U.S. patent number RE34,732 [Application Number 07/967,122] was granted by the patent office on 1994-09-20 for waterproof optical fiber cable.
This patent grant is currently assigned to Mitsubishi Cable Industries, Ltd.. Invention is credited to Yasuo Ijiri, Eiji Iri, Takashi Kaneko, Kotaro Mio, Takeshi Shintani.
United States Patent |
RE34,732 |
Iri , et al. |
September 20, 1994 |
Waterproof optical fiber cable
Abstract
An optical fiber cable comprising a water blocking layer, an
optical fiber disposed inside the water blocking layer and a water
blocking material filling the space between the water blocking
layer and the optical fiber, the water blocking material comprising
a grease having a worked penetration of .[.85.]. .Iadd.300
.Iaddend.to 475 as measured according to ASTM-D-712 at room
temperature.
Inventors: |
Iri; Eiji (Hyogo,
JP), Kaneko; Takashi (Hyogo, JP), Shintani;
Takeshi (Hyogo, JP), Mio; Kotaro (Hyogo,
JP), Ijiri; Yasuo (Hyogo, JP) |
Assignee: |
Mitsubishi Cable Industries,
Ltd. (Hyogo, JP)
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Family
ID: |
26478233 |
Appl.
No.: |
07/967,122 |
Filed: |
October 27, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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637540 |
Aug 3, 1984 |
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Reissue of: |
039806 |
Apr 15, 1987 |
04711523 |
Dec 8, 1987 |
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Foreign Application Priority Data
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Aug 11, 1983 [JP] |
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58-147792 |
Aug 11, 1983 [JP] |
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58-147793 |
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Current U.S.
Class: |
385/109; 385/100;
385/113 |
Current CPC
Class: |
H01B
7/288 (20130101); G02B 6/4494 (20130101) |
Current International
Class: |
G02B
6/44 (20060101); G02B 006/44 () |
Field of
Search: |
;385/109,113,100 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0032268 |
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Dec 1980 |
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EP |
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0067009 |
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May 1982 |
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EP |
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58-147792 |
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Aug 1983 |
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JP |
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58-147793 |
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Aug 1983 |
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JP |
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Other References
IEEE International Conference on Communications, Vo. 3, pp. 13-17,
Jun. 1983, pp. 7D.4.1-7D.4.3, Philadelphia, US, IEEE, New
York..
|
Primary Examiner: Bovernick; Rodney B.
Assistant Examiner: Wise; Robert E.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Parent Case Text
This is a Reissue Application for U.S. Pat. No. 4,711,523, issued
Dec. 8, 1987, which matured into a patent from Ser. No. 39,806,
filed Apr. 15, 1987.
This application is a continuation, of now abandoned application
Ser. No. 637,540, filed Aug. 3, 1984, and now abandoned.
Claims
What is claimed is:
1. An optical fiber cable comprising a water blocking layer, an
optical fiber disposed inside the water blocking layer and a water
blocking material filling the space between the water blocking
layer and the optical fiber, the water blocking material comprising
a grease having a worked penetration of .Badd..[.150.]..Baddend.
.Iadd.300 .Iaddend.to 450 at room temperature and of at least 85 at
-30.degree. C. as measured according to ASTM-D-217, said grease
comprising an organic liquid having a viscosity at 40.degree. C. of
6 to 5000.degree. c.st. and 3 to 35 parts by weight per 100 parts
by weight of said organic liquid of a thickener.
2. An optical fiber cable as defined in claim 1 wherein the water
blocking material further comprises a water absorbing agent in an
amount of 10 to 400 parts by weight per 100 parts by weight of the
grease.
3. An optical fiber cable as defined in claim 1 wherein the grease
is at least one member selected from the group consisting of
calcium soap grease, aluminum soap grease, lithium soap grease,
calcium complex soap grease, aluminum complex soap grease,
bentonite grease, and polyurea grease.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a waterproof optical fiber cable
having incorporated therein a filler, namely a water blocking
material, for preventing water from penetrating into the cable from
outside.
2. Description of the Prior Art
When the sheath of an optical fiber cable ruptures locally, water
naturally ingresses into the cable to impair the light transmission
characteristics of the cable.
A system has been proposed for optical fiber cables for early
detection of a break in the cable sheath and therefore ingress of
water into the cable by monitoring the pressure of a gas filled in
the interior of the cable to a high pressure. However, the proposed
monitoring system is costly and requires expensive cable
systems.
