Filling material

Details Filling material Filling material

1999-07-30

2001-02-13

Ullah, Akm E. (Department: 2874)

Optical waveguides

Having particular optical characteristic modifying chemical...

C385S147000, C523S116000

Reexamination Certificate

active

06188828

ABSTRACT:

The invention relates to a filling material, in particular for optical waveguide cables, which contains polyoxyalkylenes as basic fluids, and the use of such filling materials in electrical and optical devices.
Optical waveguides are used for the conducting of optical signals, and for this purpose are laid in the form of optical waveguide cables. Optical waveguide cables feature in general the following composition (“loose tube” design): A cable sheathing as an outer delimitation surrounds one or more cores. Located in the cores are one or more optical waveguides. Both the interior of the cores and the inside space of the cable sheath is filled with a filling material. Gel-like filling materials are used for preference in the cores. The intermediate space between the individual cores and the cable sheathing as the outer delimitation may likewise be filled out with a gel-like substance. For economic reasons, the filler material is in this situation mostly a more economically-priced material, such as a wax. The optical waveguide itself consists mostly of silicon dioxide, but may also consist of polyolefins, fluorinated hydrocarbons, or other plastics, or contain these. Mention may be made at this point of polycycloolefins (in particular, copolymerisates and terpolymerisates of cycloolefins with short-chain olefins), which in turn may be coated with other plastics. There are also other cable designs in existence, such as “slotted core” cables, in which the optical fibres are located in slots around a circular core, in which situation the slots are filled with a gel-like substance, or “ribbon” cables, in which the fibres rest on broad ribbon strips, several of which are in turn are combined to form a block.
Nowadays, in loose-tube designs the cores of the cables are usually filled with a gel-like substance, in order to protect the optical waveguides (the equivalent of optical fibres) against gross mechanical or chemical effects, such as the influence of moisture. In other cable designs, too, gel-like filling materials are used, such as, for example, with “slotted core” cables or “ribbon” cables. The consistency of the filling materials is to be adjusted in such a way that with the fibre(s) in the state of rest a specific retention capacity will be achieved. The gel-like substance under load produces, under load, a threshold value, in order to protect the optical waveguides against transverse forces (structural viscosity with flow limit). The filler material is intended in this situation to occupy at all times the space available in the cores. At the same time, reciprocal effects of the filling material with the core(s), threw cable sheathing, or the optical waveguide or its coating, must be avoided as far as possible. In addition to this, the filling materials are also intended to be sufficiently proof against dripping out, especially under high temperatures, and must not become too rigid at low temperatures.
Usually, the gel-like substance is based on a mineral and/or synthetic oil, which is thickened with a thixotropicalisation medium (such as colloidal silicic acid); if appropriate, however, other hydrocarbon polymers can also be added, in most cases caoutchouc rubbers such as SEBS, SIS, SI, and SB (S=styrene, I=isoprene, E=ethylene, B=butadiene), in order to reduce the leaching of oil, and an anti-oxidation agent.
From the patent literature, a plurality of different compounds are known as the base fluid of the filing compounds, such as, for example, mineral/synthetic oils, silicone compounds, weakly-crosslinked hydrocarbon oils, polyolefins, EP-caoutchouc rubbers (E=ethylene, P=propylene) and halongenised biphenyls.
The German Patent Specification DE-A1-36 22 211, or its U.S. subsequent application U.S. Pat. No. 4,839,970, describe a filling material for optical waveguide cores and/or optical waveguide cables, which contain 50 to 99% by weight polypropylene glycol, to which are added, as thixotropicalisation agents, between 50 and 1% by weight highly-dispersed silicon dioxide, aluminium dioxide, aluminium hydroxide, and/or an organic compound containing halogen. The polypropylene glycol has, for preference, a molecular weight from 2000 to 3500 g/mol. If the filling material is used in the optical waveguide cores, the polypropylene glycol is contained in the compound in the proportion of 99 to 96% by weight, and the thixotropicalisation agent in the proportion of 1 to 4% by weight. As a filling material for the optical waveguides, a compound is recommended of 92 to 50% by weight polypropylene glycol and 8 to 50% by weight thixotropicalisation agent. This filling material does not attack polyurethane acrylate as a fibre coating material.
The material from which the cores are extruded during manufacture consists mostly of polyester, polybutyl enterphthalate, or a comparable plastic, which at least in part consists of polar groups. Because this type of plastic is relatively expensive, it is recommended from the financial point of view that a change be made to more economical olefinic polymers, such as LD polyethylene, HD polyethylene, or polypropylenes. Almost all the filling materials on the market are based, however, on a mineral and/or synthetic oil, which impairs the mechanical properties of the olefinic plastics which come in contact with it, because the oil migrates into these plastics and so changes their properties. Thus, for example, the migration of the oil reduces the tensile strength significantly. In order to be able to use the more economical olefinic substances as core materials, new migration-free core filling materials are required.
The objective of the invention is to provide such a filling material for optical waveguide cables which feature a suitably low migration for core materials and/or cable sheathings and/or cable coatings made of olefinic polymers, and, at the same time, are sufficiently non-polar to take effect as a moisture block.
In addition to this, the filling material must be resistant to ageing both chemically and physically, and must as far as possible retain its properties over a wide temperature range (−60° C. to +80° C.) both in respect of its Theological behaviour as well as in respect of its chemical compatibility with the other active substances of the optical waveguide cable. It should effectively be able to absorb tensile and pressure forces, and keep them from the optical waveguides, as well as, right from the outset, have no inclination to the absorption of water. Likewise, the compound must be easy to process when filling the cables and cores, and must not, even after long use or under the influence of increased or reduced temperature, lead to the separation of the phases, base fluid, or colloidal particles. In addition to this, hydrogen and water must be effectively kept away from the optical waveguide.
A filling material for optical waveguide cables which fulfils these objectives is the object of the invention according to claim
1
. This consists of a compound which contains, as the base fluid, one or more polyoxyalkylenes, of which the alkylene units in each case feature 2 to 5, for preference 2 to 3, carbon atoms, and which, related to the alkylene unit, features in each case 2 to 4, for preference 2 to 3, ether compounds, and as colloidal particles contains oxides and/or hydroxides of silicon and/or aluminium, as well as at least one surfactant.
In particular, the polyoxyalkylenes contained in the filling materials according to the invention have the general structural formula:
A−[O−X]
n
−Z,
where
A and Z are end groups, which are usually hydrogen, hydroxy, or C1 to C5 alkyl groups, in which situation A is for preference an alkyl group and Z a hydroxy group;
X is a non-branched or branched saturated alkylene group with 2 to 4 carbon atoms, for preference 2 or 3, such as, for example, ethylidene —CH
2
—CH
2
— or 1,2-propylidene —CH
2
—CH(CH3)— or 1,3-butylidene —CH
2
—CH
2
(CH
3
)—CH
2
—, in which case X can be different for each n, and
n is a whole n

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