CA1256821A - Optical fibres with coating of diorganopolysiloxane and catalytic photoinitiator - Google Patents
Optical fibres with coating of diorganopolysiloxane and catalytic photoinitiatorInfo
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- CA1256821A CA1256821A CA000469072A CA469072A CA1256821A CA 1256821 A CA1256821 A CA 1256821A CA 000469072 A CA000469072 A CA 000469072A CA 469072 A CA469072 A CA 469072A CA 1256821 A CA1256821 A CA 1256821A
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- epoxy
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- optical fiber
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- photoinitiator
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
- C03C25/10—Coating
- C03C25/104—Coating to obtain optical fibres
- C03C25/106—Single coatings
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- General Chemical & Material Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
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- Epoxy Resins (AREA)
- Surface Treatment Of Glass Fibres Or Filaments (AREA)
Abstract
60SI-740 OPTICAL FIBERS WITH COATINGS OF DIORGANOPOLYSILOXANE AND CATALYTIC PHOTOINITIATOR Novel coating compositions for coating optical fibers are provided which utilize ultraviolet radiation-curable epoxy-functional or vinyl-functional diorganopolysiloxanes on a core of high transparency silica glass together with a catalytic amount of a photoinitiator, to form flexible, loosely adherent, and environmentally stable primary coatings. Such coatings assist in preventing attenuation of light impulses transmitted through the core fiber or reduce the level of signal "noise". Use of the particular coating compositions allows high-speed production of such optical fibers.
Description
~ 60SI-740 Since the discovery of a suitable light source in the laser around 1960, the only technical obstacle to lightwave communications over great distances was the development of a suitable ~ransmission medium. Air, or S example~ although penetrable by light, was unsuitable because rain, fog, and other atmospheric conditions could weaken (or "att~nuate") the light signal. Development of the glass fiber lightguide, or optical fiber, provided an excellent and relatively inexpensive transmission medium.
Modern optical fibers typically consist o~ a core o~ high transparency silica glass, which transmits the light, surrounded by a transparent coating of lower re~ractive index than the core. The coating acts as an internal mirror, reflecting the light back into the core and thus preventing loss of the light signal outside the optical path.
While the lower refractive index coating theory has provided serviceable lightguides for relatively short-distance telecommunications (e.g., building-to-building or intramural), for lons-distance telecommunica-tions (e~g., transcontinental), where many lightguides may be bundled together, the problem o~ signal "noise" becomes more important than signal attenuation. To a partic~lar information-carrying lightwave, any incidental lightwaves (carrying other information) or signals disrupting to the first lightwave are "noise" ~rom which the desired informa-tion must be extracted. It has been found that signal noise can be minimized in lightwave transmissions by coatings of hi~he_ refractive index than the core fiber.
~s~
There is thus a continuing search for coating materials having either a higher or a lower refractive index than the core fiber material. For silica glass optical fibers, the reference point is 1.47, the refractive index of silica glass fiber. Suitable materials will have refractive indices lower, pr~ferably less than 1.45, or higher, preferably greater than 1.50.
In the production of fiber optics cable for telecommunications, the material used for primary coatings must be very flexible, must not adhere too closely to the glass fiber core (to permit joining and other manipulations), and must maintain its integrity and optical characteristics in changeable environments, including temperature cycles of from -60 to -~80C.
Many fiber optics proclucers have adopted heat~curable polydimethylsiloxane coatiny compo~itions as the primary lightguide coatings. The uncoated optical fiber is typically drawn through the silicone composition, then through an eight-inch over at 800C
for curing. The time required to fully cure the silicone composition has become the limiting factor in increasing line speeds in producing optical fibers:
Since higher oven temperatures (or longer ovens) cause oxidation of the silicone and also begin to affect the drawn fibers, line speeds cannot be increased beyond about 30 meters/minute with commercially available thermally cured silicone coatings.
The desire to attain higher production speeds has led optical fiber producers to investigate ultraviolet radiation (UV)-curable materials, but a coating composition having a combination of properties comparable to the silicone materials has not as yet been found.
~2 ~ 8Z 1 60SI-740 It has now been discovered that certain UV-curable polysiloxane compositions provide novel coating materials for optical fibers which exhibit the desired combination of proper~ies for optical fiber cladding layers. The discovery includes both low refractive index and hiyh refractive index compositions, all of which cure rapidly on brief exposure to ultraviolet radiation, thus ofering significant advantages in safety, cure rat~, and cost over thermally cured silicone materials.
SUMMARY OF THE INVENT ION
Accordingly, it is an object of the present invention to provide a aster curing alternative to thermally cured polydimethylsiloxane compositions or the primary coating layer of optical fibers.
It is a further object of the present invention to provide a coating material ~or optical fibers which 2Q is easily and safely applied, and which ma~ be cured by brief exposure to ultraviolet radiation.
It is a further object of the present invention to provide novel low refractive index coating compositions and high refractive index coating compositions.
I* is a further object of the present invention tG provide coated optical fibers which are efficiently and inexpensively produced and can be adapted to a wide 30 variety of lightwave telecommunications usés.
~25682~ 605I-740 It is a fuxther object o~ the present invention to provide a method for applying a primary coating to an optical fiber core which will allow increased production line speeds while providing a cured coating which is flexible~ not closely adherent to the core fiber, and capable of withstanding dramaLi~ changes in environmental conditions~
These and other objects are accomplished herein by an ultraviolet radiation-curable coating composi-tion comprising (A) a diorganopolysiloxane comprising units of the formula RRISio, wherein R is hydrogen or a monova-lent hydrocarbon radical of from 1 to 8 carbon atoms and R' is hydrogen, a monovalent hydrocarbon radical o~ from 1 to 20 carbon atoms or a monovalen~ organic radical o~
Erom 2 to 20.carbon atoms having vinyl or epoxy ~unc--tionality, and (B) a catalytic amount of a photoinitiator.
Also contemplated by the present invention is an op-tical fiber comprising:
(A) a core of high transpar~ncy silica glass; and IB) a coating layer deposited on said core comprising an ultraviolet radition-curable silicone coating composition comprising (il a diorganopolysiloxane comprising unitq o~ the ~ormula RR'Sio, wherein R is hydrogen or a mono~alent hydrocarbon radical of from 1 to 8 carbon atoms and R7 is hydrogen, a monovalen~ hydrocarbon radical of from 1 to 20 carbon atoms or a monovalent organic radical of from ~ to 20 carbon atoms having ~inyl or epoxy functionality, and ~ii) a catalytic amount of a photo-initiator; said coa~ing layer having a refractive index higher or lower than said silica glass.
_ 6 Another feature of the present invention is a method for the high-speed production of an optical fiber comprising:
(1) Applying to a core fiber of high transparency silica glass an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopolysiloxane comprising units of the formula RR'SiO, wherein ~ is hydrogen or a monovalent hydrocarbon radical of from 1 to 8 carbon atoms and K' is hydrogen, a monovalent hydro-carbon radical of from 1 to 20 carbon atoms or a monova-lent organic radical o~ from 2 to 20 carbon atoms having vinyl or epoxy functionality, and ~ii) a catalyt.ic a~lount o~ a photoinitiator; and
Modern optical fibers typically consist o~ a core o~ high transparency silica glass, which transmits the light, surrounded by a transparent coating of lower re~ractive index than the core. The coating acts as an internal mirror, reflecting the light back into the core and thus preventing loss of the light signal outside the optical path.
While the lower refractive index coating theory has provided serviceable lightguides for relatively short-distance telecommunications (e.g., building-to-building or intramural), for lons-distance telecommunica-tions (e~g., transcontinental), where many lightguides may be bundled together, the problem o~ signal "noise" becomes more important than signal attenuation. To a partic~lar information-carrying lightwave, any incidental lightwaves (carrying other information) or signals disrupting to the first lightwave are "noise" ~rom which the desired informa-tion must be extracted. It has been found that signal noise can be minimized in lightwave transmissions by coatings of hi~he_ refractive index than the core fiber.
~s~
There is thus a continuing search for coating materials having either a higher or a lower refractive index than the core fiber material. For silica glass optical fibers, the reference point is 1.47, the refractive index of silica glass fiber. Suitable materials will have refractive indices lower, pr~ferably less than 1.45, or higher, preferably greater than 1.50.
In the production of fiber optics cable for telecommunications, the material used for primary coatings must be very flexible, must not adhere too closely to the glass fiber core (to permit joining and other manipulations), and must maintain its integrity and optical characteristics in changeable environments, including temperature cycles of from -60 to -~80C.
Many fiber optics proclucers have adopted heat~curable polydimethylsiloxane coatiny compo~itions as the primary lightguide coatings. The uncoated optical fiber is typically drawn through the silicone composition, then through an eight-inch over at 800C
for curing. The time required to fully cure the silicone composition has become the limiting factor in increasing line speeds in producing optical fibers:
Since higher oven temperatures (or longer ovens) cause oxidation of the silicone and also begin to affect the drawn fibers, line speeds cannot be increased beyond about 30 meters/minute with commercially available thermally cured silicone coatings.
The desire to attain higher production speeds has led optical fiber producers to investigate ultraviolet radiation (UV)-curable materials, but a coating composition having a combination of properties comparable to the silicone materials has not as yet been found.
~2 ~ 8Z 1 60SI-740 It has now been discovered that certain UV-curable polysiloxane compositions provide novel coating materials for optical fibers which exhibit the desired combination of proper~ies for optical fiber cladding layers. The discovery includes both low refractive index and hiyh refractive index compositions, all of which cure rapidly on brief exposure to ultraviolet radiation, thus ofering significant advantages in safety, cure rat~, and cost over thermally cured silicone materials.
SUMMARY OF THE INVENT ION
Accordingly, it is an object of the present invention to provide a aster curing alternative to thermally cured polydimethylsiloxane compositions or the primary coating layer of optical fibers.
It is a further object of the present invention to provide a coating material ~or optical fibers which 2Q is easily and safely applied, and which ma~ be cured by brief exposure to ultraviolet radiation.
It is a further object of the present invention to provide novel low refractive index coating compositions and high refractive index coating compositions.
I* is a further object of the present invention tG provide coated optical fibers which are efficiently and inexpensively produced and can be adapted to a wide 30 variety of lightwave telecommunications usés.
~25682~ 605I-740 It is a fuxther object o~ the present invention to provide a method for applying a primary coating to an optical fiber core which will allow increased production line speeds while providing a cured coating which is flexible~ not closely adherent to the core fiber, and capable of withstanding dramaLi~ changes in environmental conditions~
These and other objects are accomplished herein by an ultraviolet radiation-curable coating composi-tion comprising (A) a diorganopolysiloxane comprising units of the formula RRISio, wherein R is hydrogen or a monova-lent hydrocarbon radical of from 1 to 8 carbon atoms and R' is hydrogen, a monovalent hydrocarbon radical o~ from 1 to 20 carbon atoms or a monovalen~ organic radical o~
Erom 2 to 20.carbon atoms having vinyl or epoxy ~unc--tionality, and (B) a catalytic amount of a photoinitiator.
Also contemplated by the present invention is an op-tical fiber comprising:
(A) a core of high transpar~ncy silica glass; and IB) a coating layer deposited on said core comprising an ultraviolet radition-curable silicone coating composition comprising (il a diorganopolysiloxane comprising unitq o~ the ~ormula RR'Sio, wherein R is hydrogen or a mono~alent hydrocarbon radical of from 1 to 8 carbon atoms and R7 is hydrogen, a monovalen~ hydrocarbon radical of from 1 to 20 carbon atoms or a monovalent organic radical of from ~ to 20 carbon atoms having ~inyl or epoxy functionality, and ~ii) a catalytic amount of a photo-initiator; said coa~ing layer having a refractive index higher or lower than said silica glass.
