NZ242146A - Radiation-curable coatings for optically useful articles (especially fibres): coated optical fibres - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £42146 24214b Priority Date(s): Curnpidta Specific2lion Fi'.ad: Class: *>,. fr».Gfei pa~ ••• *£*0* * Publication Date: t: n i ' V-• I .J. J j ■ ■ ■ ' * . • • tt• • rTi •••••• NO DP.AV.'i tN / " NEW ZEALAND PATENTS ACT. 1953 V z .'X «C ^ 14 APR 1992 ** r° No Date: COMPLETE SPECIFICATION ULTRAVIOLET RADIATION-CURABLE COATINGS FOR OPTICAL FIBERS AND OPTICAL FIBERS COATED THEREWITH S am +fWe. BORDEN, INC., of 180 East Broad Street, Columbus, Ohio 43215, United States of America r a ivi hiew Tewj u^A hereby declare the invention for which-i""/ we pray that a patent maybe granted to roe-/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- I A Ced* 0*05*9 A 0*05*9, 2 r4 b TITLE OF THE INVENTION: ULTRAVIOLET RADIATION-CURABLE COATINGS FOR OPTICAL FIBERS AND OPTICAL FIBERS COATED THEREWITH BACKGROUND OF THE INVENTION: COATED OPTICAL FIBERS IN GENERAL The present invention relates to radiation-curable primary and secondary coatings for optical fibers and to optical fibers containing such coatings.

Until recently, the optical fiber industry was concentrated on so-called "long haul" applications, wherein optical fibers were used to traverse lone distances such as in transoceanic or transcontinent/.. cables. In such applications, optical fibers required shielding with voluminous protective cabling material ii» sheltered subterranean or submarine environments and thus were not directly exposed to environmental hazards.

A recent trend in the optical fiber market is in local area networks for fiber-to-the-home uses. The fibers in such uses are directly exposed to much harsher conditions than previous applications of glass fibers, including severe temperature and humidity extremes. Consequently, previously used coatings do not perform veil under such adverse conditions; hence, a need existed for the development of higher performance coatings. Such coatings needed to be able to withstand the above conditions, i.e., to possess thermal, oxidative and hydrolytic stability, and to protect the fiber over the long term, i.e., over twenty-five years' time. 24?146 Optical fibers used for light transmission can ba prepared which, immediately after drawing, tre exceptionally strong and have vary fav intrinsic defects. However, such pristine fibers are very easily flawed by exposure to environmental conditiona including dust and moisture. Even a small flaw can reduce the strength of a fiber by an order of magnitude, rendering it brittle and eaaily broken by a weak external force. Therefore, optical glass fibers have, in tha prior art, bean clad with at laaat one raain coat immediately after their preparation, whoee minimum requirement ia to protect tha underlying pristine fiber from such external forces.

Typically, at least two coatinga, a primary, or buffar, coating and a aecondary coating, have been uaed. The inner, or primary, coating is applied directly to the glass fiber and, when cured, forms a soft, rubbery, compliant material which aarves as a buffar to cushion and protect the fiber by relieving the atresses created when the fiber is bent, cabled or spooled. Such stress might otherwise induce microbending of the fibers and cause attenuation of the light traveling through them, resulting in inefficient signal transmission. The secondary coating is applied over the primary coating, and must function aa a hard, tough protective outer layer preventing damage to the glass fiber during processing and use.

PRIMARY COATING Certain characteristics are desirable for the primary coating, and others for the secondary coating. For example, the primary coating must maintain adequate adhesion to the glass fiber during thermal and hydrolytic aging, yet be strippable therefrom for splicing purposes. The modulus of the primary coating '4Ap*i<> 92 242146 must be low to cushion and protect tha fiber by raadlly ral laving tha stresses on tha fibar which can induca microbendlng and conaaguant lnafflclant signal transmission. This cushioning affact must ba maintained through tha temperature ranga in which tha f ibars Bay ba expoaed throughout thair lifetime. Thus, it is nacaaaary for tha primary coating to hava a low glaav transition temperature (Tg). This low glass tranaltion temperature will asaura that tha coating rasa ins in its rubbary stata throughout tha poasibla usa taaparatura ranga.

Howavar, eimply having a low Tg doas not ansura good optical loss charactariatica at low temperatures. Sinca tha coafficiant of thermal expansion of tha sacondary coating and tha glass ara appreciably different, whan lowar temperatures ara ancountarad, tha aacondary coating contracts mora savaraly than doas tha glaas, thus inducing anothar form of strass. Tha primary coating thus ahould ba choaan so that it will raliava this stress. Tharafora, it ia dasirabla for tha Tg of tha primary coating to ba lowar than tha lowast usa taaparatura, yat high anough so that its modulus increasas as tha temperature ia lowered. This characteristic will offset the difference of the coefficients of thermal expansion between the secondary coating and the glass, thus minimizing microbending and tha resulting signal attenuation. In order to attain this property, the ahape of the modulua versus temperature curve (i.e., the modulus of the primary coating at low temperatures) is of vital importance.

The primary coating should also have a relatively high refractive index, i.e., greater than that of tha cladding material of the fiber to be coated. This high refractive index allows for a refractive index differential between the glass cladding and the primary .4 24214ti coating. Till* differential Allow arrant light signals to ba refracted avay fro* tha glaas cora.

Anothar requisite quality of tha primary (buffar) coating is rasistanca to moisture. Moisturs will rapidly dagrada tha strength of tha coating itaalf as wall aa tha underlying glass fibers under stress. The reaction is one of hydrolysis and streas corrosion. Moisture will alao adveraely affect the adhaaion of the primary (buffer) coating to the glaas, resulting in possible delamlnation. It is therefore deairable for the coating to be aa hydrophobic as possible. Preferably, the primary coeting should have a water absorption value of less than 5% by weight, and more preferably lass than 2.5% by weight.

SECONDARY COATING Similarly, the secondary coating must have a number of essential and optimal gualitiea. The eecondary coating must function as a hard protective layer which allowa the fiber not to be damaged during its processing and use. Consequently, this secondary coating should have a relatively high glass transition temperature (Tg), i.e., about 50*C, and a high modulus, i.e., about 100,000 psl. It is desirable for the secondary coating to have a Tg higher than its highest use temperature, because at or near tha Tg of a polymer, many physical propartiea such as modulus, tensile strength, thermal expansion coefficient, moisture absorptivity, and so forth, change dramatically with email changes in temperature. This results in large changes in the fiber characteristics.

Furthermore, like the primary coating, the secondary coating should undergo minimal changes in physical properties on exposure to moisture. Many polymeric coating materials experience significant U AP*199: 2421 hydrolysls, plasticization, softening, and loaa of protaetlva function in tha praaanca of water. Therefore, it la daairabla that tha aaeondary coating ahould also ba as hydrophobic as posaibla. A hydrophobic secondary coating also anhancas tha ability of the primary coating to keep vatar away froa tha glaaa fibar ltaalf, and thus inhibits aolstura induced hydrolysis and streas corrosion of tha glass fibar.

Alao, tha aaeondary coating Bust have a high refractive index, i.e., preferably highar than that of tha cladding aaterial of tha glass fibar, to enable it to atrip out arrant light, as with tha prlaary coating, especially in aabodimanta where the primary coating is omitted.

Another important property of aaeondary coatings is tha coefficient of friction (COF). A low COF facilitates winding and unwinding of tha fibars on spools; it also allowa tha fibera to alida easily along each other in a cable structure, thus rallaving streas. However, if the COF is too low, the fibars will have a reduced tendency to stay aligned on the spool. The COF is largely daterminad by tha cure propartias of tha secondary coating; if the coating haa a good hard surface cure, its COF will tend to ba low. Various slip additives can be added to lower tha COF; however, deleterious effacta such aa aurfaca tanaion problems, contamination, volatilization and blooming may raault from their usa.

DESIRABLE FEATURES FOR BOTH COXTTWGS Still other desirable properties exist which apply to both tha primary and secondary coatings. For example, fiber manufacturers ara aotivatad to coat the fibers as rapidly as possible to attain the economy of faster cure speeds, as these result in higher lin?£ / U 2421' ■p««ds. The cura spMdi of coating materials My ba datarmlnad by conatructing a UV doaa varaua Modulus curva. Tha lowest UV doaa at vtoich tha coating sodulus exhibits doaa indapandanca ia conaidarad ita eura apaad. There is therefore a daaand for faatar curing coatinga; for example, high line spaads ara obtain ad with primary and sacondary coatinga which say ba appliad wet-on-wet and aisultanaoualy ultraviolat light-cured. Ona vay of doing this la daacribad in U.S. Patant 4,474,130, iaauad Octobar 2, 1984 to Carl R. Taylor, which patant ia expreaaly incorporatad harain by rafaranca.

According to this patant, an optical fibar ia paaaad through a coating applicator cospriaing first and aacond dias. Tha firat dia confinaa a first coating liquid ovar a portion of tha fibar*a length. A aacond coating liquid is appliad onto tha fibar through a claaranca batwaan tha first and aacond dias. Tha claaranca is suff iciantly asall so that aubatantially no recirculation of tha aacond coating liquid occurs in tha vicinity of tha point of application to tha fibar. Tha aacond coating liquid is prafarably appliad at a fraa surfaca; that is, not in eontact with aithar tha first or aacond dias in tha issadiata vicinity of tha point of application to tha fibar. Additional coatinga can ba appliad in a alsilar manner.

Another desirable objective for both primary and aaeondary UV-curable coatinga ia to minimize the amount of unbound material In tha coating after cure. Evan when the cured coatings are conaidared 100% aolida, there may still exist a small amount of material which doaa not chemically bind into tha polymer network on curing. Examplea of auch materials used in tha coatings include unreacted monomer, unreacted photoinitiator, certain non-functional additives and ao forth. The preaence of exceasiva amounts of such materials is undesirable, inasmuch aa volatilization of au<^i H 242146 coaponents over tlae aay ehuga tha pbyiial properties of the coating. For example, volatile asterials froa the priaary coating aay permeate into the aaeondary coating, tending to plasticise it and resulting in strength loss. Also, volstile aaterlals aay cause production of unpleasant odors.

Still other laportant qualities of both optical fiber coatings are viscosity and shslf lifs. Good shelf life is considered foraulstlon stability of at laast six to twelve months. Viseosity can typically be soaewhat adjusted by regulation of the teaperature at which the coatings are applied. However, it is advantageous to sat the viacosity high enough so as to aaintain proper rheology and handling of the coating on application, but low enough to facilitate bubble raleaae and to ainiaize the aaount of heat needed in the preparation. Excessive heating ia undesirable inasauch as it asy reault in preaature gelling or viscosity buildup due to possible thermal initiation of polymerisation.

PRTQR ART COATTUCS Various single or double layer fiber coatings exist in the prior art. Aaong these are epoxy- or urethane-based resins. However, aany of these resins cure slowly; or have poor hydrophobicity; poor hydrolytic, thermal and oxidative stability; and undesirable yellowing properties.

There have also been developed priaary (buffer) coatings which cure on exposure to ultraviolet radiation. Such prior art primary coatings, however, have conventionally not been very moisture resistant and have some of the same deficiencies as above.

To obviate these flaws, the primary-coated optical fibers of the prior art have been topcoated with a tough and flexible overcoat which possesses superior . v \ HAPRfr 242146 resistance to aolsture and atom ion. Prior art coatinga have included extruded nylon "jacket" coatinga, which are, however, Bors expensive and Bore difficult to apply than would be an ultra viol at-cured coating.

Therefore, the present invention seeks to provide priaary and secondary coatinga having aaxiaal thermal, oxidative and hydrolytic stability, wherein the priaary coating ie adequately adherent to the glaaa fiber yet strippable therefrom; provides edeguate cushioning of the fiber? has a relatively low glass transition teaperature; and is capable of relieving stress upon the fiber. The secondary coating Bust function as a hard protective layer; have a relatively high glees transition teaperature and high aodulus; be hydrophobic to resist Boisture; have a high refractive index; and have an appropriate coefficient of friction value. Zn addition, the two coatings can be foraulated for wat-on-vet application, with siaultaneous radiation curing at coaaercially acceptable cure speeds. \ '44P*I992 HT or TO IHYHffiQH* Accordingly, in preferred embodiments of the invention, radiation-curable priaary and secondary coatings for optical fibera have been provided. The priaary coatings have refractive indices greater than those of their fibar substrates, and relatively low glass transition teaperetures and aoduli (i.e., lea* than about -20*C and lass than about 500 psl, respectively). The secondary coatings have relatively high glass transition teaperetures (i.e., about 50*C) and aoduli of about 100,000 psl. The secondary coatings alao have refrective indicea greater than those of the cladding material of the optical fiber, for stripping out errant light in a aonocoat application. An optical fiber coated with the secondary coating alone, or vlth the primary and eecondary coatings of the present invention, has also been developed.

