GB2140582A

GB2140582A - Plastics light guiding fibre

Info

Publication number: GB2140582A
Application number: GB08413401A
Authority: GB
Inventors: Bernhard Piotrowski; Volker Hofmann; Egon Lang; Bernhard Janser
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1983-05-28
Filing date: 1984-05-25
Publication date: 1984-11-28
Also published as: DE3319536C1; GB8413401D0; JPS59232303A; GB2140582B

Abstract

A plastics light guiding fibre is formed of a monofilamentary transparent core and a sheathing therearound, the core being a polyamide core consisting of or containing an amorphous polyamide produced from an aromatic dicarboxylic acid or an aromatic dicarboxylic acid methyl ester and the sheath being formed of or comprising a fluorine-containing polymer. The polyamide may be a polymer of tere- or isophthalic acid methyl ester and 2,2,4- or 2,4,4-trimethylhexamethylene- diamine.

Description

SPECIFICATION Plastics light guiding fibre This invention relates to a plastics light guiding fibre comprising an amorphous transparent polymer monofilament core and a fluorpolymer light transmissive sheath.

When it has been desired to transmit information in the form of signals by means of light conductive cables over great distances, in general, glass fibre cables with a damping of less than 10 dB/km have hitherto been found to be suitable. Light guiding cables formed of plastics, in spite of the essentially high damping of the cables in contrast to the damping of glass fibre cables, can, on account of their greater numeric aperture and of the greater possible core diameter of the fibre as a result of their production method, take up correspondingly more light output at light sources, for example LED, of large surface area.

With plastics light guiding fibres in lengths up to about 40 metres the clearly lower coupling losses compensate for the advantage of lower damping with light guides formed of glass fibres.

Further advantages in contrast to glass fibres lie in the greater flexibility, the lower weight, the lower production costs and the simpler handling of plastics light guiding fibres.

The light guiding of light conveying fibres is based on the principle of total reflection at the boundary surface between core material and sheathing of the plastics light guiding fibres formed from core material and sheathing. Accordingly, when producing plastics light guiding fibres, optically transparent polymers used as core material are enveloped in sheathings formed from other polymers which, in contrast to the core materials, possess lower refractive indices. Generally, the numerical value of the refractive index of the core material should be approximately 3% greater than that of the material of the casing. The thickness of the casing should therefore amount to 3 to 5 times the wavelength of the supplied light.

Polymers such as, for example, polystyrene, polymethylmethacrylate, polymethylacrylate and copolymers thereof are generally used as core material, whereas, for example fluorpolymers, including fluorinated esters of acrylic acid or methacrylic acid are employed for the sheathing (see German Offenlegungsschrift 2741153).

The sheathing takes place generally by dip coating from solutions of the covering material, by concentric spinning or by sheathing in a coextrusion procedure.

The known polymers for manufacture of the core material are limited in their use at temperatures of above 100 C, inasmuch that, above the glass transition temperature, the refractive index decreases to a significant extent with increasing temperature and therefore, standard optical parameters for the transmission performance of the light guide, such as, for example, the numerical aperture are changed.

The numerical aperture NA = sin 0 = (n1 -n 21/2 defines the opening angle, with only the ray portion of a punctiform light source, which falls within the angle 2 being guided in the fibre core. n1 signifies the refractive index of the core material and n2 the refractive index of the sheathing. In addition to considering these optical parameters in designing an optical fibre, it is also necessary to consider mechanical parameters, such as, for example, modulus of elasticity, tensile strength and their temperature dependence which are determined by the glass transition temperature.

Furthermore, the flame resistance of the hitherto described polymers is sufficient for the core material under certain conditions.

According to the present invention, there is provided a plastics light guiding fibre formed of a monofilamentary transparent core and a sheathing therearound, the core being a polyamide core consisting of or containing an amorphous transparent polyamide produced from an aromatic dicarboxylic acid or an aromatic dicarboxylic acid methyl ester and the sheath being formed of or comprising a fluorine-containing polymer.

An optical fibre embodying this invention represents a plastics light guiding fibre capable of special uses at elevated temperatures of 100 C or more while, at the same time, guaranteeing an improved flame resistance.

