Optical fibre element comprising an optical fibre housing constituted by a polyolefin material, and an H2-absorbing buffer

Abstract: The optical fibre element comprises at least one optical fibre housing constituted by a polyolefin material having at least one additive which protects it against degradation due to oxidation, heat or the proximity of metals, and (b) at least one H₂-absorbing buffer. The additive is selected from the group comprising anti-oxidants, stabilizers and metal deactivators and causes a reduction in the hydrogen absorption capacity of less than 30% in the or each H₂-absorbing buffer when the or each buffer has been in contact with said polyolefin containing the or each additive for 30 days at 100°C in an air atmosphere saturated with water vapour at 150 mbar.

Description: The present invention relates to an optical fibre element which comprises a housing for optical fibres, constituted by polyolefin material comprising at least one additive which protects it against degradation, and an H 2 -absorbing buffer. In this specification, the expression "optical fibre element" is used to indicate elements for the transmission and/or processing of optical signals such as, for example, optical fibre cables, joints for optical fibre cables, terminals for optical fibre cables, amplifiers with active core optical fibres, optoelectronic repeaters, optical fibre sensors and such like. It is known that, to enable them to be handled, optical fibres are coated with a protective sheath. In the production of optical fibre elements, such as, say, cables, the optical fibres coated with said protective sheath are placed in appropriate housings generally constituted by polyolefin material. Examples of such housings are loose sleeves described in US-4.143.942, 4.153.332, 4.676.590, 4.688.889, and UK-1.598.540 and grooved cores described in US-4.199.224, 4.491.386, 4.668.889, 4.690.498; EP-A-280.279; UK-1.448.793, 2.021.282, 2.099.173, 2.164.471, 2.170.921, 2.172.410, 2.174.822, and FR-2.200.535. It is also known that in optical fibre elements other structures of polyolefin material can be present. It is further known that hydrogen exerts harmful effects on optical fibres and jeopardizes their efficiency. It has, therefore, been proposed to incorporate, in optical fibre elements, some compositions capable of absorbing hydrogen before it exerts its harmful effects on the fibres. In this specification such compositions are, for short, referred to by the expression "H 2 -absorbing buffers". The Applicant has developed H 2 -absorbing buffers substantially consisting of compositions comprising at least one unsaturated organic compound of silicon and at least one hydrogenation catalyst selected from the group comprising the salts and the organic and inorganic compounds of the transition metals. Examples of these compositions are described in US-4.688.889 and in the Italian patent applications Nos. 20.833 and 20834, both dated 2 July 1990. EP-A-0 287 244 discloses an optical fiber cable having a layer of linear medium density polyethylene that has certain defined properties which provides advantages in the manufacture and use of said cable. In particular, said layer can be extruded at a relatively low temperature and said polyethylene relaxes relatively quickly consequently the extrusion line can be run at a relatively high speed. This document does not recognizes, however, that some possible additives of polyethylene poison the hydrogenation catalyst of H 2 -absorbing buffers. It has now been unexpectedly observed that some polyolefin materials poison the hydrogenation catalyst, based on transition metals, of the H 2 -absorbing buffers. Studies carried out with the object of identifying the cause of such poisoning have shown that this must be looked for in some additives added to protect the polyolefin against degradation due to oxidation (anti-oxidants) and/or heat (stabilizers) and/or the