The radiation-curable priaary coating for an optical fiber of the present invention coapriees, in one preferred embodiment: (A) from substantially 20 percent to substantially 80 percent by weight of an acrylated urethane oligomer which is the reaction product of (1) a hydrocarbon polyol; (11) an non-aromatic polyisocyanate; and (ill) an endcapping monomer selected froa hydroxyalkylacrylate and hydroxyalkylaethacrylate; (B) from substantially 5 percent to substantially 50 percent by weight of an alkyl acrylate or aethacrylate monomer having between 6 and 18 carbon atoms in the alkyl moiety; (C) from substantially 5 percent to substantially 60 percent by weight of a monomer or oligomer having (1) an aromatic moiety, (2) a moiety containing acrylic or methacrylic unsaturation, and (3) a hydrocarbon moiety, which 242146 monomer or oligomer is capable of increasing the refractive Index of the composition; (D) from substantially 0.1 percent to substantially 3.0 percent by weight of an organofunctional • liana edhesion promoter; and (E) from substantially 1.0 percent to substantially 10 percent by weight of a photoinltlator, all of the above stated percentages by weight for the priaary costing being baeed on the total weight of (A), (B), (C), (D) and (I).

The priaary coating say optimally contain other materials, such as at least one chain transfer agent, preferably a mercapto-functional chain transfer agent, and at least one stabilizer.

The invention also coapriaes a radiation-curable secondary coating for an optical fiber comprising, in one preferred embodiment: (I) from substantially 20 percent to substantially 80 percent by weight of an aliphatic urethane eery late oligomer based on a polyester; (II) from substantially 20 percent to substantially 60 percent by weight of an acrylated or methecrylated compound selected from the group consisting of isobomyl acrylate; isobomyl methacrylate; C, to Cu saturated hydrocarbon diol diecrylates; C, to C,# saturated hydrocarbon diol dlmethacrylates; and mixtures thereof; (III) from substantially 1 percent to substantially 10 percent by weight of a photoinitiator, all of the stated percentages by weight for the secondary coating being besed upon the total weight of (I), (II) and (III) wherein the percentages selected from within the stated ranges add up to 100%.

The secondary coating may optimally contain at least one stabilizer.

A coated optical fiber has also been developed. In one embodiment, the optical fiber comprises an optical fiber coated only with a secondary coating layer a 242146 described above. In another preferred eabodleant, a coated optical fiber coeprising an optical fiber, tha applied priaary coating layar aa described above, and tha applied secondary coating layar aa deacribed above, has been davalopad.

A process for prsparing a coated optical fiber has also baan devalopad. Zn ons eabodiaent, tha process coaprisas applying to an optical fiber a priaary coating layer as daacribad above; applying atop tha diocloaad priaary coating layar a aaeondary coating layer as deacribad hereinabove; and preferably radiation-curing tha two coating layers siaultaneoualy.

Tha coating coapoaitiona of the invention are also useful for other coating and protective purposea. They can ba foraulatad to be useful on glass, ceraaic, granite, and aarble surfaces, and the like.

DESCRIPTION QT THE PREFERRED EMBODIMENTS' The invention relates in part to radiation-curable priaary and secondary coatings for optical fibera. The optical fibers which are coated aay coaprlae a glass care and a glaas cladding layer. The core, for exaaple, aay comprise silica doped vith oxides of geraaniua or phoaphorus and the cladding, a pure or doped silicate such as fluorosilicate. Alternately, the fibers aay coaprise a polyaer-clad silica glaaa core. Exaaples of such polyaer claddings include organoailoxanea such as polydiaethylslloxane or a fluorlnated acrylic polyaer. The priaary coating ahould have, lnfcgr alia, the following properties: aoisture resistance; ease of coating and stripping; low volatiles content; low modulus over the life of the fiber; low glaas transition teaperature; and long shelf life. The secondary coating should fora a hard protective layer; have a relatively high aodulua and glaas transition teaperature; and also 2421^ be aoisture resistant. Both coating* should be transparent; nonaalodorous; fast curing; and rssaln adherent, avsn upon aging in high hast and huaidity anvironsants.

THF PPTM1BV tmimR) GOATTMC Tha priaary coating composition of tha praaant invention contains fiva ingredients, (A) through (E).

A. Ths Hvdrocarbon-Based Oligomer Ths first ingredient is a apecific hydrocarbon-based oligoaer (A). Thia coaponent coapriaea from about 20 percent to about 80 percent by weight of the composition based on the total weight of all the A through E ingredients of the composition. Preferably, this oligomer comprises from about 30 percent to about 70 percent, and more preferably about 45 percent to about 65 percent by weight of the coapoeition, baaed on total weight of the A through E ingredients.

The particular hydrocarbon-baaed oligomer uaed in the present invention was chosen to impart good thermal, oxidative and hydrolytic stability to tha system.

It is known in the art that various types of UV-curable oligomers exist which may yield a soft, compliant, low glaas transition temperature-type coating. One system known in the art is acrylate-endcapped polybutadiene-type rubber or rubber-aodified aery la ted monomers as base resins. While these systems have excellent low teaperature properties and are suitably hydrophobic, their internal carbon-carbon double bonds (unsaturation) make them susceptible to oxidation over a long period of time.

It ia also known in the art to employ acrylated silicones as base resins in such compositions. While J ' '4 APR 1992 2 ': Z 1 thass bava good low temperature properties and hydrophobic!ty, they ara difficult to formulate vith a suitably high rafractiva index, tend to hava poor tharmal stability, and aay ba auacaptibla to bydrogan outgaaaing which can load to signal attanuation in fibars so coatsd.

Yat anothar aystaa known in tha art involvaa tha use of acrylatsd fluorocarbons. While thaaa ara suitably hydrophobic and thsrsally stable, thsy ara typically incompatible vith sost non-halogenated organic cospounds. Additionally, thsy are vary expensive relative to other systaas.

To overcoae aany of the dlsadvantagaa of the prior art syetaas, tha present invention utilizes a urethane aerylata systaa baaed wholly or partially on a hydroganatad polybutadiene backbone. Zn general, urethane acry late systaas baaed on polyethers or polyesters have been known, and could be foraulated to form soft, low aodulus, low Tg buffer coatings. However, systeas based on polyethers or polyesters were usually characterized by poor water realstanca and by thermal instability. Additionally, known urethane oligoaers based on aroaatic isocyanates displayed thermal instability and tended to yellow. While poly ether-based urethane acrylates have excellent low Tg properties, they ara generally not hydrophobic enough for optical fiber applicatione and are susceptible to oxidation. Polyester-based urethane acrylates, on the other hand, have good theraal stability but are susceptible to hydrolysis.

Thus, the present invention uses an oligoaer which obviates aany of ths above probleaa.

Tha oligoaer (A) utilized in the present invention is the reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polyisocyanats; and (iii) an endcapping monomer.

KS i . | I Tbe hydrocarbon polyol (1) is provided by a linear or branched hydrocarbon containing a plurality of hydroxyl end groups, and providing a hydrocarbon backbone to the oligoaer. The hydrocarbon portion is from about 600 to about 4,000 molecular weight. Molecular weight in this case is determined by gel permeation chromotography <GPC), using a methylene chloride solvent, as measured against polystyrene molecular weight standards. By "hydrocarbon" is meant a non-aromatic compound containing a majority of methylene groups (-CH,-) and which aay con tali. Internal unsaturation and/or pendent unaaturation. Fully saturated (i.e., hydrogenated) hydrocarbons are preferred because the long term stability of the cured optical fibsr coating increases as the degree of unsaturation decreases. Suitable hydrocarbon polyols include hydroxyl-terminated, fully or partially hydrogenated 1,2-polybutadiene; 1,2-polybutadiene polyol hydrogenated to an iodine number of from 9 to 21; fully or partially hydrogenated polyieobutylene polyol; mixtures thereof, and the like. Preferably, the hydrocarbon polyol is substantially fully hydrogenated, and thus a preferred polyol is hydrogenated 1,2-polybutadiene .

The polyisocyanate component (ii) is non-aromatic. Oligomers based on aromatic polyisocyanates effect yellowing in the cured coating. ?;on-aromatic polyisocyanates of from 4 to 20 carbon atoms may be employed. Suitable saturated aliphatic polyisocyanates include isophorone diisocyanate; dicyclohexylmethane-4,4* —diisocyanate; 1,4-tetramethylene diisocyanate; 1,5-pentamethylene diisocyanate; 1,6-hexamethylene diisocyanate; 1,7-heptamethylene diisocyanate; 1,8-octamethylene diisocyanate; 1,9-nonamethylene diisocyanate; 1,10-decamethylane diisocyanate; 2,2,4-trimethyl-l, 5-pentamethylene diisocyanate; 2,2'- M •15 dlaetbyl-1,5-penta»ethylenediisocyanate; 3-mathoxy-l, 6-hexamethylene diisocyanate; 3-butoxy-l, 6-haxaaethylana diisocyanate; omega, omega •-dip ropy lather diisocyanate f 1,4-cyclohexyl diisocyanate; 1,3-cyclohexyl diisocyanate; trimethylhexamethylene diisocyanate; and mixtures thereof. Xeopborone diisocyanate is ths preferred non-aromatic polyisocyanate.

Ths reaction rate between the hydroxy 1 -terminated hydrocarbon and the diisocyanata say ba increased by use of a catalyst in the amount of 100 to 200 ppm. Suitable catalysts include dibutyl tin dilaurate, dibutyl tin oxide, dibutyl tin di-2-hexoate, stannous olsate, stannous octoate, lead octoata, ferrous acetoacetate, and amines such as triethylai.dne, diethylmethylamine, triethylenedlaulne, dimethyl-athylamine, morpholine, H-•thyl morpholine, piperazine, N,N-dimethyl benzylamine, N,N-dimethyl laurylamina, and mixtures thereof. A preferred catalyst is dibutyl tin dilaurate.

The endcapping monomer (ill) is a hydroxyl-terminated aliphatic acrylate or methacrylate conforming to the formula wherein R** R4 and R5 are independently selected fr*a the group consisting of hydrogen, methyl, ethyl or propyl, m is an integer from 1 to 10, and p is 0 or 1. Suitable hydroxyl-terminated monoacrylates which may be used as the endcapping monomer include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate. Hydroxyethyl acrylate is preferred because it iaparts a faster cure ratio to the polyurethane oligomer. The molar ratio of the polyol, 242146 diiaocyanata and andcapping aonoaar is preferably approxiaataly 1:2:2.

A prafarred oligomer la baaad on tha forsula R1 la a llnaar or branched hydrocarbon polyaar of froa 600 to 4,000 aolecular weight aalaetad froa tha group conaiating of fully or partially hydroganatad 1,2-polybutadlana; 1,2-polybutadlana hydroganatad to an lodina nuabar of froa 9 to 21; and fully or partially hydroganatad polyiaobutylana; R2 ia a linaar, branchad or cyclic allcylana of froa aix to tvanty carbon atona; and X and Q ara indapandantly aithar (a) a radical of tha foraula: vharain R1, R4, and R5 ara indapandantly hydrogen, aethyl, ethyl or propyl, a ia an intagar froa 1 to 10, and p ia aithar zero or one, or (b) a aaturatad alkyl radical of froa nina to tvanty carbon atoaa, vith tha proviao that tha abova oligoaar Bust possess at laaat ona acrylata or aathacrylata tarainal (and) group.

Tha abova-daacribad oligoaar ia diacloaad in U.S. Patant 4,786,586 to Lea at al., which patant ia harain incorporated by rafaranca.

Tha abova-daacribad oligoaar ia particularly auitabla because ita aaturatad hydrocarbon backbone givaa tha oligoaar auitabla hydrophobicity and thermal X0jp(HR,NHf0R10fpniRsMHjJ0Q O 0 0 0 vhara o M APR 1992 24?" 46 stability. The glaas transition teaperature of the oligomer is approximately -20*C and say ba lowered by blanding vith additives, discusaad infra.

Tha primary coating containing this oligosar has a vstar absorption valua of lass than 51 by vaight, and prafarably lass than 2.5%.

B. Tha Acrvlate-Functlonal Monomer Tha aacond aaaantial component of tha composition of tha primary coating compoaition is an alkyl acrylata or methacrylate-based monomar (B). Tha alkyl portion (moiety) of tha monomar has batvaan 6 and 18 carbon atoms, and prafarably batvaan 8 and 15, and tharafore ia hydrocarbon in character. This monomar (B) may ba aithar straight chain or branched. This component comprises from about 5 percent to about 50 parcant by vaight of tha composition, baaad upon the total vaight of the A through E ingrediants of tha composition. Preferably, it comprises from about 7.5 parcant to about 30 percent, and more preferably froa about 10 percent to about 20 parcant by vaight of the composition, based upon the total vaight of tha five components (A), (B), (C), (D) and (E).

