CA1129583A

CA1129583A - Actinic radiation-curable formulations

Info

Publication number: CA1129583A
Application number: CA317,606A
Authority: CA
Inventors: Dennis D. Howard
Original assignee: Lord Corp
Current assignee: Lord Corp
Priority date: 1978-01-03
Filing date: 1978-12-08
Publication date: 1982-08-10
Also published as: JPS54107998A; US4133723A; SE7812777L; FR2413413A1; GB2012290A; ZA786933B; GB2012290B; AU4284478A; DE2856407A1; AU527571B2

Abstract

Abstract Energy-curable compositions which can be cured in the presence of air by exposure to actinic radiation contain at least one unsaturated urethane oligomer, said oligomer comprising the reaction product of at least one poly(alkylene oxide) polyol, at least one polyisocyanate, and at least one unsaturated active hydrogen-containing compound.

Description

295~3~

This invention relates to radiation-curable composi-tions. More particularly, the invention relates to actinic radi-ation-curable compositions characterized by a reduced sensitivity to oxygen in~ibition during the curing process.
During the latter part of the past decade, significant advances have been made in the radiation processing of commer-cial products. The increased interest in energy-curable systems has been catalyzed by recently-enacted or impending legislation by federal, state and local governments which restrict the amount of solvent and other pollutants that can be vented to the atmos-phere, and the increased concern expressed by individuals and unions over the possible toxic effects of prolonged exposure to volatile organic materials, as well as the sky-rocketing cost of solvents derived from petroleum coupled with a grim prospect of material unavailability. Generally, the energy-curable sys-tems are 100% reactive systems, i.e., substantially all of the components react to produce the final product. As is well-known, the curing of such systems can be effected by several means, including exposure to high energy ionizing radiation; photopoly-merization by actinic radiation in the presence of a photoiniti-~"
ator; and by exposure to chemical free radical-generating agents~ -usually at an elevated temperature.

~ .

295~3 A particular def ciency of all radiation curable compositions which cure via ~
free radical addition mechanisrn is a sensitivity tb oxygen inhibition during the curing process. Oxygen inhibition is not a serious problem when cure is effected by exposure to high energy ioniæing radiation or by exposure to thermally-acti~Jated 5 fi ee radical-generating agents . Oxygen inhibition does materially affect com-positions which are cured by expasure to actini~ radiation, such as ultraviolet light.
A typically actinic radiation-curable resin system contains an oligomer, which may or may not contain reactive functional groups ~such as double bonds), 10 a crosslinking agent, a reactive diluent for viscosity controt, and a photosensitîæer or photoinitiator. By selecting an oligomer which contains at least two points of re~ctive ursaturation, or a reac+,ive diluentwhichlikewise contains atleas~ t~ro points of reactive unsaturation, one may eliminate the need for a crosslinkin~
agent per se. Control over the properties of the cured systems can be exercised 15 via the structure of the oligomer backbone, including such factors as degree of chain-branching, types of functional groups, number and types of ur~saturated bonds, molecular weight, etc.; ~unctionality and Level of crossl;mking a~ents;
naturs and level of reactive diluent; kin~ and level OI th~ sensiti7er or photo-initiator; and the like. An e~emplary oligomer which has obtained widespread 20 commercial acceptance and which can be cured by exposure to actinic radiation in the absence of a crosstinking agent per se is an unsaturated urethane oligorner obtained by reacting an isocyanate-functional prepolymer with unsaturated com-pou~ds containing an isocyanate-reactive active hydrogen group. Before any poly-meriz~Ltion can OCCUI^, free radicals must first be produced via the photoinitiator 25 The production of free radicals by the photoinitiator is a wave length function of the actinic radlation. Once the radicals are formed~ propagation of polymer growth llZ9SB;~

rapidly advances through chain reaction. Oxygen in the ground or unexcited state is itself a radical and is highly reactive with other radicals. Thus, chain growth can be terminated by the oxvgen radical, resultincr in uncured or tacky surfaces and, more importantly, the photoinitiator itself when in the free radical state can 5 be capped and made ineffective.
The adverse effect of oxygen inhibition can be at least reduced by curing in an inert gaseous environment (nitrogen, argon, carbon dioxide, and the like).
While effechve, the use of inert gas environments is generally cumbersome anc~
economically ~nattrachve. Other methods which have been suggested for reducing 10 the air inhibition effect on actinic energy-curable compositions include improved design of energy sources, increasing photoinitiator level, use of more reactive dilu~nt s~s~ms, ~ncl use of natl~ral and synthetic wa~es. E~cepi for the impro~ed energy sources `which must be proved out, the suggested rnethods directly affect ultimate properties of the cured systems and are not susceptible to widespread 15 utilization. There remains a compelling need for means to reduce the sensitivity of actinic radiation-curable compositions to o~ygen inhibition during the curing process, since the problem will increase in importance as the acceptance by ~dustry of radiation-curable systems increases.
Gruber U. S. Patent No. 4, 017, 652 dis~loses that oxygen inhibition of the 20 phQtopolymerization of resins containing acrylic groups can be abated by emptoying a p~}otocatalyst system containing (1) as a photosensitizer, at least one aromatic ~etone- or aromatic aldehyde which has a triplet energy in the range of from about 54~ilocalories per mole to a~out 72 kilocalories per mole and which promotes Fotymerization through bimolecular photochemical reactions of the energ~r donor 25 type,-and, (2), as a photoinitiator, at least one aromatic ketone which generates a radical pair by way oi unimolecular homotysis resut~ng from photoexcitation. A

