Optical fiber cables and components thereof containing an homogeneous barrier composition capable of protecting optical fibers from hydrogen, and relative homegeneous barrier composition

Abstract: An optical fibers cable and the relative components comprise a barrier mixture, to protect the optical fibers, comprising (a) at least a silicon unsaturated organic compound having more than 0.2 mmoles of unsaturated groups per 100 g of said compound, (b) at least a catalyst selected from the group comprising inorganic and organic complexes of transition metals and organic salts of transition metals; said barrier mixture is a further object of the invention and consists of an homogeneous phase.

Description: This invention relates to optical fiber cables and components thereof containing a homogeneous barrier composition or mixture suitable to protect optical fibers from hydrogen; it also relates to a method for preparing said composition or mixture and said homogeneous barrier composition or mixture per se. It is known that hydrogen is detrimental to optical fibers of optical cables and impairs their efficiency. Some compositions able to capture hydrogen before it contacts the optical fibers of optical cables have been therefore proposed. US-B-4,688,889 teaches to capture hydrogen by means of an hydrogen fixing filler for cables and components thereof containing such filler which comprises: (a) at least an unsaturated organic silicone having more than 0.2 mmoles of unsaturated groups per 100 g of said compound and having the following general formula: wherein: R and R' are selected from saturated or unsaturated aliphatic radicals and aromatic radicals, R" and R''' are aliphatic unsaturated radicals, and n is an integer; and (b) at least a catalyst selected from the group consisting of transition metals, inorganic and organometallic salts of transition metals and organometallic acids of transition metals. As it is also apparent from the pertinent examples, the catalysts according to said patent are typically in the form of powders, either free or supported onto suitable solid inert materials. In turn, UK-A-2,172,410 teaches to capture hydrogen with a hydrogen trapping powder which is free or, preferably, supported on a flexible film of paper or polymeric material. As an example of a powder suitable for capturing hydrogen, the said patent mentions palladium on carbon. EP-A-0 164 238 describes a curable composition comprising an organosiloxane, a methylhydrogensiloxane, a platinum-type catalyst and an alkynyl compound, which is used for coating optical fibers, and which is cured to form a rubbery material after coating. Examples of suitable platinum-type catalysts include very finely divided platinum powder possibly adsorbed on a carbon powder support (page 7, line 4 to 9). Furthermore, it is also known that microbendings substantially reduce optical fibres efficiency (G. Grasso et al. "Microbending effects in single mode optical cables" - International Wire & Cable Symposium Proceedings 1988). Now, it has been found that the particles of the powders forming the materials of US-B-4688889 and UK-A-2172410 cause microbendings when they are contacted with optical fibres. Said materials are thus less effective than they could be if they were directly contacted with the optical fibres; moreover, also the manufacturing of optical cables is more difficult than it could be if a composition were available, directly applicable in contact with the optical fibres to exert an effective barrier function against hydrogen without causing the drawbacks (microbendings) of known compositions. On the other hand, it does not appear that any composition was disclosed consisting of a homogeneous phase, comprising an unsaturated silicone organic compound of formula I and a hydrogenation catalyst, having high hydrogen adsorbing power. Therefore, this invention aims to provide a composition having all the above cited features for use in the production of optical cables and components thereof. This object has been surprisingly achieved by dissolving a catalyst selected from the group comprising inorganic and organic complexes of transition metals and organic salts of transition metals in a volatile organic solvent, mixing the thus obtained solution with an unsaturated silicone organic