It has also been proposed to provide a water blocking layer beneath
the cable sheath and fill the inside space of the layer with a
water blocking material in order to directly prevent water from
entering the interior of the cable even when a break occurs in the
cable sheath, for instance, in IECE-JAPAN-NCR (The Institute of
Electronics and Communication Engineers of Japan, National
Convention Record) No. 1901 (Page 7-344) 1981, IECE-JAPAN-NCR No.
366 (Page 2-102), No. 1810 (Page 7-252) and No. 1811 (Page 7-253),
1982. The proposal has the advantage of being economical because
the above monitoring system is made unnecessary. Water blocking
materials known for use in optical fibers are solid or a highly
viscous liquid at room temperature. Accordingly such a material is
melted by heating before being filled into the cable during the
cable making process. The conventional water blocking material has
the following drawbacks because the material invariably solidifies
or becomes highly viscous while contracting when cooled after
filling.
(i) Owing to contraction, a clearance occurs at the interface
between the water blocking layer and the water blocking material or
at the interface between the water blocking material and the
optical fiber in the cable core, with the result that water, if
entering the cable, runs through the clearance longitudinally of
the cable.
The optical fiber, which is thin, flexible and therefore easily
bendable, is restrained by the water blocking material which
rapidly becomes viscous or consistent when cooled after filling.
Moreover, the contraction of the material causes microbending of
the fiber and results in an increased light transmission loss.
Especially when the cable is used during winter or in a cold
climate, the material undergoes more marked contraction and
produces a greater restraint to entail a further increased light
transmission loss.
(iii) Because the water blocking material is difficult to remove
from the cable after solidification, it is difficult or requires a
long period of time to make high precision cable connections.
SUMMARY OF THE INVENTION
The present invention provides an optical fiber cable comprising a
water blocking layer, an optical fiber disposed inside the water
blocking layer and a water blocking material filling the space
between the water blocking layer and the optical fiber, the water
blocking material comprising a grease which has a worked
penetration of 85 to 475 as measured according to ASTM D-217 at
room temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1, 2, 3 and 4 are sectional views showing embodiments of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
It is generally well known that the grease is defined as a
colloidal or micellar dispersion of solid thickener in a natural or
synthetic organic liquid. The greases constituting water blocking
materials useful for the present invention are those defined as
above and having suitable softness, i.e. a worked penetration of 85
to 475 as measured according to ASTM D-217 at room temperature,
excluding those which are too soft or solid.
Unlike many mixtures, greases are a dispersion of thickener in an
organic liquid and have a special structure as stated above, so
that the penetration or consistency thereof has a very low
temperature dependence. The greases to be used in this invention
retain satisfactory softness without solidification at room
temperature and even at considerably low temperatures of below
0.degree. C. and therefore have the following advantages.
(i) Many of the greases can be filled into cables at room
temperature without the necessity of heating, whereas they have
relatively low flowability in the cable. Certain kinds of water
blocking materials incorporated in optical fiber cables according
to the invention substantially do not flow down even if the cable
is installed in an inclined or vertical position.
(ii) With some of the greases which are difficult to fill at room
temperature, or in order to achieve an improved filling efficiency,
it is advantageous to suitably heat the grease before use.
Nevertheless, the grease still retains satisfactory softness when
thereafter cooled to room temperature or even when cooled to a low
temperature of below 0.degree. C. Thus, the grease is unlikely to
restrain the optical fiber, rendering the fiber free of
microbending during use.
(iii) The present greases do not solidify over a wide range of
temperatures including room temperature, making cable connections
easy.
The greases to be used in the present invention are a colloidal or
micellar dispersion of solid thickener in a natural or synthetic
organic liquid and have a worked penetration of 85 to 475 as
measured according to ASTM D-217 at room temperature. Examples of
useful natural organic liquids are mineral oils such as transformer
oil, spindle oil, cable insulatin oil, machine oil, vegetable oils
such as rosin oil, castor oil, olive oil and arachis oil and the
like. Examples of useful synthetic organic liquid are hydrocarbons
such as .alpha.-olefin oligomers, polybutene, esters such as
di-octyl sebacate, di-octyl adipate and other esters which are used
as plasticizers for polyvinyl chloride, glycols such as
polyethylene glycol, polypropylene glycol, and other organic
liquids such as silicon oils. Of these, liquids suitable for use
have a viscosity at 40.degree. C. of 4 to 10,000 c.st., preferably
6 to 5,000 c.st., more preferably 10 to 1,000 c.st. and a pour
point of up to 0.degree. C.
