Coating processes – Optical element produced – Polarizer – windshield – optical fiber – projection screen – or...
Reexamination Certificate
2000-04-24
2001-07-10
Beck, Shrive (Department: 1762)
Coating processes
Optical element produced
Polarizer, windshield, optical fiber, projection screen, or...
C427S163100, C427S389700, C427S421100, C427S424000, C118S313000, C118S315000, C118S316000, C118S325000, C385S123000, C385S141000, C428S375000, C428S378000, C428S392000
Reexamination Certificate
active
06258404
ABSTRACT:
The invention relates to the production of wireframe elements coated with at least one fine film of a coating, such as a protective material, in particular.
The invention relates particularly, but not exclusively, to the production of optical fibres.
Optical fibres are composed of silica and comprise many micro-cracks on their surface. When these fibres are placed under stress (e.g. when they are bent), these cracks are propagated and may cause the rupture of the fibre. This phenomenon is particularly accentuated if the fibre is located in a damp environment. Therefore, it is necessary to protect silica fibres with a waterproof protective coating to increase their stress corrosion factor “n”. This factor “n” accounts for the waterproofing and therefore the service life of the fibres: the higher the factor “n”, the greater said waterproofing will be.
Conventional optical fibres are generally coated with a double acrylate based polymer coating (a flexible primary coating coated with a rigid secondary coating) and have a factor “n” of approximately 20. Such a double coating has the disadvantage of being relatively permeable to water and various industrial manufacturers have tried to reduce its permeability or deposit a thin waterproof film under it.
In terms of the research on the waterproofing of the coating, the developments in progress known to date thus relate to:
the use of a primary coating containing an adhesion promoter which improves the fibre's resistance to water and moisture. This primary coating is coated with a conventional secondary coating and would make it possible to obtain a factor “n” of 30;
the use of a fluorinated secondary coating in which grafting fluorine atoms, a hydrophobic element, onto the urethane-acrylate oligomers present in the base resin improves the fibre's resistance to water and humidity. The factor “n” obtained using such a process is of the order of 40.
However, these two coatings still appear to show a certain sensitivity to humidity.
In terms of the research on the use of a thin waterproof film, the waterproof materials currently available are particularly composed of:
ceramics such as silicon carbides and nitrides, titanium carbides;
certain metals such as aluminium, zinc, copper, etc.
carbon.
Such a thin film generally has a thickness of a few tens of nanometers and is protected by a conventional double coating with a minimum thickness of 40 &mgr;m. This type of waterproof deposit makes it possible to obtain a factor “n” greater than 100.
However, it is currently economically difficult to envisage the use of such waterproofing materials, particularly carbon, for the production of optical fibres intended for distribution networks; considerable additional industrialisation is required to reduce their implementation cost.
In terms of the optical fibre production processes known in the state of the art, the double protective coating mentioned above is a photopolymerisable resin deposited on the silica using pressurised dies of a defined diameter according to the thicknesses to be deposited. The silica fibre passes through the centre of these dies continuously supplied with resin. The resins used are viscous (some thousands of mPa.s) to prevent any flow outside the die. This type of process is not suitable for deposits of a thickness less than 10 &mgr;m since, for very thin films, the risks of friction of the fibre on the walls of the die are considerable.
The ceramics or carbon used to waterproof the fibre are deposited using a very specific process : the “CVD” (“Chemical Vapor Deposition”) process. Such a process requires the use of gaseous reactants. Metals are deposited in the molten state on the silica. Their cooling induces micro-bends and, therefore, high attenuations (10 dB/km). In addition, the deposition speed is limited by the cooling time of the metal.
It is also important to note that to be able to adapt to existing civil engineering works, the optical fibre cables intended for future distribution networks must have a very compact structure. In order to reduce size while enabling good protection of fibres, it is recommended to protect them with the finest possible film with good adhesion qualities on silica while offering a good resistance to water and humidity.
Therefore, this invention aims to propose a resin and an application process on fibre making it possible to reduce the diameter of a fibre while improving its stress corrosion factor “n”.
The invention also aims to disclose such a process which eliminates the risk of friction and weakening of the optical fibre during the deposition of the coating.
The invention also aims to propose a resin with improved adhesive properties on silica and, therefore, particularly suitable to form a waterproofing film on a silica fibre.
The invention also aims to propose a process which may use other resins and/or have other applications than optical fibres, such as the deposition of fine coatings, either promoting adherence or uncoupling (coloured or not), the deposition of surface treatment agents or colouring inks, on any type of wireframe element.
Another aim of this invention is to propose a device for the application of such a process which may be easily integrated into state of the art fibre drawing towers used to produce optical fibres. In this respect, it should be noted that state of the art fibre drawing towers are conventionally composed of a preform softening furnace, followed by a cooling system, a silica diameter measuring device, at least one coating deposition die, at least one coating drying furnace, a coated fibre diameter measuring device and a device used to recover and reel the fibre.
These different aims are achieved with the invention which relates to a process for depositing at least one fine film of a liquid agent on a wireframe element designed to form a waterproof coating on said wireframe element, characterised in that it consists of spraying said liquid agent on said wireframe element with spraying means, said wireframe element and said spraying means being in relative movement with respect to each other.
Therefore, the invention proposes to use the spraying of a liquid agent on a wireframe element to coat said element with a fine film of such an agent and offers the advantage of eliminating any contact between the wireframe element and the liquid agent deposition means.
In this respect, it should be noted that spraying is a widely used method to deposit liquid films on large substrates or to mark other objects with large surface areas. However, to the Applicant's knowledge, this process had never been proposed to treat wireframe elements. Since the state of the art spraying processes are applied to large substrate surface areas, they indeed imply little or no loss of the sprayed product. Therefore, their use on wireframe elements, in which significant losses of sprayed product would have been expected, was not an easy task. As explained below, the Applicant has solved this problem by designing a specific device for the application of such a process according to the invention.
It is also important to note that the literature also describes some wire coating processes with liquid agents.
One of these processes consists of passing a wire on inking rollers. Such a process has the disadvantage of involving contact with the wire, making it unsuitable for the deposition of a resin on fibres such as silica fibres (weakening, electrostatics).
Another process consists of passing the wire through a horizontal bath. Such a process is completely unsuitable for the deposition of coatings on optical fibres which move vertically.
A further process consists of passing the wire through a vertical bath, with the wire pulled upwards to prevent of the flow of liquid outside the bath. Since conventional state of the art fibre drawing towers use gravitational fibre movement, it would not be possible to adapt this process to such towers.
Finally, it is also important to note that, in the state of the art, a process consisting of depositing a fluid polymerisable resin o
Desaunay Jean-Louis
Morgand Annie
Ruello Yves
Beck Shrive
Calcagni Jennifer
France Telecom
Merchant & Gould P.C.
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