IE56995B1 - Optical fibre cables and cable components containing fillers - Google Patents

Description

The present invention is concerned with optical fibre cables and components of such .cables, containing fillers. f In optical fibre cables, it is desirable to r> prevent the optical fibres from absorbing hydrogen because such absorption attenuates signals transmitted at wavelengths greater than 1 micron, which are the wavelengths used in telecommunications, and degrades the mechanical characteristics of the fibres.

Hydrogen can reach the optical fibres from the atmosphere outside the cable by diffusion through the various materials of which the cable is formed, from the materials of tho cable itself which had absorbed hydrogen during their manufacturing processes, and I 5 also by decomposition or degradation of certain of the cable materials during use. It appears that hydrogen can be evolved from all or most of the component 1 parts of optical fibre cables, that is their metallic or plastics sheaths, their plastics cores, their metallic armouring layers, and the tubes in which the optical fibres are loosely housed. Hydrogen can also ! be formed as a result of chemical reactions between ' fe the cable materials and adventitious traces oi water present in liquid or vapour form.

It is an object of the invention to provide a barrier between the optical fibres of such a cable and the other components thereof, the barrier being capable of chemically blocking hydrogen so that it is prevented from reaching the optical fibres. To this end, we have developed a filler composition which is capable of providing such a barrier.

According to one aspect of the present invention, there is provided an optical fibre cable comprising a sheath, an optical core housing one or more optical fibres and a body of a filler partially or wholly surrounding the optical fibre(s), the filler being chemically reactive to hydrogen and comprising (a) an unsaturated silicone compound of the formula: __ R1 __ n in which R and R^r which can be the same or different, are saturated or unsaturated aliphatic groups or aromatic groups, and R^, which can be the same or different, are unsaturated aliphatic groups, and n is an integer, the compound containing more than 0.2 millimoles of unsaturated groups per lOOg of the compound, said silicone compound being present in the filler in a free and unreacted state, and (b) a catalyst which is a transition metal, an inorganic salt of a transition metal, an organometallic salt or acid of a transition metal, iron pentacarbonyl or chloroplatinic acid, the catalyst being unsupported or supported on an inert carrier.

According to another aspect of the invention, there is provided an optical fibre cable component comprising a tube loosely housing one or more optical fibres, the tube being filled with a filler as described above. *9 For a belt ci understanding of the invention, preferred embodiments oi an optical fibre cable and cable component will now be described, by way oi example, with reference to the accompanying drawings, ι n whic h: figure 1 is a perspective vie* of an optical fibre cable with parts partially removed in order better to show the structure, and Figure 2 is a perspective? view of a portion of an optical fibre cable component.

As shown in figure 1, the optical fibre cable comprises an optical core 1 formed oi' plastics material mid provided with a plurality of helically arranged grooves 2 on its outei surface. loosely housed in the grooves 2 surrounded by a sheath ύ.

Optical fibre’s 3 are The core 1 is The grooves 2 are filled with a filler* in such a way that the optical fibres 3 are embedded in the filler and are preferably not in contact with any other part of the cable. ln the embodiment shown in Figure 1, the optical fibres are bare, but in other embodiments they may be provided with a protective adherent sleeve or a protective tube in which they ore loosely housed. ln the latter case, the tube is preferably filled with a filler.

Although it is preferred that the filler should surround and be in coni act wi t h the optical fibre(s), it is not essential and the filler may be located iri portions of the cable spaced from the optical fibres. Thus in a cable according to th·· invention, the spaces containing the filler may surround, entirely or partially, cable components in which the optical fibres are housed and which form the optical core of the c fa b 1 e .

For example, the optical fibre πιΙΊν of the invimtioh van comprise an optical fibre core formed of a plurality of tubes, themselves devoid of filler, Γ» containing optical fibres, in which the tul.es are laid up· together and enclosed in «’in outer sheath and a filler is present in at least some of the spaces between the tubes themselves and betueen the tubes and the outer sheath. bimilarly the optical fibre 1() core can be formed of a plurality of' grooved elements having optical litres housed in the grooves, in which the elements are laid up together and enclosed in ati outer sheath and the filler is present in ot least some ol the spaces between the elements themselves arid betueen tin· t5 elements and the outer sheath and/or in at least some of tin· grooves bousing the optical fibres.