_ 3 _ ~Z9583 preferred photocatalyst system is benzophenone and isobutyl benzoin eth~r. The proposed photocatalyst systems are effective in reducing oxygen inhibition; how-ever, they suff~r fro~ +~.e de;licienc~ that thR tim~e required for cure in ~ygen is longer than the time required to cure the same formulation i~ an inert environ-5 ment. The increased cure cycle is highly disadvantageous, because of itsdeleterious effect on many substrates, such as warping and charrin~. rnere is a need for energy curable compositions which not only can be cured in the presence of oxygen, but also can be cured at rates approaching those encountered when curing is effected in inert atmospheres.
Continued research into the development of energy curable compositions wbich can be cured by exposure to actinic radiation in the presence of air has resulted in the discovery that unsaturabd urethane oligomers derived i~om certain hereinafter described polyols can, in combination with photocatalyst systems comprising at least one compound which promotes polymerization through bi-15 molecular photochemical reactions of the energy donor type or hydrogen ab-straction type and at least one compound which generates a free radical pair by way of unimolecular homolysis resulting from photoexcitation, be cured by exposure to actinic radiation in the presence of air in an unexpectedly short cure cycle. It was also discovered that (1) ultimate properties of the cured compositions can be 20 enhanced by incorporating into the curable formulations at least one chain transfer agent and, (2), certain chaintransfer agents are effecti~re in ~rther increasing rate of cure. --The present invention is based on the discovery that the nature of the poly31which ls employed in forming energy-cura~le unsaturated urethane oligomers does 25 materially affect the curing rate in air of such oliyomers. ~ore particularly, it has been discovered that the use of poly(alkylene oxide) polyols as precursor .

.

-- 4 ~

~1295~33 compounds for actinic radiation-curable unsatura~ed urethane oligomers affords compositions which can be cured in air at a rate which is commercially significantly more rapid than can be obtained with unsaturated urethane oligomers prepared from polyester polyol precursors. The discovery was particularly unexpected 5 because ~there is no significant difference in the cure rate of unsaturated urethane oligomers prepared from polyester polyols or poly(alkylene o~de) polyols when cure is effected in an inert atmosphere. While the phenomenon is not understood, nor has a theoretical explanation been entirely forrnulated, the progression is on the order of poly(tetramethylene oxide) polyol~poly(prophylerle ox~de) polyol~
10 polyester polyol. Unsaturated urethane oligomers derived solely from poly(ethylene oxide) polyols gel too rapidly to permit an effective evaluation of such polyethers;
however, unsaturated urethane oligomers derived from block copolymers of ethylene glycol and at least one othér glycol or alkylene oxide, as well as such oUgomers derived from a mixture of two or more poly(alkylene oxide) polyols~
15 do cure in air at a rate at least equivaLent to the cure rate of un~aturated oligomers derived from poly(prophylene oxide) polyol.
~hus, in accordance with one aspect of the inventionr there are pro~ided novel unsaturabd uret~ne oligomers comprising the reaction product of (i), a~
least one organic isocyanate compound having at least two isocyanate groups; ~ii), 20 at least one poly(alkylene oxide) polyol; and, (iii) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactlve active hydrogen group.
Iil a second aspect of the invention, there are provided novel energy curable compositions cornprising (a), unsaturated urethane otigomers comprising ~5 the reaction product of (i), at least one organic isocyanate compourld having at least t~o isocyanate groups, (ii), at least one poly(alkylene oxide) polyol, and~

5 _ -, , -:: . :

5~3 .
(iii), at least one unsaturated addition-polymerizable monomeric compound havinga single isocyanate-reactive active hydrogen group; (b), at least one reactive monomer dlluent; (c), a photocatalyst system comprising (1~ at least one compound - which promotes free radical addition polymerization through bimolecular photo-chemicaL reactions of the energy donor type or hydrogen abstraction type and, (2), at least one compound which promotes fxee radical additon polymerizatl on b~
generating a radicat pair by way of unim.olecular homolysis resulting ~rom pho~o-excitation; and, optionally, (d), an effective amount of at least one chain-tran~fer agent; and, also optionally, (e), up to aoout 75 percent by weight of at least one unsaturated urethane oligomer derived from a non~poly(alXylene oxide) polyot precursor, said weight percent being based on total weight of (2) and (e).
- ~ Additionally, the invention provides a process for coating a substrate w;~ich comprises applying to a surface of the substrate the energy-curable ~ompositionsof ~his invention and exposing such coated substrate to acting radiation in the presence of air whereby the coating is cured into a hard mar and abrasion resistarlt film. The invention also contemplates articles of manufacture comprising a substrab having a desired geometrical configuration and size having thereon a cured wear coating, said coating being formulated, applied and cured according to the concepts of the herein-described invention.
The novel unsaturated urethane oligomers of the present inven~ion are characterized by the presence of at least one ethylenically unsaturated group having the structure - CH = C~, preferably having the structure CH2= ~, said group preferabty being terminally located; and having a main carbon-carbon chainor backbone consisting essentially of at least one poly(alkylene o~de) polyol, said main chain or backbone being separated from said ethylenicalty unsaturated group .-- 6 --.