Useful thickeners include, for example, metallic soaps such as
higher fatty acid salts of Ba, Sr, Zn, Pb, Cd, K, Na, Ca, Li, Al
and like metals; non-soaps such as bentonite, silica gel and
phthlocyanine; polyurea compounds such as those having 2 to 20 urea
bonds and a molecular weight of 100 to 5,000; amino acid-type oil
gelling agents such as N-lauroyl-L-glutamic acid-.alpha.,
.beta.-di-n-butyramide; cellulose derivatives such as quaternary
ammonium salt of cellulose and fatty acid esters of dextrin;
etc.
When the thickener is used in an excessive amount, the worked
penetration of the grease becomes more dependent on temperature,
permitting the grease to exhibit a decreased worked penetration at
lower temperatures. On the other hand, if the amount of the
thickener is too small, the grease becomes flowable within the
cable even at low temperatures, giving rise to the problems to be
described later.
The thickener is used in an amount of 1 to 50 parts by weight,
preferably 2 to 40 parts by weight, more preferably 3 to 15 parts
by weight, per 100 parts by weight of the natural or synthetic
liquid.
Examples of suitable greases are greases of metallic soap type such
as sodium soap grease, calcium soap grease, aluminum soap grease,
lithium soap grease, calcium complex soap grease, aluminum complex
soap grease, greases of the non-soap type such as bentonite grease,
silica gel grease, polyurea grease, etc. Other useful greases are
disclosed by Hiroshi Horiguchi in Lubricants and Greases (pages
402-419, Sankyoshuppan Co., Ltd., Tokyo, February 1970).
Greases less than 85 in worked penetration are hard and therefore
need to be softened by heating before filling. Such greases tend to
solidify at low temperatures. On the other hand, greases greater
than 475 in worked penetration have excessive flowability so that
when contained in a cable installed in a inclined or vertical
position, the grease will flow down the interior of the cable,
possibly producing a head inside a lower cable portion that could
cause a break in the sheath or creating a space within an upper
cable portion. Accordingly it is preferable to use greases having a
worked penetration of 100 to 450, more preferably 150 to 450, most
preferably 200 to 400 at room temperature. More preferred greases
are those having a worked penetration of 100 to 450, especially 120
to 385, at roomtemperature, especially at 25.degree. C. and at
least 85, especially at least 100, at -30.degree. C.
The water blocking material to be used in the present invention may
consist singly of such a grease but can be a mixture of a grease
and other chemicals such as an anti-oxidant, pigment, water
absorbing agent, etc. However, the amounts of chemicals other than
the grease need to be limited to such ranges that will not impair
the foregoing characteristics of the grease.
When a grease containing a water absorbing agent is used as the
water blocking material, water, if entering the cable, is absorbed
by this agent to prevent the water from flowing through the cable
longitudinally.
While the water absorbing agent can be silica gel, quick lime or
like inorganic material having a good ability to absorb water, the
agent is preferably a material having a high capacity to absorb at
least an amount of water which is equivalent to its own weight.
Examples of such highly absorbent agents are organic agents
including starch modified with acrylic acid and like graft polymer
of starch, graft polymer of cellulose, carboxymethylcellulose,
acrylic acid polymer etc.
These organic water absorbing agents have the advantage that even
if admixed with the grease in a large amount, the agent will not
noticeably impair the foregoing characteristics of the grease.
Moreover, use of a large amount of the agent prevents migration of
water very effectively. The organic water absorbing agent is used
in an amount of 10 to 400 parts by weight, preferably 20 to 300
parts by weight, per 100 parts by weight of the grease.
The mixture of grease and water absorbing agent need not fill the
entire space inside the water blocking layer of the optical fiber
cable but may be applied to a portion which is likely to be exposed
to water penetrating into the cable. For example, the mixture is
provided in the form of a thin layer beneath the water blocking
layer or immediately above the optical fiber, and the remaining
space is filled only with the grease.
