CA1093876A

CA1093876A - Jacketed optical filamentary material with thermoplastic core

Info

Publication number: CA1093876A
Application number: CA286,480A
Authority: CA
Inventors: Martval J. Hartig
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1976-09-13
Filing date: 1977-09-12
Publication date: 1981-01-20
Also published as: NL7710035A; NL185541C; JPS6110802B2; DE2741153C2; GB1565724A; JPS6160404B2; JPS5336246A; NL185541B; FR2364472B1; DE2741153A1; FR2364472A1; IT1114146B; JPS5844403A

Abstract

ABSTRACT OF THE DISCLOSURE
An optical filamentary material with a thermoplastic optically transparent core and a lower index of refraction sheath is spaced from a protective jacket by a heat shield which thermally protects the optical filamentary material during extrusion and application of a jacketing polymer.

Description

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The present invention relates to an optical filamentar~ material having a thermoplastic protecti~e jacket and, more particularly, an optical filamentary material contai~ing a core made ~rom an optically ~ransparent thermoplas~ic polymeric material.
Optical filamentary materials are well lonown in the art for transmission of light along a filament length by multiple internal reflections of light.
Great care is -taken to minimize light losses along the length of the filament or, in other words1 internal reflec~ions are made as total as possible so th~t light applied ko one end of the optical filameIltary material is efficiently transmitted to--the opposite end of the material. The light transmitting portion or core of the optical filamentary material is surrounded by a shea~h having a lower index of refrackion which minimizes the escape or absorption of light along the length of the filamen~. This sheath is normally transparent since an opaque sheath tends -to absorb light. Also, the sheath is con~entionally made ~rom a substantially amorphous material to minimize light scattering and absorption~
Optical filamentary materials can be di~ided in~o two general classes dependent upon the type of optically transparent core material. A first class o~
core material is thermoplastic in nature while a second class is made from glass~ The first class is generally superior both in toughness and in ease of making connec-tions while the second class is generally superior in light transmission~
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The present invention relates to a cable ~or transmission of light comprising (a) a cylindrical core of a substantially amorphous optically transparent thermo~
plastic polymeric material9 . (b) a substantially amorphous transparent polymeric sheath for (a) having an index of refraction at least 0.1% lower, and (c) an extruded polymer jacket which is exterior of (a) and (b~;
~he improvement comprising (i, use in ~a) of an optically transparen~
material having a second order -transi-tion temperature from 80C. to ~40~C.;
(ii) ( ~loymerLt)of a heat shield between (iii) use in ~c) of a polymer extruded at a temperature at least equal to the second order transition tem~erature of the material used in Detailed Descriptlon o _the Invention : ;~
The types of substantially amorphous thermo-plastic polymeric materials suitable for an optically transparent cylindrical core of the optical filamen~ary material are varied. "Optically transparentq~ as employed herein means a light transmission o~ at least 50~0 per 30 centimeters in a portion of the spectr~m between 550 to 1100 nanometers~ This degree of ~rans~
mission need not extend over the entire spectrum.
The polymers employed for the core have a second order transition temperature~Tg~ in a range from ~0G~ to 1~0C.

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Reprssentative core materials include acrylic and polystyrene homopolymers and copol~mers including those disclosed in British Pa~ent 1,037,498 e~g~, acrylic resins which include polyalkyl meth-acrylates and copolymers thereof containing at least 70 percent by weight of units derived from an alkyl methacrylate, where the alkyl groups contain from 1 to 6 carbon atoms, such a~ polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate~ poly-butyl methacrylate, polyisobutyl me~hacrylate andpolycyclohexyl methacrylate and interpolymers thereoE.
Copolymers of units derived from methyl methacrylate and up to 30 weigh-t percent by weigh-t of units derived ~rom ethyl acryla-te or methyl acrylate? and up to 15 weight percent by weight of units derived from 2 ethyl hexyl acrylate are examples of useful polymers~
Polymethyl methacrylate and copolymers thereof con-taining at least 70 percent by weight polymethyl methacrylate are preferred because they are readil~
available in high quality at a moderate cost and are very transparent. ~lso useful are those optically transparent polymers in which deuterium atoms have at least been par~
tially substituted ~or hydrogen atoms. Suitable resins for core materials are also disclosed in U. SO Paten~
3,5569635 and U~ S. Patent 3,77996~7.
The diameter of the cylindrical optically transparent core varies from rela-tively thin to rela-tively thick core constructionsO A suitable diameter range is 0.1 to ~ mm. Thicker core constructions .
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can also be used but tend to introduce undesirable bulkiness~ Also~ attenuation tends to increase with unduly thick cores, A relatively thick core has the advantage in the ability to capture a greater proportion of in-ciden~ light if the light source is large, e.g., from a L$D (light emitting diode). However~ if a light source is small, e~g.~ a laser~ a relatively thin core is preferred in capturing inciden~ light.
The sheath material for application to th~ optic-10 ally transparent core is substantîally ~morphous and trans-parent with an index of refraction at least 0~1% lower than the core material~ These properties of the sheath reduce scattering of light which would otherwise result in an increase of attenuation of transmitted light.
Examples of suitable sheath materials include those disclosed in British Patent Specification 19037,498 such as polymers and interpolymers o~ vinyl fluoride, vinylidene fluoride, tetrafluoroeth~lene, hexafluoro-propylene, trifluoromethyltrifluorovinyl ether~ per-20 fluoropropyl~rifluorovinyl e~her and fluorinatedesters of acrylic or Inethacrylic acids having the structure X(CF2)n(CH2)mOC ~ G - GH2 o Y
wherein X is selected from the group consisting of F~
H~ or Cl, and n is an integer of from 2 to 10~ m is an integer from 1 to 6 and Y is either CH~ or H~