proximate metals (metal deactivators), in spite of the fact that, usually, their quantity is only of the order of 2.5 x 10 -2 to 5 x 10 -2 parts by weight with respect to the quantity of H 2 -absorbing buffer in contact with the polyolefin material. The additives which inactivate the H 2 -absorbing buffer are identified by means of a test, described in detail later, with which it is possible to measure the quantity of hydrogen absorbed by a H 2 -absorbing buffer before and after it has been placed in contact with a polyolefin, protected against oxidation and/or heat degradation, for 30 days at 100°C in an air atmosphere saturated with water vapour at 150 mbar. On the basis of the experience acquired, it has been established that the additives can be considered non-inactivating when the capacity of residual absorption of the H 2 -absorbing buffer, which has been in contact with the polyolefin which contains them for 30 days at 100°C in an air atmosphere saturated with water vapour at 150 mbar, is greater than 70%. In one embodiment, the present invention relates to an optical fibre element according to claim 1. In a further embodiment, the present invention relates to an optical fibre cable according to claim 3. A typical example of a H 2 -absorbing buffer is described in example 1 of the US patent 4.688.889; said H 2 -absorbing buffer is substantially constituted by (a) 90 parts by weight of a vinyl-terminated polydimethylsiloxane, with no chain unsaturations and having a content of unsaturated groups equal to 7.4 mmol per 100 g of product, b) 0.2 parts by weight of palladium powder having an average size 48 microns and (c) 10 parts by weight of colloidal silica. Examples of optical cables and of components thereof in the production of which it is useful to employ the present invention are those described in the following documents: US-4.688.889, UK-A-2.172.410. EP-A-280.275, FR-A-2.200.535, UK-A-1.598.540, UK-A-2.021.282, uK-A-2.099.173, UK-A-2.164.471, UK-A-2.170.921, UK-A-2.174.822, US-4.143.942, US-4.153.332, US-4.199.224, US-4.491.386, US-4.491.387, US-4.676.590 and US-4.690.498. Examples of suitable antioxidants and stabilizers according to the present invention are those which do not contain any atoms of nitrogen, phosphorus or sulphur in their molecule. Typical examples of additives suitable for accomplishing the present invention are: pentaerythritol-tetrakis-[3-(3',5'-di-tert.butyl-4'-hydroxyphenyl) -propionate] (IRGANOX 1010 by Ciba Geigy), octadecyl-3-(3',5'-di-tert.butyl-4'-hydroxyphenyl)-propionate (IRGANOX 1076 by Ciba Geigy), 2,2'-methylene-bis-(4,6-dimethylphenol) (PERMANAX 28 HV by Rhône-Poulenc), 2,2'-methylene-bis-(4-methyl-6-tert.butyl-phenol) (ANTIOXIDANT 2246 by Bayer), 2,2'-methylene-bis-(4-ethyl-6-tert.butylpnenol) (ANTIOXIDANT 425 by Cyanamid), 1,6-hexanediol-bis-[3-(3',5'-di-tert.butyl-4-hydroxyphenyl) propionate] (IRGANOX 259 by Ciba Geigy), and triethyleneglycol-bis-[3-(3-tert.butyl-4-hydroxy-5-methyl-phenyl) -propionate] (IRGANOX 245 by Ciba Geigy). The following tests and examples are used to illustrate the present invention without, however, limiting it in any way. TESTS The capacity of absorbing hydrogen on the part of H 2 -absorbing buffers was assessed by measuring the pressure drop in a hermetically-sealed container, containing the H 2 -absorbing buffer under examination in a hydrogen atmosphere. The apparatus used is an automatic commercial apparatus for the measurement of pressure in the range from 1000 to 1 mbar. The apparatus is formed by assembling a fixed-volume chamber provided with two valves (one of which is of the pin-type to regulate the flow of hydrogen and the other of the usual type for connection to a vacuum pump), with a commercial pressure transducer type E 8510 connected to a commercial digital reader type EMV251, both made by the firm Edwards Alto Vuoto S.p.A.. Inside the apparatus there is a glass container. The control unit providing a