1~2~S~;~

by two urethane groups. Such unsaturated urethane oligomers comprise the reaction product of i) at least one org~rAic isocyanate c o~pound having at least two iso-cyanate groups;
iij at least one poly(alkylene oxide) polyol; and iii) at least one unsaturated addition-polymerizable monoraeric compound having a single isocyanate-reactive active hydrogen group;
there being present an excess of isocyanate compound with respect to the hydroxyl groups of said poly(alkylene oxide) polyol;
said unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being present in an amount suf-ficient to provide at least one molar equivalent of active hydrogen group with respect to isocyanate reactivity. The invention contemplates unsaturated urethane oLigomers having at least one reactive isocyanate moiety, as well as such oligomers having substantially no reactive isoc~7anate functionality, with the latter oligomers being especially preferred. An especially preferred class of unsaturated urethane oligomers are the acrylated urethane oligomers, urethane oligomers which h~ve been modified by incorporatIng into the oligomeric molecule one or more acrylic grouDs having the structure CH2= C - ~OO -~ wherein X is hydrogen, haLogen or - X ~ -an alkyl group of 1 to 8 carbon atoms.
The isocyanate compounds which are employed in forming the unsaturated urethane oligomers in accordance ~ith the present invention can be any organic ~socyanate compound having at least two free isocyanate groups. Included within the purview of suitabl~ polyisocyanates are aliphatic, cycloaliphatic, and aromatic polyisocyanates, as these terms are generally interpreted in the art. Thus it will - . - 7 ~

! ` . . ... , .. : -.. . -- - -:

~L~Z95~33 be appreciated th~t any of the known polyisocyanates such as alkyl and alkylene polyisocyanates, cycloalkyl and cycloalkylene polyisocyanates, aryl and arylene polyisocyanates, and combinations such as alkylene, cycloalkylene and alXylerle arylene polyisocyanates, can be employed in the practice of the prèsent invention.
S~itable polyisocyanates include, without limitation, tolylene-2,~-diisocyanate, 2,2,4-trimethylhexamethylene-1, 6-diisocyanate,hexarnet~ylene-1, 6-d~isocyanate, diphenylmethane-4, 4' -diisocyanate, triphenylmethane -4, ~', 4i' -triis ocyanate, polymethylene polyphenylisocyanate, m-phenylene di -isocyanate, p-phenylene diisocyanate, 2, 6-tolylene diisocyanate, 1, 5 -naphthalene diisocyanate, naphthalene-1,4-diisocyanate, diphenylene-474'-diisocyanate, 3~3'-bi-tolylene-4, 4' -diisocyanate, 1, 4-cyclohe~ylene dimethylene diisocyanate, xylylene-1, 4-diisocyanate ~ xylylene-1, 3 -diisocyanate, cyclohex~l-1, 4-diisocyan3 toJ 4, ~' -methylene-~is(cyclohexyl isocyanate~, 3, 3' ~imethyldiphenylmethane-4, 4t _ diisocyanate, isophorone diisocyanate, the product obtained by reacting trimethylol is propane and 2, 4-tolylene diisocyanate in a ratio of 1:3, and the like. Ihe diisocyanate compounds are preferred, with 4, 4' -methylene-bis(cyclohexyl isocyanate) beiny especiaUy preferred.
It is an essential feature of the novel unsaturated ure~llane oligomers of the present invention that such oligomers contain as a backbone the residu~ a~ at least one poly(alkylene oxide) polyol. The polytalkylene o~de) polyols which rnus~
be employed in t~le practice of this invention are poly(alkylene oxide) compounds containing at least two hydroxy groups. Such compounds are normally obtained ~rom the polymerization, including block copolymerization, of cyclic ethers such æ
alkylene oxides, dioxolane and tetrahydrofuran, the condensation of glycols, or the condensation of cyclic ethers with glycols. They are well-known articles of commerce, and are also called polyalkyelen ether glycols) polyalkylene glycols, 5i93 polyalkylene o~de glycols, polyglycols and polyoxyalkylene glycols. Preferred poly(alkylene oxide) polyols have from 1 to 9, preferably 1 to 6, carbon ator~Lsin the alkylene chain separating each pair of oxygen atoms and have a number avera~
molecular weight in the range from about 250 to about 4000, preferably Irom about 250 to ahout 2500. Not all the alkylene units need be the same. Poly(alkylene oxide~
polyols for~ed the copolymerization or condensation of mixtures of dif~rent cyclic ethers, glycols or glycols and cyclic ethers can be used, as can poly(all.~ylene oxide~
derived from cyclic ethers such as dioxoLane, which affords a polyol having the îormula HO(CH2-0-CH2CH20)nH, where n is an integer greater than 1. The alkyle~e nn;ts can be a straight chain or a branched chain, as in poly(propylene o~de) polyol. ~ the case where the alkylene unit is ethylene, it has been found advan-tageous to incorporate the unit into a copolymer, for example~ as a copolymer ofethylene oxide and propylene oxide, with up to about 80 weight percent o. such copolymer comprising ethylene oxide. Representative poly~alkylene o~de) po~yols include poly(ethylene oxide) polyols, poly(propylene oxide~ po~yols, poly(tetra-methylene oxide) polyols, poly(nonamethylene oxide) polyols, polytoxymethylene-ethylene oxide) polyols, poly(ethylene oxide-propylene oxide copolyxner) po~yols, and po~y~pentaerythritol-ethylene oxide) polyols. Thus the poly(aLkylene oxide~
polyols will generaUy have from ~ to 6 hydroxyl groups, with such polyols hayIn~2 hydroxyl groups being presently preferred. Preferred poly(alkylene oxide) polyols are poly(propylene oxide) diol, poly(ethylene oxide-propylene oxide) diol and poly(tetramethylene oxide) diol, with the latter being especially preferred.Unsaturated addition-polymerizable ~nonomeric organic compounds having a single isocyanate-reactive hydrogen group which can be employed in the practice of the present invention include any of such compounds which have been previous~y used to introduce an unsaturated polymeriæable moiety into a molecule via reaction between the active hydrogen group and a reactive Isocyanate moiety. Preferably, .