_ 6 Another feature of the present invention is a method for the high-speed production of an optical fiber comprising:
(1) Applying to a core fiber of high transparency silica glass an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopolysiloxane comprising units of the formula RR'SiO, wherein ~ is hydrogen or a monovalent hydrocarbon radical of from 1 to 8 carbon atoms and K' is hydrogen, a monovalent hydro-carbon radical of from 1 to 20 carbon atoms or a monova-lent organic radical o~ from 2 to 20 carbon atoms having vinyl or epoxy functionality, and ~ii) a catalyt.ic a~lount o~ a photoinitiator; and
(2) Exposing said coated core fiber to ultraviolet radiation of sufficient intensity and for a sufficient period of time to cure said coating composition on said core fiber to form a flexible, loosely adherent, environ-mentally stable coating thereon, which coating layeris of a lower or higher refractiYe index than the core fiber.
4 A method for advantageously controlling the refractive index and viscosity of the disclosed polysi-loxane coating materials is also contemplated.
For the purposes of the present invention, the term l'loosely adherent" refers to a desired property of the primary coating lay~r o~er a glass optical fiber meaniny that the coating layer does not adhere so strongly to the core fiber as to inhibit the common mechanical operations performed with optical fibers, such as joining.
_ 7 - The texm does not reer to the optical relationship between ~he core and the cladding (primary coating) layer. The term "environmentally stable" refers to the ability of the coating material of the present invention to maintain its integrity and optical characteristics through en-vironmental changes to which fibers are routinely exposed, particularly cycles in temperature between the extremes of about -60C and ~80C.
D~TAILED DESCRIPTION OF THE INVENTION
The coated optical fibers of the presen-t invention are prepared by ~pplying a rapidly curable, UV-curable, epoxy-~urlctional or vinyl-functional silicone coating composition to a trarlsparent silica glass fiber and then subjecting i~ briefl~ to ultraviolet radia~ion. The coated optical fibers of the present invention exhibit all of the desired properties seen in thermally cured polydimethylsiloxane-coated fibers while providing the increased production capability, reduced e~ergy expenses, and safety of ultraviolet radiation curing.
Ultraviolet radiation IW~ is one of the most widely used types of radiation because of its low cost, ease of maintenance, and low potential ha~a~d to industrial users. W -curable compositions not only exhibit a very short curing time ~ut also avoid the high energy costs, environmental restrictions and safety hazards associated with the use of heat-curable materials.
The W-curable compositions employed in the p~e~ent invention are basically comprised of two components~
an epoxy-functional or ~inyl-functional organopolysiloxane base polymer combined with (ii) a photoinitiator capable 3S of promoting rapid cure of the composition on exposure to ultraviolet radiatio~.
~l2~
The epoxy-functional organopolysiloxane base polymers contemplated by the present invention are com-prised of units having the general Iormula RR'SiO, where R is hydrogen or a monovalent hydrocarbon radical of from 1 t~ 8 carbon atoms and where R' can be the same as R or a monovalent organic radical of from 2 to 20 carbon atoms having epoxy functionality. The epoxy-silicone polymer may have up to about 20% by weight epoxy-functional groups and must be capable of curing, or cross-linking, when combined with a suitable photoinitiator and exposed to ultraviolet radiation. The cured polymeric composition must be of a lower or higher refractive index than the optical fiber core and exhibit 1exibility, loose adhesion to the core fiber, ~nd ~nvironm~ntal stability.
Preferred epoxy-Eunctional polydiorganosiloxanes contemplated by the present invention are more specifi~
cally dialkylepoxy-chainstopped polydialkylalkylepoxysi-` loxane copolymers wherein the polysiloxane units contain lo~er alk~l substituents, notably, methyl groups. Theepoxy functionality is obtained when certain of the hydrogen atoms on the polysiloxane chain of a polydimethyl-methylhydrogensiloxane copolymer are reacted in a hydrosilation addition reaction with other organic molecule5 which contain both ethylenic unsatura-tion a~d epoxide functionality. Ethylenically unsaturated species will add to a polyhydroalkylsiloxane to form a func-tion~lized polymer in the presence of catal~tic amounts of a precious metal catalyst. Such a reaction is the cross-linking mechanism for other silicone compositions,however, in the present invention, a controlled amount of such cross-linking is permitted to take place in a silicone precursor fluid or intermediate, and this is referred to as "pre-crosslinking". Pre-crosslinklng of ~ 60SI-740 _ g the precursor silicone fluid means that there has been partial cross-linking or cure of the compasition and sffers the advantages to the present invention of enabling swift W -initiated cure with :Little expense for energy and elimination of the need for a solvent.
The UV-curable epoxy-functional silicone inter-mediate fluid comprises a pre-crosslinked epoxy-functional dialkylepoxy-chainstopped polydialkyl-alkyl-epoxy silicone copolymer fluid which is the reactionproduct of a vinyl- or allylic-functional epoxide and a v.inyl~~unctional siloxane crosslinking Eluid havlng a viscosity o~ approximately l to lO0,000 centipoise at 25C with a hydrogen-functional siloxane precursor fluid having a viscosity of approximately l to lO,000 centipoise at 25C in the presence of an effective amount of precious metal catalyst for facilitating an addition cure hydrosilation reaction between the vinyl-functional crosslinking fluid, ~inyl-functional epoxide, and hydrogen-Eunctional siloxane precursor fluid.
The unsaturated epoxides contemplated ar~ any of a number of aliphatic or cycloali-2S phatic epoxy compounds having olefinîc moietieswhich will readily undergo addition reaction to -SiH-functional groups. Examples of such compounds include l-methyl~4-isopropenyl cyclo-hexeneoxide (limoeneoxide; SC~I Corp.); 2j6 dimethyl 2,3-epoxy-7-octene (SCM Corp.) and 1/4-dimethyl-4-vinylcyclohexeneoxide (Viking Chemical Co.~. Limoneneoxide is pre~erred.
~5 ` ~2~ 60SI-740 _ 10 _ O "
The precious metal catalys~ for the hydrosilation reactions involved in the present invention may be selected from the group of platinum-metal complexes which inclu~es complexes of ruthenium, rhodium, 5: palladium, osmium, iridium and platinuIn. Examples of such hydrosilation catalysts suitable for the purposes herein are described in U.S. 3,220,972 lLamoreaux), U.S. 3,715,334 (Karstedt), U.S. 3,775,452 (Karstedt) and U.S. 3,814,730 (Karstedt) .
In the present invention, the vinyl-Eunct:ional siloxane cro~slinking f}uid can be selected from the group consisting oE dimethylvinyl-chai~stopped linear polydimethylsiloxane, dimethylvinyl chainstopped polydimethyl-methylvinyl siloxane copolymer, tetravinyl-tetramethylcyclotetrasiloxane and tetramethyldivinyldi-siloxane. The hydrogen-functional siloxane precursor fluid can be selected from the group consisting of tetrahydrote~.am2thyl-cyclotetrasiloxane, dimethylhydrogen-chainstopped linear polydimethylsiloxane, dimethylhydrogen-chainstopped polydimethyl-methylhydrogen siloxane copolymer and tetramethyldihydrodisiloxane.
Preferred photoinitiators for the epoxy-functional base polymers of the present invention include iodonium salts having the general formula, \ Y~j ~æ~
~ 11 wherein X is selected from SbF6, AsF6" PF5, or BF4 and wherein R" is a monovalent alkyl or haloalkyl radical of from 4 to 20 carbon atoms and n is a whole number equal ~o 1 to 5, inclusive. These compounds have been S found to be highly efficient in promoting ~he W -initated cationic ring-opening curing mechanism for epoxy-functional polysiloxanes, as disclosed in U.S~ 4,279,717 IEckberg et al.) . -Preferred of the iodonium salt photoinitiators utilized with the epoxy-functional silicones of the present invention are diaryl iodonium salts derive& from "linear alkylate" dodecylbenzene. Such salts have the general formula, ~S~+X~
wherein X equals SbF6, AsF6, PF6 or BF4. These bis(~-dodecylphenyl) iodonium salts are very effective initiators for ~he W cure of a wide ~ariety of epo~y-functional silicones.
"L~near alkylate" dodecylbenzene is known commer-cially and is prepared by Friedel-Craft alkylation cf benzene with a C(ll 13~ a-olefin cut. Consequently, the alkylate contains a preponderance of branched chain dodecylbenzene, but there may in fact be large amounts of other isomer~ of dodecylbenzene such as ethyldecyl-~ 2 5~ 60SI-740 benzene, plus isomers of undecylbenzene, tridecylbenzene, etc. Note, however, that such a mixtux2 is responsible for the dispersive character of the linear alkylate derived catalyst and is an aid in keeping the material fluid.
These catalysts are free-flowing, viscous fluids at room temperature.
The preferred bis(dodecylphenyl) iodonium salts are alkane-soluble and water-insoluble, and they dis-perse well in the preferred epoxy-functional polysiloxanes utilized in the coating compositions of the present invention. Bis(4-n-tridecylphenyl) iodonium hexafluor-oantimonate and bis(4-n-dodecylphenyl) iodonium hexa~luoroankimonate are most preerred.
The vinyl-functional base polymers contemplated herein are actually photoreactive terpolymers capable of curing on exposure to W radiation in the presence or certain radical photoinitiators. The terpolymers are mixed dimethylvinyl- and trimethyl-chainstopped linear polydimethyl-methylvinyl-n,ethylhydrogensiloxane terpoly-mer fluids and can be synthesized by acid equilibration of polymethylhydrogen siloxane fluid, tetramethyl-tetravinylcyclotetrasiloxane (methylvinyl tetramer) andoctamethylcyclotetrasiloxane ~dimethyl tetramer).
These vinyl-functional terpolymers are curable i~ the presence of polya~omatic photosensitizers having at least ~wo benzene rings which may be fused or bridged by organic radicals or hetero rad cals such as oxa, thio, and the like. Preferred among these photo-sensitizers are benzophenone and t-butylanthra~uinone.
~2 ~ ~ 60SI-740 The terpolymers may also be cured in the presence of certain perbenzoate esters having the general formula:
R3-o_o-c ~
where R3 is a monovalent alkyl or aryl group and 2 is hydrogen, alkoxy, alkyl, halogen, nitro, amino, primary and secondary amino, amido, and the like. The nature of Z will affect the stability of the peroxy bond, and electron-poor substitutent stabilizing the peroxy bond, and an electron-rich substituent making the peroxy bond more reactive~ Pre~erred perbenzoate esters lnclude t-butylperbenzoate and its para-substituted derivatives, including t-butylper~p-nitrobenzoate, t-butylper-p-methoxybenzoate, t-butylpex-p-methylbenzoate, and t-butylper-p-chlorobenzoate. The photoreactive polysiloxane ter-polymers of the present invention/ and photoinitiators effectively used therewith, are disclosed in Canadian Patent Application Serial Number ~ o~ filed ~/oY~nl er 30, /~ ~If The amount o photoinitiator employed is not critical, so long as proper curing is effected. As with any catalysts, it is preferable to use the smallest effective amount possible; howe~er, for purposes of illustration, catalyst levels of the aforementioned compounds from about 1% to 5~ by weight have been found suitable. Com~inations of photoinitia~ors ~re also contemplated.