Referring to FIGS. 1 to 4 wherein like reference mumerals designate
similar parts throughout, there is shown optical fiber cores 1 each
comprising a single optical fiber or a strand of a multiplicity of
optical fibers, a tension member 2, a water blocking layer 3 formed
by enclosing an assembly of cores 1 with a water blocking tape with
a longitudinal lap or by winding a water blocking tape around the
assembly, a sheath 4, and water blocking material 5 filling the
space inside the water blocking layer 3.
The water blocking tape can be a tape made of a metal, such as
copper, aluminum, lead or the like, or an organic high polymer
having high water blocking ability, such as polyvinylidene
chloride, polychlorotrifluoroethylene, biaxially oriented
polypropylene or the like. It is desirable that the water blocking
tape be at least single-faced with an adhesive layer to adhere the
tape to itself at the lap and more preferably be double-faced with
an adhesive layer to adhere the water blocking layer 3 to the
sheath 4. The sheath 4 itself may be of water blocking structure or
may be made of a water blocking material so as to be serviceable
also as a water blocking layer in place of the water blocking layer
3.
The tension member 2, which is not always needed, is preferably
used because optical fibers generally have low mechanical strength.
As shown in FIGS. 1 to 4, tension members 2 of various structures
and materials are usable.
With reference to FIG. 1, the optical fiber core 1 comprises an
assembly of six optical fibers 12 arranged around a tension member
11 in the form of a string of organic polymer fiber, such as
Kevlar.RTM.. A holding tape 13 is wound around the assembly. An
electrically insulated cable is used as the tension member 2,
around which eight optical fiber cores 1 are arranged.
With reference to FIG. 2, a rod of organic polymer reinforced with
a fiber such as glass fiber, carbonfiber Kevlar.RTM., is used as
the tension member 2, around which eight optical fiber cores 1 are
arranged. The water blocking layer 3 is provided at a distance t
from the surface of the optical fiber core 1. Although not always
necessary, the difance or spacing t, if provided, enables the water
blocking material present in the space to serve as a cushion, which
will protect the fiber cores 1 from some impact or external force
that could act on the cable. The distance t (the shortest distance
between the inner surface of the water blocking layer 3 and the
optical fiber cores 1) is preferably at least 1 mm, more preferably
2 mm to 1/2 of the largest outside diameter of the core
assembly.
With reference to FIG. 3, eight optical fiber cores 1 are arranged
around the tension member 2 comprising a strand of organic polymer
strings or metal wires. A holding tape 6 is wound around the
assembly of the cores 1 to fasten the cores 1 to the tension member
2. As in the cable of FIG. 2, the water blocking layer 3 is
provided at a distance t from the core assembly.
Because the water blocking material filling the interior of the
cable of the invention is soft as already described, the optical
fiber cores 1 will be displaced from one another or are even likely
to cross one another by handling and bending during cable making
and installation, resulting in an increased light transmission
loss. The optical fiber cores can be positioned in order with one
another by winding the cores around the tension member arranged
with a large pitch. To avoid the above objection more effectively,
it is desirable to wind the holding tape 6 around the optical fiber
cores thus assembled as seen in FIG. 3 to fasten the cores 1 to the
tension member 2. For the same purpose as above, the holding tape
13 is wound around the assembly of optical fibers 12 in FIG. 1.
To permit the water blocking material 5 to fill the interior space
of the cable effectively, the holding tapes 13 and 6 are preferably
porous tapes, such as those of woven fabric of natural or synthetic
fiber or perforated nonwoven fabric of like material. When an
impermeable film tape is used as the holding tape, it is preferable
to apply the tape by gap winding. The holding tape 13 or 6, when
having a small width, will locally exert a pressure on the optical
fibers 12 or optical fiber cores 1 to cause microbending of the
fibers or cores. It is therefore desirable that the tapes have a
width approximate to 2 to 5 times the outside diameter of the
optical fiber 12 or the core 1 for which it is used.
With reference to FIG. 4, the tension member 2 consisting of a wire
strand is provided thereon with a spacer 7 made of an organic
polymer, such as polyethylene, polypropylene, nylon and the like.
The spacer 7 has in its outer periphery a plurality of helical
grooves 21 which are slightly larger in width and depth than the
outside diameter of the optical fiber core 1. The core 1 is
accommodated in each groove 21 as embedded in the water blocking
material 5 filling the groove. A holding tape 6 of the foregoing
structure is wound around the spacer 7 in the same manner as above.