-~L~2~58;3 the active hydrogen group is hydroxy. Illustrative of unsaturated addition-poly-merizable monomeric organic compounds having a single isocyanate-xeactive 2ctive hydrogen group are 2-hydrox.yethyl acryiate, 2-hydroxyethyl meth2crylate,

2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate~ N-hydroxyrnethyl 5 acrylami~de, N-hydroxymethyl methacrylamide, diethylene glycoL monoacrylate, diethylene glycol monomethacrylate, glycerine dimethacrylate J trirnethylol propane dimethacrylate, and the like. The amount of such compounds will be s~mcient to provide at least one molar equivalent of ac~ive hydrogen group with respect to isocyanate functionality, and preferably is suf~icient to afford an active 10 hgdrogen group: NCO ratio, with respect to the amount of totaa free hydroxyL
fi~nctions, of at least 1:1, with a small excess, 10 mol percent or less, ~eing expecially preferl ed.
The novel unsaturated urethane oligomers can be prepared by any of several known reaction routes, including (1) simultaneous reaction of polyisocyanate~
15 poly(alkylene oxide) polyol and unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group; and (2) reaction of polyisocyanate and unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive acti~e hydrogen group to form an unsaturated isocyanate-filnctional compound which is then reacted with the poly(alkylene oxide~
20 polyol, the amount of unsaturated isocyanate being sufficient to consume all hydroxyl groups of the polyol with excess isocyarlate ~nctions being preferabLy reacted with additional unsaturated polymerizable monomeric compound. The preferred method of Eorming the herein described oligomers is, (3) a two-step process comprising, (1), contacting poly(alkytene oxide polyol with sufficient 25 polyisocyanate to form an isocyanate-functionat urethane prepolymer, arid, ~
contacting such urethane prepolymer with unsaturated addition-polymerizable .

monomeric organic compound haviny a single isocyanate-reactive active hydroger group to produce the desired oligomer having at least one unit of ethylenic un-saturc.~.on pel molecule, wi'~h acrylated uret~ne o'igomers, especially acrylated urethane oligomers having substantially no free isocyanate ~nctionality, being 5 especiall~y preferred. In formirlg the herein described oligomers, there ~il~ be employed at least a slight excess of polyLsocya~iate with respect to the hydroxyl fh~ctions of the polyol. Preferably, the amount of polyisocyanate will be suf~icient to provide an NCO:OH ratio, with respect to the hydroxyl groups of the poly(alky-lene o~ide ether) polyol, of at least 2. 1:1, preferably at least 2. 3:1, and especially at least 2. 5:1, with an NCO:OH ratio in the range of about 2. 5-5:1 being particularly preferred. Tne oligomers of this invention can be prepared neat, as can the intermediates in tne multi-step processes, but are preferably prepared in the presence of a diluent phase which is copolymerizable with the unsaturated urethane oligomer but is otherwise inert during the particuLar process of prepari~g the oUgomers. Because the various methods of preparing unsaturated ureth~ne resins arewell-known, forexample, see U. S. PaterltNo. 3,7Q0,643, itis considered that any detailed dlscussion of such methods is unnecessary.
As noted, the en~rgy-curable compositions of the present invent~on com-prise a mixturç of i) at least one unsaturated urethane resin prepared in accordance with this invention;
ii) a reactive diluent system comprising at least one unsaturated addition-polymerizable monomeric compound which is copolymerizable with said unsaturated urethane resin, and preferably containing at least one acrylic and/or methacrylic 2S acid ester containing at least 4 carbon atoms in the non-acid moiety;
ili) an effective amount of a photocatalyst system comprising a mixture of (1) at least one compound which promotes free radical addition polymerization .