--._ .. ... _ .. -- .. . . . .. ....... .... .. .. ._ ,. . _ _ _ ._ .. , . ... , . . _._ ... ~ _ . _. . __ .. . _ .. ...
~ ~ .
The epoxy-functional and vinyl-functional poly-siLoxanes described above typically have a low refractive index, i.e., less than 1.47, where the non-epoxy or non-~inyl substituents along the siloxane polymer chain are S hydrogen or lower alkyl. The refractive index of the polysiloxanes can be raised by for.~ulating polymers which also contain diphenylsiloxy units.
As discu~sed previously, an epoxy-functional 10 polydiorganosiloxane may be obtained by reacting a vinyl-functional epoxide with a SiH-containing polydiorgano-siloxane, such as polydimeth~l~methylhydrogen siloxane copolymer. To achieve a higher refractive index, a diphenylsiloxy-containing and SiH-containing polysiloxane 15 can be synthesized by co-hydrolysls of diphenyldichloro silane, dimethyldichloro silane, and methylhydrogendi-chloro silane, and this polymer could theoretically be reacted with a vinyl-functional epoxide to obtain epoxy functionality on the polymer. However, small quanities 20 of acid residues associated with, and very difficult to remove from, such linear high-phenyl SiH polymers act to open the oxirane ring of the epoxides, resulting in poly-siloxanes which are not photoreactive. A further difficulty with this approach is that in order to raise 25 the refractive index above 1.50, the polymer must contain more than 30 mole percent (greater than 50 weight percent) diphenylsiloxy unitst making the high-phenyl polysiloxanes vexy costly.
An important feature o~ the present invention is the di~cover~ of a cost~effective way to produce W -curable epoxy-functional silicones having a refractive index greater than 1.47, making the present compositions suitable for a wider range of fiber o~tic coati.ng applications. In ~2~ 60SI-740 preferred features of the invention, high refracti~Je index compositions are prepared by reacting a SiH-containing polysiloxane with both a vinyl-functional aromatic com-pound of from l to 20 carbon atoms (to obtain on-chain 5 aromatic substituents) and vinyl-functional epoxides (to obtain epoxy-functional substituents).
The vinyl-functional aromatic compound contains at ]east one aromatic ring and at least one aliphatically lO unsaturated site capable of reacting via hydrosilation addition with an SiH group to form a car~on-silicon bond.
Ethenylbenzene (styrene) is most preferred, however many other vinyl aromatic compounds will suggest themselves to per ons skilled in this art, and ~hese are intended to be 15 included herein.
In reactions with SiH-containing polysiloxanes, the vinyl aromatic compound and the unsaturated epoxide may be introduced simultaneously (and compete or hydride 20 reaction sites) or, preferably, in tandem, which allows more control over the degree of epoxy ~unctionality and refractive index of the final product. Since raising the refract.ive index o~ the composition is the chief purpose of employing such vinyl aro~atic compounds, reacting 25 these compounds first and adding epoxy functionality second is most preferred. The exact relative amounts of vinyl aromatic compound and ~inyl-functional epoxide employed will vary over a wide range, depending on the r~fractive index desired and the degree of reactivity 30 desired. By judicious selection of the reactant~, their amounts, and the reaction conditions, high refractive index epoxy-functional silicones which are tailored to specific requirements may be produced~ In view of this, simple experimentation with the processing perameters is contem-35 plated.
, Combination of the iodonium salt photoinitiators with other known photoinitiators is also comtemplated.
Preferred among such catalyst blends are combinations of iodonium salts with free-radical photoinitiators such as acetophenone derivatives. Even (1:1) blends of diaryl iodonium salts with diethoxy acetophenone are most preferred.
The present W -curable silicone coating composi-tions are applied to the optical fibers by methods well 10 known in the art. Typically, for example, uncoated optical fibers are drawn through a coating solution and then in-line through a curing chamber. ~s discussecl above, the curing step has been found heretofore to be the limit-ing factor in the speed at which the coating operation can 15 be perormed. U~e of epoxy-functional silicone coating compositions c~red by brief exposure to ultraviolet radia-tion in accordance with the present discovery provides a flexible, loosely adherent, environmentally stable primary coating on the silica glass core fiber which can 20 be applied at increased line speeds and without subjecting the coating material or fiber of high oven temperatures.
With the increased line speeds made possible with the compositions o~ the present invention, it has been 25 di~covered (see, i.e., Examples 1-3, infra.) that the viscosity of the coating compositions becomes an additional property which the industrial producer of optical fibers must be concerned with. In general, it is seen that viscosities below about 1000 cps do not permit "we~ting"
30 ~oating) of the fiber where the production speed is high, at viscosities greater $han about 10,000 cps, entrainment of air bubbles in the coating occurs, leading to imperfections in the primary coating that cause signal attenuation.
~;25~
~ or the epoxy-functional silicones produced via hydrosilation addition of vinyl-functional epoxides to an SiH-containing polysiloxane, the viscosity of the final product has been hard to predict, as it is dependent no only on the viscosity of the SiH-containing precursor but also on the degree of epoxy functionality. For example, a 90 cps precursor fluid containing 1 weight percent methylhydrogensiloxy units converted to an epoxy-functional silicone incorporating 18 weight percent limoneneoxide has a viscosity of about 400 cps; while a 200 cps precursor fluid containing 10 weight percent methylhydrogensiloxy unit converts to an epoxy-functional silicone of 3,000 cps viscosity and a 200 cps precursor fluid containing 6 weight percent methylhydrogensiloxy units incorporating 11.7 weight percent limoneneoxide has a viscosity oE
100 cps.
It has now been discovered that simultaneous addition of a vinyl MQ silicone resin and the vinyl-functional epoxide to a given SiH-containing polysiloxane provides products where the viscosity is dependent on the resin content. The vinyl MQ resins contemplated are polysiloxanes having primarily monofunctional ~M) units or tetrafunctional (Q) units The vinyl groups of the resin compete with the vinyl-functional epoxide for available hydride sites in the polysiloxane. The resin is thereby incorporated into the epoxy-functional polysiloxane product.
The vinyl MQ resins are made up of M units having the formula Y3Sio1/2 and Q units having the formula sio4/2, with the ratio of M to Q units being roughly 0.5 to 1.0 and preferably about 0.65. The Y groups may be, independently, the same or different monovalent hydrocarbon radicals of no more than 2 carbon atoms, and _18 _ at least 1 Y group must be vinyl. Such radicals include, for example, methyl, ethyl, vinyl or etnynyl. Methyl and vinyl are preferred~ A general discussion of these resins is found in Chapters 1 and 6 of Noll, Chemistry and ~echnoloqy of Silicones (2nd Ed., 19683.
In features of the present invention which make use of the foregoing discovery, the final W -curable polysiloxane product will contain pendent siloxy groups corresponding to the incorporated MQ resins. For these polysiloxanes, the definition o the R' radical in the formulas described above would be expanded to include a branched org~nosiloxane radical comprised of from 1 to 200 Q siloxy units oE the ormula SiO4/2 and M siloxy units having the Eormula Y3SiOl/2, wherein Y is a monova-lent hydrocarbon radical of 1 or 2 carbon atoms. It is understood also that the terms "diorganopolysiloxane'l and "organopolysiloxane ~ase polymer" as used herein to describe the epoxy~ and vinyl-functional polymer products of the invention are broad enough to cover such branche~
polysiloxane pendent groups.
Where high refractive index materials are desired, a further method for modifying the viscosity of the coating compositions, which also introduces refractive index-raising aromatic groups into the system, is to employ aromatic glycidyl ethers as reactiv diluents.
The aromatic glycidyl ether reactive diluents also pro-vide additional epoxy functionality and so may enhance the curing characteristic~ of the present coatin~
compositions, as was disco~ered for silicone paper r~lease compositions by the addition o~ epoxy polymers in Canadian Patent Applicatio~ Serial Number ~28~142 filed May 13, 1983.
~1 60SI-740 19 _ In order that persons skilled i.n the art may better understand the practice of the inventi.on, the following examples are provided by way of illust.ratiQn, and not by way of limitation.
Three epoxy-functional silicone coating composi-tions were prepared for optical fiber coating trials as follows:
Sample 1 _ 5 parts by weight of a 250 cps dimethylv:inyl-chainstopped polydimethylsiloxane fluid, 320 parts by weight o~ limoneneoxide, and 1 part by weight of a platinum catalyst (platinum-octyl alcohol complex) were added to 1,000 parts by weight of toluene. 1,000 parts by weight of a 150 cps dimethylhydrogen-chainstopped polydimethyl-methylhydrogen silox~ne copolymer fluid containing abou~, 8.7 weight percent _SiH groups were added slowly to the stirring mixture at room temperature over 1 hour. The reaction mixture was then refluxed at 1~0C for 21 hours, at which point 30 parts by weight of n-hexene were added and refluxing continued for 4 hours more. The solvents were stripped under a vacuum at 130C to yield a 1,000 cps limoneoxide-functional polysiloxane fluid containing about 17.2 weight percent limoneneoxide groups.
~ .
.~
~2 ~ 60SI-740 o Samples 2_& 3 Two other limonenPoxide-func~ional products designated Sample 2 and Sample 3 were ,prepared following the same procedure as for Sample 1~ above. Sample 2 was a 680 cps fluid containing approximately 14O0 weight percent limoneneoxide groups; Sample 3 was a 700 cps fluid containing approximately 11.7 weight percent limoneneoxide groups.
All three compositions were combined with 1.5 weight percent o bis(dodecylphenyl) iodonium hexa~luoroantimonate cationic pho~oinitiator.
lS Each coating composition was applied to 10 mil diameter pure silica glass fiber immediately after it was drawn. The coating device consisted of a small cup fitted with a 0.025-inch orifice at its base. Coating was accomplished by pulling the drawn optical fiber down through the test composition, then through the orifice to regulate coating thickness. The coated fiber was passed immediately through a nitrogen-inerted curing chamber where it was exposed to a single ocused 300 watt, 10 inch long Fusion Systems "H" ultraviolet lamp. The coated iber was finally wound on a taKe-up roll.
The coated fibers were observed to make sure the coating was fully cured. The line speed was gradually increased in order to determine the line speed at which the coa~ing on the ~iber would not cure completely, ~ha~ is, in oxder to discovex the point a~ which line speed surpassed cure rate.
, .
~25~
With each of the samples studied, the coating compositions still cured completely at line speed at which the coating rate was surpassed. In other words, "wetting" (coating) of the op~ical fiber by the silicone fluids ceased at line speeds where complete curing was still observed. For the ~hree sample compositions, complete curing was ob~erved under the following condi~
tions:
Loss of Wetting Coating Thickness lOCompositions(meters/min.l ~microns) Sample 1 50 125 Samp}e 2 30 120 Sample 3 33 120 The~e results compare favorably with the maximum line speed of approximately 30 meters per minute observed with commercially available heat-curable silicone systems.
XAMPI,~S ~-7 ~ 00 pbw o~ linear 60 ~ps dimethylhydrogen-chain-stopped polydimethyl methylhydrogensiloxane fluid con-taininy 10 weight percent methylhydrogensiloxy units were dissolved in 600 p~w ~exane. To this solution ~containing l.0 mole of active SiH groups) were added 152 pbw limoneneoxide (1 mole), about 25 ppm platinum in the form of a soluble complex catalyst, and varying levels of a vinyl MQ silicone resin. The reaction mixtures were reflu~ed for four hours, after which the unreacted SiH was removed by reaction with hexene.