The monomer is selected to ba one that is compatible vith the very hydrophobic oligomer discussed above. It is also chosen to ba one which is soft-curing and vhich has a lov Tg, thus lovering the Tg of tha composition including it. Suitable axamples of c, to Cia alkyl acrylate or methacrylate-based monomers include haxyl acrylate; hexyl methacrylate; 2-athylhexyl acrylate; 2-athylhexyl methacrylate; iaooctyl acrylate; isooctyl mathacrylate; octyl acrylate; octyl methacrylate; decyl acrylate; decyl methacrylate; isodecyl acrylate; isodecyl methacrylate; lauryl acrylate; lauryl methacrylate; stearyl acrylate; stearyl M APR 1992 242146 * , -i§- aethacrylate; Cu-Cu hydrocarbon diol diacrylates; cu-Cu hydrocarbon diol diaethacryletesr and aixtures of tha above. Preferred alkyl acrylate aonoaers include stearyl acrylate, lauryl acrylate and isodecyl acrylate. A particularly preferred one is lauryl acrylate. The alkyl acrylate or aethacrylate-based aonoaer should be used in a quantity sufficient to adjust the total priaary coating composition to a viscosity in tha ranga of about 2,000 cps (centipoises) to 10,000 cps, measured by a Brookfield viscometer, model LVT, spindle speed of 6 rpm, spindle number 34, at 25*C.

C. The Mononar or OIIoctt Containing An Aromatic Moletv The next ingredient is a aonoaar or oligoaer (C) which is capable of adjusting the refractive index of the coapositlon. Tha aonoaer or oligoaer (C) contains at least (1) an aronatic aoiety, (2) a aoiety containing acrylic or aethacrylic unsaturation, and (3) • hydrocarbon aoiety. This compound should be used in an aaount effective for its stated purpose not in excess of about 60 percent by weight, and generally should comprise from about 5 percent to about 60 percent by weight, preferably froa about 10 percent to about 40 percent by weight and more preferably, from about 15 percent to about 30 percent by weight of the composition, based upon total weight of the ingredients (A) through (E).

The aonoaer or oligomer (C) may be used to increase the refractive index for the reasons specified above. Tha aroaatic aoiety of the aonoaer or oligoaer is itself capable of raising the refractive index; however, the hydrocarbon aoiety is required to increase the compatibility of this monomer vith the hydrocarbon-baaed oligoaer (A). The aoiety containing acrylic n *b'r ' c 242146 methacrylic unsaturation renders tha compound compatible vith tha systam as a whole, inaamuch aa it haa aval labia raactlva acrylic unsaturation which allows it to croaalink vith tha rsat of tha cospoaitlon upon ultraviolat curing, thus minimising volatilsa contant of tha cursd systas. Samples of aromatic monomars or ollgomara additionally containing hydrocarbon charactar and a vinyl group includa polyalkylsna glycol nonylphanylathar acrylatas such as polyathylana glycol nonylphanylsthsr acrylata or polypropylana glycol nonylphanylathar acrylata; polyalkylsna glycol nonylphanylsthsr mathacrylatas such as polyathylana glycol nonylphanylathar mathacrylata or polypropylana glycol nonylphanylathar mathacrylata; and mixtures of thasa. In aach caaa tha phanyl group sarvas to incraasa tha rafractiva indax of tha coating and tha nonyl componant rsndars tha composition somewhat mora hydrophobic and, therefore, cospatibls with tha hydrophobic oligoaar (A). Tha rafractiva indax of tha compoaition including this monomar or oligomar is at laast about 0.005 highar than that of tha composition ■ comprising only (A), (B), (D) and (E). A suitable primary coating composition may, for example, hava a rafractiva indax of graatar than or aqual to 1.48.

Tha rafractiva indax of tha priaary coating muat be highar than that of tha cladding of tha fibar. If the fibars coated with tha coating compoaition of the prassnt invention ara down-doped, i.e., contain dopants which lower tha refractive index of the fiber itself, tha rafractiva indax of the coating will be diffarant enough from that of tha fiber so that arrant signals will be refracted away even without the incorporation of this componant. Therefore, in such embodiments, the monomer or oligomer (C) is not essential to the composition. v 1 ,4*PKl992 • ') -w- ... :• i ',146 0. Tha idhaalon Pn»otir The fourth ingredient is an edheslon promoter (D). Adhesion becomes s particularly pertinent problea in high huaidlty and high teaperature envlronaents, where delaainetion is aore of e risk.

Zt is known in the art to use either ecid-functional aeterials or orgenofunctlonal silenes to proaots adhesion of resins to glass. While acid-funetional aaterials are operative herein, orgenofunctlonal silanes are preferred. Acid-functional aaterials are less preferred, however, because of their possible corrosivity towards the aaterials, and their tendency to lose their adhesion properties on exposure tc aoiature. Silenes tend to be aueh aore suitable in terxs of these factors and, therefore, are the adhesion proaotars of choice. Additionally, it is useful to have an adhesion proaoter having a functionality which binds in with the systea during cure, again to ainiaize the quantities of unbound volatiles. Various suitable orgenofunctlonal silanes include but are not Halted to aaino-functional silanes; aercapto-functional silanes; aethacrylate-functional silanes; acrylaaido-functional silanes; allyl-functional silanes; vinyl-functional silanes; and ecrylate-functional silanes. The adhesion proaotars preferably are aethoxy-or ethoxy-substituted as well. Preferred orgenofunctlonal silane* include but are not Halted to aercaptoalkyl trialkoxy si lane, aethacryloxyalkyl trialkoxy silane, aainoalkyl trialkoxy sil&ne, mixtures thereof, and the like. Methacrylated silanes are desirable, inasmuch as they bind in well vith the cured systea, but tend to slow the cure speed of the systea down by an order of Magnitude. The mercapto-functional adhesion proaoters also cheaically bind in during cure, but do not appreciably slow down the cure speed of the systea. ,, ^ L / -»- '1146 lost preferred orgenofunctlonal silanes that enhance adhesion In huaid conditions include 3-aiinopropyl trlethoxy lilme , 3-aethacryloxypropyltriaethoxy silane, 3-eercaptopropyl trlaethoxy silane and 3-aercaptopropyl (gaaaa-aercaptopropyl) trlethoxy silane, and alxtures thereof. A particularly preferred adhesion proaoter is 3-aercaptopropyl trlaethoxy silane.

The silane coaponent should be incorporated into the coapositlon in a snail but effective aaount to enhance the adhesion of the coapositlon to the surface of an inorganic substrate, in this sabodiaent, glass, and in other eabodiaents, glass, enaael, aarble, granite or the like. The silane coaponent coaprises froa about 0.1 percent to about 3.0 percent by weight of the coapositlon, based on total weight of the five A through E ingredients. Preferably, the silane coaprises froa about 0.2 percent to about 2.0 percent, and aore preferably froa about 0.3 percent to about 1.0 percent, based on the total weight of the oligoaer, alkyl acrylate or aethacrylate, aultifunctional aonoaer, photoinitiator and silane.

E. The Photoinitiator A fifth ingredient of the priaary coating coapositlon is a photoinitiator (E). The photoinitiator, when used in a snail but effsctive aaount to proaote radiation cure, aust provide reasonable cure speed without causing preaature gelation of the coapositlon. Further, it aust not interfere with the optical clarity of the cured optical coating. Still further, the photoinitiator aust itself be thermally stable, and non-yellowing and efficient.

Suitable photoinitiators include the following: hydroxycyclohexylphenyl keto n e .22. / ^ j bydroxynthy lpbmy lprop inoni ; dlaetboxyphsnylacetophenone; 2 -■•thy 1-1 - [ 4 - (methyl thio)phenyl] -2-aorpholino-propanone-l; l-(4-iaopropylphenyl) -2 -hydroxy-2 -methy lpropan-1 -one; l- (4-dodecylphenyl)-2-hydroxy-2-methylpropan-l-one; 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone; diethoxyacetophenone; 2,2-di-aec-butoxyacetophenone; diethoxy-phenyl acetophenone; and alxtures of thaaa.

Tha photoinitiator prafarably coaprises froa about 1.0 percent to about 10.0 percent by weight of tha coapoaition, based upon tha total coaposition of the A through E Ingredients. Preferably, the aaount of photoinitiator is froa about 1.5 percent to about B.O percent, and aore preferably about 2.0 percent to about 7.0 percent by weight, based upon total vaight of A through E ingredients. A particularly preferred photoinitiator is hydroxycyclohexylphenyl ketone. Tha photoinitiator should be choaen such that a cure spaed, as aeasured in a dose versus aodulus curve, of less than 1.0 J/ca2, and preferably less than 0.5 J/cm2 is required, when tha photoinitiator is used in the designated aaount.

Optional Components Various optional coaponents aay ba used in tha priaary coating beyond the five A through E coaponents. For exaaple, optional chain transfer agents aay be used to control the aodulus and glass transition temperature of tha coating. The curing of aery late-containing monomers or oligomers is a free radical process. One vay known in the art to control the molecular vaight and, consequently, the modulus and glass transition temperature of a free radical polymerization product is to uae one or more chain transfer agents. It is 5146 c f, Q ■ • Apr/992r, 24?146 postulated that tha addition of a chain transfer agent to a formulation lovers the Molecular weight of a polyaer produced and results in a lower Modulus, lovar glaas transition teaperature coating.

Preferred chain tranatar agents ara Mercapto compounds, optionally having a hydrocarbon chain of at least eight carbon atoas. Exsaples of suitable aercapto chain transfer egents include aethyl thloglycolata; aethyl-3-aercaptoproplonate; ethyl thloglycolate; butyl thioglycolate; butyl-3-aercaptoproplonate; isooctyl thloglycolate; isooctyl-3-aercaptopropionate; isodecyl thioglycolate; isodecyl-3-aercaptopropionate; dodecyl thioglycolate; dodecyl-3-aercaptopropionate; octadecyl thioglycolate; and octadecy 1-3 -aercaptopropionate. Parathlocresol; thioglycolic acid; and 3-aercaptopropionic acid aay also be used, but aay display soaa incompatibility with tha resin and aay produce odor probleas.

A particularly preferred chain transfer agent is octadecyl-3-aercaptopropionate (ODKP).

The chain transfer agent aay, if used, coaprise froa about 0.1 percent to about 10.0 percent by weight of the coaposition based upon the total weight of the A through E ingredients. Preferably, the chain transfer agent coaprises froa about 0.25 percent to about 5.0 percent by weight, and still aore preferably froa about 0.5 percent about 4.0 percent by weight, based on the total weight of the five A through E coaponents. A suitable chain transfer tgant, when incorporated at about a 1.0 percent by weight level, lowers the glaaa transition temperature of the coaposition by about 3*C, lovers the aodulus by about 100 pal, and apparently increases the adhesion of the coating to the glass fiber. When greater than about 2.0 percent by weight of the chain transfer agent is incorporated in the coaposition, the aodulus and glass transition v 14APD *24 24?148 taaperature of tha coaposition ere desirably levered, but the shelf life is reduced soaevhat.

To iaprove shelf life (storage stability) of the uncured coating, as veil as to increase tharasl and oxidative stability of the cured coating, one or aore stabilisers aay be Included in the coaposition. Examples of suitable stabilisers Include tertiary aaines such as diethylethanolaaine and trihexylaaine; hindered aaines; organic phosphites; hindered phenols; aixtures thereof; and the like. Soae particular exaaples of antioxidants which can be used Include octadecyl-3-(3 •, 5 *-di-tert-butyl-4'-hydroxyphenyl) propionate; thiodiethylene bis (3 f 5-di-tert-butyl-4-hydroxy) hydrocinnaaate; and tetrakis [Methylene (3,5-di-tert-butyl -4 -hydroxyhydrocinnaaate) ] aethane.

When a stabilizer is used, it aay be incorporated in an aaount froa about 0.1 percent to about 3.0 percent, based on the veight of the A through E ingredients. Preferably, it is included in the range froa about 0.25 percent to about 2.0 percent by veight, and aore preferably in the range froa about 0.5 percent to about 1.5 percent by veight, based on the total veight of the A through E ingredients. Desirable properties of a stabilizer include (1) non-aigration (probably enhanced by lov polarity) and (2) basicity (to allov it to help in neutralizing residual acid vhich aight prematurely initiate polyaerization). Preferred stabilizers are octadecyl-3-(3',5•-di-tert-butyl-4'-hydroxyphenyl) propionate and trihexylaaine.