~2~ 3 through bimolecular photochemical reactions of the energy donor type or h~drogenabstraction type and (2) at least one compound which promotes free radical poly-meri~ation b~ sener~ting a radical p~ir b~ way of unir~olec11ar homol5~s res l~n~, from photoexcitation;
i~) optionally, an effectlve amount of at least one chain trar~sfer agent;
and v) optional~y, up to about 75 percent by weight of at least one unsaturated urethane oligomer, preferably an acrylated urethane otigomer, said oligomer having as a polyol precursor at least one non-poly(alkylene o~ide) polyol.
Reactive diluent systems which can be employed in the energy curable com-positions of this invention include any of such systems which have been or are being used for this purpose. Broadly, suitable reactive diluent systems compriseat least one unsaturated addition-polymerizable monomeric compound which is copolymerizable with the unsaturated urethane oligomer upon exposure to acting radiation. The reactive diluent can be monofunctional or pol~unctional, with respect to polymerizable moieties. A single poty~nctional reactive diluent can be used, as can mixtures thereof; or a combinatîon of one or more monofunctio~
reactive diluents and one or more polyfilnctional reactive diLuents can be used.Such combinations of mono- and polyunctional reactive diluents are presently preferred. Generally, the reactive diluent system will comprise ~om about 10 to about 65, preferably about 15 to about 50, weight percent, based on total weightof unsaturated urethane oligomer and reactive diluent, of the energy curable compositions of the invention. Particularly preferred reactive diluents are un-saturated addition-polymerizable monofunctionat monomeric compounds selected from the group consisting of esters having the general formula ~Z~5~3~
o ~H2= C - C - O - R, lo wherein Ris hydrogen or methyl, and R is an aliphatic or cycloaliphatic grcup 5 having from 4 to 18 carbon atoms. Representative of such preferred reactive mono~Leric diluents, withoutlimit~tion thereto, are hexyl acrylate, cyclohex~l ac~ylate, 2~thylhexyl acrylate octyl acrylate, nonyl acrylate, stearyl acrylateJ
and the corresponding methacrylates. ILlustrative of other reactive monofunctional and polyfunctional monomeric diluents which can be employed are styrene, methyl 10 methacrylate, butyl acrylate, isobutyl acrylate, 2-phenoxy acrylate, 2-methoxy-ethyl acrylate, 2-tN,N-diethylamino)-ethyl acrylate, the corresponding methacrylat~s, acrylorLitrile, m~thyl ~crylonitrile, methacrylamide, neopentyl glycol diacrvlate.
ethylene glycol diacrylate, hexylene glycol diacrylate, diethylene glycol diacrytate, trimethylolpropanetriacrylate,pentaerythritoldi-, tri-, ortetra-acrylate,the 15 corresponding methacrylates, vinyl pyrrolidone, and the Uke. At the present time, it is preferred that the reactive diluent systemcontain at least one acxylic and~or methacrylic acid ester having at least 6 car~on atoms in the non-acid moie~, with such acrylic acid esters being preferred~ Reactive diluent systems are well- ;nown to those skilled in the art of radiation curing and th~ seLection of an approoriate ..
80 diluent systemL in any given instance is sufficie~Ltly encompassed by such knowledge as to require no ~urther discussion here.
Compounds ~hich are effective to promote free radical addition polymeriza~
through bimolecular photochemical reactions of the energy donor or hydrogen ... ..
abstration types are well-known, as are compounds which are effective to promote 25 free radical addition polymerization by the generation of free radicals by way of unimolecular homolysis resulting from photoexcitation. Such compounds are described as photosensitizers and photoinitiators, respectively, by at least one ~'' ' ' ' '~, , - ~ - 13 -. . ..... .

: " . . . : ' . , . , `

29S~3 patentee, seeGruberU. S. PatentNo. 4,017,652and, forthepurposeog establishing some measure of consistency with respect to nomenclature, that ~escription will be follc~Jed herein. With respect to photopolymerization ~rocesses, photosensitizers are not good initiators per se, but do readily absorb protons to produce an excited molecule which then interacts either by hydrogen abstraction or through energy transfer with a second molecule to produce free radicals whichare capable of initiating addition polymerization reactions. Unlike the photo-sensitizers which form free radicals through interaction with a second molecule,photoinitiators absorb protons to produce an excited molecuLe which can cleave to produce free radicals which are capable of initiating addition polymerizationreactions.
The photocalalysL systems of the present invention can employ, in co;n-bination, an effective amount of an admixture comprising, (1) an effective amount of at least one photosensitizer which is effective to promote free radical addition poL~merization through bimolecular photochemical reacti~s of the energydonor or hydrogen abstraction types and, (2), an effective amount of at least o~e photoinitiator which is effective to promote free radical addition poly-merization by generating free radicals by way of unimolecular homolysis resulting from photoexcitation. Such mixtures generally will comprise from about 0. 01 to about 50, preferably from about 0.1 to about 15 parts by weight, per 100 parts by combined weight of unsaturated urethane oligomer and reactive diluent, of such photosensitizer and from about 0. 01 to about 10, preferabl~r from about 0. 05 to about 7, parts by weight, per 100 parts by combined weight of unsaturated urethane oligomer and reactive diluent, of such photoinitiator.
Particular~y preferred photosensitizers, which are an essential first component of the photocatalyst systems employed in the practice of this invention, J.

