CA2003865A1

CA2003865A1 - Thixotropic gel and its use as a filling compound for fibre-optic cables

Info

Publication number: CA2003865A1
Application number: CA002003865A
Authority: CA
Inventors: Wilfried Poppe; Frank Lubczyk
Original assignee: Individual
Current assignee: HB Fuller GmbH
Priority date: 1988-11-24
Filing date: 1989-11-24
Publication date: 1990-05-24
Also published as: DE3839596A1; FI895612A0; EP0371374A1; JPH02203930A

Abstract

Abstract A thixotropic gel based on a synthetic hydrocarbon oil and a hydrophobic thixotropic agent is described. The synthetic hydrocarbon oil consists of a hydrated polyalkylene, which is a polymer of 1-octen, l-nonen, l-decen, l-undecen and/or l-dodecen or a mixture of these polymers. The gel is particularly well-suited for use as a filling compound in the manufacture of fibre-optic cables.

Description

A thixotropic ~el and its us_ as a fillinq compound for fibre-oDtic cables The invention relates to a thixotropic gel comprising a synthetic hydrocarbon oil, a thixotropic agent and also optionally an organic thickener, a mineral oil and other additives. The in~ention also relates to the use of such a thixotropic gel for fibre-optic cables as a core-filling compound, i.e. a compound for filling the thin cladding surrounding each individual optical fibre in a fibre-optic cable, and also as a cable-filling compound, i.e. a compound for filling the space between the outer tubing of a fibre-optic cable and the cladded optical fibres which it contains.

lO Thixotropic gels and their use as a filling compound in fibre-optic cables are known.

In DE-A 27 28 642 a longitudinal water-tight fibre-optic cable with a loose casing is described, in which a viscous substance which does not flow or drip in the cable is introduced into the loose 15 casing. A lightly cross-linked silicone resin, a polyester resin, a thermoplastic polyurethane rubber or an expanded polystyrene in oil is used as the filling compound.
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EP-B Q 029 198 describes a fibre-optic cable in which at least one lightguide in the form of a fibre is arranged in the inside of a 20 protective casing and the remaining inner space is filled with a gelatinous substance. The gelatinous substance consists of a mixture of an oil and a thixotropic agent. It additionally contains an organic thickener which consists wholly or partly of halogenated and/or halogen-free hydrocarbon polymers. Aromatic or 25 aliphatic hydrocarbon oils, paraffin oil, silicone oil and halogenated, especially chlorinated biphenylene are used as the oil.

. , -A filling compound for fibre-optic cables is described in US-A
4 701 016, which consists of an oil or a mixture of oils, colloidal particles and, in some cases, organic thickeners. Paraffin oil, naphthenic oil, polybutene oil, vegetable oil based on triglyceride, polypropylene oil, chlorinated paraffin oil and polyesters are used as the oils. The colloidal particles consist of hydrophobized pyrogenic silicic acid, precipitated silicic acid and clay.

The filling compound in the fibre-optic cable is intended to ensure that if possible no tensile or compressive forces are exerted on the sensitive optical fibre, because its attenuation increases in an undesirable manner under mechanical stress. For this reason thixotropic gels are preferably used as the filling compound which do not flow at rest but when under mechanical stress liquefy temporarily, so that the optical fibre is buffered from the external influence.

Furthermore, the filling compound serves to prevent the penetration of water into the intermediate space between the optical fibre and cable casing. The filling compound must finally be compatible with the coatings used as protective coatings on the optical fibres and with the protective casing of the core and possibly also with the outer cable casing.
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Filling compounds based on silicone oil have the disadvantage that, due to its tendency to creep with the passing of time, the silicone oil coats the cable connection elements and electronic components, and this can lead to faults. For this reason filling compounds which contain silicone oil are hardly used today.

Filling compounds which contain halogenated hydrocarbons have the disadvantage that the halogen content can have a corrosive effect.

For these reasons, gels based on hydrocarbons are preferred for the production of fibre-optic cables. The known gels based on hydrocarbons are however unsatisfactory in various respects.

Gels based on paraffin oil have the disadvantage that the paraffin crystallizes at low temperatures, e.g. in the winter. The formation of crystals produces undesirable mechanical stress on the optical fibres. Many of the known gels based on hydrocarbons, and particularly those products which are suitable for processing at a higher temperature, lose their thixotropic properties at low temperatures. Below the pour point of the fluid phase, in fibre-optic cables these gels result in a considerable deterioration in the attenuation behaviour. For this reason a gel based, for example, on a white oil with a pour point of -25C, as described in US-A 4 701 016, is not suitable for use in regions with severe winters.