With the optical fiber cable of this construction, each optical
fiber core 1 is protected at three sides thereof by the wall of the
spacer 7 defining its groove 21 and is restained at the outer side
by the holding tape 6, while being enclosed in the water blocking
material. Accordingly the optical fiber 1 is fully protected from
external forces.
TABLE 1
__________________________________________________________________________
Water Blocking Material (pars by weight) Ingredients WB1 WB2 WB3
WB4 WB5 WB6 WB7 WB8 WB9 WB10 WB11 WB12 WB13 WB14 WB15
__________________________________________________________________________
Witco compound #5B 100 -- -- -- -- -- -- -- -- -- -- -- -- -- --
polyurea grease -- 100 -- -- -- -- -- -- -- -- -- 100 100 -- --
polyurea grease -- -- 100 -- -- -- -- -- -- -- -- -- -- -- --
polyurea grease -- -- -- 100 -- -- -- -- -- -- -- -- -- -- --
calsium soap grease -- -- -- -- 100 -- -- -- -- -- -- -- -- -- --
aluminum soap grease -- -- -- -- -- 100 -- -- -- -- -- -- -- -- --
lithium soap grease -- -- -- -- -- -- 100 -- -- -- -- -- -- 100 100
lithium soap grease -- -- -- -- -- -- -- 100 -- -- -- -- -- -- --
aluminum complex soap -- -- -- -- -- -- -- -- 100 -- -- -- -- -- --
grease calsium complex soap -- -- -- -- -- -- -- -- -- 100 -- -- --
-- -- grease bentonite grease -- -- -- -- -- -- -- -- -- -- 100 --
-- -- -- starch modified with -- -- -- -- -- -- -- -- -- -- -- 100
40 -- -- acrylic acid polysodium acrylate -- -- -- -- -- -- -- --
-- -- -- -- -- 50 -- Na-carboxymethyl -- -- -- -- -- -- -- -- -- --
-- -- -- -- 50 cellulose Worked at 25.degree. C. Solid 320 290 210
320 300 280 300 280 300 260 300 320 270 270 Penetration at
-30.degree. C. Solid 170 145 105 160 150 130 160 140 160 120 140
160 135 135
__________________________________________________________________________
EXAMPLES 1-14, COMPARATIVE EXAMPLE 1
Table 1 shows the compositions of various water blocking materials
and the worked penetration values of the materials at 25.degree. C.
and -30.degree. C.
Six optical fibers, each comprising a G1-type optical fiber element
having a core diameter of 50 .mu.m and a cladding diameter of 125
.mu.m and covered with a nylon jacket, were stranded around a
tension member of piano wire. A perforated tape of vinylon fiber
nonwoven fabric (tape width: 10 mm) was applied over the strand by
winding around the assembly with a 1/3 lap to prepare an optical
fiber core 1. Eight of such optical fiber cores 1 were stranded
around a tension member consisting of steel wire strand. An
aluminum laminate tape was wrapped around the resulting assembly
with a longitudinal lap to form a water blocking layer, which was
then covered with a polyethylene sheath. Thus, an optical fiber
cable of the structure shown in FIG. 1 was prepared which had an
outside diameter or 23 mm. While applying the aluminum laminate
tape, the water blocking material shown in Table 1 was filled into
the inside space. The water blocking materials WB-2 to WB-15 usable
according to the invention all have such a worked penetration that
they can be filled into cables at room temperature. However, in
order to substantiate that the materials can be filled at a higher
temperature and then cooled without adversely affecting the
transmission loss characteristics of optical fibers, some of the
materials were filled at a high temperature. Unlike these, WB-1
used in Comparative Example 1 is solid at room temperature and was
therefore heated to 105.degree. C. and filled in a molten
state.
Table 2 shows the water blocking materials used in Examples and
Comparative Example, the temperatures of the materials to be filled
and the characteristics of cables measured by the following
methods.
Loss-wave length characteristics
A test sample 500 m in length and wound on a drum was maintained at
25.degree. C., and the loss was measured at 0.85 .mu.m and 1.30
.mu.m by the CUT BACK method.
Loss-temperature characteristics
The same sample was tested for loss characteristics at temperatures
of 60.degree. C. and -30.degree. C. at 0.85 .mu.m by the CUT BACK
method.