l~Z~58;3 are aromatic ketones and-aromatic aldehydes which can exist in a triplet state, especially such ketones and aldehydes which have a triplet energy in the range from about 54 to about 72 kilo-calories per mole. Such photosensitizers are described in Gruber U.S. Patent No. 4,017,652 and Osborn et al U.S. Patent No. 3,759, 807.
Photoinitiators, which are an essential second compon-ent of the photocatalyst systems employed in the practice of this invention, are preferably selected from compounds having the formula O R

1. ~ - C - C - R2 wherein R , R2 and R are independently hydrogen, hy-droxyl, halogen, alkyl of 1 to 12, preferably 1 to 8, carbon atoms, alkoxy of 1 to 12, preferably 1 to 8, carbon atoms, or phenyl, providing that Rl, R2 and R3 are not concurrently all hydrogen, hydroxyl, halogen, or alkyl; and wherein at least one of Rl, R2 or R3 is preferably hydroxyl or alkoxy. The alkyl, alkoxy and phenyl groups can be substituted with moieties which will not interfere with the function of the compound as a photo-initiator. Representative substituent moieties or groups include halogen, alkyl of 1 to 8 carbon atoms, alkoxy having from 1 to 8 carbon atoms in the alkyl group, carboxy and carbalkoxy having from 1 to 8 carbon atoms in the alkyl groups. Photoinitiators in which the alkyl, alkoxy and phenyl groups are unsubstituted ~ `
are preferred. A second class of preferred photoinitiators has the formula X

~L~2~35~33 . .

O O
-' _~ C - C - oR5 j wherein R4 is hydrogen, halogen, alkoxy containing from 1 to 8, preferably 1 to 4, carbon atoms or alkyl containing from 1 to 8, preferably 1 to 4 carbon 5 atoms; and R5 is hydrogen, alkyl containing from 1 to 22 carbon atoms, benzyl, phenyl, hydroxyalkyl containing from 1 to 12 carbon atoms, haloalkyl containin~
from 1 to 12 carbon atoms,alkoxyalkyl wherein the alkoxy portion contains from 1 to 8 carbon atoms and the alkyl portion contains from 1 to 12 carbon atoms~
and phenoxyalkyl wherein the alkyl portion contains from 1 to 12 carbon atoms, 10R5 being preferably hydrogeri7 alkyl of 1 to 12 carbon atoms, ben~yL or pherlyl.
-Particularly preferred photoinitiator compounds are represented by the formulae C O
~ C-CH-R62 , ~_ C-CH2-Rb , ~C-CH

(~C-C-R8, ~C-CH {~ , wherein R6 is halogen; R7 isan al~yl group having from 1 to 12, preferably 1 to 8, carbon atoms; and R8 is hydrogen, alkyl of 1 to 12 carbon atoms, aryl o 6 to 20 14 ring carbon atom~s, and cycloalkyl of 5 to 8 ring carbon atoms. Where a plurality of R6 or R7groups are found OD the molecule, they can be the same or different.

The photoinitiators which are employed in combination with the here-tofore described photosensitizers in the practice of the invention are well-known ~rticles of corn.merce. A representative liSti!lg of such compourlds can be found in U. S. Patent No. 4,017,652, column 4, lines 46-63; U. S Patent No.
4,024,2~6, column 4, lines 18-37; and U. S. Patent No. 3,71a, 293, column 1, line 41 through column 2, line 13.
PresenMy preferred photocatalyst systems comprise admixtures of, (a), benzophenone and benzoin isobutyl ether and, (b), benzophenone and 2,2-diethoxyacetophenone .
Substantially any of the known chain trans~er agents can be employed in the practice of the present inventiorl. Generally, such compounds, whe~ utilized~
wilt be employed at levels not axceeding about 15 parts by weigl.lt, per 100 paris of combined weight of unsaturated urethane oligomer and reactive diluent, and pre~erably will be employed in the range from about 0.1 to about 5 parts by.
w~ight. Representative chain transfer agents for addition polymerization re-actions include benzene; toluene; ethylbenzene; isopropylbenzene; *-butylbenzene;
cyclohe~ne; heptane; n-butyl chloride; n-butyl bromide; n-butyl iodine; n-butyt alcohol; n-butyl disulfide; acetone; ace~c acid; chloroform; carbon tet~chloride;
carbon tetrabromide; butylamine; triethylamine; ~-butyl mercaptan; n-bu~l mercaptan; tertiary aliphatic amines such as triethanolamine and ~t-butyt diethanolamine; 2-ethylhexane-1,3-dithiol; 1,10~decanedithiol; 1,2-ethanedithiol;
1,3-pro~anedithioli 1,6-octanedithiol; 1,8-octanedithiol; 1,10-octadecanedithiol;
rn-ben2enedithiol; bis-(2-mercaptoethyl) sulfide, p-xylylenedithiol; pentaerythritol tetra-7-mercaptoheptanoate; mercaptoacetic acid triglyceride; pentanethiol;
dodecanethiol; glycol mercaptoacetate; ethyt mercaptoacetate; and esters of thioglycolic and mercaptopropionic acids. Fre~rred chain transfer agents in-clude both monothiols and polythiols; the polythiols having a molecular weight in ~ 17 - -''~

