide a coating that reduces the
friction between the sheath and ducting during blown installation
and assists in dissipating static electrical charges generated
during installation. It has been found that this coating does not
produce any appreciable variation in the transmitted properties of
the fibres.
[0041] By the time the optical fibre unit has travelled from the
oven 82 to the winding device 110, it will have cooled to a
temperature in the region of 25.degree. C. If desired a blower (not
shown) can be provided downstream of the ovens 82, 84 to assist in
cooling the optical fibre unit.
[0042] It will be understood that by making multiple passes through
the ovens 82, 84, the liquid content of the liquid coating is
evaporated without raising the temperature of the sheath to a level
that could damage the sheath.
[0043] As observed by the Applicants, if the temperature of the
polymeric material forming the sheath exceeds the softening point
of the material, irreversible changes in the sheath can be
produced. For example, the sheath may distort and become oval in
cross-section, which may in turn result in an attenuation of the
signal transmitted by the optical fibre elements. In order to avoid
said undesirable changes, the temperature of the polymeric material
is thus preferably kept below its softening temperature. The
softening temperature can be determined, for instance, according to
ASTM D1525-00 (Standard Test Method for Vicat Softening Temperature
of Plastics). Preferably, the temperature is kept about at
10.degree. C. below the softening temperature of the polymeric
material forming the sheath of the optical fiber unit.
[0044] In embodiments run by the Applicants, the sheath materials
were a low smoke zero halogen and a PVC. The softening temperature
of the polymeric sheath material was approximately 70.degree. C.
and by making multiple passes through the drying chambers as
described, it was ensured that the temperature of the sheath did
not substantially exceed 60.degree. C. The coated optical fibre
units produced by the Applicants using this process were provided
with a uniform layer of ultra fine graphic particles and no
appreciable deterioration in the optical properties of the fibre
elements was detected. It will be appreciated that the specific
temperatures mentioned above are given by way of example and may be
altered to suit the material from which the sheath is made.
[0045] The use of a coated thin-walled sheath loosely housing the
optical fibre elements provides an optical fibre unit for blown
installation that has many advantageous features as compared with
the optical fibre units presently commercially available for blown
fibre installation. One advantage is that the low temperature
performance of the unit is improved. This is because the optical
fibre elements are not in close contact with the sheath so that
when the sheath contracts when subject to low temperatures, the
optical performance of the fibres will not be affected.
[0046] A further advantage of the thin-walled sheath is that it
permits easy break out of the optical fibre elements making it
unnecessary to provide a ripcord.
[0047] Yet another advantage of the thin-walled sheath is the
improved flexibility of the optical fibre unit when there is a high
fibre count. As previously mentioned currently available products
consist of a bundle of optical fibre elements tightly packaged in a
resin sheath. A tight package of eight fibres in a resin sheath
results in a relatively inflexible unit that can restrict
installation performance along difficult routes. Using a coated
thin-walled sheath, the Applicants have produced a twelve-fibre
optical fibre unit that has improved flexibility and installation
performance even along difficult routes.
* * * * *