A preferred priaary coaposition for coating an optical fiber, then, coaprises the folloving: (A) froa about 45 percent to about 65 percent by veight of an aliphatic urethane acrylate oligoaer having as a backbone a hydrogenated 1,2-polybutadiene polyaer; (B) froa about 10 percent to about 20 percent by veight of lauryl acrylate; 242146 (C> fro* about 15 parcant to about 30 parcant by vaight of polypropylana glycol nonylphenyl athar acrylata; (D) froa about 0.3 parcant to about 1.0 parcant by vaight of gamma aarcaptopropyl trimethoxy ailane adhaaion promotsr; (E) froa about 2.0 parcant to about 7.0 parcant by vaight of hydroxycyclohaxylphanyl ketone photoinitiator; (T) froa about 0.5 parcant to about 4.0 parcant by vaight of octadecyl-3-mercaptoproplonate, a chain tranafar agent; and (C) froa about 0.5 parcant to about 1.5 parcant by vaight of octadacyl 3-(3• ,5'-di-tert-butyl-4 hydroxyphenyl) propionate; vharain all of tha atatad percentages ara parcantagaa by vaight, baaed upon total vaight of (A) through (E), inclusive.

THE SECONDARY COATTNG The aoat important propartiaa of tha aaeondary optical fibar coating ara again good thermal, oxidative and hydrolytic stability; hardnaaa; high modulus; high glass transition teaperature; and high rafractiva indax. Tha aaeondary coating of tha praaant invention vaa thus formulated to poaaaaa these and other qualities. Again, tha aaeondary coating of tha praaant invantion conpriaas (Z) froa about 20 parcant to about 80 parcant by vaight of an aliphatic urethane acrylata oligoaar baaed on a polyester; (ZI) froa about 20 parcant to about 60 percent by veight of an acrylatad or mathacrylatad compound selected from the group consisting of hexanadiol diacrylate; haxanadiol dimathaerylata; isobomyl acrylate; isobomyl aethacrylate; C, to aaturatad hydrocarbon diol diacrylates; C, to C14 aaturatad hydrocarbon diol dinethacrylatesi and mixtures thereof; and (ZZZ) from about 1.0 parcant to about 10 parcant by vaight of a photoinitiator, all of tha statad percentages by vaight baing basad upon tha total vaight of (Z), (ZZ) and (ZZZ).

Z. Tha Aliphatic Drathana Aervlata Ollooaar Tha first asaantial coaponent (Z) of tha aaeondary coating coaposition is an aliphatic urathana acrylata oligoaar basad on a polyester.

Commonly used oligoaers in UV-curing systeas include acrylated polyesters, epoxies and urethanes. Acrylatad polyesters are undesirable inasauch as they are susceptibla to hydrolysis on high teaperatura hydrolytic aging. Acrylated epoxies have unaccaptabla thermal and oxidative stability probleas and are prone to yelloving. With respect to the acrylated urethanes, both aroaatic and aliphatic isocyanate-based urethanes are available. The aroaatic urethanes have poor thermal and oxidative stability, but the aliphatic urethanes do not possess these deficiencies.

The backbone of aost commercially available urethane acrylates is of a polyether or polyester nature. Both of these backbones have inherent disadvantages. The polyethers are generally hydrolytically stable, but are susceptible to oxidation. The polyesters, on the other hand, are oxidatively stable but susceptible to hydrolysis. Polyesters can be protected from hydrolysis by aaxiaizing the foraulation hydrophobicity via the selection of hydrophobic monomers, initiators, additives, and so forth, and/or by selection of inherently hydrophobic polyesters. Foraulation hydrophobicity can be improved in the saae aanner vhen polyether-based urethanes are used...

APR ■ 46 However, vith polyether-based urethanes, it is also necessary to sdd various tharsal stabilizers and antioxidants. Thus, the preferred approach is to use hydrophobic polyester-based urethanes that are protected fros hydrolysis via selection of other formulation constituents so as to saxisise overall foraulation hydrophobicity. This is important because the overall physical properties of the coating are dramatically reduced if it absorbs water.

A suitable base oligomer, then, is an aliphatic urethane oligomer having a polyester backbone. An example of a particularly desirable one is an acrylated aliphatic urethane oligomer, containing 75 percent oligomer solids in a hexanediol diacrylate solvent. A suitable oligomer is Cargill 1512, available fros Cargill Inc., Minneapolis, MN, which comprises 75 percent by weight of an acrylic aliphatic urethane oligomer based on a polyester in 25 percent by weight hexanediol diacrylate. The oligoaer component coaprises froa about 20 percent to about 80 percent by weight, aore preferably 30 percent to about 80 percent by weight, and still aore preferably froa about 40 percent to about 80 percent by weight of the total weight of the essential coaposition, dry solids basis, the above percentages being based on the weight of oligoaer only.

II. The Acrvlate-Functional Compound Component: The second component in the secondary coating is an acrylated or aethacrylated compound (II). The function of this coapound is to adjust the viscosity of the coating to one which renders it easy to apply to the buffer-coated fibers. The coapound is one which is hydrocarbon in nature so as to render it hydrophobic and to Bake it coapatible with the rest of the systea, < ah£ u / c ' '4 *42146 28- preferably vblcfa contains • bicyclic structure so that it is lev shrinking.

Suitable aonoaers include isobomyl acrylate; isobomyl methacrylate; C« to Cw saturated hydrocarbon diol serylates or aethacrylates such ss s mixture of Clt end Cu diol diecryletes or dimethacryletes, or hexanediol diacrylate or hexanediol dimetbacrylete, or mixtures of these. A mixture of isobomyl acrylete and hexanediol diacrylate (the hexanediol diacrylate being provided as the reactive solvent for the oligomer) is a preferred constituent. The acrylated or methacrylatad component (ZZ) comprises from about 20 percent to about 60 percent by veight of the coaposition, mors preferably from about 25 to about 50 percent, and still aore preferably froa about 30 to about 40 percent by veight, based on total veight of the (Z), (ZZ) and (ZZZ) components, dry solids besis. zzz. iht Phptplnitlatpr As vith the priaary coating, a photoinitiator (ZZZ) is a desirable coaponent of the secondary coating. Any of the acceptable photoinitiators disclosed as suitable for the primary coating are again suitable; again, the preferred photoinitiator is hydroxycyclohexylphenyl ketone. The photoinitiator is used in an amount that is effective to initiate radiation curing of the coaposition, and may comprise from about 1.0 percent to about 10 percent by veight, based on the total veight of (Z), (ZZ) and (ZZZ), preferably from about 1.5 to about 8 percent by veight, and more preferably froa about 2.0 percent to about 7.0 percent by veight of the photoinitiator, based on the veight of the (1), (ZZ) and (ZZZ) coaponents, is used.

Generally, a lover level of photoinitiator is acceptable and desirable in the secondary coatii^r v \ 14 A 2 4 2• b relative to the primary coating. First of all, the aaeondary coating has a highar acrylata functionality relative to the primary, and ia inherently faster curing than the primary. Xiao, in order to maximize the amount of light available to cure the primary coating through the aaeondary coating, it ia iaportant not to use too auch photoinitiator in the aaeondary coating, as in the caae where the coatings are applied vet-on-vet and than simultaneously cured.

As vith the primary coating, various stabilizers may be incorporated, including but not limited to one or more of organic phosphites, hindered phenols, hindered aaines, mixtures thereof, and the like. A particularly preferred stabilizer ia thiodiethylene bis (3,5-di-tert-butyl -4 -hydroxy) hydrocinnamate. When used, the stabilizer may be present in amounts of from about 0.1 percent to about 3 percent by veight, more preferably from about 0.25 percent to about 2 percent by veight, and still more preferably froa about 0.5 to about 1.5 percent by veight, based on the veight on the total veight of tha (I) oligomer, (ZI) monomer and (ZZZ) photoinitiator.

A preferred secondary coating coaposition for coating an optical fiber, then, coaprises the folloving: (I) froa about 40 percent to about 80 percent by veight of an aliphatic urethane acrylate oligomer based on a polyester; (ZZ) froa about 30 percent to about 40 percent by veight of a mixture of isobomyl acrylate and hexanediol diacrylate; and (ZZI) froa about 2.0 percent to about 7.0 percent by veight of hydro xycyclohexylphenyl ketone photoinitiator, vherein all of the stated percentages are by veight based upon total veight of (I), (XX) and (ZZI). 14 | f u Hore preferably, this coapositlon also includes fros •bout 0.5 psrcsnt to about 1.5 peresnt by vaight, basad on ths veight of tha cosposition, of s stabilissr such •s thiodisthylsns bis (3,5-di-tsrt-butyl-4-hydroxy) hydrocinnaaate.

Tha aodulus of tha aaeondary costing should ba at lsast about 40,000 psi. Tha rslativsly high aodulus of ths sscondsry costing ralativs to ths priasry rssults in dssirsbls properties, such ss cut-through rssistsncs and alcrobending rssistsncs, and in ths formation of slick fibers, allowing for sssy spooling snd unspooling.

In s prsfsrrsd sabodiasnt, ths sscondsry costing of ths invsntion aay bs ussd ovsrtop a priaary coating. Howsvsr, in anothsr sabodiasnt, optical fibsrs asy be coated dirsctly with the sscondsry costing, ©sitting a priaary coating lsysr. Such conditions whsrs only a sscondsry costing asy suffics includs those in which ths fibsr will not be sxpossd to sxtrsass in teapereturs; to high huaidity; or to an sxessaivs saount of bonding.

Such usss aight includs long haul applications such as transocsanic or transcontinsntal cables wherein the fibers are enclosed in cabling saterial.

PREPARATION OF A COATED OPTICAL FIBER The invention also relates to s process for prsparing a coatsd optical fiber. The process coaprisss (i) applying to an optical glass fiber s priaary coating layer coaprising (A) froa about 20 percent to about 80 percent by veight, bassd upon totsl wsight of (A). (B), (C), (D) and (E), of an acrylatsd urethane oligoaer which is the reaction product of (i) a hydrocarbon polyol; (ii) an aliphatic polyisocyanate; and (iii) an endcapping aonoaer selected fros the group consisting of hydroxyalkylacrylate and hydroxyalkylaethacrylate; 14 Apr /992 242146 (B) fros about 5 parcant to about SO parcant by vaight, baaed upon total vaight of (A), (B), (C), (D) and (E), of an alkyl acrylata or aathacrylate aonoaer having 6 to 18 carbon atoas in tha alkyl aoiety; (C) froa about 5 parcant to about 60 parcant by vaight, baaad upon total vaight of (A), (B), (C), (D) and (E), of a aonoaer or oligoaar having (1) an aroaatic aoiaty, (2) a aoiaty having acrylic or aathacrylic unsaturation, and (3) a hydrocarbon aoiaty which aonoaar or oligoaar is capabls of incraasing tha rafractiva indax of tha coaposition ralativa to that of a coaposition containing only (A), (B), (D) and (E); (D) froa about 0.1 parcant to about 3.0 parcant by vaight, basad upon total vaight of (A), (B), (C), (D) and (E), of an organofunctional silana adhasion proaoter; and (E) froa about 1.0 parcant to about 10 parcant by vaight, basad upon total vaight of (A), (B), (C), (D) and (E), of a photoinitiator; (ii) applying atop said priaary coating layar a secondary coating layar comprising (I) from about 20 parcant to about 80 parcant by weight, based upon tha total veight of (I), (II) and (III), of an aliphatic urethane acrylate oligoaer based on a polyester; (II) froa about 2 percent to about 60 percsnt by veight, based upon the total veight of (I), (II) and (III), of an acrylated or aathacrylated coapound selected froa the group consisting of isobomyl acrylate; isobomyl nethacrylate; C, to Cx, saturated hydrocarbon diol diacrylates; C, to C14 saturated hydrocarbon diol dimethacrylates; and mixtures thereof; and (III) from about 1 percent to about 10 percent by weight, based upon the total weight of (I), (II) , ahd"/" (III), of a photoinitiator; and, preferably, / f44PRl992 242146 (111) radiation-curing Id li&U Mid priMry and aaeondary coating layers.

In an alternate eabodlaent, the process coaprises applying only the secondary coating of tha invention to the optical fiber and radiation-curing the secondary coating Id ll£U* The priaary and/or secondary coatings My be applied and cured by any aethod known in the art. A preferred aethod, whereby two coatings are applied wet-on-wet, is disclosed in U.S. Patent 4,474,830 to C.

Taylor of AT&T Bell Laboratories. Tha coating or coatings My then be cured iD situ. preferably by ultraviolet irradiation, to obtain a cured polymeric coating. Alternatively, the priaary coating My be applied and cured, after which the secondary coating My be applied and cured.