~2~5i~3 the range from about 95 to about 20, 000 and having the general ~ormula R9 (SH)m, wherein R9is a polyvalent organic moiety and m is at least 2, being especially 5 preferred. During the investigation into the phenonemon oE curing the herein-described unsa~rated urethane oligomers derived from poly(aLkylene o~ide) polyols, it was discovered that the polythiols, when used in combination with the herein described photocatalyst syste~s, provide a totally unexpected improvement, of a synergistic nature, in cure rate upon exposure to actinic 10 radiation in the presence of air. Particularly preferred polythiols include glycerol trithioglycolate; pentaerythritol tetrathioglycolate; pentaerythxitol tetrakis ~3-mercaptopropionate); i~imethylolpropane tris(thioglycoaal.e~; ~L-methylolpropane tris~-mercaptopropionate~: ethylene glycol bis(thioglycolate);
ethylene glycol bis~-mercaptopropionate) and poly(propyler~e oxide ether~ -glycol bis~-mercaptopropionate) .
As noted, unsaturated urethane oligomers having as a polyol precurso~
a compound which is not a poly(alkylene oxide) poly can be combined with the novel poly(alkylene oxide) polyol-based unsaturated urethane oligomer. In such cases, the coating compositions should contain at least about 25 percent by total weight of combined unsaturated urethane oligomers of at least one poly~alkylen~
oxide) polyol-based unsaturated urethane oligomer. Represen~tive polSTol pre~
- cursors for such other unsaturated urethane oligome~s are polyesters, including caprolactone polyol polyesters.
Preferably, the coating compositions of the invention will also contaIrl from about 0.1 to about 10 parts by weight, per lQ0 parts combined wei~ht of acrylic urethane oligomer and reactive diluent, of acrylic acid.

1:~295~;~

The invention compositions can also include pigments, fillers wetting agents, flatting agents, flow control agents, and other additives typically present in coatiing compositions. In some applications, the inclusion of minor amounts of inert solvents can be advantageous. Such additive materials are weLl-5 known to.those skilled in the art and do not require further elaboration herein.
Also well-known are the concentrations at which such additives are used.
The coating compositions of this invention are prepared by conventional methods such as blending. The cornpositions can be applied to wood, metal, fabric and plastic substrates in an econornical and efficient manner using cori-10 ~entional industrial techniques and provide smooth, uniform films which arerapidly cured to dried films having excellent physical and chemical properties.
- T~e compositions are particularly noteworthy in ~t they ca~ be cured i n the presence of air at rates equivalent to those obtained in inert at~nospheres.
The improved coating compositions of this invention can be applied and 15 cured b~ any of the conventional known methods. Applica~ion can be by roll coating, curtain coating, airless spray, dipping or by any other procedure.
Th~ cure can be efiected by exposure to any high energy source, such as ionizing radiation, or low energy source, and are especially suitable for curing by exposure to actinic radiation,~such as ultraviolet light radiation, in the presence 20 of molecular oxygen. The equipment utilized for curing, as well as the ap-propriate time for curing, and the conditions under which the curin~ is effected are well-known to those skilted in the art o~ radiation curing and do not require further elaboration herein.
The invention is illustrated in greater detail by the following Examples, 25 but these examples are not to be construed as limiting the present invention.
All parts, percentages and the like are in parts by wei~ht, unless otherwise indicated.

. . , , .:

., ~ . , .
, ~1~9S83 E~AMPLE I
Several acrylated urethane resins are prepared employing as precursor compounds 4, ~' -meth5rlene-bis (cycloheY.yl isocS~ar~te), 2 -hydroxyethyl acr~late and polyester polyol or poly(alkylene oxide) polyol; with 2-ethylhexyl acrylate serving ~s inert reaction medium. In each instance, the polyol is reacted with an egcess of the polyisocyanate compound in 2-ethylhexyl acrylate to form a~
isocyanate-functional prepolymer in 2-ethylhexyl acrylate; the prepolymer is reacted with 2-hydroxyethylacrylate in the presence of 2-ethylhexyl acrylate reaction medium to form the acrylated urethane oligomer having at least two terminal ethylenically unsaturated groups and substantially no free isocyanate fi~ctions. ~!epending upon the amount of 2-ethylhexyl acrylate which is employedas reaction medium, the acrylabd urGthane composi~on is rIeat, that is, 100 percent resin solids, or a syrup of-acrylated urethane oUgomer in 2-ethylhexy~
acrylate reactive monomer diluent at resin solids concentration of 70 or 90 per-cent by weight. The acrylated urethane oligomer resins are further charac-terized in Table I.

EXAMPLE I~ -Formulations are prepared employing Resin A from Example I accordin~
t;o the schedules of ~able II.
Compositions A-G are coated onto aluminum substrates to provide a wet film thicl~ness of 1. 5 mil. Compositions C and E-K are coated onto vinS~l sheeting to provide a wet film thic~ness of 1. 5 rnil. The thus coated subs .rates are cured by exposure to ultraviolet light (200 watts/in. mercury lamp) at a line speed of 50 feet per minute The exposure time required in separate passes through the curing unit to obtain a tac~s-free,mar-resistant finish is reported in Table III.

