IE852999L - Optical fibre cables and cable components containing¹fillers - Google Patents

Description

The present invention is concerned with optical fibre cables and components of such .cables, containing fillers.

In optical fibre cables, it is desirable to prevent the optical fibres from absorbing hydrogen because such absorption attenuates signals transmitted at wavelengths greater than 1 micron, which arc the wavelengths used in telecommunications, and degrades the mechanical characteristics of the fibres. Hydrogen can reach the optical fibres from the atmosphere outside the cablo by diffusion through the various materials of which the cable is formed, from the materials of the cable itself which had absorbed hydrogen during their manufacturing processes, and 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 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 the cable materials and adventitious traces ol water 3 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 5 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, 10 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 15 (a) an unsaturated silicone compound of the formula: ^ R Si — 0 R1 jn in which R and R1, which can be the same or different, are saturated or unsaturated aliphatic groups or 20 aromatic groups, R^ 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 organomotal]ic salt or acid of a transition metal, iron pentacarbonyl or chlorop]atinic acid, the catalyst being unsupported or supported on an inert carrier.

According to another aspect of the invention, there is provided an opticiil fibre cable component comprising a tube loosely housing one or more optical fibres, the tube being filled with a filler as described above.

Kor a better und(-r s t.andi rif of the invent ion, preferred embodiments of an optical fibre cattle and cable component will now be described, by way oi example, with reference to the nc c ompa r.y i ny drawing, r> 3 fi which: 1 ijt,ure 1 is. a perspective vie* oi an optical fibre cable with parts partially removed in order better to show the structure, and Ki&ure 2 it a perspective view of a portion ol' 10 An optica] fibre cable component.

As shown in figure 1, the optical fibre cable comprises an optical core 1 formed ol* plastics material and provided with a plurality of helically arranged grooves 2 on its outet surface- Optica] fibres 3 arc IT) loosely housed in the grooves 2. The core 1 is surrounded by a sheath 'i.

The grooves 2 are filled with a liller in such a way thai the optical fibres I are embedded in the filler and are preferably not in 20 contact with any other part of the cable* In 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 are loosely housed. In the latter 2 5 case, the tube is preferably filled with a filler.

Although it is preferred that the filler should surround and be in contact with 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 the 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 6 c h b 1 e .

For pxatnplr, the optical fibre cablr of the invention can comprise an optical fibre core formed of a plurality of tubfi.s , themselves devoid of f iller, r» containing optical fibres, in which the tul.es /ire laid up together and enclosed in an outer sheath and a filler is present in at lea s t s o in e p of the spaces between the tubes themselves rind Leueen the tubes and the outer sheath. Similarly the optical fibre . o tore can be formed of a plurality of grooved elements luivnij: optical fibres housed in the grooves, in which the elements are laid up together and enclosed in an outer sheath and the filler is present in at least some of the spates between the elements themselves and between the t5 elements and the outer sheath and/or in at least some of the grooves housing the optical fibres.

A preferred embodiment of cable component is shown in hi pure 2 and comprises a tube 5 of plnhtics or metallic material in which at least one optical fibre (> 110 is loosely housed. I ne interior of the tube 5 i-s completely filled with a filler.

Although the article shown in Figure 2 will usually be used as o cable component, it may, of course, also be used as an optical fibre cable by itself* 25 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 hydrogenntion catalyst. The silicone, in the presence of the catalyst, has a high reactivity with hydrogen at room tempernture, 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 35 diffusing into or through the cable or cable component 7 and thus prevrnts it i ewchinj:, the optical fibrels). i'he high reactivity toward.*- hydrogen of the fillers is probably due to u low acliviitiim energy at room temper.* t ure l"or the r> hy <t rog eii.i t i on reaction when usiny th» uiis.i t imm t ed silicone compounds ol the invention in association with t lie s |.e t i f l e<l hv dr ogen.i t j on ( iitajvsis; this a 1 J ow hy <1rog e na t i on to take place a 1 room t emprra t ui e even in the pi c-M ilt o ol only tract amounts ol hydioyen* 1 (► As indicated above, the silicone should contain more than O.L' millinioles of unsaturated groups per lOOg oi the compound and it is preferred that it contains from 2 to J00 millimoles- of unsaturated groups on th«* same basis. In the above formula, n is preterably 1 r> an integer of from 100 to 2000.