COATED OPTICAL FIBERS OF THE INVENTION The invention further relates to optical fibers, and especially to glass optical fibers, that are coated with the secondary coating of the invention alone, or coated with both the priMry and secondary coatings. The priaary coating surrounding the fiber fonas a cured polyaeric material having a glass transition teaperature, Tg, of at least -20*C, and preferably lower, i.e., about -30*C, or even lover.

The Tg of the cured priMry coating should be lover than the lovest use teaperature, but high enough so that its aodulus increases as the temperature is love red.

This characteristic offsets the difference in the coefficients of thermal expansion between the secondary coating and the optical fiber, and thus ainiaizes m.icrobending and resultant signal attenuation.

The cured secondary coating should have a relatively high Tg, generally approximately 50*C, and a; L!% 14 APR 1992 '•2146 high modulus, i.e., about 100,000 psl. Zt is desirable for ths sscondsry costing to havs a Tg hlghsr than its highsst uss temperature. nils is because at or nsar ths Tg of ths polymer, ths physical propsrtiss change dramatically vith snail changss in temperature.

Whan cured, the tvo coatings of ths invsntion confsr extraordinary thermal, hydrolytic and oxidative stability to the fiber and relievs stress thereon. Optical fibers having applied thereto both the primary and sscondary coatings of the invention are highly moisture resistant and otherviee protected froa environmental damage.

The coating compositions of ths pressnt invsntion have been disclosed hereinabove for use aa optical fiber coatings. Hovever, it is to bs understood that these coatings may be used in any embodiment vherein stable, moisture resistant coatings ars desired, especially for coating the surface of an optically useful article. For example, the coatings may be used for such diverse end uses as coating sheet glass (i.e., in the preparation of safety glass) to coating vinyl materials (e.g., in preparing no-vax floors). Other optically useful articles vhich may be prepared include, but are not limited to, photosvitches, photorelay devices, microelectronic devices, photocoupling devices, and so forth.

EXMPlCi The folloving Examples serve to further illustrate the invention. In these examples and elsevhere throughout this application, all parts and percentages are by veight, on a dry solids basis, and all temperatures are in degrees centigrade unless expressly stated to be othervise. In all of the examples, cure speeds were measured vith an International Light IL 745- - • 14 242146 A radiometer vith model A309 light bug. Unlike in the remainder of the application, where percentages by weight referred to the total weight of either the A through E ingredients for the primary coating, or the I through ZIZ ingredients for the secondary coating, respectively, parts sy weight in the Examples refers to the total composition described in that Example, including all components. The optional Ingredients are identified by an asterisk (*) in the Examples. The other components are essential for use, if the exemplified coating is to meet the rigorous requirements for a commercially acceptable coating for optical glass fiber. ' c V £ * '4 apr tin > 0 242146 rY"Blt T Primary Coating for Optical Fibars An ultraviolet-curable, priaary coating coaposition vaa made up as follows: Inorodlent Part« bv toifht. aliphatic urathaxia acrylata oligoaar with saturated hydrocarbon backbone (A) 55.00 polypropylene glycol nonylphenylether acrylate (C) 19.50 lauryl acrylata (B) 14.50 hydroxycyclohexylphenyl ketone photoinitiator (E) 6.00 octadecy1-3-mercaptopropionate chain transfer agent * 2.75 octadecyl-3-(3•, 5•-di-tert-butyl-4'-hydroxyphenyl) propionate stabilizer * 1.50 gamma-mercaptopropyl trinethoxy silane adhesion promoter (D) 0.75 The viscosity of the uncured coating was 40C-5 cps (at 25*C using a Brookfield viscometer, model LVT, 6 rpm, #34 spindle).

A six oil coating of this composition was applied to a flat glass sheet using a Bird applicator and cured in air at 0.7 J/cm* using a 200 watts par inch medium pressure mercury vapor lamp.

The cured primary coating which resulted had a glass transition temperature of about -39.6*C, and a cured film refractive index of 1.492. The effect of temperature on modulus was as follows: 25'C: 153.0 psir^t 0*C: 167.8 psi; -20*C: 864.7 psi; -40*C: 49,807 psi;.' f U Apr /992 36- 242146 -60°C: 199,0X8 psi. Ths curs speed, ss determined by s modulus versus doss curve, was determined to bs about 0.3 J/CB*.

Natsr absorption of ths sample was msasursd as follows. Ths cured film was aquilibratsd at 50% (±5%) relative humidity and 23'C (12*C) for 48 hours. The sample was weighed and a weight "A" recorded. The sample was then soaked for 24 hours at 25*C in distilled water, then patted dry and weighed. This weight was recorded as "BM. The sample was next placed in a vacuum oven under 10mm Hg pressure at 25*C for 24 hours, removed, and again equilibrated at 50% (±5%) relative humidity at 23'C (±2*C) for 48 hours and weighed. This third weight was recorded as "C". Percent water absorption measured as B-C x 100% A was about 1.48%.

Other samples of this 6 mil thick coating were tested as follows to determine the effect of accelerated aging on various properties. The samples were equilibrated at 50% (±5%) relative humidity and 23*C (±2*C) for 48 hours and then placed on clips and hung in an environmental chamber under the following accelerated aging conditions: (1) 125"C for 7 days; (2) 93.3*C for 10 days; (3) 93.3*C for 30 days; (4) 93.3*C, 95% relative humidity, for 10 days; (5) 93.3'C, 95% relative humidity, for 30 days. ■ o\ X <4 apk w;: 242146 After the designated time period, the samples vere removed end again equilibrated for 48 hours. The following properties were recorded. These data indicate excellent stability against thermal end hydrolytic •trees. 125*C, 7 flttVI weight change -7.68% 93.3*C, 93.3'C, . 95% 95% relative relative 93.3*C, 93.3'C, humidity, humidity, 10 flBYI 3Q 30 davB -6.71% -6.98% -0.71% -1.62% Tg midpoint -34.6'C -34.6#C -36.6*C -35.5*C -36.6'C Znstron modulus change (at *C) +33.1% +39.4% +37.9% +27.9% +19.5% EMMlt II Another Primary Coating for Optical Fiber An ultraviolet radiation-curable priaary coating was aade up as follows: Inqrtflicnl Parts bv weight aliphatic urethane acrylate oligoaer with saturated hydrocarbon backbone (A) 56.00 polyethylene glycol nonylphenyl ether acrylate (C) 25.00 isodecyl acrylate (B) 11.75 hydroxymethy lpheny 1 - propanone photoinitiator (E) 6.00 thiodi ethylene bis (3,5—di—tert-butyl-4-hydroxy) hydrocinnamate stabilizer * 0.50 J 4 APR $92* 242146 guu aereaptopropyl trlaethoxy silane adhesion proaoter (D) 0.75 Tha above foraulation used several different ingredients, and aomevhat diffarant proportions, than vera used in Exaapla I. Thia foraulation had a viacoaity of 5650 cpa at 25*C using a Brookfield viscometer, aodel LVT, 6 rpm, #34 spindle, and a rafractiva indax of 1.4849 at 21.6*C. Whan coated onto a glaaa plata in tha saaa aannar as in Exaapla I and cured in air at 0.7 J/cm* under a medium pressure 200 vatta par inch aercury vapor laap, tha resultant 6 ail thickness coating had a aodulus of 295.8 psi, a Tg of -28.7'C, good adhesion to glass and lov vatar abaorption (2.02%). The coating perforaed vail in high huaidity and dry accelerated aging teats.

E*»bp1# hi A Further Primary Coating for Optical Fiber The folloving priaary coating vas formulated: Ingredient aliphatic urethane acrylate oligoaer vith saturated hydrocarbon backbone (A) polyethylene glycol nonylphenylether acrylate (lover HW polyethylene glycol than that of Exaapla ZI) (C) octyl/decyl acrylate (B) hydroxyaethylpheny1-propanona photoinitiator (E) thiodiethylene bis (3', 5 *-di-tert-butyl-4-hydroxy) hydrocinnaaate stabilizer * gamma-mercaptopropyl Parts bv Weight 56.00 .00 11.75 6.00 ^ <y s o 0.50 .. * J f ,4^P(?I992' ^ ,o/ 242146 triaethoxy silane adhesion (D) 0.75 This foraulation demonstrated tha usa of alternate (B) and (C) aaterials. This foraulation had a viscosity of 3890 cps at 25*C using a Brookfield viscometer, aodel LVT, spindle #34, 6 rpm. When applied to a glass plate as in Exanple I and cured in air at 0.7 J/ca# under 200 watt per inch aediua pressure aercury vapor laap, it had a aodulus of 276.0 psi, good adhesion to glass, and low water absorption (1.89%).

Example TV Another Priaarv Coating for Optical Flbere The following priaary coating was fornulated: Inqrtdlcnt Parts bv Weight aliphatic urethane acrylate oligoaer vith saturated hydrocarbon backbone (A) 64.00 polyethylene glycol nonylphenylether acrylate (saae MW as in Exanple III) (C) 8.00 isodecyl acrylate (B) 20.50 hydroxyaethy lpheny 1 * propanone photoinitiator (E) 6.00 thlodiethylene bis (3 •, 5 • -di-tert-butyl-4 • -hydroxy) hydrocinnaaate stabilizer * 0.50 r / ^ o * v z ganaa-nercaptopropyl triaethoxy silane adhesion promoter (0) 0.35 , l4APRm isooctyl-3-nercaptopropionate chain transfer agent * 0.65 This foraulation demonstrated the use of different proportions of ingredients, the use of an alternate 242146 chain transfer agent, and the use of a lev concentration of the coaponent (C) to adjust the refractive index. The foraulation had a viacoaity of 5950 cpa at 25*C uaing a Brookfield viscometer, model LVT, 6 rpa, 134 ■pindie, and a refractive index of 1.4796 at 21.5'C. When applied to a glaaa aheet aa a 6 ail coating aa in Exaapla J and cured in air at 0.7 J/ca* under a aediua preaaure 200 watts per inch aercury vapor leap, it had a aodulua of 2B0 pai, a Tg of -31.2*C, good adheaion to glaaa, and low water absorption (1.41%). exMPit y A Slower Curing Primary Coating for Optical Flbarg A radiation curable priaary coating waa foraulated aa followa: Ingraflitnt Parta bv Wight aliphatic urethane acrylate oligoaer with saturated hydrocarbon backbone (A) 54.00 polypropylene glycol nonylphenylether acrylate (C) 19.50 lauryl acrylate (B) 14.00 hydroxycyclohexylpheny1 ketone (E) 6.00 octadecyl-3-aercaptopropionate chain tranefer agent * 4.00 octadecyl-3(3',5'-di-tert-butyl-4 '-hydroxy phenyl) propionate atabilizer * 1.50 gaaaa-aethacryloxypropyl triaathoxyailane adheaion proaoter (D) 1.00 o\ * '4 APR ™ 41- The viscosity of ths uncursd costing vss 3750 cps (st 25*C using s Brookfield viscometer, aodel LVT, 6 rpa, 134 spindle).

When coated on a glass sheet at 6 ails and cured as in prsvious examples, the coating adhered veil under high huaidity conditions but cured such slover than the coating of Exaapla I. Siailar formulations can be prepared that have much more rapid rates of curs, by substituting acrylated silanes for the methacrylated silane ussd in this Example.

The cured primary coating vhich resulted had a glass transition temperature of about -39.4'C, a modulus of 155.5 psi, and a cured film refractive index of 1.492. The cure speed vas determined to be 0.5 J/cm2, and the vater absorption vas 1.40%, both being determined according to the methods of Example I.

Weight change, glass transition teaperature and Instron modulus change vere measured under the same conditions as in Example I and recorded to be as follovs. Again, excellent hydrolytic and thermal stability vas observed. 125'C, i days veight change -7.94% 93.3'C, 93. 3*C, IP days 3Q days -6.84% 93.3'C, 93.3'C, 95% 95% relative relative humidity, humidity, davs 30 days -7.19% -1.97% -1.58% Tg midpoint -35.9*C -36.1'C -35.5'C -35.7-C -36.4*C Instron aodulus change (at *C) +33.8% +36.1% +36.0% +20.1% +10.9% „ > " i < 0 A \ 14 APR 1992 -42 242146 ataroit yx A Secondary Coating for Optical Flbera A radiation-curable, aaeondary coating compoaition vaa Bade up aa follows: Ingriditnt Parte bv Weight aliphatic urethane acrylate oligoaer with polyeater backbone, in 25% (baaed on weight of oligomer end advent only) hexanediol diecrylate solvent * (solvsnt only is optional) (I) 82.00 laobomyl acrylate (II) 13.00 hydroxycyclohexylpheny1 ketone photoinitiator (III) 4.00 thiodiethylene bis (3,5-di-tert-butyl-4'-hydroxy) hydrocinnaaate stabilizer * 1.00 A six ail coating of the above coapoaition was applied to a glaas plats using a Bird applicator. The coating waa cured in air at 0.7 J/ca2 uaing a aediua pressure 200 watts per inch mercury vapor leap. The reaulting film of the aecondary coating exhibited a aodulus of about 103,700 psi, a water absorption of about 1.68%, and a cured filn refractive index of about 1.506. The cure speed, as determined by a modulus versus dose curve, vas determined to be about 0.3 J/cm2. The UV transmisaion of the uncured coating was determined to be about 73% by calculating the ratio of the light transaission of a 1 ma quartz slide containing a 1 ail coating of the uncured composition to that of the slide without the coating on it.