digital reading of the pressure has a resolution of 1 mbar, and the indication of pressure is independent of the composition of the gas and of atmospheric pressure. The tests have been carried out at a constant temperature of 23°C. After weighing the glass container to an accuracy of 0.01 g (weight A), the H 2 -absorbing buffer under examination was placed in the container; the glass container was then weighed a second time (weight B). The glass container containing the H 2 -absorbing buffer under examination was inserted into the apparatus and vacuum was applied for about 1 to 2 hours. After leaving the system in a static vacuum for at least 12 hours, the container was connected to a hydrogen cylinder until the digital pressure indicator indicated a desired pressure (generally some 500 or 1000 mbar). The hydrogen cylinder cock was closed, and the time and the hydrogen pressure were noted. After 24 hours the residual hydrogen pressure was read. The hydrogen absorption capacity expressed in normal cm 3 /g was calculated with the following formula: P - Pr x V x 273 1013 x 273 + C x B - A where P = initial hydrogen pressure, Pr = residual hydrogen pressure after 24 hours of test, C = temperature, in °C, during the test, V = free volume of the apparatus after insertion of the H 2 -absorbing buffer under examination, B = weight of the glass container with the H 2 -absorbing buffer, A = weight of the empty glass container. For each sample of H 2 -absorbing buffer, the above test was carried out twice, and the average of the two values obtained was made. The above test was carried out on H 2 -absorbing buffers before and after having been in contact with samples of loose sleeve, grooved cores or stamped plates of polyolefin material comprising at least one additive which protects it against degradation. Said samples were smeared with a quantity of H 2 -absorbing buffer in the same ratio as used on average in an optical cable. More in particular, 3 g of H 2 -absorbing buffer were smeared on each linear meter of loose sleeve or of grooved core. The same quantity was also smeared on two types of small plates having a surface area of 200 cm 2 and weighing 10 g and 5g, respectively. Each sample treated in this way was aged at 100°C in a large sealed test tube in the presence of air (150 mbar) and saturated water vapour. After one month, the H 2 -absorbing buffer was recovered, and its residual hydrogen absorption capacity was measured with the method described above. Unless otherwise indicated, the values given in relation to the compositions described in the following examples refer to parts by weight. EXAMPLE 1 Two meters of grooved core constituted by a material having the following composition: polypropylene 100 calcium stearate 0.05 pentaerythritol-tetrakis-[3-(3',5'-di-tert.butyl-4'-hydroxyphenyl)propionate] (IRGANOXTM 1010 by Ciba Geigy) 0.10 distearyl-thio-dipropionate (IRGANOXTM PS 802 by Ciba Geigy) 0.20 hydrazide of 3,5-di-tert.butyl-hydroxy-benzyl)-propionic acid (IRGANOXTM MD 1024 by Ciba Geigy) 0.20 tris-(2,4-di-tert.butylphenyl)-phosphite (IRGAFOXTM 168 by Ciba Geigy) 0.05 were spread with 6 g of an H 2 -absorbing buffer having an initial hydrogen absorption capacity of 1.9 normal cm 3 /g. After aging, the residual hydrogen absorption capacity was 0 normal cm 3 /g. The material of this example can thus be classified as highly poisonous. EXAMPLE 2 Two meters of grooved core constituted by a material having the following composition: polypropylene 100 calcium stearate 0.05 pentaerythritol-tetrakis-[3-(3',5'-di-tert.butyl-4'-hydroxyphenyl) - propionate] (IRGANOXTM 1010 by Ciba Geigy) 0.30 hydrazide of 3,5-di-tert.butyl-hydroxy-benzyl)-propionic acid (IRGANOXTM MD 1024 by Ciba Geigy) 0.20 tris-(2,4-di-tert.butylphenyl-phosphite (IRGAFOXTM 168 by Ciba Geigy) 0.05 were spread with 6 g of an H 2 -absorbing buffer having an initial hydrogen absorption capacity of 1.9 normal cm 3 /g. After aging, the