Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-06-11
2001-09-18
Ullah, Akm E. (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C521S128000
Reexamination Certificate
active
06292613
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fibres provided with a hydrophobic protective coating, to a cable comprising at least one such fibre surrounded by a protective sheath and to a process for producing these fibres.
The invention also relates to optical fibres provided with a hydrophobic protective coating as well as to a process for producing a fibre-optic interconnection device.
BACKGROUND OF THE INVENTION
Optical fibres comprise a lightguide which, as its name suggests, has the purpose of conducting light waves.
When this lightguide is made of silica, it is fundamental to protect this silica from being attacked by the chemicals normally or accidentally present in the external environment. In particular, moisture (or more precisely, OH
−
ions) embrittles the silica or quartz of the optical fibres by penetrating the micropores inherent in its crystalline structure, thus degrading the optical properties of the lightguide. The chemical attack on the silica, accelerated by the mechanical (bending, tensile, etc.) stresses to which the optical fibre is subjected, over time produces fracture initiators on the lightguide.
Various protective coatings have been proposed so as to remedy these drawbacks. Thus, it is known to provide silica optical fibres with a coating made of an epoxy acrylate resin. This coating is applied immediately after drawing the optical fibre, or even simultaneously therewith. It prevents the drawn quartz from oxidizing, blocks the micropores present in the fibre and increases the mechanical strength of the fibre.
However, the epoxy acrylate has the drawback of being permeable to OH
−
ions, and is therefore water-soluble, and to moisture, which results in the destruction or blistering of the epoxy acrylate protecting the fibre, the protection against the external environment then losing its effectiveness over time.
Consequently, the optical fibre coated with an epoxy acrylate is normally placed in microtubes internally coated with a petroleum jelly so as to protect it from the undesirable effects of moisture.
However, such a structure has an extremely poor mechanical strength because of the presence of the protective microtube, which is moreover subject to folding and has an elasticity which lends itself poorly to effective protection of the fibre.
Furthermore, the protective system consisting of the microtube internally coated with petroleum jelly does not allow a very high fibre density (namely, a large number of fibres per cable) to be obtained, because of the diameter of the microtube which it is necessary to adopt in order to allow the jelly to be deposited. By way of example, it is enough to point out that, for an optical fibre only 250 &mgr;m in diameter, the tubes have a diameter of 1.5 to 2.5 mm.
It has also been proposed to coat the optical fibre with a film of UV-crosslinkable silicone, as described in Patent FR 2,628,847. However, silicones have a strong affinity for water. It is therefore necessary to provide an external sheath made of a rigid plastic, for example polyetherimide. This external sheath has the drawback of increasing the diameter of the fibre up to 1 mm, a diameter which, once again, does not allow a very high fibre density to be obtained in cables.
In addition, since silicones are pollutants, they have to be recycled after the fibres have been used.
A drawback common to all these solutions of the prior art is the incompatibility between the quartz of the optical fibre and the coating used for protecting the latter, resulting in insufficient adhesion of the protective coating, which is applied in a loose manner to the optical fibre.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide for a fibre, especially an optical fibre, and for a cable comprising at least one such fibre which better meet the practical requirements than the previously known fibres of the same type, while having a low manufacturing cost, especially in that the fibre according to the invention includes a coating which:
exhibits improved chemical resistance to the external medium, especially to water and moisture,
has an improved mechanical strength, for a given diameter, and
is chemically compatible with the core of the fibre, especially with quartz, while interacting with the latter so that there is effective interaction with the quartz.
The subject of the present invention is a fibre provided with a protective coating, wherein the said protective coating comprises at least one layer of a crosslinked epoxidized-polydiene oligomer.
DESCRIPTION OF THE INVENTION
Mention may be made, by way of non-limiting examples, of textiles (polyester, polyamide or polyurethane) fibres, metal (steel, copper or aluminium) fibres and glass fibres (which can be used, for example, as reinforcement for various materials, whatever their fields of application). Any flexible elongate body whatsoever, provided with the abovementioned protective coating, is also included with in the context of the present invention.
Advantageously, the thickness of the said layer of a crosslinked epoxidized-polydiene oligomer is between 20 and 60 &mgr;m, preferably between 20 and 40 &mgr;m.
The epoxidized-polydiene oligomer is such as the one described in Patent Application EP 0,859,038. Thus, the epoxidized-polydiene oligomer has, for example, a number-average molecular mass M
n
of between 500 and 10,000 g/mol, preferably between 1000 and 5000 g/mol.
The diene, which is the base monomer of the polydiene, is a conjugated diene which may be selected from the group comprising butadiene, isoprene, chloroprene, 1,3-pentadiene and cyclopentadiene.
The epoxidized-polydiene oligomer may be functionalized at the ends of the chain by hydroxyl or epoxy functional groups, this functionalization allowing the number of reactive functional groups to be increased during crosslinking.
The epoxidized-polydiene oligomer may also be partially hydrogenated.
The epoxidized-polydiene oligomer is, for example, a hydroxytelechelic polybutadiene, i.e. a polybutadiene functionalized at the ends of the chain by hydroxyl functional groups, comprising at most 25%, preferably about 1 to 8%, of epoxy functional groups on the chain and comprising, after epoxidation, 70 to 80%, preferably 75%, of 1,4 units.
The viscosity of the epoxidized-polydiene oligomer is, for example, less than 100 Pa.s at 30° C., preferably less than 40 Pa.s at 30° C.
Mention may be made especially of PolyBd 600/605 materials from Elf Atochem, PolyBd R 45 EPI from Idemitsu Petrochemical and Kraton Liquid Polymer EKP 206 and 207 materials from Shell.
The epoxidized-polydiene oligomer may also comprise vinyl and/or acrylic comonomers, such as styrene and acrylonitrile.
Additives, such as reactive diluents, wetting agents, degassing agents, antioxidants, UV stabilizers, spreading agents, rheological agents, solvents, plasticizers and colorants, may be added to the epoxidized-polydiene oligomer.
The term <<reactive diluent>> should be understood to mean a composition formed by small liquid molecules, of low viscosity (between 5×10
−3
and 40×10
−3
Pa.s at 25° C.), having a low vapour pressure, a high flash point and a high boiling point, the role of which is to reduce the viscosity of the epoxidized-polydiene oligomers. The reactive diluent may furthermore increase the weight content of reactive functional groups of the epoxidized-polydiene oligomer.
In addition, the term <<wetting agent>> should be understood to mean chemical substance capable of lowering the surface and interfacial tensions of a liquid medium, thus resulting in an increase in the dispersion of the liquid over a defined surface.
The reactive diluent may be a difunctional cycloaliphatic epoxy (sold, for example, by 3M under the reference CYRACURE UVR 6110) or a vinyl ether (for example 1,4-butanediol monovinyl ether), while the wetting agent may, for example, be a fluorinated surfactant such as FLUORAD sold by Borlöcher.
According to a preferred embodiment of the fibre according to the in
Fort Fibres Optiques Recherche et Technologie
Morgan & Lewis & Bockius, LLP
Ullah Akm E.
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