compound, and removing the solvent from the thus prepared mixture. In the present description and in the appended claims, the expression "volatile organic solvent" means an organic fluid having the following properties : a vapour pressure higher than 200 Pa at 20 °C; 1 part by volume dissolves at least 0,001 parts by weight of a catalyst of the present invention; and it is mixable with the unsaturated silicon organic compounds of the formula I. The barrier compositions of this invention are substantially different from those disclosed by US-B-4688889 because they do not contain metal or crystalline particles at the microscopic and K-ray diffraction inspection. An object of the present invention is to provide optical fiber cables and components thereof containing this particular homogeneous barrier composition which is, per se, also a further object of this invention as hereinafter defined. A further object of this invention is therefore a spreadable barrier composition capable of chemically adsorbing hydrogen according to claim 1. The preferred unsaturated silicone organic compounds of this invention have from 2 to 100 mmoles of unsaturated groups per 100 g of compound; most preferably, they have from 5 to 80 mmoles of unsaturated groups per 100 g. Typically, n is an integer from 10 to 2000. Preferred meanings of R and R' are 1-4 C alkyl, 2-10 C alkenyl and phenyl. In turn, R" and R''' are preferably the same or different 2-10 C alkenyl. Typical examples of catalysts are palladium acetate; palladium, platinum or phodium acetylacetonate; dimeric allylpalladiumchloride (PdCl)(C 3 H 5 )) 2 ; tetrakis(triphenyl phosphine)-palladium; bis-(chlorodicarbonyl)-rhodium and bis(dibenzyl-indeneacetone)-palladium. The amount of catalyst (parts of transition metal in the homogeneous barrier composition of this invention) is preferably of from 5 to 2000 ppm and, most preferably, 100 to 200 ppm. The barrier composition according to this invention may also contain suitable additives such as, for example, thickening agents. Examples of suitable thickening agents are colloidal silica having an average particle size of from 10 to 20 nm. Another object of the invention is to provide a method according to claim 4. The removal of the solvent is preferably performed by evaporation. The pressure may range from atmospheric pressure to 1.33 x 10 -4 bar while the temperature preferably ranges from 15 to 80° C. Typical examples of solvents according to the present invention are lower aliphatic ketones such as, for example, acetone and methyl ethyl ketone; lower aliphatic halogenated hydrocarbons such as, for example, chloroform, methylene chloride and carbon tetrachloride; aromatic hydrocarbons such as, for example, benzene, toluene and xylene. The person skilled in the art will easily estimate with good approximation the amount of hydrogen gas that may penetrate from outside into an optical fibre cable or that may generate inside the cable (release of hydrogen gas adsorbed by the materials of the cable during the manufacturing processes or formed by decomposition of some of said materials) depending on to the cable structure, the materials of which it is formed, and the operating conditions. He is therefore in a position to estimate the minimum amount of homogeneous barrier mixture to be applied case by case. Examples of optical cables and components thereof, which may be advantageously manufactured with the barrier composition of this invention to protect the optical fibres from hydrogen, are disclosed in the above cited documents US-B-4688889 and UK-A-2172410, and also in the followings: EP-A-280279, FR-A-2200535, UK-A-1598540, UK-A-2021282, UK-A-2099173,UK-A-2164471, UK-A-2170921, UK-A-2174822, US-B-4143942, US-B-4153332, US-B-4199224, US-B-4491386, US-B-4676950 US-B-4491387 and US-B-4690498. The following example will illustrate the present invention without, however, limiting it in any way. EXAMPLE 1 vinyl terminated polysiloxane oil having a content of vinyl groups of 7.8 mmoles/100g 96.00g palladium acetate containing 47% of Pd 0.03g (corresponding to 141 ppm of Pd) colloidal silica 3.97g (average particle diameter = 12 nm) 6 g of a 0.5% solution of palladium acetate in acetone were added under stirring to the vinyl terminated polydimethyl siloxane oil and the solvent