Stripping the solvents, unreacted limoneneoxide, and hexane under vacuum resulted in the following epoxy functional poiymers:
~ Limonene- ~ MQ Viscosity Compositions oxide* resin** (cPs) Sample 4 19.6` 0.0 340 Sample 5 18.5 7.6 900 Sample 6 14.3 11.5 1976 Sample 7 16.1 12.8 3800 * Weight percent limoneneoxide incorporated in polymer.
** As weight percent resin solids after stripping solvents.
Cure was evaluated by blencliny 100 parts by weight (pbw) of each sample w.ith 1.5 pbw diethoxy acetophenone and 1-5 pbw (Cl2~l25Ph)2IsbF6 (a ~ree-radical/cation.ic co-catalyst system disclosed for curing epoxy-functional silicones in the aforementioned Canadian Application Serial Number 428,142, filed May 13, 1983). The complete coating compositions were manually applied as 2 mil coatings on polyethylene kraft paper using an adhesive coater and exposed to two focused medium pressure mercury vapor ultraviolet lamps in a PPG 1202 ultraviolet processor. Cure was evaluated qualitatively at various conveyor speeds (varying exposure time), UV
intensities, and cure environments, with the following results:
~ ~ ~ 60SI-740 o W Power ~ure Line ~
~le (Watts) AIM (meters/sec) Cure 4 400 Air 2.0 E~cellent cure-no ~r~ no migration, gocd adhesion - 4 300 N2 2.0 400 Air 2.0 "
400 N2 2.5 "
300 N2 2.5 '~n~ed' - easily r~d off ~ strate 6 400 Air 2.0 Cured - fa~ adhesion to subs~ate 6 400 N~ 2.0 Excellent cure no ~ ar -good adhesion 7 400 Air 2.0 Excellent cure - no ~ ~r, good adhesion 7 400 N2 2.0 "
It can be seen by comparisons with the control composition (Sample 4) that incorporation of vinyl MQ
resins, while allowing formulation of epoxy-functional silicone compositions within a specific target viscosity range, does not make a signiicant qualitative difference n cure.
90 pbw of a 10,000 cps epoxy-~u~ctional poly-siloxane incorporating 11.3 weight percent limoneneoxide were blended with 10 pbw of 1,2-epoxy dodecane (ViXolox, 1~, Viking Chemical Co.)., resulting in a 4200 cps blend.
The dual catalyst of Examples 4-7 was added and the complete composition applied to a 10 mil optical fiber by the same method as in Examples 1-3, above, up to a drawing speed of 60 meters/minute. At this speed, the coating became too thin (less than 80 microns) and the fiber entering the coating bath was so ho~ that thermal oOSI-740 ~2~
degradation (smoking) of the coating composition was apparent; however, the coating still cured at this speed on exposure to a 300 Watt W source. These results indicate that using the compositions of the present inven-tion, line speeds for production of optical fibers may bedoubled with the proper formulation. In addition, it is evident from this example that the omega-epoxy C(8 11) aliphatic hydrocarbons preferred as cure-enhancing . reactive diluents as disclosed in the aforementioned Canadian Patent Application Serial Number 428,142, filed May 13, 1984, are useful as viscosity controlling agents for the optical fiber coating compositions herein.
200 pbw of a linear 75 cps trimethyl-chainstopped polydimethyl-methylhydrogensiloxane fluid having 44.9 weight percent methylhydrogensiloxy units (1.5 moles of active SiH groups) were disbursed in 400 pbw hexene with 126 p~w styrene (1.27 moles). 0.35 pbw platinum catalyst were added, the reaction mixture was agitated and slowly heated to 60C, at which point an exotherm occurred, taking the temperature to 75C be~ore falling back to around 65~C, where is was maintained for 1 hour. Infrared analysis showed 0.23 moles unreacted SiH, indicating that essentially complete addition of the styrene had taken place. 60 pbw limoneneoxide were then added (0.4 moles) and the reaction mixture returned to 69C and maintained at this temperature, with agitation, for 64 hours. The produc~ exhibi~ed only .007 moles of unreacted SiH, which was removed by brief reaction with hexene. The solvents and unreacted monomers were stripped to yield a viscous ~luid product (11,680 cps) having a refractive index of 1.492. This fluid, desi~nated Sample 9, incorporated 33.0 weight percent styrene and 13.1 weight percent ~ 25 linomeneoxide. Three other compositions were prepared in similar fashion to give the following.
~igh~ % ~ight % Viscosit~ Refractive ~ Styrene Limon~ide (cps) Index Sample 9 33.0 13.1 11,680 1.4920 Sa~ple 10 32.9 14.4 3~100 1.4902 Sample 11 29.1 29.1 88,000 1.4930 Sample 12 31.8 22.1 21,000 1.4970 Blends of the above polymers with cresyl glycidyl ether (DY 023, Ciba Geigy) were prepared to yield the following compositions:
~4ight ~ Visoosity Refractive G~sitions D~ 023 ~ Index ~_ 155a~pla 9A 20~0 1,200 1.4990 Sample lOA 25.0 2,500 1~4992 ~ple llA 25.0 3,600 1.5080 Sample lZA 25.0 1,680 1.5030 The W cure characteristics of the above ~-phene~hyl-and lim~neneoxide-substituted polysiloxane fluids described above were qualitatively tested by adding 4 weight percent of a 1:1 blend of diethoxyacetophenone and (Cl~H25Ph)2ISbF6, coating the ca~alyzed mixtures onto polyethylene kraft substrates and then exposing the coated substrates to W radiation as described pre~iously.
The following results were observed:
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- 2 6 ~ ç~82~- 6 0 S I 7 4 0 2~ ~2 ~
~ 3 ~ ~0 ~ ~
o ~
, ,q U~ o o o o o o o o tq sl ~ ~ ~ ,i ,i ,~
C~
~ ~
a Q
~ z~
c~ ~
u~
w c x u~
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-~3 ~ ~ o o o o o o o o ~ 3 o o o o ~ o o o O O
E~
a~
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It was observed that the diaryl salt catalyst was much more soluble in the ~-phene~hyl epoxy-functional silicones than in the low refractive i.ndex epoxy-functional silicones described in prior examples. This would permit highex concentrations of the catalyst if needed for faster cure. In addition, the presence of ~-phenethyl sub-stituents evidently affords fast cure with lower epoxy loads, and the above-descri~ed e-ther blends evidently cure equally well in air or inert atmospheres, making the high refractive index compositions very efficient coating materials.
! ~ high cu~e sp~ed c~n be maintained with as much as 25~ of the c~esyl glycidyl ether present. Other aromatic epoxy monomers such as bisphenol A diglycidyl ether or epoxy novolak resins are expected to be compatible with the epoxy-functional silicones as well.
A low refractive index (below 1.43) polysiloxane composition was prepared as follow~:
60 pbw of a trimethy~-chain~topped polydimethyl hydrogen siloxane fluid ~25 cps), 84 pbw sym-tetramethyl-tetravinylcyclotetrasiloxane, and 1056 pbw octamethylcyclo-tetrasiloxane were agitated for 17 hours under a nitrogen atmosphere.at 100C in the presence of 6 pbw Filtrol 20 acid equilibration catalyst. 6 pbw of MgO were added to neutralize the acid and the mixture held an additional hour at la0C, at which point the neutralized reaction product was stripped at 165C under 48 mm Hg vacuum for 2 hours. 829 pbw of the fluid product were treated with 20~8 pbw benzophenone, stirred or 15 minutes at 70C, then cooled to below 50C. 40 pbw t-butylperbenzoate ~J~L
were added and the complete mixture stirred 10 minutes before filtering to remove the solid Filtrol and MgO, giving a 1800 cps fluid product.
The composition was applied to polyethylene kraft paper at a 2 mil thickness, then exposed to 40Q watts total W lamp power in a PPG 1202 proce~sor. Curing a~
different line speeds afforded the following results~
Curing 10 Line Speed ATM Cure 50 ft/min. AIR Some smear, otherwise well cured 100 ft/min. N2 Well cured to smear-free coating;
thick section cured OK
200 ~t/min. N2 Slight smear detected, but otherwise satisfactory 15 300 ft/min- N2 Partially cured ~ easily smeared and rubbed o~
400 ft/min. N2 Surface cure only ("skin" formed) The same CQr.position was applied to a 10 mil diameter optical ~iber as described previously, then cured by exposure to a single Fusion Systems 300 ~att "H" lamp in an inert atmosphere. The material wetted the fiber satisfactorily up to a drawing speed of about 35 meters/minute. A well-cured 140 micr~n thick coating was obtained. At greater ~peeds, coating thickness rapidly diminished, although the material appeaxed to cure completely at speeds above 40 mekers/minute.
It is expected that high refractive index vinyl-functional polymers, W -curable in the presence of perbenzoate catalysts, may be prepared, in accordance with disclosure herein, which are comprised of four different units, e.g., methylvinyl^, diphenyl r ~ dimethyl-, and methylhydrogen-siloxy unit~.
_29 _ 300 pbw styrene (2.88 moles) were added to 800 pbw toluene and a pla~inum complex catalyst: (furnishing 25 ppm platinum to the complete mixture)~ The solution was heated to 80C, at which point 400 pbw trimethyl-chainstopped linear polydimethyl-methylhydrogensiloxane fluid (21 cps viscosity~ having 69 weight percent methylhy~rogensi.loxy units (4.61 moles SiH total) were slowly added over a 4 hour period as the reaction mix~ure was held at a temperature of 81-84C. After stirring a ~ hour, 289 pbw limoneneoxide ~1.9 moles) were added and the reaction mixture refluxed at 82C ~or 17 hours, then 90C
for 22 hour~, ~t which point unreacted SiH-containing units were down to about 2.4 weight percent. Unreacted SiH was removed by xeaction with hexane, and the product was stxipped at 140C under vacuum for 40 minutes to yield 888 pbw of a 18,800 cps fluid. Assuming quantitative addition of styrene, the product, designated Sample 14, included 31.9 weight percent styrene and 25.4 weight percent limoneneoxide. The refractive index of this material was 1.503, Coating compositions of suitable viscosities were prepared by blending Sample 14 with various epoxy-~unctional reactive diluents selected from the following:
____ _ _ _ , DY023 ~Ciba Geigy) = c~3~~CEI2CH2~CH~CH2 cresyl glycidyl et:her CY179 (Ciba Geigy~ a \OCH2 -C~Or~/
EPON 825 ~Shell Chemicals) =
H2C-CH-CH2-O ~ clcH3)2 ~ O-CH2-~H!CH2.
E~ch composition was catalyzed with 5 weight percent of a 1:1 blend o~ diethoxyacetophenone and (C~2H25Ph)2~SbF6;
the for~ulations are outlined below:
DY023 CY179 Epon Refractive Compositions ~Wt.%) (Wt.%) 825(Wt.~) Index 1~C 20 2Q 1 51~
The compositions were coated on polyethylene kraft substrates at 3 coating tbickness of 1 mil, then cured in a PPG QC1202AN processox as pre~iously described. The cure perormance was racorded as follows:
~~
, ~Zi~
Composi- UV Powers Line Speed tions Atm. (Watts) (meters~sec.) Cure 5ample 14 Air 400 1.0 Excellent cure, good anchorage.