Weight change and Instron modulus change (here measured at 85*C) were measured under the same conditions as in Example I and recorded to be as follows. Again, excellent hydrolytic and thermal stability vaa observed. \ '4APRI9 43 242146 125*C, 7 day veight change -4.60% Instron aodulus change at (85*C) 417.2% 93.3"C, 93.3'C, 95% 95% relative relative 93.3*C, 93.3'C, humidity, humidity, dav 30 dftYi IP dflYl *0 <*av -3.91% -4.30% -0.85% -1.10% +18.3% +34.3% -4.3% -23.9% EXAMPLE YXI Another Secondary Coating for Optical Fibers A secondary coating identical to that of Kxaftple VI, except for containing 14.00% isobomyl acrylate and no optional stabiliser, vas formulated. The coating, when applied to glass and cured as above, had good tensile properties, cure speed, vater absorption, UV transmission and stability, but yelloved on dry age testing.

Exarole VIII A Coatino Having a High To and High crpiglinX Ptnsity A coating composition vas formulated as follovs: Ingredient part« bv v*iaht aliphatic urethane acrylate oligoaer vith polyester backbone (I) (uaed as a mixture containing 12% hexanediol acrylate) dipentaerythritol monohydroxy pentaacrylate a mixture of linear CJt and C13 diol diacrylates 60.00 15.00 IO.M- | 40 -44* isobomyl acrylate (XI) 11.00 hydroxycyclohexylphenyl ketone photoinitiator (ZZZ) 4.00 Tha aliphatic urethane acrylate oligoaer (I) is believed to heve imparted good properties. Formulations such as the above perform veil on thermal, oxidative, and hydrolytic aging tests, with almost no yelloving characteristics. The oligoaer (Z), as available coanercially, cures to a lover aodulus than the oligoaer used in Example VI in solution.

The aixture of C14 and C19 diol dlacrylates vas used as a viscosity adjuster in conjunction vith the isobomyl acrylata.

The above foraulation vas applied to glaas as a 6 mil coating using the coating technique of Exaaple I, and UV-cured. it had a high Tg and high crosslink density as compared to the coating of Example VI.

A similar formulation vas prepared, but incorporating about 0:5 parts by veight of a 50:50 mixtures of bis (2,4-di-t-butylphenyl) pentaerythritol phosphite and thiodi ethylene bis (3,5-di-t-butyl-4-hydroxy) hydrocinnaaate, as a stabilizer package. On evaluation, hydrolytic stability deteriorated, probably because of the use of the phosphite. This is undesirable for optical fiber coatings, but is not a problem for many other coating applications. When the hindered phenol is used above as the stabilizer at the 1% level, hydrolytic stability is again acceptable for optical fiber coating use. c V "V £ ^ \ 14 APR J992^ > 242146 gy»»nl« TY A rurthtr Coating Formulation The following coating coaposition was prepared: Inqrtfllwit Parti by Weight aliphatic urethane eery late oligoaer with polyeeter backbone (I) 59.50 dipenteerythritol monohydroxy pentaacrylate 14.50 isobomyl acrylate (II) 11.00 a mixture of linear C14 and C13 diol diacrylates 10.00 hydroxycyclohexylphenyl ketone photoinitiator (III) 4.00 thiodiethylene bis (3,5-di-tert-butyl-4-hydroxy) hydrocinnaaate stabilizer * 1.00 This coating coaposition exhibited a slightly slower curing rate than the foraulation of Example VI, apparently, based on cure speed versus modulus data. This data may have given a false impression because of the high Tg and high crosslink density of this coating. However, the hydrolytic aging properties of this coating, while good, were not guite as good as those of the Example VI coating. Its viscosity and room temperature moduli were similar to those of the Example VI formulation. Its properties overall are such that it is an acceptable secondary coating for glass optical fibers. 14 APR J9, S 242146 eONCIHSIOH Optical glaaa fibars coated vith the primary and secondary coatinga of the preaent invention heve been designed to possess several important qualities rendering the coeted fibers useful for many applications and particularly auitabla in local aree natvorks for fiber-to-the-home uaea.

The primary coatinga, vhen cured, poaaeaa a refractive index graater than that of tha underlying fiber (i.e., about 1.48), a modulus of less than about 500 psi and a glass tranaition temperature of leas than about -20*C, and preferably lees than about -30"C. The primary coatings are sufficiently hydrophobic to resist moisture penetration and consequent hydrolysis of the underlying optical fibers; have a sufficiently low modulus to cushion and protect the fibers; and a sufficiently low glass transition temperature so as to remain rubbery and thus act as a cuahion to the glass fibers throughout the possible use temperature range of the fibers.

The secondary coatings after cure function as a hard, protective layer having a glass transition temperature of about 50*C, and a modulus of about 100,000 psi. Furthermore, the secondary coatings are resistant to moisture and have an appropriate coefficient of friction for their desired use. The secondary coatings have a coefficient of friction allowing the coated fibers to slide easily along each other vhile staying aligned on a spool.

Both the primary and secondary coatings have suitable viscosities for coating and, vhen cured, contain minimal quantities of unbound reactants (volatiles) and have good shelf life characteristics. o i ~ 14 *Pk I9K The present invention peraits the production of costing formulations seating these criteria, end the aanufacture of coated optical fibers veil suited for use in fiber-to-the-hoae applications.

There are aany uses for coetings that are prepared in accordance vith the Invention, that do not have to neet the etringent requirements iaposed on optical fiber coatings. Thus useful coatings for aany purposes aay be forauleted, comprising: (A) froa about 20 percent to about 60 percent by veight of an acrylated urethane oligoaer vhich is the reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polyisocyanate; and (iii) an endcapping aonoaer selected froa the group consisting of hydroxyalkylacrylate and hydroxyalkylmethacrylate; (B) a lov Tg, soft curing, hydrocarbon aonofunctional acrylate aonoaer; (C) a chain transfer agent comprising a hydrocarbon chain having at least eight carbons in its hydrocarbon chain; and (D) a stabilizer or antioxidant that imparts added shelf life and storage stability to the coating composition, the combination of (B), (C), and (D) vith (A) having the effect of producing a coating of mutually compatible ingredients, that is radiation-curable. Preferably, the (B) component comprises from about 5 percent to about 50 percent by veight (based on the total veight of (A) and (B)) of an alkyl acrylate or methacrylate monomer having betveen 6 and 18 carbon atoms in the alkyl moiety, and the glass transition temperature of the coating containing it is -20*C or less. The composition may be, in one embodiment, used as a primary coating for an optical fiber, the coating having an uncured liquid viscosity at 25*C of about 4,000 to 10,500 cps and a .9 *6 cured aodulus of less than 500 psi (at room teaperature, based on a 6 ail thick fila).

In other eabodiaents, coapositions of this kind can be formulated to be useful as interlayers for laainated safety glass, and as coatings for electronic devices such as photocells and photosvitches, for exaaple.

In still other eabodiaents, the coaposition additionally aay comprise any or all of (C) froa about 5 percent to about 60 percent by veight of a aonoaer or oligoaer having (1) an aroaatic aoiety, (2) a aoiety containing acrylic or aethacrylic unsaturation, and (3) a hydrocarbon aoiety, which aonoaer or oligoaer is capable of increasing the refractive index of the coaposition relative to that cf a coaposition containing only (A) and (B); and/or (0) an aaount of an organofunctional silane adhesion pronoter that is effective to pronote adhesion to the surface of a vitreous substrate; and/or (E) an anount of a photoinitiator that is effective to pronote radiation-curing of said coating, the coaposition incorporating (C) and/or (D) and/or (E) preferably still having glass transition teaperature, uncured liquid viscosity, and cured tensile aodulus and storage stability in the saae ranges as in the coaposition absent these coaponents.

While the invention has been disclosed in this patent application by reference to the details of preferred eabodiaents of the invention, it is to be understood that this disclosure is intended in an illustrative rather than in a limiting sense, as it is conteaplated that Dodifications vill readily occur to those skilled in the art, vithin the spirit of the invention and the scope of the appended claims. '4 APR 199}' ' ' ^ 0 -o-

Claims (2)

