CA2024379A1

CA2024379A1 - Primary coating compositions for optical glass fibers

Info

Publication number: CA2024379A1
Application number: CA002024379A
Authority: CA
Inventors: Erwin S. Poklacki; Timothy E. Bishop
Original assignee: DeSoto Inc
Current assignee: DeSoto Inc
Priority date: 1989-09-01
Filing date: 1990-08-31
Publication date: 1991-03-02
Also published as: WO1991003503A1; AU6406490A

Abstract

Abstract of the Disclosure Polyurethane (meth)acrylate oligomers having a (meth)acrylate functionality of about 1.9 or less and photocurable liquid coating compositions including the oligomer are disclosed. These compositions comprise the oligomer and a mono(meth)acrylate.

Description

` 2024~79 ~. , .. . -, ..
~ - .
PRIMARY COATING COMPOSITIONS FOR OPTICAL GLASS FI~ERS

~echnical Field This invention relates to polyurethane (m-th)acrylate oligomersi and coating compositions eontaining the same which ar- suitable a~ primary coatings for optical glass fibers The coatings exhibit a redueed modulus and improved adhesion to glass Back~round of the Invention Optical glass fibers ar- freguently coated with two sup~rpos-d photocured coatings ~he coating which contacts th- glas~ i- a rolatively soft, primary ~ ;
coating The out-r, exposed coating is a much harder s-condary coatlng that provides resistance to handling forc--, such a~ those neounter-d when the fiber is eabl-d The coating of optical glass fibers with photocured coating compositions, usually usiing --ultraviol-t light, ii w-ll known today Photocuring eompo~ition- ar- s-l-ct-d b-cau~- of th-ir rapid cure Jp--d F~t-r cur- iopeod i- gen-rally desirable to incr-a~- th- produetion of optical gla-s fibers Important prop-rtie~ of th- cured coating includ- adh-~ion to th- gla~-, resistance to wat-r ; 25 ab~orption and r-sistanc- to microbending especially at low ~-rvic- t-mperatures Conv-ntional compositions typically include an acrylate-t-rminated polycarbonate diol-based ;
polyurethanes Coating- produced from these ~ f '~'~'''.'~.,~,' conv-ntional composition- hav- an acrylate functionality ~ ;
of 2 or mor- and ar- too hard to b- utilized as primary -coating-. Th-~- eoatings can also exhibit poor adhesion ~nd poor r--i-tanc- to microb-nding When th- usual mono~meth)acrylate th-rs having a low glass transition 3S t-mper~tur- ar- added to th-s- compo~ltion~ in an amount uffieient to provid~ adequat- flexibility, the water -~ -'~ ~' .", ~ 202~379 r~sistance and adhesion o~ the coating can be und--irably reducQd Th- present invention provides compositions suitabl- tor us- ag a primary optical glass fiber S eoating and eomprises a polyur-thane ~meth)acrylate oligom-r having a (meth)aerylat- tunctionality ot about 1 9 or 1-5~ and a mono(meth)acrylat- Coatings produced ther-from ar- soft and fl~xibl- while retaining good wat-r resistanc- and adh~sion Summarv of the Invention Thi- inv-ntion provid~s n-w polyurethane ~m-th)acrylat~ oligomers and photocurable liguid coati~g eompo-itionJ containing th- sam- Tho eoating eompo-ition i- suitabl- tor us- as a primary coating for lS optieal glas- fib-rs Th- oligom-r eomprises the r-aetion product ot ~ prepolymer or admixtur- of pr-polym r-, a diisocyanat-, and a hydroxy ~m-th)aerylat-, and has a ~meth)aerylat- funetionality ~;
of about 1 9 or 1--- Pret-rr-d pr-polym-rs ar-polyearbonat- diols that ar- pr-s-nt in an amount uttiei-nt to provid- xe-s- hydroxy tunetionality as ~ eompar-d to th- tr-- nitrog-n-earbon-oxyg-n group ~NC0) ;;; tunetionality ot th- dii-oeyanat- a- redueed by tho ~; hydroxy tunetionality ot th- hydroxy ~m~th)aerylat- to 2S aehi-v- th- d-sir-d ~m-th)aerylate funetionality The ` eoating eompo-ition eomprises ~1) the polyurethan~
~mQth)aerylat- oligomer; and ~2) a mono~meth)acrylat- ! ~'' '';
having a glaJ~ transition t-mp-raturo ~T9) below ;~
about -20C
Th- eoating eompo-itlon ean also inelud- a small a ount ot a mono-thyl-nieally un-aturat-d material having ~ T~ gr-at-r than about 40C. and a strong eapaeity tor hydrog-n bonding Conv-ntional photoinitiator-, stabiliz-rs, .. ...
; 3S adh--lon promoter- and th- lik~ ean b~ pres-nt in the ~ ~; eoating eomposition ." ~ ';
. : -2~2~37g ~ ;
:: :

Coatings produced from the present coating composition have a high adhesion to glass, low water absorption and fast cure speeds. These coatings are flexibl-, exhibiting a very low ten~ile modulus, e.g., ;
S preferably le5g than about 1.5 megapascals (MPa).
A~ previously discuQsed, many conventional coating compositions include an acrylate-terminated polyurethane.having an acrylate functionality of 2 or more utilize a mono(meth)acrylate which is usually a ;:
polyether to provide, and ad~ust, the flexibility of the coatings made therefrom. However, these monotmeth)acrylate polyethers, which typically have a T
of less than about -40C, reduce the water resistance and th- adhesion of the coating. In contradistinction, lS th- present composition utilizes a polyurethane ~meth)acrylate oligomer having a (meth)acrylate functionality of about 1.9 or les~ which imparts flexibility to the coatings. This enables the ~-~
composition to better accommodate (1) the convent~onal mono~meth)acrylat- polyethers, as by reducing the amount utiliz-d, and ~2) a relatively higher T9, i.e., less than about -20C., mono~eth)acrylat- without sacrificing water resistance and adhesion to obtain the desired flexibility. In one embodiment of the present invention, the mono(meth)acrylate includes a (meth)acrylate of an alkoxylated phenol to obtain coatings that are even more flexible and maintain satisfactory water resistance and adhesion.
Coatings produced from the present composition can contain unreacted hydroxy groups if excess hydroxy functionallty i- utilized in the production of the oligomer. Unreacted hydroxy groups ar- conventionally expected to reduc- the water resistance of a coating due to the group's hydrophilic nature. However, the present coatings exhibit less loss of water resistance than is ` '' ~.