The use of gels based on hydrocarbons with low pour points as a filling compound for fibre-optic cables has also been tried. These gels however are problematic with regard to their processing.
Usually when an optical fibre core or cable is manufactured, the filling compound and the plastic covering are co-extruded. The filling compound is exposed to a high temperature of, for example, 200C in the extruder. This processing temperature lies above the flash point of the synthetic polybutene oil with a pour point of -35C which is used according to US-A 4 701 016. An additional disadvantage is that the known gels based on hydrocarbons with low pour points have an undesirably high vapour pressure at the high processing temperature.

-The object of the invention is to improve a thixotropic gel of the type mentioned above in such a way as to overcome the 200386~

aforementioned disadvantages. Firstly, the gel must also be suitable as a filling compound for fibre-optic cables in regions with cold winters. And secondly, it must be possible for it to be processed problem-free at a high temperature.

The object is achieved with a thixotropic gel of the type mentioned above, in which the synthetic hydrocarbon oil comprises a hydrated polyalkylene, which is a polymer of l-octen, l-nonen, 1-decen, 1-undecen and~or l-dodecen or a mixture of these polymers. Preferred embodiments of the invention result from the sub-claims.

The gels according to the invention are surprisingly well-suited ; for the production of fibre-optic cables. They behave neutral to the other construction materials used in fibre-optic cables. They have good oxidation stability. They can be easily processed at high temperatures. They keep their thixotropic properties down to temperatures below -50C. Because the gels according to the invention essentially contain only hydrophobic materials, they prevent the penetration of water into a fibre-optic cables fil led with them.

The synthetic hydrocarbon oils used according to the invention have a special, particularly highly branched structure. Because of this branching these oils have a low temperature dependence as regards their viscosity. The length of the branching also has a considerable effect on the pour point, which generally lies below -40C and preferably below -50C.

Hydrated polyalkylenes, as used according to the invention, are commercially available. They are usually produced by polymerisation, either thermal or catalytic, of the monomers in the presence of a di- tert.-alkylperoxide or a Friedel-Crafts catalyst such as aluminium chloride or boron trifluoride.

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According to the invention the preferred average value of the chain length of the monomers is about 10 carbon atoms. Particularly preferred are l-decen, or olefin mixtures which are rich in this olefin.

Usefully, the synthetic hydrocarbon oil used according to the invention has a dynamic viscosity at room temperature of 5 to I o4 mPa.s The dynamic viscosity i5 preferably from 200 to 400 mPa.s.
The kinematic viscosity of the suitable, co~nercially available products is from 10 to S00 mm2/sec. at 40C.

These branched hydrocarbon polymers have good shear stability.
They can therefore be worked into gels in high-speed mixers with the other constituents without any problem.

They are easily miscible with mineral oils and many natural and synthetic polymers. It is therefore possible to modify the gels ` 15 in the invention by adding further substances.

A suitable thixotropic agent is pyrogenic silicic acid. In particular hydrophobic, pyrogenic silicic acid is the preferred thixotropic agent when the gel according to the invention is used as a core filling compound in fibre-optic cables. In this silicic acid the surface is chemically modified with silane. In addition hydrophobized precipitated silicic acid also comes into consideration.

Another suitable thixotropic agent is hydrophobized clay such as, for example, tetra-alkylammonium derivatives of montmorillonite.

Finally, metallic soaps such as aluminium soaps of long-chain fatty acids are also suitable thixotropic agents.
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200;~865 In general the thixotropic agents have a B.E.T. surface area of about 50 to about 400 m2/g.

In order to ensure that the oil remains fixed in the gel phase even when under extreme conditions for a long period of time, it is useful to add an organic thickener. Suitable thickeners are described in EP-A 29 198 and US-A 4 701 016. A typical thickener is a hydrocarbon polymer with a viscosity of 103 to 105 mPa.s at 180 degrees C.

Other suitable thickeners are thermoplastic rubbers, in particular 10 styrene-(ethylene-butylene) blockcopolymers and styrene-(ethylene-propylene) blockcopolymers. These materials are used in proportions below 10~ by weight, based on the total weight of the gel.

For reasons of economy it may be desirable for the gel according to the invention to contain mineral oil or another natural or 15 synthetic polymer as a further constituent. When these additional oils are used the advantages of the invention are in some circumstances only obtained to a lesser degree. For gels containing mineral oil as a further constituent it is particularly preferred to use thermoplastic rubber as a thickener.

20 It can be useful to add an antioxidant to the thixotropic gel.

In addition, colorants can be added to the gel for labelling purposes.

Inorganic fillers, e.g. kaolin, chalk or the like can also be admixed, particularly when the gel is used used as a core-filling 25 compound.