Water blocking effect
The sheath and the water blocking layer were removed over a length
of 25 mm form a 2 m long cable test piece approximately at its
midportion. A vertical polyethylene pipe filled with water to a
height of 1000 mm was connected to the exposed core assembly
portion. After allowing the test piece to stand for 14 days, the
test piece was checked for distance of water penetration, from the
midportion.
TABLE 2
__________________________________________________________________________
Characteristics of Optical Fiber Cable Comparative Loss-wave length
Loss-temperature Running Water Example Water Temperature at
25.degree. C. at 0.85 .mu.m blocking effect or Blocking of Filling
at 0.85 .mu.m at 1.30 .mu.m at 60.degree. C. at -30.degree. C.
(distance of water Example Material (.degree.C.) (dB/km) (dB/km)
(dB/km) (dB/km) penetration, mm)
__________________________________________________________________________
Co. Ex. WB1 105 3.5 1.0 4.3 10.5 note 1 Ex. 1 WB2 room temp 2.3
0.56 2.3 2.8 less than 100 Ex. 2 WB3 " 2.5 0.56 2.7 2.9 " Ex. 3 WB4
60 2.3 0.55 2.3 2.3 " Ex. 4 WB5 room temp 2.4 0.59 2.4 2.6 " Ex. 5
WB6 " 2.4 0.60 2.5 2.5 " Ex. 6 WB7 " 2.5 0.58 2.7 2.8 " Ex. 7 WB8
60 2.4 0.57 2.4 2.8 " Ex. 8 WB9 room temp 2.3 0.54 2.3 2.6 " Ex. 9
WB10 " 2.6 0.70 2.7 3.0 " Ex. 10 WB11 " 2.5 0.56 2.5 2.9 " Ex. 11
WB12 " 2.3 0.56 2.3 2.8 less than 20 Ex. 12 WB13 " 2.5 0.62 2.5 3.0
" Ex. 13 WB14 " 2.4 0.60 2.4 2.6 " Ex. 14 WB15 " 2.4 0.58 2.4 2.4 "
__________________________________________________________________________
note 1 28-30 drops of water leaked from each end of the cable
The cable of Comparative Example 1 has greater loss characteristics
than those of Examples apparently owing to the microbending of the
optical fibers which resulted from cooling of the filled WB-1 and
the consequent contraction. The loss value of the cable in
Comparative Example 1 at -30.degree. C. greatly increased from the
loss value of 25.degree. C. This is attributable to the fact that
the optical fibers, already restrained by WB-1 which was solid at
room temperature, further suffered from more marked microbending
due to the contraction at -30.degree. C. Further the poor water
blocking effect observed with the cable of Comparative Example 1 is
apparently due to a water channel produced within the cable by the
contraction of WB-1 after filling.
In contrast, the cables of Examples, irrespective of whether the
water blocking material was filled at room temperature or as heated
at a high temperature, have water blocking properties and exhibit
outstanding low-loss characteristics at a low temperature of
-30.degree. C. as well as at room temperature. Although the water
blocking materials to be used in this invention undergo contraction
due to a decrease of temperature, the materials nevertheless do not
adversely affect the light transmission loss characteristics of
optical fibers presumably because they retain high flexibility even
at low temperatures without restraining the optical fibers.
EXAMPLES 15, 16
Twelve of the same nylon-jacketed optical fibers as used in Example
1 were assembled at a pitch of 150 mm, around a tension member of a
steel wire strand having a diameter of 2.6 mm. A holding tape
consisting of perforated vinylon nonwoven fabric having a thickness
of 0.1 mm was wound around the assembly with a 1/3 lap. A water
blocking material, WB-9, listed in Table 1 was filled into the
space inside the tape layer, an aluminum laminate tape was wrapped
around the resulting assembly with a longitudinal lap, and the
assembly was further covered with a polyethylene sheath by
extrusion. Thus, an optical fiber cable having an outside diameter
of 13 mm was prepared (Example 15).
In Example 16, an optical fiber cable was prepared in the same
manner as in Example 15 with the exception of using no holding
tape.
The cables of Examples 15 and 16 were moved over a length of 1.5 m
around a metal wheel, 138 mm in diameter, in frictional rubbing
contact with its peripheral surface five times by applying a
tensile force of 100 kg. The loss characteristics of the cables of
0.85 .mu.m were determined before and after the above procedure by
the abovementioned method. The resulting increment of loss was 0.2
dB in the case of Example 15 and 4.5 dB in the case of Example
16.
* * * * *