~` 202~379 expected for the amount of excess hydroxy functionality pro~ent ~ail-d Descri~tion of the Preferred Embodiment~
Although this lnvention is susceptible to S embodim-nts in many diffor-nt form~, preferred mbodim-nt~ of th- inv-ntion are shown It should be und-rstood, how-v-r, that th- pr-sent disclosurQ is to b- eonsid-r-d as an x-mplification of the principles of th- inv-ntion and is not intended to limit the invention to mbodiment~ illustrat-d A- pr-viously discussed, th- photocurable liguid eoating eomposition- disclosod herein ar-uitabl- for U5- as a primary eoating for optical glas~
fib r- Th- coating eomposition eompris-s ~1) the lS polyur-than- ~m-th)aerylat- oligom-r having a ~m-th)aerylate funetionality of about 1 9 or les~ and ~2) th mono~moth)aerylat- having a glass transition t-mp-ratur- ~T~) b-low about -20C
; Th- t-r~ ~funetionalityn, and various grammatieal form- th-r-of, indieat-s th- averag- number ~;
of group- pr-~-nt p-r mol-eul- of th- ref-rr-d to mat-rial that ar- eapabl- of parti¢ipating in a eh-mical r-aetion Th- numb-r a-~oeiat-d with tho term funetionality d-seribes th- av-rag- number of reactive ;~
group~ pr-s-nt p-r moloeul- For exampl-, tho phrase "a ~meth)aerylat- funetionality of about 1 9 or less" means that for a given sampl- of th- oligomer, th- sum of the ;~
meth)aerylat- group~ present divided by the number of ~ ;
oligomer mol-eule~ pre~-nt 1- about 1 9 or 1 Th- t-r~ ~meth)aerylat-~, and variou~
grammatleal forma th-r-of, id-ntlfl-J ster~ that are ;~
the reaetion produet of an aerylie or a mothaerylie aeid with the hydroxy group, or group~, of an aleohol or ~ oth-r hydroxy eontaining organie eompound ;~ 3S Th- t-r~ ~glas~ transition temperaturen, and ; variou~ grammatieal form~ th-reof, i~ defined a~ th- ~ ;
-: : :
:.'" ~"".
., . ~..~.
~... . , ~. .
~;~

;~` 202~379 ~

temperature at which the homopolymer of the referred to mat-rial ehanges from a vitreouQ state to a plastie ~ -state The polyurethane (meth)acrylate oligomer is the r-aetion produet of a prepolymer or mixture o~ ~`
prepolymer~, an orqanic diisocyanate and a hydroxy ~m-th)aerylat-Th- prepolymer 1~ a carbon chain that can compri~- oxyg-n and/or nitrogen atoms, the terminal ~m th)aerylat- funetionality i8 added to the prepolymer by U8- of th- diisoeyanat- Seleetion of the prepolymer ean aff-et the phy~ical properties of the eoatings produeed ~rom th- oligomer-eontaining composition ~^
Th- prepolymer has at least one prepolymér funetional group that is reactive with the isocyanate group, g , a hydroxy, m-rcapto, amine or similar group Pr-sently, a pr-ferred prepolym-r functional group i- the hydroxy group If th- prepolymer is mono~unctional it i- used in admixture with other polyfunetional pr-polym-r- in a proportion to obtain the d--ired (m-th)aerylat- funetionality of the oligomer Th- prepolymer, or admixtur- thereof, pr-t-rably ha- ~ funetionality Or about 1 5 to about 3, mo-t pref-rably about 1 8 to about 2 S, group- that are r-aetiv- with th- isoeyanat- group Th- numb-r av-rag- moleeular weight of the pr-polym-r i- about S00 to about 2,000, preferably about 800 to about 1,800, daltons Th- term "dalton~, in its various grammatical ~-form-, d-rines a unit of mas- that is 1/12th th- mass of ~-~
earbon-12 Pr-polym-r~ are s-leeted fro~ th- group eon-l~tlng Or polyearbonat-~, poly-st-r~, polyethers and mixtur-- th-r-ot 3S Th- polyearbonat- diol~ ar- eonventionally produeed by th- aleoholy-i~ ot di-thylearbonat- wlth a ~;

202~37g diol Th- diol is an alkylene diol having about 2 to about 12 earbon atoms, g , 1,4-butane diol, 1,6-hexane diol, 1,12-dodecane diol and th~ lik- Pref-rably, the diol ha- about 4 to about 8 carbon atoms Mixtures of S th-J- diol- c~n also b- utiliz-d The poIycarbonate diol ean eontain ether linkages in the backbone in addition to carbonat- groupo Thuo, polycarbonate copolym-r- o~ alkyl-n- oxid- monom-ro and the previously d-ocribed alkyl-n- diol~ ar- suitabl- Suitable alkyl-n- oxide monomers includ- ethylene oxide, t-trahydro~uran oxid- and the like The~e copolymers -produe- eured eoatings that xhibit a lower modulus and al~o inhibit cryotallinity o~ th- liquid coating eomposition, aJ compar-d to polycarbonate diol homopolym-r- Admixtur-o o~ polycarbonate diolo and ;~
polycarbonate copolym-rs ean b- utilized ;-Suitable polycarbonat- diols includ- Duracarb 122, comm rci~lly availabl- from PPG Industries and ... . ...
Permanol KM10-1733, comm-rcially availabl- ~rom ~ 20 P<rmuthan-, Ine , MA Duracarb 122 is produeed by the aleoholysi- Or di-thylearbonat- with h-xan- diol Illu~trativ- poly--t-r- inelud- polybutyl-ne adipat-, polycaprolaeton-~ and th- lik-Illustrativ- poly-ther~ inelud- poly(propylene ~ ~;
~- 25 oxid-), poly(tetram-thyl-ne glyeol) and the like A wid- variety o~ diiooeyanates alone or in admixtur- wit~ one another ean b- utilized Repr-o-ntat$v- diisoeyanateo inelud- isophorone dii-oeyanat- (IPDI), tolu-n- dii~oeyanate, methyl-ne diphenyl dii-oeyanat-, h-xam-thyl-n- diisoeyanat-, eyeloh-xyl-n- dii~oeyanat-, m-thyl-n- dicyclohexan~
dilJoeyan~t-, 2,2,4-trim thyl h-xam-thyl-n- ; ~;
dll~ocyanat-, m-phenylen- diioocyanat~
4-ehloro-1,3-phenyl-n- diisoeyanat-, 4,4'-biph-nyl-ne ;;
3S dlisoeyanat-, 1,5-naphthylen- diiJocyanate, 1,4-t-tram thyl-n- dliooeyanat-, 1,6-hexamethylene ., - . - . -~;