Sample 14 Air 600 2.0 "Skin-cure"
Sample 14 Air 600 2.0 Excellent cure, good anchorage.
Sample 14A Air 400 1.5 Excellent cure.
Sample 14A Air ~00 2.0 Surface cure only.
Sample 14A N2 400 2.0 Surface cure only.
Sample 14A Air 600 2.5 Excellent cure.
Sample 14B Air 400 1.5 Excellent cure, good anchorage.
Sample 14B Air ~00 2.0 Evidence of surface cure.
Sample ~B ~ir 600 2.0 Excellent cure.
Sample l~C Air ~00 1.5 Smear-free, yood anchorage.
Sample 14C Air 400 2.0 Surface cure only.
Sample 14C Air 600 2.5 Excellent cure.
Modifications and variations in the present invention are obviously possible in light of the foregoing disclosure. For instance, it is anticipated that limonenedioxide (or other polyepoxide monomers) will prove to be a useful epoxy-functional diluent for high refractive index epoxy-functional polysiloxane compositions in light of the working examples. Also, modification of the epoxy-functional or vinyl-functional polysiloxane compositions described herein with additives to enhance the curing characteristics, such as disclosed in commonly assigned Canadian Appln. S.N.
428,142, filed May 13, 1983, and Canadian Appln. S.N.
469,075, filed November 30, 1984 may be advantageous ~L2~ . 60 sI -740 ;
in particular situations. It is understood, however, that these and other incidental changes in the particular embodiments of this invention are within the full intended scope of the appended claims.
4 A method for advantageously controlling the refractive index and viscosity of the disclosed polysi-loxane coating materials is also contemplated.
For the purposes of the present invention, the term l'loosely adherent" refers to a desired property of the primary coating lay~r o~er a glass optical fiber meaniny that the coating layer does not adhere so strongly to the core fiber as to inhibit the common mechanical operations performed with optical fibers, such as joining.
_ 7 - The texm does not reer to the optical relationship between ~he core and the cladding (primary coating) layer. The term "environmentally stable" refers to the ability of the coating material of the present invention to maintain its integrity and optical characteristics through en-vironmental changes to which fibers are routinely exposed, particularly cycles in temperature between the extremes of about -60C and ~80C.
D~TAILED DESCRIPTION OF THE INVENTION
The coated optical fibers of the presen-t invention are prepared by ~pplying a rapidly curable, UV-curable, epoxy-~urlctional or vinyl-functional silicone coating composition to a trarlsparent silica glass fiber and then subjecting i~ briefl~ to ultraviolet radia~ion. The coated optical fibers of the present invention exhibit all of the desired properties seen in thermally cured polydimethylsiloxane-coated fibers while providing the increased production capability, reduced e~ergy expenses, and safety of ultraviolet radiation curing.
Ultraviolet radiation IW~ is one of the most widely used types of radiation because of its low cost, ease of maintenance, and low potential ha~a~d to industrial users. W -curable compositions not only exhibit a very short curing time ~ut also avoid the high energy costs, environmental restrictions and safety hazards associated with the use of heat-curable materials.
The W-curable compositions employed in the p~e~ent invention are basically comprised of two components~
an epoxy-functional or ~inyl-functional organopolysiloxane base polymer combined with (ii) a photoinitiator capable 3S of promoting rapid cure of the composition on exposure to ultraviolet radiatio~.
~l2~
The epoxy-functional organopolysiloxane base polymers contemplated by the present invention are com-prised of units having the general Iormula RR'SiO, where R is hydrogen or a monovalent hydrocarbon radical of from 1 t~ 8 carbon atoms and where R' can be the same as R or a monovalent organic radical of from 2 to 20 carbon atoms having epoxy functionality. The epoxy-silicone polymer may have up to about 20% by weight epoxy-functional groups and must be capable of curing, or cross-linking, when combined with a suitable photoinitiator and exposed to ultraviolet radiation. The cured polymeric composition must be of a lower or higher refractive index than the optical fiber core and exhibit 1exibility, loose adhesion to the core fiber, ~nd ~nvironm~ntal stability.
Preferred epoxy-Eunctional polydiorganosiloxanes contemplated by the present invention are more specifi~
cally dialkylepoxy-chainstopped polydialkylalkylepoxysi-` loxane copolymers wherein the polysiloxane units contain lo~er alk~l substituents, notably, methyl groups. Theepoxy functionality is obtained when certain of the hydrogen atoms on the polysiloxane chain of a polydimethyl-methylhydrogensiloxane copolymer are reacted in a hydrosilation addition reaction with other organic molecule5 which contain both ethylenic unsatura-tion a~d epoxide functionality. Ethylenically unsaturated species will add to a polyhydroalkylsiloxane to form a func-tion~lized polymer in the presence of catal~tic amounts of a precious metal catalyst. Such a reaction is the cross-linking mechanism for other silicone compositions,however, in the present invention, a controlled amount of such cross-linking is permitted to take place in a silicone precursor fluid or intermediate, and this is referred to as "pre-crosslinking". Pre-crosslinklng of ~ 60SI-740 _ g the precursor silicone fluid means that there has been partial cross-linking or cure of the compasition and sffers the advantages to the present invention of enabling swift W -initiated cure with :Little expense for energy and elimination of the need for a solvent.
The UV-curable epoxy-functional silicone inter-mediate fluid comprises a pre-crosslinked epoxy-functional dialkylepoxy-chainstopped polydialkyl-alkyl-epoxy silicone copolymer fluid which is the reactionproduct of a vinyl- or allylic-functional epoxide and a v.inyl~~unctional siloxane crosslinking Eluid havlng a viscosity o~ approximately l to lO0,000 centipoise at 25C with a hydrogen-functional siloxane precursor fluid having a viscosity of approximately l to lO,000 centipoise at 25C in the presence of an effective amount of precious metal catalyst for facilitating an addition cure hydrosilation reaction between the vinyl-functional crosslinking fluid, ~inyl-functional epoxide, and hydrogen-Eunctional siloxane precursor fluid.
The unsaturated epoxides contemplated ar~ any of a number of aliphatic or cycloali-2S phatic epoxy compounds having olefinîc moietieswhich will readily undergo addition reaction to -SiH-functional groups. Examples of such compounds include l-methyl~4-isopropenyl cyclo-hexeneoxide (limoeneoxide; SC~I Corp.); 2j6 dimethyl 2,3-epoxy-7-octene (SCM Corp.) and 1/4-dimethyl-4-vinylcyclohexeneoxide (Viking Chemical Co.~. Limoneneoxide is pre~erred.
~5 ` ~2~ 60SI-740 _ 10 _ O "
The precious metal catalys~ for the hydrosilation reactions involved in the present invention may be selected from the group of platinum-metal complexes which inclu~es complexes of ruthenium, rhodium, 5: palladium, osmium, iridium and platinuIn. Examples of such hydrosilation catalysts suitable for the purposes herein are described in U.S. 3,220,972 lLamoreaux), U.S. 3,715,334 (Karstedt), U.S. 3,775,452 (Karstedt) and U.S. 3,814,730 (Karstedt) .
In the present invention, the vinyl-Eunct:ional siloxane cro~slinking f}uid can be selected from the group consisting oE dimethylvinyl-chai~stopped linear polydimethylsiloxane, dimethylvinyl chainstopped polydimethyl-methylvinyl siloxane copolymer, tetravinyl-tetramethylcyclotetrasiloxane and tetramethyldivinyldi-siloxane. The hydrogen-functional siloxane precursor fluid can be selected from the group consisting of tetrahydrote~.am2thyl-cyclotetrasiloxane, dimethylhydrogen-chainstopped linear polydimethylsiloxane, dimethylhydrogen-chainstopped polydimethyl-methylhydrogen siloxane copolymer and tetramethyldihydrodisiloxane.
Preferred photoinitiators for the epoxy-functional base polymers of the present invention include iodonium salts having the general formula, \ Y~j ~æ~
~ 11 wherein X is selected from SbF6, AsF6" PF5, or BF4 and wherein R" is a monovalent alkyl or haloalkyl radical of from 4 to 20 carbon atoms and n is a whole number equal ~o 1 to 5, inclusive. These compounds have been S found to be highly efficient in promoting ~he W -initated cationic ring-opening curing mechanism for epoxy-functional polysiloxanes, as disclosed in U.S~ 4,279,717 IEckberg et al.) . -Preferred of the iodonium salt photoinitiators utilized with the epoxy-functional silicones of the present invention are diaryl iodonium salts derive& from "linear alkylate" dodecylbenzene. Such salts have the general formula, ~S~+X~
wherein X equals SbF6, AsF6, PF6 or BF4. These bis(~-dodecylphenyl) iodonium salts are very effective initiators for ~he W cure of a wide ~ariety of epo~y-functional silicones.
"L~near alkylate" dodecylbenzene is known commer-cially and is prepared by Friedel-Craft alkylation cf benzene with a C(ll 13~ a-olefin cut. Consequently, the alkylate contains a preponderance of branched chain dodecylbenzene, but there may in fact be large amounts of other isomer~ of dodecylbenzene such as ethyldecyl-~ 2 5~ 60SI-740 benzene, plus isomers of undecylbenzene, tridecylbenzene, etc. Note, however, that such a mixtux2 is responsible for the dispersive character of the linear alkylate derived catalyst and is an aid in keeping the material fluid.
These catalysts are free-flowing, viscous fluids at room temperature.
The preferred bis(dodecylphenyl) iodonium salts are alkane-soluble and water-insoluble, and they dis-perse well in the preferred epoxy-functional polysiloxanes utilized in the coating compositions of the present invention. Bis(4-n-tridecylphenyl) iodonium hexafluor-oantimonate and bis(4-n-dodecylphenyl) iodonium hexa~luoroankimonate are most preerred.
The vinyl-functional base polymers contemplated herein are actually photoreactive terpolymers capable of curing on exposure to W radiation in the presence or certain radical photoinitiators. The terpolymers are mixed dimethylvinyl- and trimethyl-chainstopped linear polydimethyl-methylvinyl-n,ethylhydrogensiloxane terpoly-mer fluids and can be synthesized by acid equilibration of polymethylhydrogen siloxane fluid, tetramethyl-tetravinylcyclotetrasiloxane (methylvinyl tetramer) andoctamethylcyclotetrasiloxane ~dimethyl tetramer).
These vinyl-functional terpolymers are curable i~ the presence of polya~omatic photosensitizers having at least ~wo benzene rings which may be fused or bridged by organic radicals or hetero rad cals such as oxa, thio, and the like. Preferred among these photo-sensitizers are benzophenone and t-butylanthra~uinone.
~2 ~ ~ 60SI-740 The terpolymers may also be cured in the presence of certain perbenzoate esters having the general formula:
R3-o_o-c ~
where R3 is a monovalent alkyl or aryl group and 2 is hydrogen, alkoxy, alkyl, halogen, nitro, amino, primary and secondary amino, amido, and the like. The nature of Z will affect the stability of the peroxy bond, and electron-poor substitutent stabilizing the peroxy bond, and an electron-rich substituent making the peroxy bond more reactive~ Pre~erred perbenzoate esters lnclude t-butylperbenzoate and its para-substituted derivatives, including t-butylper~p-nitrobenzoate, t-butylper-p-methoxybenzoate, t-butylpex-p-methylbenzoate, and t-butylper-p-chlorobenzoate. The photoreactive polysiloxane ter-polymers of the present invention/ and photoinitiators effectively used therewith, are disclosed in Canadian Patent Application Serial Number ~ o~ filed ~/oY~nl er 30, /~ ~If The amount o photoinitiator employed is not critical, so long as proper curing is effected. As with any catalysts, it is preferable to use the smallest effective amount possible; howe~er, for purposes of illustration, catalyst levels of the aforementioned compounds from about 1% to 5~ by weight have been found suitable. Com~inations of photoinitia~ors ~re also contemplated.