residual hydrogen absorption capacity was 0.3 normal cm 3 /g. The material of this example is thus slightly better than that of example 1 but it is still highly poisonous. EXAMPLE 3 Two meters of grooved core constituted by a material having the following composition: polypropylene 100 calcium stearate 0.05 pentaerythritol-tetrakis-[3-(3',5'-di-tert.butyl -4'-hydroxyphenyl)-propionate] (IRGANOXTM 1010 by Ciba Geigy) 0.50 hydrazide of 3,5-di-tert.butyl-hydroxy-benzyl)-propionic acid (IRGANOXTM MD 1024 by Ciba Geigy) 0.20 tris-(2,4-di-tert.butyl-phenyl)-phosphite (IRGAFOXTM 168 by Ciba Geigy) 0.05 were spread with 6 g of an H 2 -absorbing buffer having an initial hydrogen absorption capacity of 1.9 normal cm 3 /g. After aging, the residual hydrogen absorption capacity was 1.3 normal cm 3 /g. In spite of a distinct improvement over the material of Examples 1 and 2, the material of this example is still moderately poisonous. EXAMPLE 4 Two meters of grooved nucleus constituted by material having the following composition: polypropylene 100 calcium stearate 0.05 pentaerythritol-tetrakis-[3-(3',5'-di-tert.butyl -4'-hydroxyphenyl)-propionate] (IRGANOXTM 1010 by Ciba Geigy) 0.25 octadecyl-3-(3',5'-di-tert.butyl-4'-hydroxyphenyl) -propionate (IRGANOX 1076 by Ciba Geigy) 0.25 were spread with 6 g of an H 2 -absorbing buffer having an initial hydrogen absorption capacity of 1.9 normal cm 3 /g. After aging, the residual hydrogen absorption capacity was 1.6 normal cm 3 /g. The material of this example is thus not poisonous. EXAMPLE 5 A small plate having a surface area of 200 cm 2 and constituted by 10 g of a material having the following composition: polypropylene 100 glycerylmonostearate 0.05 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol) (Antioxidant 2246 by Bayer) 0.25 1,6-hexanediol-bis-[3-(3',5'-di-tert.butyl-4-hydroxyphenyl) -propionate] (IRGANOX 259 by Ciba Geigy) 0.25 were spread with 6 g of an H 2 -absorbing buffer having an initial hydrogen absorption capacity of 1.9 normal cm 3 /g. After aging, the residual hydrogen absorption capacity was 1.7 normal cm 3 /g. The material of this example is thus not poisonous.

Claims: An optical fiber element comprising (a) at least one optical fiber housing and (b) at least one H 2 -absorbing buffer which substantially is a composition comprising at least one unsatured organic compound of silicon and at least one hydrogenation catalyst selected from the group comprising salts and organic compounds of transition metals, characterized in that said housing is made of a polyolefin material comprising at least one additive which protects it against degradation due to oxidation, heat or the proximity of metals, and in that said additive is selected from the group comprising anti-oxidants, stabilizers and metal deactivators which do not contain any atoms of nitrogen, phosphorus or sulphur in their molecule, whereby said additive causes a reduction in the hydrogen absorption capacity of less than 30% in the, or each, said H 2 -absorbing buffer when the, or each, said buffer has been in contact with said polyolefin containing the, or each, said additive for 30 days at 100°C in an air atmosphere saturated with water vapour at 150 mbar. An optical fiber element according to claim 1, characterized in that the additive is selected from pentaaerythritol-tetra kis-[3-(3',5'-di-tert.butyl-4'-hydroxy-phenyl)-propionate], 2,2'-methylene-bis-(4,6-dimethyl-phenol), 2,2'-methylene-bis-(4-methyl-6-tert.butyl-phenol), 1,6-hexanediol-bis-[3-(3',5'-di-tert.butyl-4-hydroxyphenyl)-propionate], and triethylene glycol-bis-[3-(3-tert.butyl-4-hydroxy-5-methylphenyl)-propionate]. An optical fiber cable comprising an optical fiber element according to claim 1 or 2.

Inventors: BOSISIO CLAUDIO, CAMPANA ANTONIO, BOSISIO, CLAUDIO, CAMPANA, ANTONIO
Applicants: PIRELLI CAVI SPA, PIRELLI CAVI S.P.A.
Application year: 1991
Main classification: G02B6
IPC codes: G02B6, G02B1, C03C25