~l ` 20243~g :

diisocyanat-, l,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, and the like A
pr-~erred dii~ocyanate is IPDI
The hydroxy (meth)acrylat- can be a S mono~m-th)aerylat- or a poly(meth)acrylate Monohydric monoaerylates ar- pr-sently preferred The ~m-th)acrylat- terminal group in the oligomer is introduced with a urethane linkage by the reaction of th- isocyanat- group with a hydroxy group of the hydroxy ~m-th)acrylat-Suitabl- monohydric acrylates are the Ct-C~
alkyl acrylatos Illustrativ- of these acrylates are 2-hydroxy-thyl aerylato, 2-hydroxypropyl acrylate, and th- lik- Al~o ~uitabl- ar- reaetion products o~
lS 2-hydroxyl-thyl acrylate with one or more molecules o~
eaprolacton- Mixtures of these acrylates are also uitabl- The methacrylate counterparts of the above aerylat-s ean also b- utillzed Th- r-aetion to produe- th- oligomer is pr-f-rably eonduet-d in a diluent whieh reduce~ the vl~eo-lty of th- oligomer Thi~ us- o~ the diluent r--ults ln tb- formation o~ an oligomer-diluent admlxture havlng a vi-eo~ity that faellltates produetion o~ the eoating eomposition, albeit produetion ean oeeur as at an l-vat-d temperature which further reduees the vl~eo~lty I The diluent is preferably not reaetive in the oligomer synthe~is but is reaetive during the eure af ;~
th- eoating eompo~ition Th- admixing of th- diluent having a (meth)a¢rylat- funetional1ty o~ about 1 and the oligomer arlt~o-t~¢ally r--ult- ln th- av-rag- (meth)aerylat-fun¢tlonallty o~ th- oligomer-dilu-nt admixture being lower than th- ~m th)aerylat- funetionality of th-ollgomer How-v-r, th- oligom-r o~ th- pres-nt lnventlon has a (meth)aerylat- ~unetionality of about ~` ` 2~24379 !

1 9 or 1-~- before th- diluent is added du~ to the ch-mical r-action of producing the oligomer Th-s- diluQnt~ contribute to th- low modulu Or th- cur-d ~ilm and h-nce typically hav- a 1~ below S about -20C
Illu~trativ- of th-~- diluQnts are octyl/decyl acrylat- (an admixtur- of octyl aerylate and decyl aerylat-), polyt-tram-thyl-ne glyeol diaerylate, the mono~m-th)aerylat-s illu~trated hQreinafter, the like, and mixtur-~ th-reof A minor amount of a cataly~t for the ur-thane-forming r~action i~ typieally utilized, g , about 0 03 to about 0 1, pr-f-rably about O oS weight p-re-nt of dibutyl tin dilaurate ~-~lS A minor amount, i - , l-s~ than about 0 1 ;
-~ w-ight p-re-nt, Or a inhibitor ean b- present to control ;`~; th- ollgom-r produeing r-actlon Illustrative ;~
~` inhlbltor~ inelud- butylat-d hydroxy toluene, ` ph-nothlazln-, and th- llk-A parg- of in-rt ga~, g , dry air, nitrog-n, earbon dioxid- or th- lik , 1- utiliz-d to n-ure that th-r- 1- no moi-tur- pr---nt whieh ean ;`~
; adv-r--ly af~-et th- produetion or th- oligom r i~!~
Th- r-aetant- ~or th- produetion Or th- ~;
S ollgo~-r, i - , th- pr-polym r, th- diisoeyanate,~and `;
~9~ the hydroxy ~m-th~aerylat-, ean b- eom ined and riacted lmultaneously in a suitabl- v~sel -I ;
A pr~f-rr-d meithod of produeing th-polyur-than- tm-th)aerylat- oligom r i~ to introdue- th~
3Q~ dllu-nt, th- dii-oeyanat- and th- inhibitor into th~
ve---l and l-vat- th- t-mp-ratur- th-r-or to about 30C. to about 50C. while agltatlng and ~parglng wlth ~` an lnert ga- Th- agltatlon and th- parg- ar~
~i malntain-d throughout th- r-aetion. N-xt, th- eatalyst 3S ean be introdue-d lnto th- v-~-l Th- hydroxy j~ ~meth)aerylat- 1~ then ~lowly lntrodueed into th-,.x~
,I.......

~ 2024379 vessel, typically over a time period of about 15 minutes to about on- hour After the addition of the hydroxy (m-th)aerylate is eompleted, th- reaetion is maintalned at an elevated temperatur- for a time period sufficient to eonsume substantially all ot tho hydroxy funetionallty Or th- hydroxy ~meth)aerylate and produce a ~meth)acrylate-terminated ur-thane isocyanate For xample, at a temperature of about 30C to about 50C , substantially all of the hydroxy functionality is consumed in a time period of about 0 5 to about 2 hours Th- temperaturQ of th- reactants can then be increased to facilitat- admixing by further reducing the viscosity Subsequently, the prepolymer is introdueed into th- v-s~el and roact-d with th-~meth)acrylat--terminated urethan- isocyanate After introduction of the prepolymer, the temperature of the reaetant~ i~ further elevated to about 50C to about 70C and maintain-d at that temperature for a time p-riod sufficient to reduc- the NC0 content to les~ than about 0 2 p-re-nt, pr-f-rably 1eSJ than about 0 1 p-re-nt of th- oligomer Typieall~, this redueed NC0 eont-nt i~ aehi-v-d in a tim- p-riod of about 1 5 to about lO hour~, alb-it this reaetlon ean b- l-ft to run ov-rnight without advor~ely affeeting the oligomer 2S After th- de~ired NC0 content i~ achi-ved, additional diluent ean be added to produee an oligomer-diluent admixtur- having the desired viscosity at th-temperature at which subsequent admixing of the oligom-r-diluent admixture with the other eonstituents of th- pr---nt coating eomposition i- performed Thi- methoa ~f produeing th- oligomer is pr-f-rr-d b~eauJ- r-aetion of all of th- hydroxy funetlonality of th- hydroxy (m-th)aerylat- i- desired and thi- may not oeeur if th- prepolymer is reaet-d with th- diisoeyanato first or with the diisocyanate and the hydroxy (moth)acrylate -- 202~37~ ~ ~

, :.