--._ .. ... _ .. -- .. . . . .. ....... .... .. .. ._ ,. . _ _ _ ._ .. , . ... , . . _._ ... ~ _ . _. . __ .. . _ .. ...
~ ~ .
The epoxy-functional and vinyl-functional poly-siLoxanes described above typically have a low refractive index, i.e., less than 1.47, where the non-epoxy or non-~inyl substituents along the siloxane polymer chain are S hydrogen or lower alkyl. The refractive index of the polysiloxanes can be raised by for.~ulating polymers which also contain diphenylsiloxy units.
As discu~sed previously, an epoxy-functional 10 polydiorganosiloxane may be obtained by reacting a vinyl-functional epoxide with a SiH-containing polydiorgano-siloxane, such as polydimeth~l~methylhydrogen siloxane copolymer. To achieve a higher refractive index, a diphenylsiloxy-containing and SiH-containing polysiloxane 15 can be synthesized by co-hydrolysls of diphenyldichloro silane, dimethyldichloro silane, and methylhydrogendi-chloro silane, and this polymer could theoretically be reacted with a vinyl-functional epoxide to obtain epoxy functionality on the polymer. However, small quanities 20 of acid residues associated with, and very difficult to remove from, such linear high-phenyl SiH polymers act to open the oxirane ring of the epoxides, resulting in poly-siloxanes which are not photoreactive. A further difficulty with this approach is that in order to raise 25 the refractive index above 1.50, the polymer must contain more than 30 mole percent (greater than 50 weight percent) diphenylsiloxy unitst making the high-phenyl polysiloxanes vexy costly.
An important feature o~ the present invention is the di~cover~ of a cost~effective way to produce W -curable epoxy-functional silicones having a refractive index greater than 1.47, making the present compositions suitable for a wider range of fiber o~tic coati.ng applications. In ~2~ 60SI-740 preferred features of the invention, high refracti~Je index compositions are prepared by reacting a SiH-containing polysiloxane with both a vinyl-functional aromatic com-pound of from l to 20 carbon atoms (to obtain on-chain 5 aromatic substituents) and vinyl-functional epoxides (to obtain epoxy-functional substituents).
The vinyl-functional aromatic compound contains at ]east one aromatic ring and at least one aliphatically lO unsaturated site capable of reacting via hydrosilation addition with an SiH group to form a car~on-silicon bond.
Ethenylbenzene (styrene) is most preferred, however many other vinyl aromatic compounds will suggest themselves to per ons skilled in this art, and ~hese are intended to be 15 included herein.
In reactions with SiH-containing polysiloxanes, the vinyl aromatic compound and the unsaturated epoxide may be introduced simultaneously (and compete or hydride 20 reaction sites) or, preferably, in tandem, which allows more control over the degree of epoxy ~unctionality and refractive index of the final product. Since raising the refract.ive index o~ the composition is the chief purpose of employing such vinyl aro~atic compounds, reacting 25 these compounds first and adding epoxy functionality second is most preferred. The exact relative amounts of vinyl aromatic compound and ~inyl-functional epoxide employed will vary over a wide range, depending on the r~fractive index desired and the degree of reactivity 30 desired. By judicious selection of the reactant~, their amounts, and the reaction conditions, high refractive index epoxy-functional silicones which are tailored to specific requirements may be produced~ In view of this, simple experimentation with the processing perameters is contem-35 plated.
, Combination of the iodonium salt photoinitiators with other known photoinitiators is also comtemplated.
Preferred among such catalyst blends are combinations of iodonium salts with free-radical photoinitiators such as acetophenone derivatives. Even (1:1) blends of diaryl iodonium salts with diethoxy acetophenone are most preferred.
The present W -curable silicone coating composi-tions are applied to the optical fibers by methods well 10 known in the art. Typically, for example, uncoated optical fibers are drawn through a coating solution and then in-line through a curing chamber. ~s discussecl above, the curing step has been found heretofore to be the limit-ing factor in the speed at which the coating operation can 15 be perormed. U~e of epoxy-functional silicone coating compositions c~red by brief exposure to ultraviolet radia-tion in accordance with the present discovery provides a flexible, loosely adherent, environmentally stable primary coating on the silica glass core fiber which can 20 be applied at increased line speeds and without subjecting the coating material or fiber of high oven temperatures.
With the increased line speeds made possible with the compositions o~ the present invention, it has been 25 di~covered (see, i.e., Examples 1-3, infra.) that the viscosity of the coating compositions becomes an additional property which the industrial producer of optical fibers must be concerned with. In general, it is seen that viscosities below about 1000 cps do not permit "we~ting"
30 ~oating) of the fiber where the production speed is high, at viscosities greater $han about 10,000 cps, entrainment of air bubbles in the coating occurs, leading to imperfections in the primary coating that cause signal attenuation.
~;25~
~ or the epoxy-functional silicones produced via hydrosilation addition of vinyl-functional epoxides to an SiH-containing polysiloxane, the viscosity of the final product has been hard to predict, as it is dependent no only on the viscosity of the SiH-containing precursor but also on the degree of epoxy functionality. For example, a 90 cps precursor fluid containing 1 weight percent methylhydrogensiloxy units converted to an epoxy-functional silicone incorporating 18 weight percent limoneneoxide has a viscosity of about 400 cps; while a 200 cps precursor fluid containing 10 weight percent methylhydrogensiloxy unit converts to an epoxy-functional silicone of 3,000 cps viscosity and a 200 cps precursor fluid containing 6 weight percent methylhydrogensiloxy units incorporating 11.7 weight percent limoneneoxide has a viscosity oE
100 cps.
It has now been discovered that simultaneous addition of a vinyl MQ silicone resin and the vinyl-functional epoxide to a given SiH-containing polysiloxane provides products where the viscosity is dependent on the resin content. The vinyl MQ resins contemplated are polysiloxanes having primarily monofunctional ~M) units or tetrafunctional (Q) units The vinyl groups of the resin compete with the vinyl-functional epoxide for available hydride sites in the polysiloxane. The resin is thereby incorporated into the epoxy-functional polysiloxane product.
The vinyl MQ resins are made up of M units having the formula Y3Sio1/2 and Q units having the formula sio4/2, with the ratio of M to Q units being roughly 0.5 to 1.0 and preferably about 0.65. The Y groups may be, independently, the same or different monovalent hydrocarbon radicals of no more than 2 carbon atoms, and _18 _ at least 1 Y group must be vinyl. Such radicals include, for example, methyl, ethyl, vinyl or etnynyl. Methyl and vinyl are preferred~ A general discussion of these resins is found in Chapters 1 and 6 of Noll, Chemistry and ~echnoloqy of Silicones (2nd Ed., 19683.
In features of the present invention which make use of the foregoing discovery, the final W -curable polysiloxane product will contain pendent siloxy groups corresponding to the incorporated MQ resins. For these polysiloxanes, the definition o the R' radical in the formulas described above would be expanded to include a branched org~nosiloxane radical comprised of from 1 to 200 Q siloxy units oE the ormula SiO4/2 and M siloxy units having the Eormula Y3SiOl/2, wherein Y is a monova-lent hydrocarbon radical of 1 or 2 carbon atoms. It is understood also that the terms "diorganopolysiloxane'l and "organopolysiloxane ~ase polymer" as used herein to describe the epoxy~ and vinyl-functional polymer products of the invention are broad enough to cover such branche~
polysiloxane pendent groups.
Where high refractive index materials are desired, a further method for modifying the viscosity of the coating compositions, which also introduces refractive index-raising aromatic groups into the system, is to employ aromatic glycidyl ethers as reactiv diluents.
The aromatic glycidyl ether reactive diluents also pro-vide additional epoxy functionality and so may enhance the curing characteristic~ of the present coatin~
compositions, as was disco~ered for silicone paper r~lease compositions by the addition o~ epoxy polymers in Canadian Patent Applicatio~ Serial Number ~28~142 filed May 13, 1983.
~1 60SI-740 19 _ In order that persons skilled i.n the art may better understand the practice of the inventi.on, the following examples are provided by way of illust.ratiQn, and not by way of limitation.
Three epoxy-functional silicone coating composi-tions were prepared for optical fiber coating trials as follows:
Sample 1 _ 5 parts by weight of a 250 cps dimethylv:inyl-chainstopped polydimethylsiloxane fluid, 320 parts by weight o~ limoneneoxide, and 1 part by weight of a platinum catalyst (platinum-octyl alcohol complex) were added to 1,000 parts by weight of toluene. 1,000 parts by weight of a 150 cps dimethylhydrogen-chainstopped polydimethyl-methylhydrogen silox~ne copolymer fluid containing abou~, 8.7 weight percent _SiH groups were added slowly to the stirring mixture at room temperature over 1 hour. The reaction mixture was then refluxed at 1~0C for 21 hours, at which point 30 parts by weight of n-hexene were added and refluxing continued for 4 hours more. The solvents were stripped under a vacuum at 130C to yield a 1,000 cps limoneoxide-functional polysiloxane fluid containing about 17.2 weight percent limoneneoxide groups.
~ .
.~
~2 ~ 60SI-740 o Samples 2_& 3 Two other limonenPoxide-func~ional products designated Sample 2 and Sample 3 were ,prepared following the same procedure as for Sample 1~ above. Sample 2 was a 680 cps fluid containing approximately 14O0 weight percent limoneneoxide groups; Sample 3 was a 700 cps fluid containing approximately 11.7 weight percent limoneneoxide groups.
All three compositions were combined with 1.5 weight percent o bis(dodecylphenyl) iodonium hexa~luoroantimonate cationic pho~oinitiator.
lS Each coating composition was applied to 10 mil diameter pure silica glass fiber immediately after it was drawn. The coating device consisted of a small cup fitted with a 0.025-inch orifice at its base. Coating was accomplished by pulling the drawn optical fiber down through the test composition, then through the orifice to regulate coating thickness. The coated fiber was passed immediately through a nitrogen-inerted curing chamber where it was exposed to a single ocused 300 watt, 10 inch long Fusion Systems "H" ultraviolet lamp. The coated iber was finally wound on a taKe-up roll.
The coated fibers were observed to make sure the coating was fully cured. The line speed was gradually increased in order to determine the line speed at which the coa~ing on the ~iber would not cure completely, ~ha~ is, in oxder to discovex the point a~ which line speed surpassed cure rate.
, .
~25~
With each of the samples studied, the coating compositions still cured completely at line speed at which the coating rate was surpassed. In other words, "wetting" (coating) of the op~ical fiber by the silicone fluids ceased at line speeds where complete curing was still observed. For the ~hree sample compositions, complete curing was ob~erved under the following condi~
tions:
Loss of Wetting Coating Thickness lOCompositions(meters/min.l ~microns) Sample 1 50 125 Samp}e 2 30 120 Sample 3 33 120 The~e results compare favorably with the maximum line speed of approximately 30 meters per minute observed with commercially available heat-curable silicone systems.