1. WHAT WE CLAIM IS: 1. A radiation-curable priaary coating for an optical fibar coaprising (A) from substantially 20 percent to suDstantially 80 percent by vaight of an acrylatad urethana oligoaar which ia tha reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polyisocyanate; ' and (iii) an endcepping aonoaer selected froa the group consisting of hydroxyalkylacrylate and hydroxyalkylaethacrylate; (B) from substantially 5 percent to substantially 50 percent by veight of an alkyl acrylate or aathacrylate aonoaer having between 6 and 18 carbon atoas in the alkyl aoiety; (C) from substantially 5 percent to substantially 60 percent by veight of a aonoaer or oligomer having (1) an aroaatic aoiety, (2) a aoiety containing acrylic or aethacrylic unsaturation, and (3) a hydrocarbon aoiety, which aonoaer or oligoaer is capable of increasing the refractive index of the coapoaition relative to that of a coaposition containing only (A), (B), (D) and (E); (D) from substantially 0.1 percent to substantially 3.0 percent by veight of an organofunetional silane adhesion proaoter; and (E) from substantially 1.0 percent to substantially 10 percent by veight of a photoinitiator, vherein all of the stated percentages are percentages by veight based on total veight of (A), (B), (C), (D) and (E).
2. 2. A radiation-curable priaary coating for an optical fiber according to claia 1 vherein said hydrocarbon polyol (i) is selected froa the group consisting of fully or partially hydrogenated 1,2-polybutadiene rf polyol; 1,2-polybutadiene polyol hydrogenated to an iodine nuaber of froa 9 to 21; fully or partially hydroganatad polyisobutylene polyol; and Mixtures thereof. • X radiation-curable priaary coating for an optical fiber according to claia 1 wherein said non-aromatic polyisocyanata (ii) is selected froa the group consisting of isophorone diisocyanate; dicyclohexylaethane-4,4*-diisocyanate; hexa aethy 1 ene diisocyanate; and trlmethylhexaaethylene diisocyanate. • X radiation-curable priaary coating for an optical fiber according to claia 1 vherein said oligoaer (A) is endcapped vith hydroxyethyl acrylate. A radiation-curable primary coating for an optical fiber according to claia 1 vherein said oligoaer (A) is characterized by the fornula XOCNHRaNHCORlOCNHR2NHCOQ r u i where R1 is a linear or branched hydrocarbon polyaer of fron 600 to 4,000 aolecular veight selected fros the group consisting of fully or partially hydrogenated 1,2-polybutadiene; 1,2 -polybutadiene hydrogenated to an iodine number of froa 9 to 21; and fully or partially hydrogenated polyisobutylene; R* is a linear, branched or cyclic alkylene of from six to twenty carbon atoas; and X and Q are independently either (a) a radical of tha formula: 2421A 6 -- wherein RJ' R4' and R* are independently hydrogen, methyl, ethyl or propyl,m is an integer from 1 to 10, and p is either zero or one, or (b) a saturated alkyl radical of froa nine to twenty carbon atoms, vith the proviso that said oligomer must possess at least one acrylate or methacrylate terminal group. A radiation-curable priaary coating according to claim 1 vherein said monomer (B) is selected froa the group consisting of hexyl acrylate; hexyl methacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl methacrylate; isooctyl acrylate; isooctyl methacrylate; octyl acrylate; octyl methacrylate; decyl acrylate; decyl methacrylate; isodecyl acrylate; isodecyl methacrylate; lauryl acrylate; lauryl methacrylate; stearyl acrylate; stearyl methacrylate; Clt-C13 hydrocarbon diol diacrylates; Cn^Cis hydrocarbon diol dimethacrylates; and mixtures thereof. A radiation-curable primary coating according to claim l vherein said monomer (B) is selected from the group consisting of lauryl acrylate; stearyl acrylate; isodecyl acrylate; and mixtures thereof. A radiation-curable coating according to claim 1 wherein said monomer or oligomer (C) is selected -52- •*2146 froa tha group consisting of polyalkylene glycol nonylphsnyl sthsr scrylstss; polyalkylene glycol nonylphsnyl sthsr aethacrylatea; and aixtures thsrsof. 9. A radiation-curable coating according to claia l vherein said aonoaar or oligoaar (C) is sslsctsd froa tha group consisting of polyathylana glycol nonylphsnyl sthar acrylata; polypropylana glycol nonylphanyl athsr acrylats; and aixtr.rea thsrsof. 10. A radiation-curabla priaary coating according to claia 1 vharsin said silans adhssion proaotar (D) ia sslsctsd froa ths group consisting of aaino-functional silanss; aarcapto-functional silanas, aathacrylata functional silaneii; acrylaaido-functional silanas; allyl-functional silanes; vinyl-functional silanas; acrylate-functional silanas; and aixturea thereof. 11. A radiation-curabla priaary coating according to claia 1 vherein said silans adhssion proaoter CD) is selected froa the group consisting of mercaptoalkyl trialkoxy silane; aethacryloxyalkyl trialkoxy silane; aainoalkyl trialkoxy silans; and aixturea thereof. 12. A radiatiw ^-curable priaary coating according to claia 1 vherein said silane adhesion proaoter (D) is gaaaa-aercaptopropyl trinethoxy silane. 13. A radiation-curable priaary coating for optical fibers according to claia 1 vherein said photoinitiator (E) is selected froa the group consisting of hydroxycyclohexylphenyl ketone; / hydroxynethylphenyl propanone; diaethoxyphenyl o ■, 1\\ * 1992^1 53 acetophenone t 2-aethy1-1, 4-(methyl thle) phenyl-2-aorpholino-propanone-1 ; l-(4-isopropylpheny1 )-2-hydroxy-2-aethylpropan-l-one : 1-(4-dodecy lpheny l) - 2-hydroxy-2-asthylpropan-1-onet 4 -(2-hy dr oxye thoxy) phenyl - 2 (2 -hydroxy-2 -propy 1 ketone; diethoxyacetophenone; 2,2-di-sec-butoxyacetophenone t diethoxy-phenyl acetophenonej and aixtures thereof. X radiation-curable priaary coating for an optical fiber according to claia 1 whs rein said photoinitiator (E) is hydroxycycl ohexy lpheny 1 ketone. X radiation-curable priaary coating for an optical fiber according to claia 1 additionally comprising from substantially 0.1 percent to substantially 10 percent by veight, based on total veight of (X), (B), (C), (D) and (E), of a aercapto functional chain transfer agent (F). X radiation-curable priaary coating for an optical fiber according to claia 15 vherein said chain transfer agent (F) is selected froa the group consisting of aethyl thioglycolate; methyl-3-mercaptopropionate; ethyl thioglycolate; butyl thioglycolate; butyl-3-aercaptopropionate; isooctyl thioglycolate; isooctyl-3-aercaptopropionate; isodecyl thioglycolate; isodecyl-3-aercaptopropionate; dodecyl thioglycolate; dodecyl- 3-mercaptopropionate; octadecyl thioglycolate; octadecyl-3-mercaptopropionate; and mixtures thereof. -54- *: A 6 17. A radiation-curable priaary coating for an optical fibar according to claia 15 vharain said chain transfar agent ia octadacyl-3-aarcaptoproplonata. 16. A radiation-curabla priaary coating for an optical fibar according to claia 1 additionally conprising from substantially 0.1 percent to substantially 3.0 percent by vaight, baaad on total vaight of (A), (B), (C), (D) and (E), of a stabiliser (G) aalactad froa tha group consisting of organic phosphitss; hindsrsd phsnols; amines; and aixtures tharsof. 19. A radiation-curabla priaary coating according to claia 18 vharain said stabilizar is trihsxylaaine. 20. A radiation-curable priaary coating for an optical fiber according to claia 1 additionally comprising a stabilizer (G) which is octadecyl-3-(3',5'-di-tert-butyl-4 1-hydroxy phenyl)propionate. 21. A radiation-curable primary coating for an optical fiber, comprising (A) from substantially 45 percent to substantially 65 percent by weight of an aliphatic urethane acrylate oligoaer having as a backbone a hydrogenated 1,2-polybutadiene polymer; (B) from substantially 10 percent to substantially 20 percent by weight of lauryl acrylate; (C) from substantially 15 percent to substantially 30 percent by weight of polypropylene glycol nonylphenyl ether acrylate; (D) from substantially 0.3 percent to substantially 1.0 percent by weight of gamma mercaptopropyl trimethoxy silane adhesion promoter; and 55 L^L no (E) from substantially 2.0 percent to substantially 7.0 percent by vaight of hydroxycyclohexylphenyl katonc photoinitiator, vharain all of tha stated parcantagaa ara percentagea by vaight, basad upon total vaight of (A), (B), (C), (D) and (E). A radiation-curabla priaary coating for an optical fibar according to claia 21 additionally coaprising from substantially O.b percent to substantially 4.0 percent by veight, bassd on total vaight of (A), (B), (C), (D) and (E), of octadacy1-3-aercaptopropionata. A radiation-curabla priaary coating for an optical glass fiber according to claia 22 additionally comprising from substantially 0.5 percent to substantially 1.5 percent by veight, based upon total veight of (A), (B), (C) , (D) and (E), of octadecyl 3-(3',5*-di-tert-butyl-4 •-hydroxyphenyl) propionate. A radiation-curabla secondary coating for an optical fiber coaprising (I) from substantially 20 percent to substantially 80 percent by veight of an aliphatic urethane acrylate oligoaer based on a polyester; (II) from substantially 20 percent to substantially 60 percent by veight of an acrylated or aethacrylated coapound selected froa the group consisting of isobomyl acrylate; isobomyl aethacrylate; C, to Clt saturated hydrocarbon diol diacrylates; c« to Cj, saturated hydrocarbon diol diaethacrylates; and aixtures thereof; and (III) from substantially 1 percent to substantially 10 percent by veight of a photoinitiator, vherein all of the stated percentages are percentages by veight based on total veight of (I), (II) and (III). -5«- 242146 25. A radiation-curable secondary coating for optical fibars according to claia 24 vharain aaid coapound (ZZ) ia a mixture of iaobornyl acrylate and hexanediol diacrylate. 26. A radiation-curable secondary coating for an optical fiber according to claia 24 additionally coaprising a stabiliser sslsctsd froa ths group consisting of aaines, hindered phenols, organic phosphites and aixturss thsrsof. 27. A radiation-curable secondary coating for an optical glass fibsr according to claia 26 vherein said stabilissr is thiodisthylsns bis(3,5-di-tert-buty 1-4-hydroxy) hydrocinnaaate. 28. A radiation-curable secondary coating for an optical fiber according to claia 24 vherein said photoinitiator is hydroxycyclohexylphenyl ketone. 29. A radiation-curable secondary coating for an optical fiber coaprising (I) from substantially 40 percent to substantially 80 percent by veight of an aliphatic urethane acrylate oligoaer based on a polyester; (II) from substantially 30 percent to substantially 40 percent by veight of a aixture of isobomyl acrylate and hexanediol diacrylate; and (III) from substantially 2.0 percent to substantially 7.0 percent by veight of hydroxycyclohexylphenyl ketone photoinitiator, vherein all of the ' stated percentages are by veight based upon total veight of (Z), (II) and (III) wherein the percentages selected from within the stated ranges add up to 100%. A coated optical fiber coaprising an optical fibar, a priaary coating layar and a aaeondary coating lay«r, vharain said priaary coating layar coaprises (A)' from substantially 20 percent to substantially 80 percent by vaight, baaad upon total vaight of (A), (B), (C), CD) and (E), of an acrylatad urathana oligoaer vhich is the reaction product of (1) a hydrocarbon polyol; (ii) a non-aromatic polyisocyanate; and (Hi) an endcapping aonoaer selected froa the group consisting of hydroxyalkylacrylate and hydroxyalkylaethacryl ate; (B) from substantially 5 percent to substantially 50 percent by veight, of an alkyl acrylate or aethacrylate aonoaer having betveen 6 and 18 carbon atoas in the alkyl aoiaty; (C) from substantially 5 percent to substantially 60 percent by veight of a aonoaer or oligoaer having (1) an aroaatic aoiety, (2) a aoiety containing available acrylic or uethacrylic unsaturation, and (3) a hydrocarbon aoiety, vhich aonoaer or oligoaer is capable of increasing tha refractive index of the coaposition relative to that of a composition containing only (A), (B), (D) end (E); (D) from substantially 0.1 percent to substantially 3.0 percent by veight of an organofunctional silane adhesion proaoter; and (E) from substantially 1.0 percent to substantially 10 percent by veight of a photoinitiator, vherein all of the stated percentages are percentages by veight based on total veight of (A), (B), (C), (D) and (E), and said secondary coating layer coaprises (I) from substantially 20 percent to substantially 80 percent by veight of an aliphatic urethane acrylate oligomer based on a polyester; -5«- 2421^6 (XI^: from substantially-"20 percent to substantially-60 percent by weight of an acrylated or aethacrylatad coapound aalactad froa tha group conalating of isebornyl acrylata; laobornyl aathaerylata? Ct to CM aaturatad hydrocarbon diol diacrylataa; C« to Cu aaturatad hydrocarbon diol diaathacrylataa; and mixtures tharaof; and (III) from substantially 1 percent to substantially 10 parcant by vaight of a photoinitiator, vharain all of tha above parcantagaa for aaid aaeondary coating ara parcantagaa by vaight baaed on tha total veight of (I), (II), and (III). 31. A coated optical fiber-according to claim 30, comprising a glass optical fiber, wherein said primary and secondary coating layers vara radiation cured subsequent to application on said glass fiber. 32. A coated optical fiber coaprising an optical fiber having applied thereto a coating layer coaprising (I) from substantially 20 percent to substantially 80 percent by veight of an aliphatic urethane acrylate oligomer based on a polyester; (II) from substantially 20 percent to substantially 60 percent by veight cf an acrylated or aethacrylated compound selected from the group consisting of isobomyl acrylate; isobomyl methacrylate; C« to Cu saturated hydrocarbon diol diacrylates; C» to Cit saturated hydrocarbon diol diaethacrylates; and mixtures thereof; and (III) from substantially 1 percent to substantially 10 percent by veight of a photoinitiator, vherein all of the above stated percentages are percentages by weight based on the total veight of (I), (II) and (III). / 1 t v \ es r r 242^0 33. A coated optical fiber comprising an optical fiber having applied thereto a coating layar, comprising (I) from substantially 30 percent to substantially 80 percent by weight of an aliphatic urethane acrylate oligomer basad on a polyester; (II) from substantially 25 percent to substantially 50 percent by weight of a mixture of isobomyl acrylate and hexanediol diacrylate; and (III) from substantially 1.5 percent to substantially 8 percent by weight of hydroxycyclohexylphenyl ketone photoinitiator, wherein all of the stated percentages are by weight based upon total weight of (I), (II) and (III) wherein the percentages selected from within the stated ranges add up to 100X. 34. A coated optical fiber comprising a glass optical fiber, and a continuous coating applied to and surrounding said fiber and formed of a cured polymeric material having a Tg of -20*C or lover. 