If th- prepolymer utilized is an admixture of monofunctional and polyrunctional prepolymers, the mole p-re-nt of oach can b~ sel-cted to enable use of a toiehiometrically corr-ct proportion Or prepolymer admixtur- to NCO runctionality of thc diisocyanate after th- NCO ~unetionality 1- reduc-d by th- hydroxy - -runetionality of th- hydroxy ~m th)acrylate A
toiehiom-trie xe-~ ~uppli-d by th- polyfunctional pr-polym r can b- pre~ent in the prepolymer admixture Wh-n only a polyfunctional prepolymer is utiliz~d, ~toiehiometrie xcess of the polyfunctional pr-polymer i~ add-d to th- vessel to provide an excess ;~
Or pr-polymer functionality as compared to the NC0 funetionality pr---nt aft-r th- initial NCO ;
funetionality of th- diiJoeyanat- i~ ealculated to be, ~;
or ~etually, r-due-d by th- hydroxy funetionality of the hydroxy ~meth)aerylat- T~- amount Or this exeess pr-polym-r funetionality i- that whieh i~ e~feetive to ;~ ;
provid- a low r-d modulu~ and a coating that i~ ;
atl~factorlly prot-ct~ th- fiber This use Or an .. . .. ..
xe--- of pr-polym-r funetlonality re~ults in the -~
r-duetlon of th- ~m-th)aerylat- funetlonality Or the r--ultant oligomer to about 1 9 or 1--~ beeaus~
funetional group- from dlfr-r-nt polyfunetional ;;
2S pr-polym-r mol-eul-~ ar- avallabl- to react with the NCO ' ~ funetionallty This l-~-ns th- probability that two `~`` funetlonal group~ of a ~ingl- polyfunctional prepolymer -moleeulo oaeh will react with NCO funetionality to , l - -produe- an oligomer having a ~m-th)aerylate funetlonallty of 2 or mor- When only a polyfunetional ~ `
prepolym r ia utilized, th- mol- ratio of polyfunetional -~
pr-poly~ rs diisoeyanat-s hydroxy ~m-th)aerylat- i~ in a rango of ~bout 1 4 1 8 1 0, r-sp-etlv-ly, to about ~;
1 7 2 0 1 0, r-sp-etiv-ly 3S Ther- are two pr-f-rr-d way- to d-termine th-NCO funetionality pr-~ent for th- purpos- of ealeulating -. ~
: ~ , . ..
. '' `' '~
:.' ,,, `.--- ` 2~24379 :

11 , .
th- xcess prepolymer ~unctionality required when a poly~unctional prepolym-r is utilized One way is to subtract the hydroxy ~unctionality o~ the hydroxy (m-th)acrylat- ~rom th- NCO ~unctionality Or the S diisocyanat- Alternatively, and most preferably, the hydroxy (m-th)acrylat- and the diisocyanate are reacted, as de~cribed abov-, to consum- es~entially all of the hydroxy functionality of th- hydroxy (meth)acrylate and the NCO functionality of the resultant (m-th)acrylate-t-rminated urethan- isocyanate reaction product is then conv-ntionally m asured The proper amount of prepolymer can then b- calculated Pr-f-rably, up to ~bout 40, more preferably --about 10 to about 35, p-rc-nt excess prepolymer lS ~unctionality is pr-~-nt in th- oligomer when a poly~unctional prepolymer i~ utilized Thus, i~ the pr-polym-r is a polyhydroxy prepolymer such as a polycarbonat- diol th-n xce~- hydroxy functional~ty in th- abov- amounts would b- pre~-nt Th- (meth)acrylat- ~unctionality o~ th-ollgom-r 1- about 1 9 or 1---, pr-r-rably at lea~t about 1 5 and most pr-~-rably about l S to about 1 8 Th- numb-r av-rag- mol-cular weight o~ the polycarbonat- polyur-than- (m-th)acrylat- oligomer is as ~bout 600 to about lS,000, pr-ferably about 1,000 to about 5,000 daltons ~ ;
Although de~iring not to b- bound by a -particular theory, it is presently b-lieved that polymer chain-, provided by th- pr-polymor, having unreacted t-rminal group- extending ~ro~ tho oligomer reduc- the modulu- o~ th- cur-d coatlng b-cau~- they r-main ~re- to movo ~- th- cur-d coatlng 1- ~l-x-d Changing th-l-ngth and numb-r of th-~- ~r-- polym-r chain- changes tho modulu- obtaln-d 3S An addltlonal con-titu-nt o~ the coatlng composltion is th- mono(meth)acrylat- having a T~ below 2Q2~79 ~ -about -20C As previously di~cussed, the mono(meth)acrylato can function a~ a diluent during the ~ -production of the oligom~r Th- T~ of the mono(moth)acrylato can bo a~ low as about -90C
S Suitablo mono(meth)acrylate~ include ethoxy- -othoxy-thyl ~m th)acrylate, ph-noxyethyl (meth)acrylatQ, butoxy-thyl (meth)acrylat-, nonyl-~ub~tituted ph-noxyothyl (m-th)acrylato, and tho like Oth-r suitabl- mono(meth)acrylates include the ~m-th)acrylat- of th- C~-C10, pr-ferably C~-C9, alkyl ~ub~tituted phenol that i~ alkoxylated with a C2-C~
alkyl-n- oxide ~o that it contains about 1 to about 10 mol-- of tho oxid- per mol- of tho phenol Preferably, th- ~meth)acrylat- of th- alkoxylated phenol contains ~S about 3 S to about 4 mole~ of oxid- p-r mol- of the ph-nol ;~
Suitabl- alkyl-n- oxide~ include ethylene oxid-, propyl-n- oxido, butylon- oxid-, and mixtures th-r-of Pr---ntly, thyl-n- oxid- i~ prof-rred Comm-reially availabl- illu~trativo aerylate~
of th- alkoxylat-d phonol includ- alkoxylated nonyl ;
; ph-nol acrylat-- uch a~ Aronix M-lll, Aronix M-113 and i Aronlx M-117 from Toa Go~-i, Japan Mixtur-a of th- abov- ~uitabl-;~ 2S mono~m-th)aerylat-~ can al~o b- utilizod Monoacrylates -ar- pr-f-rr-d Th- eoating eompo~ition can further include a mono-thyl-nically un~aturated material having a higb T
and a ~trong capacity for hydrogen bonding Thes-monoothyl-nically un~aturatod mat-riala typieally havo a T~ gr-at-r than about 40C and ar- illustrated by ~;
N-vinyl ~onom r~, g , N-vinyl pyrrolidono, N-vinyl caprolactam, mixtur-- th-r-of and th- lik- Whon tho (m-th)acrylat- of th- alkoxylated phonol i9 utiliz-d, it 3S i- pr-f-rabl- that tho mono-thyl-nically un~aturated mat-rlal i~ al~o utiliz-d Th- T~ of thi~ ;
, ~ ` 2 0 2 4 3 7 9 ' :.