Preferred silicones are those; in winch e: and uV which m«iv he the* same- or- different, are -^11 , -L, H , , i J -Cr|-CUf)( o/ -C^llr, and in winch W*" and , which may he the- same or different, are -C-ll^Cil^ or -Cllti-Cii = Cil . L'O l.xamples ol such pi el on »'(i compounds are vinyl- terminated polydimethy1 si 1oxanes of the formula CH2- CH- -Si - 0 Ol, C'H. CH., where ii is .is defined above. and v.i rn 1 - * <-r mi nated po] ydimcthy 1 si ] (i.v.itif .s with pendant 2') vinyl groups of the formula: CH-'CH- CH.

-Pi CH, ™3 Si -0 CH--CH.

CH-CH„ where the sum of a and b if. equal to ri. 3 Suitable catalysts for u6e in the filler ■ i r i1 , lor c x;i iiij> 1 <• , transition n't* l a I s , preferably platinum. palladium, and nickel, t ho inorganic and organometa 1 11 c &alt.s and orpanomet a 1 1 i c acids of t lii st men 3 T'cmj pent atarbony! , arid rhloroplatini< acid. The metals wall normally t>< usfd in pondered f or n..

The catalyst may be unsupported or supported on a suitable v inert carrier ■, preferably a material with a large specific surface, such as- animal or vegetable carbon, that is the f 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 such additives should not interfere* nith the reactivity of the silicone towards hydrogen.

The quantity of hydrogen that can be formed within ar» optical fibre cable- or that cars diffuse into such a 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. a 0 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 5 protect the optical fibre(s) can be calculated on the basis that each millimole of unsaturated groups present in the silicone is capable of chemically blocking a millimole of hydrogen.

The following examples of fillers for use in 10 optical fibre cables .uxi liable components according to the invention arc given by way of illustration only. Kx.tmnlc; 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 48 micrometres 0.2g Colloidal silica (optional additives) lOg The filler was prepared by mixing the siloxane 25 with the palladium and then adding the silica.

Tests wore carried out on the filler to determine 1 0 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 tho bulb could be 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 tho pressure within the bulb.

To determine the hydrogen-absorbing capacity of the filler, the walls of the bulb were covered with 15g of tho composition and t.hc bulb was then evacuated by 11 means of tho vacuum sy> torn. After the bulb h<Kl lu:fn ovocua t ed , the t,-ip was comie< tod with the hydrogen-containing vessel and the bull* was filled with hydrogen* Tho tap was then closed and the initial hydrogen pressure 5 in tho bulb 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„ Kroni 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 foilow s » In the first test, hydrogen was introduced into the bulb at a pressure of 7t>0mm Hg (101*3 kPa ) corresponding to a weight o( hydrogen of 0.0l'l5g* After 'if' hours, the pressure had 1 alien to ()7(>mm ilg (90.1 kPa) indicating an absorption of hydrogen by the filler 20 c ones pond ing to O.Olg oi' hydrogen per lOOg ol filler* After lOO hours, the hydrogen pressure had effectively reached an asymtotic value of C55nim Mg (ft7*3 kPa) indicating a maximum absorption corresponding to 0.013**g of hydrogen per lOOg of filler* In the second test, hydrogen was introduced into the bulb at a pressure of 200mm tig (26*7 kl'a) corresponding to a weight of hydrogen of 0.0038g. After **8 hours, the pressure had dropped to 130mm iig (17-3 kPa) indicating an absorption corresponding to 0*008(J& of 30 hydrogen per 100g of filler. After 100 hours, the hydrogen pressure had effectively reached on asymtotic value of 95""11 Hg (12-7 kPa) corresponding to a maximum absorption of 0*013'<g of hydrogen per 10Gg of filler, i.e. the maximum absorption of hydrogen was the same as that observed in 35 the first test.

A filler h<ivjng the following composition was prepared : V iny 1 -tormina ted polydinsethylsiloxane with pendant vinyl groups in the chain, in which n, equal to the sum ol a and b, is 3^0 nrid the content of unsaturated groups is 17.0 millimoJes pel" lOOg of compound lOOg Palladium supported on vegetable charcoal in on amount of 7«0g of palladium per 100g of charcoal 0.6g Tests to determine the hydrogen-absorbing capacity of the filler were carried out using the apparatus and procedure described in Lxample 1, but with only 3»5g °f the composition covering the walls ol t he bul b.