was removed under vacuum at room temperature in 4 hours while stirring. The thus obtained product was thickened by addition of colloidal silica powder which was dispersed by means of a baffle disperser. Finally, the mixture was homogeneized by passing through a three drum refiner. EXAMPLE 2 saturated polydimethylsiloxane oil 36.00 g polydimethylsiloxane oil having 23 mmoles/100g of vinyl groups in terminal and branched chains 10.00 g palladium acetylacetonate containing 35% of palladium (corresponding to 280 ppm of Pd) 0.08 g colloidal silica powder 3.92 g (particle average diameter = 12 nm) 16 g of a 0.5% solution of palladium acetylacetonate in acetone were added under stirring to the mixture of the polydimethylsiloxane oils and the solvent was removed under vacuum at room temperature for 8 hours while stirring. The thus obtained product was then thickened by addition of colloidal silica powder which was dispersed by means of a baffle disperser. Finally, the mixture was homogeneizd by passing through a three drum refiner. TESTS The capability of adsorbing hydrogen by the homogeneous barrier mixture of this invention was tested with a method based on measurements of the pressure drop occuring in a sealed container containing the material under examination in hydrogen atmosphere. The device was an apparatus for automatic pressure measurement within the range of from 1000 mbar to 1 mbar. The apparatus was made by assembling a fixed volume chamber having two valves (one being a pin valve to control the hydrogen feeding, and the other one being a conventional valve to provide connection with a vacuum pump) to a commercial pressure transducer type E 8510 connected with a commercially available digital lector type EMV251, both manufactured by Edwards High Vacuum SpA. Inside the apparatus is housed a glass container. The control unity provided with digital reading of the pressure has a resolution of 1 mbar and the pressure reading is indipendent from the gas composition and the atmospheric pressure. The tests were performed at a constant temperature of 23° C. The glass container was weighted with a precision of 0.01 g (weight A), and then the bottom and wall of the container were uniformly spreaded with about 10 g of the homogeneus barrier mixture under examination. When the addition of the composition was over, the glass container was weighted a second time (weight B). The glass container containing the homogeneous barrier mixture was housed in the apparatus and vacuum was applied for about 1-2 hrs. After having maintained the system under static vacuum for at least 12 hours, the container was connected to a hydrogen bottle until the digital pressure indicator showed the required pressure (usually about 500 or 1000 mbar). The hydrogen bottle valve was closed and both the time and hydrogen pressure were recorded. After 24 hours the residual hydrogen pressure was measured. The hydrogen adsorbing capability 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 is the initial hydrogen pressure, Pr is the residual hydrogen pressure after 24 hrs, C is the temperature, in centigrade degrees, during the test V is the free volume of the apparatus after spreading about 10 g of material, B is the weight of the glass container with the material A is the weight of the empty glass container. For each sample of barrier mixture the above cited test was performed twice and the mean of the obtained values was calculated. In the case of the homogenous barrier mixture of the examples, the operational conditions of the tests and the relevant results were: - composition of Example 1 chamber volume = 104.90 cm 3 free volume = 94.90 cm 3 initial hydrogen quantity = 46.8 normal cm 3 = 4.18 x 10 -3 g (corresponding to 500 mbar) final hydrogen quantity = 29.9 normal cm 3 = 2.67 x 10 -3 g (corresponding to 319 mbar) adsorbed hydrogen quantity = 16.9 normal cm 3 = 1.51 x 10 -3 g theoretical adsorption = 1.50 x 10 -3 g. - composition of Example 2. chamber volume = 102.60 cm 3 free volume = 92.60 cm 3 initial hydrogen quantity = 91.4 normal cm 3 = 8.16 x 10 -3 g (corresponding to 1000 mbar) final hydrogen quantity = 42.8 normal cm 3 = 3.82 x 10 -3 g (corresponding to 468 mbar) adsorbed hydrogen quantity = 48.6 normal cm 3 = 4.34 x 10 -3 g theoretical adsorption = 4.40 x 10 -3 g.