monoethylenically unsaturated material can be as high as about 120C
Th- wavelength of the light utilized to cure th- coating compositions of th- present invention can vary ~om-what d-p-nding upon the photoinitiator ~ cted In pr-sent practice, the light utilized is `usually in th- ultraviolet range which extends from about 200 to about 400 nanometers (nm) however, light o~
a longer wav~l-ngth, g , light having a wavelength of up to about 600 nm, preferably up to about 520 nm, can b- utiliz-d Th- photoinitiators utilized are conventional ~ ~
components of light curabl- ethylQnically unsaturated l ;
coating~ Pr-f-rr-d photoinitiators are aryl ketones, g , b-nzoph-none, ac-tophenon-, di-thoxy acetophenone, -~b-nzoin, benzil, anthraquinon-, and the like `~ Comm-rcial photoinitiators ar- illustrated by Irgacure 184 which i- hydroxycycloh-xyl phenyl k~tone and is ~ ~
available from Ciba-G-igy Corp , Ardsl-y, NY, and ~;-Tucirin TP0 which is availabl~ from ~ASF, Chattanooga, TN
` Volatil- organic solvent~ ar- preferably not ~, utillz-d in th- pr-s-nt coating composition Th- polyur-than- ~m-th)acrylate oligomer i~ ~`
2S pres-nt in th- coating composit$on in an amount in the rang- of about 30 to about 80, pr-f-rably about 45 to ~ -~
about 70 w-ight p-rcent based on th- total weight o~ the coating co~mposition Th- mono(m-th)acrylat- i8 pr-s-nt in th-coating compo-ition in an amount in th- rang- of about 10 to about 70, pr-f-rably about 20 to about SS w-ight p-rcent ba-od on th- total w-ight of th- coating compo-ition A- pr-~iou-ly di-cu~s-d, an aliguot o~ the mono(m th)acrylat- can b- utiliz-d a- ~ dilu-nt to r-duc- th- viscosity o~ th- oligomer during synthesis ~ -thereof, to produc- an oligomer-dilu-nt admixture The ,.

2~24~7g 14 ~
remainder of the mono(meth)acrylat- is admixed therewith `;
~ub~-guently Th- photoinitiator i- present in the coating compo-ition ln a rang- o~ about O S to about 10, -pre~-rably about 2 to about 6, w-ight percent based on ;~
th- total w-ight o~ th- eoating eomposition Th- mono-thyl-nie mat-rial having a high T9, wh-n utilized, i- pref-rably pr-sent in the eoating ~ ;~
compo~ition in a rang- o~ about 1 to about 15, more pr-~-rably about 2 to about 6 weight pereent based on th- total w-ight o~ th- eoating eomposition Th- vi~eo~ity o~ the eoating eomposition, as m-a~ur-d at a t-mp-ratur- o~ 2SC using a 8rook~ield vi-eom-t-r, i~ about 3,000 to about 12,000 e-ntipoi~e lS ~ep), pref-rably about 4,000 to about 10,000 ep Th- eoating eomposition ean further inelude eonv-ntional adh-slon promot-rs, light stabilizers and antioxldant~
Silan-- ar- conv-ntional adhe$ion promoters ;~`
which can b- pr-~-nt typically in an amount l-ss than -~
about 1 w-ight p-rc-nt Illustrativ- ~ilan-~ include ~; gamma m-thacryloxypropyl trim-thoxy ilan-, comm-rcially - ; ;
availabl- ~ro~ Dyna~ylan In¢ , Switz-rland under th- ;
trade d-signation MEM0 and gamma m-rcaptopropyl 2S trimethoxy silane which i~ comm-rcially availabl- from Union Carbid- under th- d-signation A-189 Conventional light stabilizer~ such a~ -hinder-d amines which provid- ultraviol-t stabilitylfor ~
....
the cur-d eompo~itlon ean b- pre~-nt in amount- leg~ ~ ;
than about 1 weight p~re-nt Illu~trativ- eomm-reial tabillzer~ $nelud- th- ~ollowlng Ciba-G-igy Corp , , ;;
Ard-ley, NY produet-: bi~(2,2,6,6,-t-tram-thyl-4-piperidinyl) ~-baeat- eomm-reially availabl- und-r th-trad- d-tignation Tinuvin 770s and Tinuvin 292 3S An illu~trative antioxidant is thiodi-thylene ~3,S-di-t-rt-butyl-4-hydroxy) hydroeinnamate, .. .., . - .
, .: , ',' '.-,;. ",..~, ` -,, 2 Q 2 4 ~ 7 ~

commercially available from Ciba-Geigy Corp under the trade designation Irganox 1035 Th- present coating compositioniq can be applled a- ~ primary coating to glasis fiber~ utilizing S conv-ntional proces~es The coating thicknes~ typically is about 10 to about 40 micron~
Th- following Examples are prQsented by way of illustration and not limitation .. ", EXAMPLE 1 Synthe i~ of the Present Polyurethane rMoth~acrylat- Oliaomer A polyur-than- ~meth)acrylate oligomer of the pr---nt invontlon wa~ prepared utilizing the reagents, and proportion~ th-reof, of TAB~ I, below The lS proc-dur- for th- ~ynthe~i- wa- ~ follows A uitabl- v-ssel having agitation, a dry air sparg-, and a heat source was provided The agitation, ~parq- and h-at ~ourc- wer- utilized during the ~ntire ynth--i~ Th- iiophoron- dii~ocyanat-, butylated hydroxy tolu-n- and about 90 w-ight p-rcent of the octyl/d-cyl acrylat- of oligo~-r A, about 90 w-ight p-rc-nt of th- ph-noxy-thyl acrylat- of oligom-r 8 or ~ ;
about 8S w-ight p-rc-nt of ph-noxy-thyl acrylat- of oligom r C w r- introduc-d into th- ve~el and th-2S t-mp-ratur- of th-s- reag-nt~ levat~id to, and maintain-d at, 40C N-xt, the dibutyl tin dilaurate wa- introduced into th- Y~S~-l. The hydroxyethyl ~-acrylat- wa~ then introduced into th- vessel over a time p-riod of about half an hour Th- reag-nti~ prei~ent in ; 30 tho ve~--l w-r- th-n react-d for a tim- p-riod of one hour At th- nd Or th- tim p-riod th- ~C0 functlonallty wa- conv-ntionally calculat-d Th- amount o~ polycarbonat- diol r-quir-d w~ d-termin-d to provide ~-120 p-rc-nt hydroxy functionality for oligom-r- A and B
and 133 p-rcent hydroxy functlonality for oligo~er C, a~
compared to th- NC0 functionality pre~-nt Th- ;

2~4~7~ ~ ~
~:

temperature of the reagents present was elevated to 60C The polycarbonate diol was then quickly introduced into the vessel and the temperature elevated to 70C This temperaturo was maintained until the NC0 S content was less than 0 1 percent The remaining proportion of the octyl/decyl acrylate, or phenoxyethyl acrylat-, for oligomer A, ~, or C, respectively, was th-n introduced into the vessel to obtain a 80 weight p-rc-nt oligomer and 20 weight percent diluent admixture Oligomer-diluent admixture A had a theoretical functionality of about 1 7 and a viscosity of about 40,600 millipascal seconds (mPa~s) at a temperature of 25C The oligomer produced from admixture A had a calculated number average molecular weight of about 3800 daltons Oligomer-diluent admixture B had a theoretical functionality of about 1 7 and a viscosity of about 88,100 mPa g at a temperature of 25C The oligomer produc-d from admixture ~ had a measured number average mol-cular weight of about 3800 daltons ~ ;
Oligomer-dilu-nt admixture C had a theoretical functionality of about 1 5 and a viscosity of about 81,100 mPa~s at a t-mperature of 25C The oligomer produced from admixture C had a calculated number av-rag- molecular weight of about 4100 daltons ~ ~
'.-". . '. ,.
, -: .. . .
' .., . ., :, '' ' .. .. .