A preferred embodiment of cable component is shown in Figure 2 and comprises a tube 5 of plastics or metallic material in which at least one optical fibre (> is loosely housed. Ine interior of the tube 5 is completely tilled with a filler.

Although the article shown in Figure 2 will usually be used as a cable component, it may, of course, also be used as an optical fibre cable by itself.

The filler comprises, as indicated above, an unsaturated silicone containing terminal and, optionally pendant vinyl groups and a catalyst which is capable of acting as a hydrogenation catalyst. The silicone, in the presence of the catalyst, has a high reactivity with hydrogen at room temperature, which i« the normal operating temperature of optical fibre cables. Further, the reaction is effectively irreversible so that the hydrogen is stably bound.

The filler is, therefore, able to bind hydrogen diffusing into or through the cable or cable component e* /. and thus prevents it teaching the optical fibrtls).

Mie high reactivity towards hydrogen of the fillers is probably d uc low activation energy at room temperature for the hydrogenation reaction when using t h« unsat υra t ed Filtcone compounds ol the invention in as so», i a t j on with the spet i f ted h \ drogenu t i <>n c «itajysts ; this allows hydrogenation to take place at room leHiperidun· even in the presence ol only trace amounts ol hydioyetn As indicated above, the silicone should contain more than 0.2 millimoles of unsaturated groups per lOOg of the compound and it is preferred that it contains from 2 to 1()() millimoles of unsatnrnted groups on the same basis. In the above formula, n is prvtvrably an integer of from 100 to 2()00.

Preferred silicones «re those in winch κ and a1 which may be the same or dil ferent, ere (Jl -L . d -CllrUI or -C, IJ, and jn which d*” «nd t which may be L’O G'V the same or different, are -Clf-Cil,, or -Cd,,-Uii = Cd , hxaniples ol such prefened compounds are vinylterminated polydimethylsiloxanes of the formula ch2- CH™3 -Si - 0 CH CH.CH„ where n is as defined above. and vinjl-terminat.ed pol ydimet hy 1 si 1 oxanes with pendant Zb vinyl groups of the formula: CH^CHCH Si O,3 Si -0 I CH-CH.

CH-CH CH, j where thr· sum of a and b is equal to n.

Suitable* catalysts for use in the filler ;i η·, for e x«-i mp 1 <·, transition »·<· l a I s . preferably platinum. palladium. and nickel, the inorganic and organometallic salts and organometallic acids of these metals. iron pent at ar bonvl , and chi oropl at i i« j c acid. lhe metals wall normally he- used in powdered form. The catalyst may he unsupported or supported on a suitable inert carrier, preferably a material with a large speciiic surface, such as animal or vegetable carbon, t fiat is the material known as charcoal.

The filler may contain additional, optional, constituents. for example additives to adjust its viscosit> if this is required for the filler to be conveniently incorporated in the cable or cable component . It is important, however, that any Ruch additives should not interfere with the reactivity of the silicone towards hydr ogen .

The quantity of hydrogen that can be iorined within ar. optical fibre cable or that can diffuse into such :i cable from outside depends on the structure of the cable, the materials of which it is formed, and the characteristics of the surroundings in which the cable is operated. i i? Each of these quantities can be determined by a person skilled in the art and on the basis of the calculated quantities, the minimum amount of silicone (and thereby the minimum amount of filler) required to protect the optical fibre(s) can be calculated on the basis that each millimole unsaturated groups present in the silicone is capable of chemically blocking a millimole of hydrogen.

The following examples of fillers for use in optical fibre cables amicable components according to the invention are given by way of illustration only. Example 1 A filler having the following composition was prepared: Vinyl-terminated polydimcthylsiloxane with no pendant vinyl groups in the chain, in which n is 360 and the content of unsaturated groups is 7.5 millimoles per lOOg of compound 90g Powdered palladium with particles having an average diameter of micrometres 0.2g Colloidal silica (optional additives) lOg The filler was prepared by mixing the siloxane with the palladium and then adding the silica.