Claims: A spreadable barrier composition capable of chemically adsorbing hydrogen, for use in protecting optical fibers of optical cables from said gas, comprising: (a) at least an unsaturated silicone organic compound having more than 0.2 mmoles of unsaturated groups per 100 g of said compound and having the following general formula: wherein: R and R', which may be the same or different, are alkyl, alkenyl or aryl R" and R''', which may be the same or different, are alkenyl, and n is an integer; and (b) at least a catalyst selected from the group comprising inorganic and organic complexes of transition metals and organic salts of transition metals characterized in that said barrier composition is a homogeneous phase formed by dissolving said catalyst in a volatile organic solvent, mixing the thus obtained solution with said unsaturated silicone organic compound, and removing the solvent from the thus prepared mixture. An optical fiber cable comprising at least an optical fiber housed in a suitable seat, said optical fiber being protected against the damaging action of hydrogen by a barrier composition according to claim 1. A component for optical fiber cables, consisting of a suitable seat wherein at least an optical fiber is loosely housed, said optical fiber being protected against the damaging action of hydrogen by a barrier composition according to claim 1. A method of preparing a homogeneous spreadable barrier composition capable of chemically adsorbing hydrogen, for use in protecting optical fibers of optical cables from said gas, comprising the steps of providing at least a catalyst selected from the group comprising inorganic and organic complexes of transition metals and organic salts of transition metals, providing an unsaturated silicone organic compound having the following general formula: wherein: R and R', which may be the same or different, are alkyl, alkenyl or aryl R" and R''', which may be the same or different, are alkenyl, n is an integer; and has more than 0.2 mmoles of unsaturated groups per 100 g of said compound; and admixing said catalyst with said unsaturated silicone organic compound, characterized in that prior to said step of admixing, said catalyst is dissolved in a volatile organic solvent, the thus obtained solution is admixed after said step of admixing, said solvent is removed from the thus prepared composition, and when desired, a thickening agent is added. A method according to claim 4, characterized in that the unsaturated silicone organic compound has from 2 to 100 mmoles of unsaturated groups per 100 g of compound. A method according to claim 5, characterized in that the unsaturated silicone organic compound has from 5 to 80 mmoles of unsaturated groups per 100 g of compound. A method according to any one of claims 4 to 6, characterized in that n is an integer comprised from 10 to 2,000. A method according to any one of claims 4 to 7, characterized in that R and R', which may be the same or different, are a 1-4 C alkyl, a 2-10 C alkenyl or phenyl. A method according to any one of claims 4 to 8, characterized in that R" and R"', which may be the same or different, are a 2-10 C alkenyl. A method according to any one of claims 4 to 9, characterized in that the catalyst is selected from the group comprising palladium acetate; palladium, platinum or rhodium acetylacetonate; dimeric allylpalladiumchloride (PdCl(C 3 H 5 )) 2 ; tetrakis(triphenylphosphine)-palladium; bis-(chlorodicarbonyl)-rhodium and bis(dibenzyl-indeneacetone)- palladium. A method according to any one of claims 4 to 10, characterized in that the amount of catalyst, in parts of transition metal in said composition, is of from 5 to 2,000 ppm. A method according to claim 11, characterized in that the amount of catalyst is of from 100 to 200 ppm. A method according to any one of claims 4 to 12, characterized in that the solvent is selected from the group comprising lower aliphatic ketones, lower aliphatic halogenated hydrocarbons and aromatic hydrocarbons. A method according to claim 13, characterized in that the solvent is selected from the group comprising acetone, methyl ethyl ketone, chloroform, methylene chloride, carbon tetrachloride, benzene, toluene and xylene. A method according to any one of claims 4 to 14, characterized in that the solvent is removed by evaporation at a temperature of from 15 to 80°C. A method according to any one of claims 4 to 15, characterized in that the solvent is removed by evaporation at a pressure of from atmospheric pressure to 1.33x10 -4 bar. A method according to any one of claims 4 to 16, characterized in that the thickening agent is a colloidal silica having an average particle size of from 10 to 20 nm.

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: C09D183, C08K3, C08L83, G02B6, C08K5, C03C25