~4 ~ 79 , ~ ~

$ABLE r ~
REAGENTS FOR THE SYNTHESIS OF POLYCARBONATE
URETHANE ACRYLATE OLIGOMERS ;
Oligomer-Diluent Admixtur~
(weiaht Dercent 8~ a I-ophoron- dii~oeyanat- 16 93 16 44 15 89 Oeytl/d-eyl acrylat- 20 00 - ~
Ph-noxy~thyl aerylat- - - 19 98 20 03 ~;
Butylat~d hydroxy tolu~n~ 0 02 0 02 0 02 D~butyl tin dilaurato0 05 0 04 0 0 Hydroxy~thyl aerylat- 4 79 4 66 4 47 Polyearbonat- diol~ 58 20 58 86 59 55 lS
~. - .
1 P-rmanol XM10-1733, comm~rcially availabl- from P-rmuthan~ Ine , MA

20 EXAMPLE 2 Coatina ComDO~ition~ of the Present ~pv-ntion ;' Aliguot~ of th- oligom-r-dilu~nt admixturQs o~ ~ ;
EXAMPLE 1 w-r- utiliz-d to pr-par- eoating eompo-ition~
of th pr---nt inv-ntion Th- eon-titu-nt~ o~ th-s-2S eompo-ition-, and proportion- utiliz-d, ar- pr-~-nt-d in TA~E II, b-low Th- eompo~ition~ w-r- pr-par-d by dmixing all of tho eonstituent~ in a suitablo ve~s~l at ~ ~-an l-vat-d t-mp-raturo o~ 55C ~or a tim- p~riod o~ 20 minut~ Sub~tantially homog~n~ous eoating eompo~ition~
w-r- produe-d , ,~

.; , ' ~:

202~379 TABLE II
COATING COMPOSITIONS
Coating Compositions (weiaht ~ercent) S Constituents ~ ~ E G ~ .`
Oligom-r-diluent ~ `~
~dmixtur- Al 70.0 70.0 - - - - - -Oligomor-diluent admixture ~82_ _ _ _ 57.0 62.0 - -Oligomer-diluQnt admixtur- C~ - - - - - - - - 69 9 Ph-noxyethyl acrylate 25.0 27.0 - - - - 25.
Lucirin TPO~ 3 0 1 0 - - - - 1 0 ,~
lS MEMO~ 1.0 1.0 1.0 1.0 1.0 '.. ::
Tinuvin 2926~ 0.5 0.5 ~ o. 5 Irganox 10357 0 5 0.5 0.5 0.5 0.5 :` .`
Aronlx M-113~ - - - - 33 0 28.0 - - .
N-vinyl ` ;
; ao pyrrolidone - - - - 4.0 4.0 - - .;
lrgacur- 184~ - 4.0 4.0 2.0 ,;
Tinuvin 7701 - - - - O S 0 4 - - ` `. `
Tri-thyl-n- ;
diamin-ll - _ _ _ _ _ _ _ 0 1 ~.. :: ....

1 Th~ oligomer-diluent admixture A o~ EXAMPLE 1 was : ;
'` utiliz-d 2 Th- oligom-r-diluent admixtur- B of EXAMPLE 1 was utilis-d.
Th- oligom-r-dilu-nt admixture C of EXAMPLE 1 wa~ ;
utiliz-d ;
~ A photoinitiator, commercially availa~le from 8ASF, Chattanooga, TN

' .~: `, ,':~

~ :.

~` 2024~7~

5 A ~ilane adhesion promoter, commercially available fro~ Dynasylan Inc , Switzerland 6 A light ;tabilizer, commercially available from Ciba-G-igy, Ardsley, NY
S ~ A antioxidant, commorcially available from Ciba-Geigy Corp , Ardsley, NY
An alkoxylated nonyl phenol acrylate, commercially availabl- from Toa Gosei, Japan 9 An aryl k-ton- photoinitiator, commercially available from Ciba-Goigy Corp , Ardsley, NY
~ A light ~tabilizer, commercially available from Ciba-Geigy, Ardsley, NY
1~ An ~mino stabilizer . . .
Som physical properti-s of the coating compositions D to H are presented in TA~LE III, below Th- proc-dure for determining each property is described h-r-inaft-r ~ ~;

~' 2 0 2 4 ~ 7~
- ~. ~.,:

''~ ~3`

- - o o ~ l 8 ~- -5 2.'' . ;'.