XAMPI,~S ~-7 ~ 00 pbw o~ linear 60 ~ps dimethylhydrogen-chain-stopped polydimethyl methylhydrogensiloxane fluid con-taininy 10 weight percent methylhydrogensiloxy units were dissolved in 600 p~w ~exane. To this solution ~containing l.0 mole of active SiH groups) were added 152 pbw limoneneoxide (1 mole), about 25 ppm platinum in the form of a soluble complex catalyst, and varying levels of a vinyl MQ silicone resin. The reaction mixtures were reflu~ed for four hours, after which the unreacted SiH was removed by reaction with hexene.
Stripping the solvents, unreacted limoneneoxide, and hexane under vacuum resulted in the following epoxy functional poiymers:
~ Limonene- ~ MQ Viscosity Compositions oxide* resin** (cPs) Sample 4 19.6` 0.0 340 Sample 5 18.5 7.6 900 Sample 6 14.3 11.5 1976 Sample 7 16.1 12.8 3800 * Weight percent limoneneoxide incorporated in polymer.
** As weight percent resin solids after stripping solvents.
Cure was evaluated by blencliny 100 parts by weight (pbw) of each sample w.ith 1.5 pbw diethoxy acetophenone and 1-5 pbw (Cl2~l25Ph)2IsbF6 (a ~ree-radical/cation.ic co-catalyst system disclosed for curing epoxy-functional silicones in the aforementioned Canadian Application Serial Number 428,142, filed May 13, 1983). The complete coating compositions were manually applied as 2 mil coatings on polyethylene kraft paper using an adhesive coater and exposed to two focused medium pressure mercury vapor ultraviolet lamps in a PPG 1202 ultraviolet processor. Cure was evaluated qualitatively at various conveyor speeds (varying exposure time), UV
intensities, and cure environments, with the following results:
~ ~ ~ 60SI-740 o W Power ~ure Line ~
~le (Watts) AIM (meters/sec) Cure 4 400 Air 2.0 E~cellent cure-no ~r~ no migration, gocd adhesion - 4 300 N2 2.0 400 Air 2.0 "
400 N2 2.5 "
300 N2 2.5 '~n~ed' - easily r~d off ~ strate 6 400 Air 2.0 Cured - fa~ adhesion to subs~ate 6 400 N~ 2.0 Excellent cure no ~ ar -good adhesion 7 400 Air 2.0 Excellent cure - no ~ ~r, good adhesion 7 400 N2 2.0 "
It can be seen by comparisons with the control composition (Sample 4) that incorporation of vinyl MQ
resins, while allowing formulation of epoxy-functional silicone compositions within a specific target viscosity range, does not make a signiicant qualitative difference n cure.
90 pbw of a 10,000 cps epoxy-~u~ctional poly-siloxane incorporating 11.3 weight percent limoneneoxide were blended with 10 pbw of 1,2-epoxy dodecane (ViXolox, 1~, Viking Chemical Co.)., resulting in a 4200 cps blend.
The dual catalyst of Examples 4-7 was added and the complete composition applied to a 10 mil optical fiber by the same method as in Examples 1-3, above, up to a drawing speed of 60 meters/minute. At this speed, the coating became too thin (less than 80 microns) and the fiber entering the coating bath was so ho~ that thermal oOSI-740 ~2~
degradation (smoking) of the coating composition was apparent; however, the coating still cured at this speed on exposure to a 300 Watt W source. These results indicate that using the compositions of the present inven-tion, line speeds for production of optical fibers may bedoubled with the proper formulation. In addition, it is evident from this example that the omega-epoxy C(8 11) aliphatic hydrocarbons preferred as cure-enhancing . reactive diluents as disclosed in the aforementioned Canadian Patent Application Serial Number 428,142, filed May 13, 1984, are useful as viscosity controlling agents for the optical fiber coating compositions herein.
200 pbw of a linear 75 cps trimethyl-chainstopped polydimethyl-methylhydrogensiloxane fluid having 44.9 weight percent methylhydrogensiloxy units (1.5 moles of active SiH groups) were disbursed in 400 pbw hexene with 126 p~w styrene (1.27 moles). 0.35 pbw platinum catalyst were added, the reaction mixture was agitated and slowly heated to 60C, at which point an exotherm occurred, taking the temperature to 75C be~ore falling back to around 65~C, where is was maintained for 1 hour. Infrared analysis showed 0.23 moles unreacted SiH, indicating that essentially complete addition of the styrene had taken place. 60 pbw limoneneoxide were then added (0.4 moles) and the reaction mixture returned to 69C and maintained at this temperature, with agitation, for 64 hours. The produc~ exhibi~ed only .007 moles of unreacted SiH, which was removed by brief reaction with hexene. The solvents and unreacted monomers were stripped to yield a viscous ~luid product (11,680 cps) having a refractive index of 1.492. This fluid, desi~nated Sample 9, incorporated 33.0 weight percent styrene and 13.1 weight percent ~ 25 linomeneoxide. Three other compositions were prepared in similar fashion to give the following.
~igh~ % ~ight % Viscosit~ Refractive ~ Styrene Limon~ide (cps) Index Sample 9 33.0 13.1 11,680 1.4920 Sa~ple 10 32.9 14.4 3~100 1.4902 Sample 11 29.1 29.1 88,000 1.4930 Sample 12 31.8 22.1 21,000 1.4970 Blends of the above polymers with cresyl glycidyl ether (DY 023, Ciba Geigy) were prepared to yield the following compositions:
~4ight ~ Visoosity Refractive G~sitions D~ 023 ~ Index ~_ 155a~pla 9A 20~0 1,200 1.4990 Sample lOA 25.0 2,500 1~4992 ~ple llA 25.0 3,600 1.5080 Sample lZA 25.0 1,680 1.5030 The W cure characteristics of the above ~-phene~hyl-and lim~neneoxide-substituted polysiloxane fluids described above were qualitatively tested by adding 4 weight percent of a 1:1 blend of diethoxyacetophenone and (Cl~H25Ph)2ISbF6, coating the ca~alyzed mixtures onto polyethylene kraft substrates and then exposing the coated substrates to W radiation as described pre~iously.
The following results were observed:
\
~"~
- 2 6 ~ ç~82~- 6 0 S I 7 4 0 2~ ~2 ~
~ 3 ~ ~0 ~ ~
o ~
, ,q U~ o o o o o o o o tq sl ~ ~ ~ ,i ,i ,~
C~
~ ~
a Q
~ z~
c~ ~
u~
w c x u~
o~ ~
-~3 ~ ~ o o o o o o o o ~ 3 o o o o ~ o o o O O
E~
a~
U~
~:25~
It was observed that the diaryl salt catalyst was much more soluble in the ~-phene~hyl epoxy-functional silicones than in the low refractive i.ndex epoxy-functional silicones described in prior examples. This would permit highex concentrations of the catalyst if needed for faster cure. In addition, the presence of ~-phenethyl sub-stituents evidently affords fast cure with lower epoxy loads, and the above-descri~ed e-ther blends evidently cure equally well in air or inert atmospheres, making the high refractive index compositions very efficient coating materials.
! ~ high cu~e sp~ed c~n be maintained with as much as 25~ of the c~esyl glycidyl ether present. Other aromatic epoxy monomers such as bisphenol A diglycidyl ether or epoxy novolak resins are expected to be compatible with the epoxy-functional silicones as well.
A low refractive index (below 1.43) polysiloxane composition was prepared as follow~:
60 pbw of a trimethy~-chain~topped polydimethyl hydrogen siloxane fluid ~25 cps), 84 pbw sym-tetramethyl-tetravinylcyclotetrasiloxane, and 1056 pbw octamethylcyclo-tetrasiloxane were agitated for 17 hours under a nitrogen atmosphere.at 100C in the presence of 6 pbw Filtrol 20 acid equilibration catalyst. 6 pbw of MgO were added to neutralize the acid and the mixture held an additional hour at la0C, at which point the neutralized reaction product was stripped at 165C under 48 mm Hg vacuum for 2 hours. 829 pbw of the fluid product were treated with 20~8 pbw benzophenone, stirred or 15 minutes at 70C, then cooled to below 50C. 40 pbw t-butylperbenzoate ~J~L
were added and the complete mixture stirred 10 minutes before filtering to remove the solid Filtrol and MgO, giving a 1800 cps fluid product.
The composition was applied to polyethylene kraft paper at a 2 mil thickness, then exposed to 40Q watts total W lamp power in a PPG 1202 proce~sor. Curing a~
different line speeds afforded the following results~
Curing 10 Line Speed ATM Cure 50 ft/min. AIR Some smear, otherwise well cured 100 ft/min. N2 Well cured to smear-free coating;
thick section cured OK
200 ~t/min. N2 Slight smear detected, but otherwise satisfactory 15 300 ft/min- N2 Partially cured ~ easily smeared and rubbed o~
400 ft/min. N2 Surface cure only ("skin" formed) The same CQr.position was applied to a 10 mil diameter optical ~iber as described previously, then cured by exposure to a single Fusion Systems 300 ~att "H" lamp in an inert atmosphere. The material wetted the fiber satisfactorily up to a drawing speed of about 35 meters/minute. A well-cured 140 micr~n thick coating was obtained. At greater ~peeds, coating thickness rapidly diminished, although the material appeaxed to cure completely at speeds above 40 mekers/minute.
It is expected that high refractive index vinyl-functional polymers, W -curable in the presence of perbenzoate catalysts, may be prepared, in accordance with disclosure herein, which are comprised of four different units, e.g., methylvinyl^, diphenyl r ~ dimethyl-, and methylhydrogen-siloxy unit~.
_29 _ 300 pbw styrene (2.88 moles) were added to 800 pbw toluene and a pla~inum complex catalyst: (furnishing 25 ppm platinum to the complete mixture)~ The solution was heated to 80C, at which point 400 pbw trimethyl-chainstopped linear polydimethyl-methylhydrogensiloxane fluid (21 cps viscosity~ having 69 weight percent methylhy~rogensi.loxy units (4.61 moles SiH total) were slowly added over a 4 hour period as the reaction mix~ure was held at a temperature of 81-84C. After stirring a ~ hour, 289 pbw limoneneoxide ~1.9 moles) were added and the reaction mixture refluxed at 82C ~or 17 hours, then 90C
for 22 hour~, ~t which point unreacted SiH-containing units were down to about 2.4 weight percent. Unreacted SiH was removed by xeaction with hexane, and the product was stxipped at 140C under vacuum for 40 minutes to yield 888 pbw of a 18,800 cps fluid. Assuming quantitative addition of styrene, the product, designated Sample 14, included 31.9 weight percent styrene and 25.4 weight percent limoneneoxide. The refractive index of this material was 1.503, Coating compositions of suitable viscosities were prepared by blending Sample 14 with various epoxy-~unctional reactive diluents selected from the following:
____ _ _ _ , DY023 ~Ciba Geigy) = c~3~~CEI2CH2~CH~CH2 cresyl glycidyl et:her CY179 (Ciba Geigy~ a \OCH2 -C~Or~/
EPON 825 ~Shell Chemicals) =
H2C-CH-CH2-O ~ clcH3)2 ~ O-CH2-~H!CH2.
E~ch composition was catalyzed with 5 weight percent of a 1:1 blend o~ diethoxyacetophenone and (C~2H25Ph)2~SbF6;
the for~ulations are outlined below:
DY023 CY179 Epon Refractive Compositions ~Wt.%) (Wt.%) 825(Wt.~) Index 1~C 20 2Q 1 51~
The compositions were coated on polyethylene kraft substrates at 3 coating tbickness of 1 mil, then cured in a PPG QC1202AN processox as pre~iously described. The cure perormance was racorded as follows:
~~
, ~Zi~
Composi- UV Powers Line Speed tions Atm. (Watts) (meters~sec.) Cure 5ample 14 Air 400 1.0 Excellent cure, good anchorage.