Hydrogen was intioduced into the bujb at a piessitje ol 7(t()nim Hg 1 101.'3 kl'a ) i: orre .spoiid I ny to a weiiht of hydrogen ol' 0.01'ifjg. After 48 hours, the pressure had fallen to 686mm Hg (91*? kl'a) indicating un absorption of hydrogen by the filler corresponding to 0.027g of hydrogen per lOOg of filler. After 100 hours, tho hydrogen pressure had effectively reached an asymtotic value of 67^mm Hg (89«6 ki'a) indicating a maximum absorption corresponding to 0*(>32g of hydrogen pei- lOOg of filler., Tho results of the 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 not dependent on tho initial pressure, i.e. quantity, of hydrogen in tho bulb. It therefore appeared that the rate of the chemical reaction between tho hydrogen .Hid the I i ) ler was independent oi' the in it i .1 I hydrogen I > 1 1 • s s 111 ■ e .

(Mi this basis it was ((nisidcicd that (In- I illers would be suitable for S absorbing trace amounts of hydrogen. 111 order to jest this hypothesis, tho fillers prepared in Lxamples 1 and 2 were tested as before, but usin^ an inii ial hydrogen pressure in the bulb ol only I . .7mm !lg (0.17 kl'a) < orrespoud i ng Id a weight of hydrogen of 2 . x 10 g. 10 After 100 hours, the bulb pressure in both eases was rt lectivelv zero, indicating that the hydrogen bad been totally absorbed by the fillers.

It is this ability to absorb trace amounts of hydrogen which renders the compositions 15 particularly suitable as hydrogen absorbents for incorporation in cables. 1 4

Claims (9)

CLAIMS:

1. An optical fibre cable comprising a shoath, an optical core housing ono or more optical fibrps 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: R2 R i Si — 0 R 1 RJ lit in which U and r', which can bo the ;;anu; or di florciit., an; s. it. united or unsaturated aliphatic groups or aromatic groups, R2 and , which can be the same or different, are unsaturated aliphatic groups, and n is an integer, the compound containing more than 0.2 I r> millimoles of unsaturated groups per lOOg of tho compound, said silicone compound being present in the filler in a free and unreacted state, and (t>) a catalyst which is a transition metal, an inorganic salt. <>f a transition metal, an org.inumcl a 1 1 i r. salt, or acid of a transition mutal, iron pentacarbonyl or chloroplatinic acid, the catalyst being unsupported or supported on an inert carrier. S 5

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 5 formula: R I R2 Si — 0 ~| R- . in which R and R1, which can be the same or different, are saturated or unsaturated aliphatic groups or aromatic groups, R2 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 por lOOg of tho compound, said silicone compound being present in the filler in a free and unreacted state, and I r> (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, tho catalyst being unsupported or supported on an inert ^0 carrier.

3. An optical fibre cable or cablo component according t.o claim 1 or claim 2, in which the silicone n e compound (a) in the filler is one in which n is an integer of from 100 to 2000 and the compound contains from 2 to 100 millimol.es of insaturated groups per 100g of the compound.

4. An optical fibre cablo or cable component according to any one of claims 1 to 3, in which in the silicone compound (a) in the filler, R and R1 are -013, -CH-Cllj, or and R2 and R3 are -ch=ch2 or -ch2-ch=ch2.

5. An optical fibre cable or cablc component according to any one of claims 1 to 4, in which the silicone compound (a) in the filler is a vinyl-terminated polydimethylsiloxane of the formula: ch2=ch Cr3 Si - I ch3 ch--=cii2 or a vinyl-terminated polydimethylsiloxane with vinyl group.*; in the chain 0/ the formula: CH3 CHT=CH. CH3 . Si CH3 Si - ch=ch2 ch=ch2 the sum of a_ and b being equal to n.

6. An optical fibre cable or cable component 1 7 according to any one of claims 1 to 5, in which the catalyst (b) in the filler is palladium, platinum, or nickel.

7. An optical fibre cable according to any one of claims 1 to 6, in which the filler is in contact with the optical fibre(s).

8. Optical fibre cables and components of such cables containing a filler substantially as herein described in either of the Examples.

9. An optical fibre cable substantially as herein described with reference to Figure 1 of the accompanying drawings. F. R. KELLY & CO., AGENTS FOR TIIE APPLICANTS.