~3 ~

; ' '''.,.'''.'' ~ 2Q24L379 Th- viscosity wa- measured using a Brookfield Mod-l RVTDV viseometer operated $n accordance with the instruetionis provided therewith The temperature o~
ach ampl- te~ted was 25C
S Th- euro speed [Joule~/sguare centimeter (J/-g cm)] indicate~ th- number ot J/sq cm required to obtain a 95% cure ot a 3 mil thick coating utilizing a "D" lamp from from Fu~ion Curing Systemi~, Rockville, MD
The "D~ lamp emit~ radiation having a wavelength of about 200 to about 470 nanometer~ with the peak radiation b-ing at about 380 nanom-ter~ and the power output th-reof i9 about 300 watts per linear inch Currently th- optical gla~s fiber coating lndu~try utillzQ- primary coating eompositions having a lS eure p--d of about 1 0 J/sq cm and this is considered to bo ad-quat- Thui~, all coating compositions for which cur- ~pe-d wa- d-termined xce-d this r-guirement - Coating compo~ition D xhibited the fastest cure ~p--d follow-d by eoating eomposition H Coating eompo-ition E did not eure a~ fast as eoating eompo-itlon- D or H but xhibit-d improved wet adhesion a~ eompar-d thar-to The eure p--d of eompo~ition E
xe--d- th- aee-ptabl- indu-trial ~tandard A film for d-t-rmination of th- moduluis of the as eoating wa~ pr-par-d by drawing down a 3 mil coating on gla-~ plat-- using a 8ird bar, eomm-reially available from Paeifie Seientific, Silv-r Spring~, MD The !`` I coatinq was cured using the "D~ lamp The eoatingiwas cur-d at a do-- of about 1 0 J/sq cm which provided eompl-t- eur- Th- film wa~ then eondition-d at 23 ~ 2C and S0 + 3% relativ- humidity tor a minimum tim~ period of 16 hour~.
Six, 0 5 ineh wide t-st sp-eim-ns were eut trom tho eur-d film parall-l to the dir-etion of the draw 3S down Triplieat- measur-m-ntis of th- dimen~ion- of each sp-eimen w-r- tak-n and th- averagi utilized Th-: : ' ^ ` 2~24~79 : , .
22 ;
modulus of thesQ specimens are then determined using an Instron Model 4201 from Instron Corp , Canton, MA, op-rated in accordance with the instruction~ provided ;
th-rewith A coa~ing having a modulus of less than about 4 ;~ ;
MPa i9 acc-ptabl- to the optical glass fiber industry alb-it a low-r modulu~ is desirablQ in many --applications The pre~ent composition satisfies this d--ir- by producing coatings having a modulus of 1 4 MPa or 1-9~ - ;
To det-rmine the dry and wet adhesion o$ a film ~-to glass, films w-re prepared by drawing down 3 mil coating~ on glas~ plates using th- Bird bar~ The ccating~ wer- cured using the "D" lamp lS Th- ~ilm~ w-r- then conditioned at a temperature Or 23 + 2C and a relativ- humidity of 50 + 5% ~or a tim- p-riod ot 7 days ~ portion ot the film was ~-;
utiliz-d to t-st dry adhesion Subseguent to dry ~ -~
adh-sion t-sting, th- remainder ot th- film to be tested tor w-t adh-~ion wa~ ~urther conditioned at a t-~p-ratur- ot 23 1 2C and a relativ- humidity of 95%
for a tim- p-riod Or 24 hours A lay-r of a ;~
poly-thyl-n- wax/wat-r lurry wa~ applied to th- surface of tho furth-r condition-d film to r-tain moi~ture 2S Th- t-~t wa- p-rform-d utilizing an apparatus including a univ-rsal testing instrument, e g , the In-tron Model 4201, and a devic-, including a horizontal support and a pulley, positioned in the testing ;~
' `' instrum-nt. ,': -' :'' Aft-r conditioning, sampl- specimens that app-ar-d to b- uniform and frQ- of d-f-ct~ w-r- cut in ;~
th- dlr-ctlon of th- draw down Each p-¢im-n wa- 6 lnch-- long and 1 inch wid- and fr-- of t-ar~ or nick~
Tho ~ir~t on- inch o~ ach ~pecimen was pe-led back from 3S th- gla~ plat- Th- plat- wa- s-cur-d to th-horizontal support with th- affix-d end o~ th~ ~p-cimen .

~`` 2~24~79 ad~acent to the pulley A wir- was attached to the p~ d-back end o~ the specimen, Nn parallel to the sp-cimen and then run through the pulley in a d$rection p-rpondicular to th- spQcimen The frQe end ot the w$re wa- ¢lamp-d in the upper ~aw of the testing instrument which was then act$vated The te~t was continued until th- av-rage force valu- b-came relativ-ly constant Currently, th- optical glass fiber industry r-guires a dry adhe~ion of at lea~t S0 grams and a wet adh-sion of at l-a~t 20 gr~ms Th- present coatings gr-atly xceed th- dry and wet adhesion reguirements of th- industry To determine the water resistance a 10 mil draw-down o~ th- composition was mad- on a glass plate lS utilizing a Bird bar Th- composition was cured utilizing the "D~ lamp to provid- a dos- of 1 0 J/sg cm Thre- te~t sa~pl-s ach having dimensions o~ 1/2~ x 1 1/2~ w-r- cut from th- cur-d coating Each sampl- was w-igh-d util$zing an analytical balanc- to obtain weight m-asur-m-nt J and th-n i~m-rs-d in ~eparat- contain-rs of d-ioniz-d wat-r Aft-r a tim- p-riod of 24 hours, th- sampl-- w-r- r-mov-d ~rom th- wat-r, blotted to remov- xc-s- wat-r on th- sur~ac- and rew-ighed to obtain w-ight m-asurement K The sampl-s wer- then plac-d in aluninum pans and ma$ntain-d there$n at ambi-nt condition~ , ambient temperatur- (about 20 - 30C ) and ambi-nt humidity, for a t$m period of 120 hours Th- samples were then rewe$ghed to obta$n weight measurement L Th- follow$ng formulations wer- ut$1$zed to calculat- th- wat-r ab~orption and the xtractables (I) % wat-r ab~orption - t~X - J)/Jl x 100 ~II) % xtractabl-s - t~ - J)/Jl x 100 Th- pr-s-nt coating compo~ition provides coatinqs which ~ati~fy or xc-ed th- commercial standard 3S o~ about 2 to about S for the diff-rence b-tw--n % water absorption and % extractables : '':

:.'. ~. :'; .:

-`` ` 2 0 2 4 3 7 ~

24 ` `
This invention has been described in terms of specific embodiments set forth in detail, but it should --bo understood that thes- are by way of illustration only and that the invention is not necessarily limited thereto Modifications and variations will be apparent from the disclosure and may be resorted to without d-partlng from the spirit of th- invention, as those skill-d in the art will r-adily understand Accordingly, such variations and modifications of the disclosed products are considered to be within the purview and scope of the invention and the following ~ , claims. ' :'

Claims

1. A photocurable liquid coating composition suitable as a primary coating for an optical glass fiber comprising (1) a polyurethane (meth)acrylate oligomer having a (meth)acrylate functionality of about 1.9 or less that is the reaction product of a prepolymer or admixture of prepolymers, a diisocyanate and a hydroxy (meth)acrylate; and (2) a mono(meth)acrylate having a glass transition temperature below about -20°C.

2. The coating composition in accordance with claim 1 wherein the prepolymer is selected from the group consisting of polycarbonates, polyesters and mixtures thereof having about 1.5 to about 3 functional groups that are reactive with the isocyanate group.

3. The coating composition in accordance with claim 2 wherein the prepolymer has about 1.8 to about 2.5 functional groups.

4. The coating composition in accordance with claim 1 wherein the number average molecular weight of the prepolymer is about 500 to about 2,000 daltons.

5. The coating composition in accordance with claim 1 wherein the number average molecular weight of the prepolymer is about 800 to about 1,800 daltons.

6. The coating composition in accordance with claim 1 wherein the prepolymer is (1) a polycarbonate diol produced from an alkylene diol having about 2 to about 12 carbon atoms, (2) a polycarbonate copolymer of an alkylene oxide and the alkylene diol or (3) an admixture of (1) and (2) wherein the prepolymer is present in an amount sufficient to provide an excess hydroxy functionality of up to about 40 percent as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate.

