Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Patent
1991-11-07
1994-04-05
Schofer, Joseph L.
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
385145, 526247, C08F21426
Patent
active
053012542
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a transparent thermoplastic molding compound from which optical objects of high transparency can be manufactured. These include especially beam waveguides, which are suitable for transmitting light signals.
Filamentous beam waveguides normally consist of a core and a sheath with different refractive indices. To transmit the light signals over long distances, firstly the core and sheath materials should absorb as little light as possible, and secondly the core material should have a higher refractive index than the sheath.
The core materials most frequently used hitherto for beam waveguides have been homopolymers and copolymers of methyl methacrylate with refractive indices of about 1.49. The principal sheath materials used have been fluorinated polymers of e.g. fluoroalkyl acrylates or methacrylates (refractive indices of between 1.37 and 1.43) or copolymers of tetrafluoroethylene, hexafluoropropene or vinylidene fluoride (refractive indices of between 1.36 and 1.39). Absorption contributions of the carbon-hydrogen bonds in the core polymers reduce the transparency of the core material and limit the transmission distance which can be achieved.
Furthermore, polymer beam waveguides have already been described which consist of polymers derived from 2-fluoroacrylic acid esters of, in particular, aliphatic alcohols, it being possible for said esters to contain deuterium atoms both in the alcohol component and in the .beta.-position of the 2-fluoroacrylic acid component (q.v. EP 128517). These polymers have refractive indices of between 1.45 and 1.60 and glass transition temperatures of between 100.degree. and 200.degree. C. According to said publication, polymeric 2-fluoroacrylic acid esters of fluorinated alcohols, with a lower refractive index, are used as sheath materials for optical fibers.
The preparation and properties of the aforementioned poly(fluoroalkyl 2-fluoroacrylates) are also known (EP 128516). They have refractive indices of between 1.36 and 1.44 and softening points of between 80.degree. and 140.degree. C.
Moreover, it has already been proposed to use beam waveguides of [sic] poly(2-fluoroacrylic acid esters) or poly(2,3-difluoroacrylic acid esters) in the core and copolymers of TFE, perfluoroalkyl vinyl ethers and .omega.-methoxycarbonyl(perfluoroalkyl vinyl ethers) in the sheath of a beam waveguide.
Copolymers which contain compounds of the formula I and other copolymerizable monomers and have high resistance to low temperatures are described in EP-A-077 998. The glass transition temperatures of thee compounds are in the range from -44.degree. to -32.degree. C.
Also known is the use of copolymers based on tetrafluoroethylene and compounds of the formula II for the preparation of aqueous dispersions (EP-A-193 963) and for the preparation of fluorinated copolymers containing ion exchange groups which are used for diaphragms in electrolysis (DE-A-26 50 979).
Copolymers of tetrafluoroethylene and a monomer of the formula (II) are described in U.S. Pat. No. 4,138,426. However, no data are give n on the properties of these polymers.
The object of the invention was to find a molding compound suitable for the manufacture of optical objects of high transparency, especially beam waveguides making it possible to achieve a long transmission distance for light signals in the wavelength region of visible light.
The invention thus relates to a transparent thermoplastic molding compound consisting of
a) 40 to 90% by weight of units derived from tetrafluoroethylene, and
b) 60 to 10% by weight of units derived to the extent of 0 to 100%, based on the sum of the compounds I and II, from compounds of formula I: --CF.sub.3 (I) derived to the extent of 100 to 0%, based on the sum of the compounds I and II, from compounds of formula II: --COO--R (II) hydrogen atom, a C.sub.6 -C.sub.10 aryl radical or a C.sub.1 -C.sub.8 alkyl radical.
The molding compound according to the invention consists of (a) 40 to 90 or preferably 70 to 85% by weight of units derived from tetrafluoroethylene.
The moldi
REFERENCES:
patent: 4116888 (1978-09-01), Ukihashi et al.
Blickle Peter
Coutandin Jochen
Herbrechtsmeier Peter
Hintzer Klaus
Wieners Gerhard
Hoechst Aktiengesellschaft
Sarofin N.
Schofer Joseph L.
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