Tests were carried out on the filler to determine its capacity for absorbing hydrogen. The apparatus used for this purpose consisted of a glass bulb having a volume of 175 cm^ which was connected via a short tube to a two-way tap by which the bulb could bo connected to either a vacuum system or a vessel containing hydrogen. A mercury manometer located on the tube between the bulb and the tap indicated the pressure within the bulb.

To determine the hydrogen-absorbing capacity of 10 the filler, the walls of the bulb were covered with 15g of the composition and the bulb was then evacuated by 1 it means of the vacuum sy.* tem. Al ter the bulb had been iViKuated, the tap wn> cutiiifi ted with the hydrogencontaining vessel and the hull· was filled with hydrogen· The tap was then closed and the initial hydrogen pressure in the bull· was noted. The exponential uptake ol hydrogen by the filler was then monitored by observing the fall in pressure within the bulb with time. The tests were conducted at 20°C.

From the data obtained it was possible to determine 10 the maximum amount of hydrogen absorbed by the filler and the time required to achieve maximum absorption.

The results of two specific tests using different initial pressures of hydrogen in the bulb were as follows.

In the first test, hydrogen was introduced into the bulb at a pressure of 0mm Hg (101.3 kPa) conespotiding to a weight oi hydrogen of O.Olk^g· After kl' hours, (he prc.ssui*(* had 1 alien to 67hmm ilg ($><>. 1 kl’a) indicating an absorption of hydrogen by the filler corresponding to O.Olg of hydrogen per lOOg oi filler.

After 1OO hours, the hydrogen pressure had effectively reached an asymtotic value of G55nim Hg (8?.3 kPa) indicating a maximum absorption corresponding to 0.013kg of hydrogen per lOOg of filler.

In the second test, hydrogen was introduced into the bulb ot a pressure of 200mm Hg (26.7 KPa) corresponding to a weight of hydrogen of O.OO38g» After kft hours, the pressure had dropped to 130mm Hg (17-3 kPa) indicating an absorption corresponding to O.OO69g of hydrogen per lOOg of filler. After 100 hours, the hydrogen pressure had effectively reached an asymtotic value of 95mm Hg (12-7 kPa) corresponding to a maximum absorption of 0.013kg oi* hydrogen per 10Og of filler, i.e. the maximum absorption of hydrogen was the same as that observed in the first test.

I 2 Example 2 Λ filler having the following composition was prepared : Viny1 -terminn ted polydimethy1 si 1oxone 5 with pendant vinyl groups in the chain, in which n, equal to t.he sum oi' a and b, is 3 Palladium supported on vegetable charcoal in an amount of 7.0g of palladium per lOOg of charcoal 0.6g Tests to determine the hydrogen-absorbing capacity of the filler were carried out using the apparatus and procedure described in Example 1, but with only 3·5& »f the composition covering the walls ol the bulb.

Hydrogen was intinduced into the bulb al a pt es s m c 01 yhOiinii Hg t 1()1.3 kPa) correspond 1 ny to a weiiht of hydrogen of O.OVifjg. After 48 hours, the pressure had fallen to 686mm Hg (91♦5 kPa) indicating an absorption of hydrogen by the filler corresponding to O.O27g of hydrogen pci' 100g of filler. After 100 hours, the hydrogen pressure had effectively reached an asymtotic value of 67^mm Hg (89*6 kPa) indicating a maximum absorption corresponding to 0«O32g of hydrogen per- lOOg of filler„ The results of thi» tests carried out at room temperature on the fillers of the examples indicated that both the maximum amount of hydrogen absorbed by the fillers and the time required for maximum Absorption are 1$ not dependent on the initial pressure, i.e. quantity, oi hydroten in the bulb. It therefore appeared that the i, rate of the chemical reaction between the hydrogen .md the I i 1 I it wax independent ot (.hi* init i .1 1 hy (I r ng< ‘ ι» ρ ι t · x s u ι · e .