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Since the sheath material reflects li~ht traveling through the core7 -the thickness of the sheath is not generally critical~ Normally, a thickness of at least two times the wave-length of light travelling through the core is employedO
An example of a suitable range of thic~ness of the sheath is 2 to 500 micronsO Excessive sheathing thicknesses can reduce ~lexibility of the final cable.
Formation of the optical filamentary material of the core and its sheath is generally by coextrusion techniques which are well known in the art such as disclosed in U. S~ Patents 3,458,615 and 3,646,186.
The optical filGmentary material with its optically ~ransparen~ core and lower index of refraction sheath is protected by a jacket since in handling and in many uses damage ~o the filamentary material could otherwise occur. Such damage either results in an increase of attenuation of ~ransmitted light or, even worse, breakage in the optical filamentary material.
In the present invention the jacket comprises a polymer which is applied by extrusion at a tempera-ture at least equal to the second order transition temperature of the core material. The application o~
such polymer directly to the optical filamentary material ~ the optically-transparent core and lower index o refraction sheath has been found to increase attenuation of light transmi~ted through the core. The extrusion `-temperature necessary to apply the pol~ner produces a detrimental effect on the abiliky of optical fil~nentary 30 material ko transmit light.

0~ 7 To overcome this effect of heat, it is re~
quired in the present invention to employ a heat shield which ther~ally protects the filamentary material during extrusion of the jacketing polymer~ The heat shield comprises a material which can be applied to the optical filamentary material without application of exces-sive heat ~i.e., at a temperature below ~he Tg of the core) and is capable o~ remaining a solid at the extrusion tempera~
ture of the jacketing pol-~er. Preferably~ the heat shield is applied as a preformed material which means it is a solid prior to, during9 and after its applicati~n to the optical filamentary materialO
The preformed material can be shaped at the time of its application to the optic fiber material9 e~g., by weaving fibers around ~he sheath. Alternatively -a tube can be positioned around the optically transpar-ent filamentary material~ The thickness of the pre-formed material is sufficient to protect the thermo~
plastic optically transparent core from excessiv~ hea.t when the jacketing polymer is applied until the jacketing polymer has been cooled externallyO
Suitable materials of construction to form the heat shield include polyesters~ po~yamide~ in~luding aramids, polyolefinc (homopolymers and copolymers), acrylics and cellulosic materials~ Examples are nylon7 wool, cotton9 polyethylene and polypropylene. Considerations which govern the choice of material employed in the heat shield include the degree of protection from heat to be impar-ted from a thickness of shielding, and desired characteristics in the final cable including strength~ elongation, burning 3o characteristics9 and ease of s-tripping ,............... .