35. The coated optical fiber of claim 34 wherein said coating comprises a primary coating layer and a secondary coating layer, both formed of cured polymeric material. 36. The coated optical fiber of claim 35 wherein both of said coating layers are formed from unsaturated materials that are radiation-curable and that are both radiation-cured jjj situ. 37. A process for preparing a coated optical fiber comprising (i) applying to an optical fiber a primary coating layer comprising 60- (A) frswn'substantial!y*20percemrto substantially*80"percent by weight of an acrylatad urethane oligoaar which is tha reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polylsocyanate; and (iii) an andcapping aonoaar aalactad froa tha group consisting of hydroxyalkylacrylate and hydroxya Iky laethacry late / (B) from substantially 5 percent to substantially 50 percent by vaight of an alkyl acrylata or aathacrylata aonoaar having batvaan 6 and 18 carbon atoas in tha alkyl aoiaty; (C) from substantially 5 percent to substantially 60 percent by waight of a aonoaar or oligoaar having (1) an aroaatic aoiaty, (2) a aoiaty containing acrylic or aathacrylic unsaturation, and (3) a hydrocarbon aoiaty, vhich aonoaer or oligoaar ia cap&bla of incraasing tha rafractiva index of tha coaposition relative to that of a coaposition containing only (A), (B), (D) and (E) ; (0) from substantially 0.1 percent to substantially 3.0 percent by weight of an organofunctional silane adhesion proaoter; and (E) from substantially 1.0 percent to substantially 10 percent by weight of a photoinitiator, wherein all of the stated percentages are percentages by weight based on total weight of (A), (B), (C), (D), and (E); and (ii) applying atop said priaary coating layer a secondary coating layer coaprising (1) from' substantially 20 percent to substantially 80 percent by veight, based upon total veight of (I), (II) and (III), of an aliphatic urethane acrylate oligoaer based on a polyester; (II) from substantially 20 percent to substantially 60 percent by veight, based upon total veight of (I), (II) and (III), of an acrylated or aethacrylated coapound selected froa the group consisting of isobomyl acrylate; isobomyl aethacrylate; C, to Clc saturated hydrocarbon diol diacrylates; C, to 61 6 saturated hydrocarbon diol diMthacrylates; and aixtures thereof; and (III) from substantially 1 percent to substantially 10 peccent by weight, baaed upon total weight of (X), (II) and (III), of a photoinitiator. A proeeas according to claia 37 vherein said priaary and secondary coating layera are radiation-cured by ultraviolet irradiation. A radiation-curable coating for tha surface of an optically useful article coaprising (A) from substantially 20 percent to substantially 80 percent by veight of an acrylated urethane oligoaer vhich is the reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polyisocyanate; and (iii) an endcapping aonoaer selected fros the group consisting of hydroxyalkylacrylate and hydroxyalkylaethacrylate; (B) from substantially 5 percent to substantially 50 percent by veight of an al)cyl acrylate or nethacrylate aonoaer having between 6 and 18 carbons in the alkyl aoiety; (C) an effective aaount not in excess of substantially 60 percent of a monomer or oliqomer containing acrylic or aethacrylic unsaturation, that is capable of adjusting the refractive index of the coaposition relative to that of a coaposition containing only (A), (B), (D) and (E) ? (D) a saall but effective aaount of an organofunctional silane adhesion proaoter; and (E) a saall but effective aaount of a photoinitiator, wherein all of the stated percentages are percentages by weight based on total weight of (A), (B), (C), (D) and (E). -62- 2421^6 40. A radiation-curable coating according to claia 39 vharain said hydrocarbon polyol (i) la aelected froa tha group consisting of fully or partially hydroganatad 1,2-polybutadiena polyol; 1,2-polybutadlana polyol hydroganatad to an iodina nuaber of froa 9 to 21; fully or partially hydroganatad polyiaobutylana polyol; and aixtures thereof. 41. A radiation-curable coating according to claia 39 vharain aaid organic polyiaocyanata (11) ia selected froa the group conaiating of iaophorone diiaocyanata; dlcyclohexylaethane-4, 4 • -diisocyanate; hexaaethylene diisocyanate; and triaethylhexaaethylene diiaocyanata. 42. A radiation-curable coating according to claia 39 vherein said oligoaer (A) is endcapped vith hydroxyethyl acrylate. 43. A radiation-curable coating according to claia 39 vherein said oligoaer (A) is characterized by the foraula R1 is a linear or branched hydrocarbon polyaer of froa 600 to 4,000 aolecular vaight selected froa the group consisting of fully or partially hydrogenated 1,2-polybutadiene; 1,2-polybutadiene hydrogenated to an iodine nuaber of froa 9 to 21; and fully or partially hydrogenated ; t t f. r • polyisobutylene; < ( where \ 14 Apa 63- R* is a linear, branched or cyclic alkylena of froa six to tvanty carbon atoui and X and Q ara indapandantly aithar (a) a radical of tha foraula: vharain R1, R*' and Rs ara indapandantly hydrogen methyl, ethyl and propyl, ■ la an integer froa 1 to 10, and p is either zero or ona, or (b) a saturated alkyl radical of froa nine to tventy carbon atoas, vith the proviso that said oligoaer aust possess at least ona acrylate or aethacrylate terminal group. A radiation-curable coating according to claia 39 vherein said aonoaer (B) is selected froa the group consisting of hexyl acrylate; hexyl aethacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl aethacrylate; isooctyl acrylate; isooctyl aethacrylate; octyl acrylate; octyl aethacrylate; decyl acrylate; decyl aethacrylate; isodecyl acrylate; isodecyl aethacrylate; lauryl acrylate; lauryl aethacrylate; stearyl acrylate; stearyl aethacrylate ; C, 4-Ci3 hydrocarbon diol diacrylates; C^-C^ hydrocarbon diol diaethacrylates; and aixtures thereof. A radiation-curable coating according to claia 39 vherein said aonoaer (B) is selected froa the group consisting of lauryl acrylate; stearyl acrylate; isodecyl acrylate; and aixtures thereof. 46. A radiation-curable coating according to claia 39 vharain said aonoaar or oligoaer (C) is sslsctsd froa tha group consisting of polyalkylane glycol nonylpheny1 ether acrylates; polyalkylene glycol nonylphenyl ether aethacrylates; and aixtures thereof. <7. a radiation-curable coating according to claia 39 vherein said aonoaer or oligoaer (C) is selected froa the group consisting of polyethylene glycol nonylphenyl ether acrylate; polypropylene glycol nonylphenyl ether acrylate; and aixtures thereof. 48. h radiation-curable coating coaprising (A) from substantially 20 percent to substantially 80 percent by veight of an acrylated urethane oligoaer vhich is the reaction product of (i) a hydrocarbon polyol ; (ii) a non-aromatic polyisocyanate; and (iii) an endcapping aonoaer selected froa the group consisting of hydroxyalkylacrylate and ♦ hydroxyalkylaethacrylate ; (B) a lov Tg, soft curing, hydrocarbon monofunctional acrylate aonoaer; (C) a chain transfer agent coaprising a hydrocarbon chain having at least eight carbons in its hydrocarbon chain; and (0) a stabilizer or antioxidant that iaparts added shelf life and storage stability to the coating coaposition, the combination of (B), (C), and (D) vith (A) having the effect of producing a coating of mutually compatible ingredients that is radiation-curable and that has a lover Tg and a lover modulus than (A) alone, and that has improved storage stability as compared to a composition of (A), (B), and (C) alone, wherein the percentages stated above are percentages by weight based on the total weight of (A) and (B). 65- 24214 49. A radiation-curable coating compoaition comprising (A) from substantially 20 percent to substantially 80 percent by veight of aaid compoaition of an acrylatad urethane oligomer vhich ia the reaction product of (i) a hydrocarbon polyol; (ii) a non-aromatic polyiaocyanate; and (iii) an endcapping monomer selected from the group consisting of hydroxyalkylacrylate and hydroxyalkylmethacrylate; (B) at least one low Tg, soft curing, hydrocarbon monofunctional scrylate monomer; (F) a chain transfer agent, (C) a stabilizer or antioxidant that imparts added shelf life and storage stability to the coating composition, and the combination of (B), (F), and (C) vith (A) having the effect of producing a coating composition of mutually compatible ingredients that is radiation- curable, wherein the percentages stated above are percentages by weight based on the total weight of (A) and (B). 50. A composition of claim 48 vherein said (B) monomer comprises from substantially 5 percent to substantially 50 percent by veight of an alkyl acrylate or methacrylate monomer having betveen 6 and 18 carbon atoms in the alkyl moiety, vherein the percentages stated above are percentages by veight based on the total veight of (A) and (B). 51. A composition of claim 48 vherein said chain transfer agent (C) comprises a mercapto-functional chain transfer agent having a hydrocarbon chain having at least eight carbons in its hydrocarbon chain. 52. A composition of claim 49 vherein said chain A * ' fj transfer agent (7) coaprises a aercapto-functional chain transfer agent having a hydrocarbon chain having at least eight carbon* in its hydrocarbon chain. 53. A coaposition of clsia 49 further comprising an aaount of an organofunctional silane adhesion proaoter effective to enhance the adhesion of said coaposition to the surfece of en inorganic substrate of glass, marble, granite, or like vitreous or inorganic surface, or to the surface of an optical fiber. 54. A coating coaposition of claia 48 further comprising an aaount of a photoinitiator that is effective to pronote radiation-curing of said coating. 55. A coating composition of claia 53 further comprising an aaount of a photoinitiator that is effective to pronote radiation-curing of said coating. 56. A composition of claim 50 that, when cured, has a lover Tg and a lower modulus than would be the case if the (A) oligomer were cured alone*, and that has improved storage stability as compared to a composition of (A) , (B), and (F) alone. 57. A composition of claim 56 wherein said cured coating Tg is -20'C or less. 58. A coating composition of claim 57 that can be used as a primary or buffer coating for an optical fiber and that has an uncured liquid viscosity at 25*C in the ranqe from substantially 4,000 cps to substantially 10,500 cps, 9 c -67- as lufurtd on a Brookfield vi»eoMt«rf model LVT, at 6 rpa, using a number 34 spindle at 25 *C. 59. A coating coaposition of claia 58 vharain said compoaition, vhan cast aa a fila of 6 ail thickness and curad, has a tanaila aodulus at room temperature of less than 500 psi. 60. A coating composition of claia 52 further comprising (C) from substantially 5 percent to substantially 60 percent by veight of a monomar or oligomer having (l) an aroaatic moiety, (2) a aoiety containing acrylic or methacrylic unsaturation, and (3) a hydrocarbon moiety vhich monomer or oligomer is capable of increasing the refractive index of the composition relative to that of a coaposition containing only (A) and (B). 61. A coating composition of claim 60 further comprising (D) an amount of an organofunctional silane adhesion promoter that is effective to promote adhesion of the composition to the surface of an optical fiber. 62. A coating composition of claim 61 further comprising an amount of a photoinitiator that is effective to promote radiation-curing of said coating. 63. A coating composition of claim 61, the combination of (B), (C), (D), (F), and (G), vith (A) having the effect of producing a coating composition of mutually compatible ingredients, that is radiation-curable, and that has a lover Tg and a lover j t r~ C '< n -68- aodulus than (A), (B), and (C) alone, and that has iaproved storage atability as coapared to a coaposition of (A), (B), and (C), alona. 64. A coating coaposition of claia 62 that haa a curad Tg of -20*C or laaa. 65. A coating coaposition of claia 63 that haa an uncurad liquid viscosity at 25"C in tha ranga from substantially 4,000 cps to substantially 10,500 cps, as measured at 25'C uaing a Brookfield Viscoaeter, Model LVT, at 6 spa, using a nuaber 34 splhdle. 66. A coating coaposition of claia 64 having a tanaile modulus at room temperature of less than substantially 500 pal. 67. An optical fiber coated vith a cured coaposition according to claia 60. 68. A radiation-curable coating coaposition coaprising (I) from substantially 20 percent to substantially 80 percent by veight of an aliphatic urethane acrylate oligoaer based on a polyester; (II) from substantially 20 percent to substantially 60 percent by veight of an acrylated or aethacrylated coapound selected froa the group consisting of isobomyl acrylate; isobomyl aethacrylate; C, to Cu saturated hydrocarbon diol diacrylatea; C, to Clt saturated hydrocarbon diol diaethacrylates; and aixtures thereof; and (ZZI) an aaount of a photoinitiator that is effective to initiate radiation curing of said coating, u Z'l 2 1 i 71. 72. vharsin *11 of the above stated pcretnUftB ara percentages by vaight based on the total vaight of (Z), (ZZ) and (ZZI). A radiation-curabla coating according to claim 68 vharain said coapound (ZZ) ia a mixture of isobomyl acrylata and hexanediol diacrylata. A radiation-curabla coating according to claia 68 additionally coaprising a stabilirar salactad froa the group consisting of aaines, hindered phenol*, organic phosphites and aixtures thereof. A radiation-curable coating according to claia 70 vherein said stabilizer is thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy) hydrocinnaaate. A radiation-curable coating according to claia 68 vherein said photoinitiator is hydroxycyclohexylphenyl ketone. An optical fiber coated vith a cured coaposition according to claia 68. 70 74. A radiation-curable priMry coating for an optical fiber accordinq to claim 1 substantially as hereinbefore described with reference to any one of the Examples. 75. A radiation-curable secondary coating for an optical fiber according to claim 24 substantially as hereinbefore described with reference to any one of the Examples. 76. A coated optical fiber according to claim 30 comprising an optical fiber, a primary coating layer and a secondary coatinq layer substantially as hereinbefore described with reference to any one of the Examples. 77. A coated optical fiber according to claim 32 substantially as hereinbefore described with reference to any one of the Examples. 75. A process fcr preparing a coated optical fiber according to claim 37 substantially as hereinbefore described with reference to any one of the Examples. 79. A radiation-curable coating for the surface of an optically useful article according to claim 39 substantially as hereinbefore described with reference to any one of the Examples. 80. A radiation-curable coating accordinq to claim 48 substantially as hereinbefore described with reference to any one of the Examples. 81. A radiation-curable coating composition accordinq to claim 49 substantially as hereinbefore described with reference to any one of the Examples r- / . -