Sample 14 Air 600 2.0 "Skin-cure"
Sample 14 Air 600 2.0 Excellent cure, good anchorage.
Sample 14A Air 400 1.5 Excellent cure.
Sample 14A Air ~00 2.0 Surface cure only.
Sample 14A N2 400 2.0 Surface cure only.
Sample 14A Air 600 2.5 Excellent cure.
Sample 14B Air 400 1.5 Excellent cure, good anchorage.
Sample 14B Air ~00 2.0 Evidence of surface cure.
Sample ~B ~ir 600 2.0 Excellent cure.
Sample l~C Air ~00 1.5 Smear-free, yood anchorage.
Sample 14C Air 400 2.0 Surface cure only.
Sample 14C Air 600 2.5 Excellent cure.
Modifications and variations in the present invention are obviously possible in light of the foregoing disclosure. For instance, it is anticipated that limonenedioxide (or other polyepoxide monomers) will prove to be a useful epoxy-functional diluent for high refractive index epoxy-functional polysiloxane compositions in light of the working examples. Also, modification of the epoxy-functional or vinyl-functional polysiloxane compositions described herein with additives to enhance the curing characteristics, such as disclosed in commonly assigned Canadian Appln. S.N.
428,142, filed May 13, 1983, and Canadian Appln. S.N.
469,075, filed November 30, 1984 may be advantageous ~L2~ . 60 sI -740 ;
in particular situations. It is understood, however, that these and other incidental changes in the particular embodiments of this invention are within the full intended scope of the appended claims.
Claims (27)
1. A coated optical fiber comprising:
(a) a core of high transparency silica glass;
and (b) a coating deposited on said core comprising an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopoly-siloxane comprising units of the formula RR'SiO, wherein R is hydrogen or monovalent hydrocarbon radical of from 1 to 8 carbon atoms, R' is hydrogen, a monovalent hydrocarbon of from 1 to 20 carbon atoms, a monovalent organic radical of from 2 to 20 carbon atoms having epoxy or vinyl functionality, or a branched organosiloxane derived from a vinyl MQ resin, a sufficient amount of R' is said epoxy or vinyl functionality to permit crosslinking, and a sufficient amount of R' is said MQ resin to control viscosity, and (ii) a catalytic amount of a photoinitiator.
(a) a core of high transparency silica glass;
and (b) a coating deposited on said core comprising an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopoly-siloxane comprising units of the formula RR'SiO, wherein R is hydrogen or monovalent hydrocarbon radical of from 1 to 8 carbon atoms, R' is hydrogen, a monovalent hydrocarbon of from 1 to 20 carbon atoms, a monovalent organic radical of from 2 to 20 carbon atoms having epoxy or vinyl functionality, or a branched organosiloxane derived from a vinyl MQ resin, a sufficient amount of R' is said epoxy or vinyl functionality to permit crosslinking, and a sufficient amount of R' is said MQ resin to control viscosity, and (ii) a catalytic amount of a photoinitiator.
2. A coated optical fiber as defined in claim 1, wherein said diorganopolysiloxane is epoxy-functional and said photoinitiator comprises, alone or in combination with a free-radical photoinitiator, a diaryl iodonium salt of the formula, wherein X is selected from the group consisting of SbF6, AsF6, PF6, and BF4 and wherein R" is a monovalent alkyl or haloalkyl radical of from 4 to 20 carbon atoms and n is a whole number equal to 1 to 5, inclusive.
3. A coated optical fiber as defined in claim 2, wherein said diaryl iodonium salt is a bis(dodecylphenyl)iodonium salt.
4. A coated optical fiber as defined in claim 2, wherein the photoinitiator is a combination of a bis(dodecylphenyl) iodonium salt and diethoxy-acetophenone.
5. A coated optical fiber as defined in claim 2, said diorganopolysiloxane has up to about 20%
by weight epoxy-functional groups.
by weight epoxy-functional groups.
6. A coated optical fiber as defined in claim 5, wherein said epoxy-functional groups are limoneneoxide groups.
7. A coated optical fiber as defined in claim 5, wherein said diaryl iodonium salt is selected from bis(4-n-tridecylphenyl) iodonium hexafluoro-antimonate and bis(4-n-dodecylphenyl) iodonium hexafluoroantimonate.
8. A coated optical fiber as defined in claim 2, wherein said coating composition also contains component (iii) in an amount sufficient to lower the viscosity of a reactive diluent selected from polyepoxide monomers or aromatic glycidyl ethers.
9. A coated optical fiber as defined in claim 8, wherein said reactive diluents are selected from the group consisting of limonenedioxide, , , .
10. A coated optical fiber as defined in claim 2, wherein the coating has a higher refractive index than the silica glass, and said diorganopolysiloxane is comprised primarily of polymeric units of the formulae, , and .
11. A coated optical fiber as defined in claim 1, wherein said diorganopolysiloxane is a terpolymer comprised of dimethylsiloxy, methylhydrogensiloxy, and methylvinylsiloxy units.
12. A coated optical fiber as defined in claim 11, wherein the photoinitiator is selected from the group consisting of perbenzoate esters and polyaromatic photosensitizers of up to 20 carbon atoms having at least two benzene rings which may be fused or bridged by an organic radical or hetero-radical.
13. A coated optical fiber as defined in claim 12, wherein the refractive index of the coating is greater than 1.5 and said diorganopolysiloxane also contains diphenylsiloxy units.
14. A method for high-speed production of a coated optical fiber comprising:
(1) applying to a core fiber of high transparency silica glass an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopolysiloxane comprising units of the formula RR'SiO, wherein R is hydrogen or a monovalent hydro-carbon radical of from 1 to 8 carbon atoms, R' is hydrogen, a monovalent hydrocarbon radical of from 1 to 20 carbon atoms, a monovalent organic radical of from 2 to 20 carbon atoms having epoxy or vinyl functionality, or a branched organosilane derived from a vinyl MQ
resin, a sufficient amount of R' is said epoxy or vinyl functionality to permit crosslinking, and a sufficient amount of R' is said MQ resin to control viscosity, and (ii) a catalytic amount of a photoinitiator; and (2) exposing said coated core fiber to ultraviolet radiation of sufficient intensity and for a sufficient period of time to cure said coating composition on said core fiber to form a flexible, loosely adherent, environmentally stable coating thereon.
(1) applying to a core fiber of high transparency silica glass an ultraviolet radiation-curable silicone coating composition comprising (i) a diorganopolysiloxane comprising units of the formula RR'SiO, wherein R is hydrogen or a monovalent hydro-carbon radical of from 1 to 8 carbon atoms, R' is hydrogen, a monovalent hydrocarbon radical of from 1 to 20 carbon atoms, a monovalent organic radical of from 2 to 20 carbon atoms having epoxy or vinyl functionality, or a branched organosilane derived from a vinyl MQ
resin, a sufficient amount of R' is said epoxy or vinyl functionality to permit crosslinking, and a sufficient amount of R' is said MQ resin to control viscosity, and (ii) a catalytic amount of a photoinitiator; and (2) exposing said coated core fiber to ultraviolet radiation of sufficient intensity and for a sufficient period of time to cure said coating composition on said core fiber to form a flexible, loosely adherent, environmentally stable coating thereon.
15. The method of claim 14, wherein said diorganopolysiloxane is epoxy-functional and said photoinitiator comprises, alone or in combination with a free-radical photoinitiator, an iodonium salt having the formula, wherein X is selected from the group consisting of SbF6, AsF6, and BF4 and wherein R" is a monovalent alkyl or haloalkyl radical of from 4 to, 20 carbon atoms and n is a whole number equal to 1 to 5, inclusive.
16. The method of claim 15, wherein said diaryl iodonium salt is a bis(dodecylphenyl) iodonium salt.
17. The method of claim 15, wherein the photoinitiator is a combination of a bis(dodecylphenyl) iodonium salt and diethoxyacetophenone.
18. The method of claim 15, wherein said diorganopolysiloxane has up to about 20% by weight epoxy-functional groups.
19. The method of claim 18, wherein said epoxy-functional groups are limoneneoxide groups.
20. The method of claim 18, wherein said diaryl iodonium salt is selected from bis(4-n-tri-decylphenyl) iodonium hexafluoroantimonate and bis(4-n-dodecylphenyl) iodonium hexafluoroantimonate.
21. The method of claim 14, wherein the application step (1) is accomplished by drawing the core fiber through a mass of said silicone coating composition and immediately thereafter through an orifice which regulates the coating thickness, and said exposure step (2) is accomplished continuously with step (1) by drawing the coated fiber through a curing chamber equipped with an ultraviolet radiation source immediately after the coating step (1).
22. The method of claim 15, wherein said coating composition also contains component (iii) in an amount sufficient to lower the viscosity of a reactive diluent selected from polyepoxide monomers or aromatic glycidyl ethers.
23. The method of claim 22, wherein said reactive diluents are selected from the group consisting of limonenedioxide,
24. The method of claim 15, wherein the coating has a higher refractive index than the silica glass, and said diorganopolysiloxane is comprised primarily of polymeric units of the formulae,
25. The method of claim 14, wherein said diorganopolysiloxane is a terpolymer comprised of dimethylsiloxy, methylhydrogensiloxy, and methyl-vinylsiloxy units.
26. The method of claim 25, wherein the photoinitiator is selected from the group consisting of perbenzoate esters and polyaromatic photosensitizers of up to 20 carbon atoms having at least two benzene rings which may be fused or bridged by an organic radical or hetero-radical.
27. The method of claim 26, wherein the refractive index of the coating is greater than 1.5 and said diorganopolysiloxane also contains diphenylsiloxy units.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000469072A CA1256821A (en) | 1984-11-30 | 1984-11-30 | Optical fibres with coating of diorganopolysiloxane and catalytic photoinitiator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000469072A CA1256821A (en) | 1984-11-30 | 1984-11-30 | Optical fibres with coating of diorganopolysiloxane and catalytic photoinitiator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256821A true CA1256821A (en) | 1989-07-04 |
Family
ID=4129263
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000469072A Expired CA1256821A (en) | 1984-11-30 | 1984-11-30 | Optical fibres with coating of diorganopolysiloxane and catalytic photoinitiator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1256821A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5381504A (en) * | 1993-11-15 | 1995-01-10 | Minnesota Mining And Manufacturing Company | Optical fiber element having a permanent protective coating with a Shore D hardness value of 65 or more |
| US5523374A (en) * | 1992-12-03 | 1996-06-04 | Hercules Incorporated | Curable and cured organosilicon compositions |
-
1984
- 1984-11-30 CA CA000469072A patent/CA1256821A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5523374A (en) * | 1992-12-03 | 1996-06-04 | Hercules Incorporated | Curable and cured organosilicon compositions |
| US5381504A (en) * | 1993-11-15 | 1995-01-10 | Minnesota Mining And Manufacturing Company | Optical fiber element having a permanent protective coating with a Shore D hardness value of 65 or more |
| USRE36146E (en) * | 1993-11-15 | 1999-03-16 | Minnesota Mining And Manufacturing Company | Optical fiber element having a permanent protective coating with a shore D hardness value of 65 or more |
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