(Mi this basis it was eons i de red that the tillers would be suitable for S absorbing triirv amounts of hydrogen. In order t-o text this hypothesis, the fillers prepared in Examples ] and 2 were t exte d ax before. hut using ; an initial hy drogen pi e x s 11 r e in the 1 >n 1 h ol on 1 y 1.Imm Hg (0.17 kl’a ) cor respond i ng t o a weight of hydrogen of 2 . ') χ 1 0 ς ii- At ί er 100 hours . the bulb pr< ssur< ‘ i n bot h ( .isos w a s et I eeli v<* 1v zero . i nd icati ng that- fhe hydrogen had been totally absorbed by the fillers.

It ix this ability to absorb trace amounts of hydrogen which renders the compositions 15 particularly suitable as hydrogen absorbents for incorporation in cables.

Claims (9)

CLAIMS:
1. I. An optical fibre cable comprising a sheath, an optical core housing one or more optical fibres and a body ot a tiller partially or wholly surrounding the 5 optical fibre(s), the filler being chemically reactive to hydrogen and comprising (a) an unsaturated silicone compound of the formula; R ι Si — 0 Rl I () in which R and r\ which can be the same ur different, are saturated or unsaturated aliphatic groups or aromatic groups, and R 3 , which can be the same or different, are unsaturated aliphatic groups, and n is an integer, the compound containing more than 0.2 r > millimoles of unsaturated groups per lOOg of the compound, said silicone compound being present in the filler in a free and unreacted state, and (b) a catalyst which is a transition metal, an inorganic salt of a transition metal, an organometallic salt, or acid ot a Iran*.; it ion metal, iron pentacarbonyl or chloroplatinic acid, the catalyst being unsupported or supported on an inert carrier.
2. 2. An optical fibre cable component comprising a tube loosely housing one or more optical fibres, the tube being filled with a filler comprising (a) an unsaturated silicone compound of the formula: R I — Si — 0 R J in which R and R 1 , which can be the same or different, are saturated or unsaturated aliphatic groups or aromatic groups, and R^, which can be the same or 10 different, are unsaturated aliphatic groups, and n is an integer, the compound containing more than 0.2 millimoles of unsaturated groups per lOOg of the compound, said silicone compound being present in the filler in a free and unreacted state, and l5 (b) a catalyst which is a transition metal, an inorganic salt of a transition metal, an organometallic salt or acid of a transition metal, iron pentacarbonyl or chloroplatinic acid, the catalyst being unsupported or supported on an inert 20 cai'rier.
3. 3. An optical fibre cable or cable component according to claim 1 or claim 2, in which the silicone compound (a) in the filler is one in which n is an integer of from 100 to 2000 and tho compound contains from 2 to 100 millimoles of insaturated groups per 100g of the compound.
4. 4. 5 4. An optical fibre cable or cable component according to any one of claims 1 to 3, in which in the silicone compound (a) in the filler, R and R 3 are -CH 3 , -CH-CHj, or and R^ and R 3 are -CH=CH 2 or -CH 2 -CH=CH 2 . 5. An optical fibre cable or cable component according to any one of claims 1 to 4, in which the silicone compound (a) in the filler is a vinylterminated polydimethylsiloxane of the formula: CH 2 =CH ch 3 Si - 0 I ch 3 ch=cii 2 or a vinyl-terminated polydimethylsiloxane with vinyl groups in the chain of the formula: ch 2 =ch ch 3 Si - 0 ι CH 3 CH 3 I Si - 0 ι CH=CH 2 ch=ch 2 the sum of a and b being equal to n.
5. 5. 6. An optical fibre cable or cable component I tr 1
6. 6. 7 according to any one of claims 1 to 5, in which the catalyst (b) in the filler ii; palladium, platinum, or nickel. 4 7. An optical fibre cable according to any one 5 of claims 1 to 6, in which the filler is in contact with the optical fibre(s).
7. 7. 8. Optical fibre cables and components of such cables containing a filler substantially as herein described in either of the Examples.
8. 8. 10
9. 9. An optical fibre cable substantially as herein described with reference to Figure 1 of the accompanying drawings.