7. The coating composition in accordance with claim 1 wherein the prepolymer is (1) a polycarbonate diol produced from an alkylene diol having about 4 to about 8 carbon atoms, (2) a polycarbonate copolymer of an alkylene oxide and the alkylene diol or (3) an admixture of (1) and (2) and wherein the prepolymer is present in an amount sufficient to provide an excess hydroxy functionality of about 10 to about 35 percent as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate.

8. The coating composition in accordance with claim 1 wherein the reaction of the diisocyanate and the hydroxy (meth)acrylate is performed prior to reaction with the prepolymer.

9. The coating composition in accordance with claim 1 wherein the (meth)acrylate functionality of the oligomer is about 1.5 to about 1.8.

10. The coating composition in accordance with claim 1 wherein the (meth)acrylate functionality of the oligomer is at least about 1.5.

11. The coating composition in accordance with claim 1 further including a monoethylenically unsaturated material having a glass transition temperature greater than about 40°C. and a strong capacity for hydrogen bonding.

12. The coating composition in accordance with claim 1 wherein the hydroxy (meth)acrylate is a monohydric monoacrylate.

13. The coating composition in accordance with claim 1 wherein the prepolymer is polyfunctional and the mole ratio of prepolymer diisocyanate hydroxy acrylate is in the range of about 1.4:1.8:1.0, respectively, to about 1.7:2.0:1.0, respectively.

14. The coating composition in accordance with claim 1 wherein the number average molecular weight of the oligomer in about 600 to about 15,000 daltons.

15. The coating composition in accordance with claim 1 wherein the number average molecular weight of the oligomer is about 1,000 to about 5,000 daltons.

16. An optical glass fiber coated with the coating composition of claim 1.

17. A photocurable liquid coating composition suitable as a primary coating for an optical glass fiber comprising (1) a polyurethane (meth)acrylate oligomer having a (meth)acrylate functionality of about 1.9 or less that is the reaction product of a prepolymer that is (a) a polycarbonate diol, (b) a polycarbonate copolymer of an alkylene oxide and an alkylene diol or (e) an admixture of (a) and (b), a diisocyanate and a hydroxy (meth)acrylate, the prepolymer having a number average molecular weight of about 500 to about 2,000 daltons and being present in an amount sufficient to provide up to about 40 percent excess hydroxy functionality as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate, the mole ratio of prepolymer diisocyanate hydroxy (meth)acrylate being in the range of about 1.4:1.8:1.0, respectively, to about 1.7:2.0:1.0, respectively; and (2) a mono(meth)acrylate having a T9 below about -20°C.

18. The coating composition in accordance with claim 17 wherein the prepolymer provides about 10 to about 35 percent excess hydroxy functionality.

19. The coating composition in accordance with claim 17 wherein the number average molecular weight of the prepolymer is about 800 to about 1,800 daltons.

20. The coating composition in accordance with claim 17 wherein the reaction of the diisocyanate and the hydroxy monoacrylate is performed prior to reaction with the prepolymer.

21. The coating composition in accordance with claim 17 wherein the (meth)acrylate functionality of the oligomer is about 1.5 to about 1.8.

22. An optical glass fiber coated with the coating composition of claim 17.

23. A polyurethane (meth)acrylate oligomer suitable in a photocurable liquid coating composition comprising the reaction product of a prepolymer or an admixture of prepolymers, a diisocyanate and a hydroxy (meth)acrylate, the oligomer having a (meth)acrylate funetionality of about 1.9 or less.

24. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the prepolymer is selected from the group of polycarbonates, polyethers, polyesters and mixtures thereof having about 1.5 to about 3 functional groups that are reactive with the isocyanate group.

25. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the number average molecular weight of the prepolymer is about 500 to about 2,000 daltons.

26. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the number average molecular weight of the prepolymer is about 800 to about 1,800 daltons.

27. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the prepolymer is (1) a polycarbonate diol produced from an alkylene diol having about 2 to about 12 carbon atoms, (2) a polycarbonate copolymer of an alkylene oxide and the alkylene diol or (3) an admixture of (1) and (2) and wherein the prepolymer is present in an amount sufficient to provide an excess hydroxy functionality of up to about 40 percent as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate.

28. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the prepolymer is (1) a polycarbonate diol produced from an alkylene diol having about 4 to about 8 carbon atoms, (2) a polycarbonate copolymer of an alkylene oxide and the alkylene diol or (3) an admixture of (a) and (b) and wherein the prepolymer is present in an amount sufficient to provide an excess hydroxy functionality of about 10 to about 35 percent as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate.

29. The polyurethane (meth)acrylate oligomer in accordance with claim 23 wherein the (meth)acrylate functionality of the oligomer is about 1.5 to about 1.8.

30. A polyurethane (meth)acrylate oligomer suitable in a photocurable liquid coating composition comprising the reaction product of a prepolymer, a diisocyanate and a hydroxy mono(meth)acrylate, wherein the prepolymer is (1) a polycarbonate diol produced from an alkylene diol having about 2 to about 12 carbon atoms, (2) a polycarbonate copolymer of an alkylene oxide and the alkylene diol or (3) an admixture of (1) and (2) and is present in an amount sufficient to provide excess hydroxy functionality as compared to the free nitrogen-carbon-oxygen group functionality of the diisocyanate as reduced by the hydroxy functionality of the hydroxy (meth)acrylate, the oligomer having a (meth)acrylate functionality of about 1.9 or less.

31. The oligomer in accordance with claim 30 wherein the mole ratio of prepolymer diisocyanate hydroxy mono(meth)acrylate is in the range of about 1.4:1.8:1.0, respectively, to about 1.7:2.0:1.0, respectively.

32. The oligomer in accordance with claim 30 wherein the alkylene diol has about 4 to about 8 carbon atoms.

33. The oligomer in accordance with claim 30 wherein wherein the number average molecular weight of the prepolymer is about 500 to about 2,000 daltons.

34. The oligomer in accordance with claim 30 wherein wherein the number average molecular weight of the prepolymer is about 800 to about 1,800 daltons.

35. A method of producing a polyurethane (meth)acrylate oligomer having an acrylate functionality of about 1.9 or less comprising the steps of:
(a) reacting a diisocyanate with a hydroxy (meth)acrylate at an elevated temperature for a time period effective to consume substantially all of the hydroxy functionality; and then (b) reacting therewith a prepolymer comprising (1) a polycarbonate diol, (2) a polycarbonate copolymer of an alkylene diol and an alkylene oxide or (3) an admixture of (1) and (2).

36. The oligomer in accordance with claim 35 wherein the mole ratio of prepolymer: diisocyanate:
hydroxy (meth)acrylate is in the range of about 1.4:1.8:1.0, respectively, to about 1.7:2.0:1.0, respectively.