In particular it has been found that transparent amorphous polyamides of the type PA 6-(3)-T, as well as transparent mixtures of such amorphous polyamides and what are usually minor amounts of crystalline or partially crystalline polyamides as core material, and fluorpolymers which are preferably vinyl fluoride/ vinylidene fluoride copolymers or mixtures of fluorpolymers and poly(meth)acrylates or polyamides as sheathing material, offer better dimensional stability at elevated temperatures and flame resistance on account of the higher glass point temperature. Such optical fibres posses particular advantage when used for the production of light guiding cables, on account of their more uniform transmission behaviour in the optimal working range of the source elements (LED) usually employed for plastics light guides, in the wave region of 800 to 900 nm.The numerical aperture of plastics light guiding fibres of the proposed type lies at 0.66 or below.

By polyamides of the type PA 6-(3)-T (see for example Saechtling, Plastics Handbook, 21st Edition, Carl Hanser Verlag, Page 277), are meant polymers and/or copolymers of aromatic dicarboxylic acid methyl esters, in particular tere- and isophthalic acid methyl esters and aliphatic bis-primary amines, for example 2,2,4- and 2,4,4-trimethylhexamethylenediamine.

Accordingly, the employment of the proposed polymers makes possible the production of light guiding fibres in the operating temperature region of 100"C and above.

The plastics light guiding fibres according to the invention possesses a damping of less than 1,000 dB/km.

The glass transition temperature for the core material is preferably 141 0C or higher and the dimensional stability of the core and sheathing material when heated lies at 1400C or above. The burning properties of the core and sheathing material are generally characterised by values according to V1 94 of V0 to V2.

The following Example illustrates this invention.

Example A light guiding core was extruded as a monofilament from a transparent amorphous polyamide of the type PA 6-(3)-T on a single screw extruder with a 3-zone longitudinal compression neck (1:2.5), length = 20 D, at cylinder temperatures of 250 to 280"C with use of a funnel shaped nozzle. Extrusion was followed by an air cooling stage. The still warm monofilament was clad by a sheathing process with a PVDF-fluorpolymer which possessed the specifications given in the Table with use of a transverse injection head and cooled in a glycerol bath. The wall strength of the sheathing was established essentially by the rate of stripping.

The characterising data of plastics light guiding fibres thus produced are given in the following Table.

TABLE Material Core material Sheathing DIN PA 6-(3)-T PVDF (MFI 265/12.5 = 150 g/10 min DIN 53 735) Diameter mm 1.8 0.2 n20 1.566 1.42 Numerical Aperture 0.66 Damping dB/km 900-1 000 Glass tran sition temperature K C 418(145) Crystalline melting point (DTA) K"C - 443(170) Dimensional stability on heating (ISO R75 Process B) K"C > 408(135) 418(145) Modulus of elasticity [DIN 53445 at 413 (140"C)1 N/mm2 550 100 Combustibility UL94 94V2 94V0

Claims

1. Plastics light guiding fibre formed of a monofilamentary transparent core and sheathing therearound, the core being a polyamide core consisting of an amorphous polyamide produced from an aromatic dicarboxylic acid or an aromatic dicarboxylic acid methyl ester and the sheath being formed of or comprising a fluorine-containing polymer.

2. Plastics light guiding fibre according to claim 1, wherein said aromatic dicarboxylic acid used as such or as its methyl ester in forming the polyamide is terephthalic acid or isophthalic acid or a mixture thereof.

3. Plastics light guiding fibre according to claim 1, wherein said polyamide is a polyamide of the type PA 6-(3)-T defined herein or a transparent mixture of such a polyamide and a crystalline or partially crystalline polyamide.

4. Plastics light guiding fibre according to claim 1,2 or 3, wherein the sheathing is formed of a copolymer of vinyl fluoride and vinylidene fluoride or a mixture of a fluorpolymer and either a poly(meth)acrylate or a polyamide.

5. Plastics light guiding fibre according to any one of claims 1 to 4, which possesses a numerical aperture having a value of 0.66 at the most.

6. Plastics light guiding fibre according to any one of the preceding claims wherein the glass transition temperature of the core material has a value of at least 141"C.

7. Plastics light guiding fibre according to any one of the preceding claims, wherein the core and sheathing material both have burning properties according to UL 94 of V 0 to V 2.

8. A plastics light guiding fibre, substantially as described in the foregoing Example.