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The following Table 1 gives an indication of the quantities in which the basic constituents can be contained in the gel according to the invention. The contents in Table 1 are given in parts by weight.
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Table 1 5 Branched synthetic hydrocarbon oil, e.g. poly-l-decen 99 - 80 10 - 89 98 - 60 10 - 88 'thixotropic agent 1 - 20 1 - 20 1 - 20 1 - 20 organic 10 thickener - - 1 - 20 1 - 20 mineral oil - 89 - 10 - 88 - 10 ,~
The invention also relates to the use of the thixotropic gel for the production of fibre-optic cables. The gel according to the invention is suitable both as a core-filling compound and as a 15 cable-filling compound.

In the following, the production of the thixotropic gel according to the invention is described with the aid of an embodiment which is explained in detail. In the comparative examples materials according to the prior art are compared.

20 The cone penetratLon given in the examples has been determined according to DIN ISO 2137. The ~lash point of the gels was determined according to DIN ISO 2592.
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, Example 1 A core-filling compound according to the invention for universal use was produced from the following constituents:

92.5 parts by weight of a synthetic hydrocarbon oil rich in poly-1-decen with a kinematic viscosity at 40C of 62 mm2~sec. and a density at 15C of 0.833 g/cm3.

7.5 parts by weight of a silane-modified pyrogenic silicic acid with a B.E.T. surface area above 150 mZ/g.

The oil was placed in a mixing vessel and heated to about 80C.
The silicic acid was added in portions under vigorous agitation.
Then it was mixed for about 1 hour at a high rate of agitation (800 to 1000 r.p.m.). After this, it was de-gassed for 30 minutes at a medium rate of agitation (400 r.p.m.) under a low vacuum. Then it was re-evacuated for a further 30 minutes under an increased vacuum (approx. 200 mbar).
~' ; 15 The properties of the gel obtained in this way are given in Table 2.

Comparative ~m~le 2 For the production of a core-filling compound for regions with a cold climate according to the prior art, 92.5 parts by weight of a mineral oil were used with a kinematic viscosity at 40C of 13 mm2/sec. and a density at 15C of 0.850 g/cm3. The procedure in Example 1 was then followed. The properties of the gel are shown in Table 2.

20038~i5 _ g .
ComParative ExamPle 3 For the production of a core filling compound according to the prior art for regions with a Central European climate, a mineral oil was used with a kinematic viscosity at 40C of 100 mm2~sec. and a density at 15C of 0.885 g/cm3. The procedure in Example 1 was then followed. The properties of the gel obtained in this way are shown in Table 2.

Table 2 Example 1 Comp. Comp.
Example2 Example 3 _____.___________________________________________________________ Flash point (C) 240 155 250 Loss from evaporation at 1.5 30 0.5 150C/24 hr. (% by weight) Cone penetration (1/10 mm) at 25C 360 360 360 ' at -45C 255 200 20 at -60C 188 145 5 ~ As Table 2 shows, the gel in Comparative Example 3 is unusable at ,, low temperatures as a core-filling compound for fibre-optic cables.
f The gel in Comparative Example 2 can only be processed to produce a fibre- optic cable with difficulty, because its flash point lies 20 below the usual processing temperature and it is very volatile at a high temperature. In contrast the gel according to the invention is satisfactory in every respect. It can be processed at a high temperature, e.g. 200C without any problem. It does not set even at temperatures down to -60C.
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Claims

1. A thixotropic gel comprising:
a) a synthetic hydrocarbon oil; and b) a thixotropic agent selected from the group consisting of pyrogenic silicic acid, hydrophobized pyrogenic silicic acid, hydrophobized precipitated silicic acid, hydrophobized clay and metallic soaps;
wherein the synthetic hydrocarbon oil consists of a hydrated polyalkylene which is a polymer of 1-octen, 1-nonen, 1-decen, 1-undecen and/or 1-dodecen or a mixture of these polymers.

2. A gel according to claim 1 wherein the hydrated polyalkylene is rich in 1-decen or consists thereof.

3. A gel according to claim 1 wherein the hydrated polyalkylene has a dynamic viscosity at 20 degrees C of 5 to 104 mPa.s.

4. A gel according to claim 2 wherein the hydrated polyalkylene has a dynamic viscosity at 20 degrees C of 5 to 104 mPa.s.

5. A gel according to claim 1, 2 or 3 and further comprising an organic thickener.

6. A gel according to claim 4 and further comprising an organic thickener.

7. A gel according to claim 1, 2 or 3 and further comprising a mineral oil.

8. A gel according to claim 4 or 6 and further comprising a mineral oil.

9. Use of the gel according to claim 1, 2 or 3 as a core-filling compound and/or cable-filling compound for the manufacture of fibre-optic cables.

10. Use of the gel according to claim 4 or 6 as a core-filling compound and/or cable-filling compound for the manufacture of fibre-optic cables.