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It is understood that the heat shield need not contact the sheath (or an outer jacket layer~.
The heat shield can be bonded to the sheath by use of adhesive.
A jacket applied by extrusion at a tempera-ture at least equal to the second order transition ~emperature o~ the thermoplastic core is positioned ex~
~erior of the heat shield. Since the primary purpose of a jacketing polymer is to protect the optical fila-mentary material~ the governing factor in the choiceof a suitable polymer i5 an ability of a polymer to be applied by an extrusion technique (at an eleva-ted temperature at least equal to the Tg of the core).
Extrusion techniques for application of such polymers are conventional and well known in the art. Suitable polymers for the jacket include polyamide~ polyurethanes3 copolyetheresters~ polycarbonates, polyolefins (homopolymers and copolymers includin~ ionomers) such as ~olye-thylene and polypropylene and melt extrudable fluorocarbons such as ~etrafluoroethylene/hexafluoropropylene copolymers.
Further considerations which govern the choice of jacketing polymers are properties desired in the final cable. These considerations include those in selection of the material for the heat shield such as strength, elongation, burnin~ rate and ease of strippabîlity~ For example, ~ood s~ri~pabili~y is needed for ease in connecting one cable to another and in connecting a cable to a li~ht source or detector.
It is within the scope of ~he present inven-tion that more than one jac~e~ be applied exterior vf .
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the heat shield. For purposes of illustration, a~irst jacketing polymer with a relatively low extrusion temperature could be applied to the heat shield followed by application of a second jae~eting polymer at a rela-tively high extrusion tempera~ureO In such case9 the ~irst jacketing pol~mer would aid in providing ther~al protection for the optical filamentary material while the second pol~mer is extrudedO
Tc further illustrate the present invention9 the following examples are provided.
Exam~
Part A -__ .
A starting optical filamentary material of a core of polymethyl methacrylate and a lower refractive index substantially amorphous transparent polymeric sheath of meth~Jl methacrylate and fluorinated esters of methacrylic acid (Tg of 50C. and refractive index 60~
lower than core) was employed. The a-ttenuation of -this optical filamentary material was 490 dB per kilome~er -20 at 655.3 nm.
A 20~ cm extruder was set up with a crosshead tubing type die e~uipped with a guide 1005 mm ID~ 2~32 mm OD and a 3~75 mm die. Six yarn tensioners were equally spaced around a 7 cm circle abo~e the guide opening and were strung ~th a 22 tex (195 denier) zero twist yarn of fibers of poly(p-phenylene terephthalamide!~ i The yarns were strung through a stainless steel needle 1.2 mm ID and 1.62 mm OD~ This needle was put into the - -entrance of the guide and the yarns pulled through the hole in the guide throu~h a-water quench ~ank to a 30 variable speed puller~

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. .. ' ~ 3~ 6 The ex-truder was heated to 175C~ and an ionic copolymer o~ ethylene and 15 weight o~0 methacrylic acid having 20~ of carboxylic acid groups neutralized by zinc ions ~Melt flow index 1~7 AS~I D-1238 9 190C. 9 2.60 g~ Condition F) was introduced into an exkruder at low speedO ~hen this ionic copol~mer appeared at the extruder outlet, the puller was started. The die was adjusted to center the yarns interior of the ionic co--polymer being extruded as a tube. Ta~eoff speed was 10 raised to 58 meters/minute and the ext~uder speed ad- -justed to give a tube about 0.9 mm ODo A~ this ~time the melt temperature ~as at 160C~ Into the needle the opt-ical filamentary material encircled by the fibers of poly(p-phenylene terephthalamide) was fed and incorp-orated into the center of the ionic copolymer tube.
This material had an attenuation of 500 dB
per kilometer at 655.3 nrn.
Part B --The material of Part A ~las o~ercoated with -~-20 copolyetherester (disclosed in Example 1 of U. S~ P.
3,651,014) by extrusion employing a melt temperature of 185C. The cable had an outer diameter of about 1.25 mm~
The attenuation was ~90 dB per kilometer at 6S5O3 n~O
Control for ~xam le 1 The procedure of Example 1 P~rt A was follo~ed except a yarn o~ fibers of poly(p phenylene terephthal-amide) was not employedO
The attenuation of this product was 1800 dB
30 per kilometer at 655O3 nm.

lOo ~ '7 Exam~le_2 The procedure of' Example 1 Part A was fQllowed including application of` the ionic copolymer disclosed in Example 1 except in place of the f'ibers poly(p-phenylene kerephthalamide) khree :L55 -tex (1~00 denier) Dacron~ polyester were used~ ~
The attenuation of this produc~ was 600 dB - ,.
per kilometer at 655.3 nm~

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Claims

WHAT IS CLAIMED IS:

1. In a cable for transmission of light comprising (a) a cylindrical core of a substantially amorphous optically transparent thermo-plastic polymeric material, (b) a substantially amorphous transparent poly-meric sheath for (a) having an index of refraction at least 0.1% lower, and (c) an extruded polymer jacket which is exterior of (a) and (b);
the improvement comprising (i) use in (a) of an optically trans-parent material having a second order transition temperature from 80°C.
to 140°C.;
(ii) employment of a heat shield between (b) and (c);
(iii) use in (c) of a polymer extruded at a temperature at least equal to the second order transition temperature of the material used in (i).