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~ ~ ~ fi ,, ~ I c~ ~ O
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o ~ O Q ~ ' .' ' . ~3 ~3 ' ' ' ' ¢ Y ~` y ,Y, y Q o : 5 5 y ~ h O ~ Lq l$

.

l~Z~

TABLE III
. . .
Time Reauired For Cure to Tack-Free ~ar-Resistant Finish Number of :~asses ALuminum Substrate Vinyl Substrate Coating Cure Rate Atmosphere Atmosphere E~ample Formulation Ft./Min. C2 N2 C~ N2 , . .

I~-A 50 6 - II-B 50 2a 1~
~-C 50 2 1 3b 2 I~-D 50 2 1 - -It-E 50 2 1 3b ~t-F 50 ~~ 2 1 3b II-G 50 2 1 3b 2 It-I . 50 1 1 2c 2 1 1 2c 2 -~-K . 50 1 1 2c a: Complete surface cure, but bulk of coating below surface is incompletely cured.
20 b: Coating is mar-resistant, but gloss retention after scrubbing is slgnificantly ~orer in comparison to compositions cured in nitrogen.
c: .As amount of thiol compound i~ increased, film toughness increases, film modulus decreases, stain resistance is unchanged and scrub resistance - ~gloss retention after scrubbing, percent of original gloss) as function of ~5 thiol compound is as follows Thiol compound, parts by weight 1 2 3 4 Gloss retention, '~i original gloss 55 70 80 82.5 At all levels of thiol compound, gloss retention af~er scrubbing and stain resistance is poorer with each of compositions H-K when cured in C2 in comparison to each of compositions H-K cured în N2 o s~

As can be seen from the data, unsaturated urethane oligomers derived from polyester polyol generally exhibit a slower cure rate in air upon exposure to actinic radiation than in an inert atmosphere such as nitrogen. However, the addition of pentherythritol tetrakis ~mercaptopropionate) chain transfer agent to the mixed photosensitizer-photoinitiator photocatalyst system is effective in increasing the rate of cure in air of unsaturated urethane oligomers derived from polyester polyols to a level equivalent to the cure rate in an inert environment such as nitrogen. When used alone, pentaerythritol tetrakis (~-mercaptopropionate~ is ineffective, insofar as curing the unsat-urated urethane oligomer compositions is concerned, in air and inert atmospheres. However, film properties of all compositions cured in air are generally poorer than are the film properties of the corresponding compositions cured in nitrogen.
Example III
A composition is prepared employing Resin B from Example I as follows:
Resin B 70 2-Ethylhexyl acrylate 35 Pentaerythritol triacrylate 1.5 Acrylic acid 1.0 Benzophenone 3 senzoin isobutyl ether Pentaerythritol tetrakis (~-mercaptopropionate) 3 The composition is coated onto aluminum and vinyl sub-s',rates to provide a wet film thickness of 1.5 mil. The thus-coated substrates are cured by exposure to ultraviolet light (200 watts/in. mercury lamp~ at a line speed of 50 feet per minute. The formulation cures in an oxygen environment to a mar-resistant surface on aluminum in one pass and on vinyl in two passes. The cure rate of ~Z9S~3 the formulation in air is essentially equivalent to the cure rate of the formulation in nitrogen, and film properties are also substantially equivalent.
Example IV
Employing Resins A and C from Example I, formulations are prepared as follows:
Formulation A B C D E
Resin A 70 52.5 35 17.5 0 Resin C a 17.5 35 52.5 100 2-hydroxyethylacrylate 35 35 35 35 35 Pentaerythritol triacrylate 1.5 1.5 1.5 1.5 1.5 Acrylic acid 1.0 1.0 1.01.0 1.0 Benzophenone 3.Q 3.0 3.03.0 3.0 Benzoin isobutly ether 1.0 1.0 1.01.0 1.0 Pentaerythritol tetrakis (~-mercaptopropionate) 3.0 3.0 3.03.0 3.0 The formulation$ are coated onto alumlnum at a wet film thickness of 1.5 mil. The thus-coated substrates are ex-posed to ultraviolet light radiation (200 watt/in. mercury lamp) in air at a line speed of 50 feet per minute. Formulation A
requires two passes through the curing unit to obtain a tack-free, mar-resistant surface. Formulations B-E cure in a single pass to a tack-free, mar-resistant surface. The data demonstrate the improvement in cure rate which is obtained by the presence of unsaturated urethane oligomers derived from poly(alkylene oxide)polyols. `

'.

~lZ~83 EXAMPLE V

Employing Resins E-K ~om Example Il Eormulations were pre~ared as follows:

Formulation A B C D_ E _ F G
Resin E 90 Resin F - 90 Resin G - - 90 Resin H ~ ~ ~ 90 - Resin I - ~ 90 - -Resin J _ _ Resin ~ - ~
Z-ethylhenyl acrylate 15 15 15 15 15 15 15 Pentaerythritol triacr~late 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Acrylic acid - 1. 0 1. 0 1. 01. 0 1. 0 1. 0 1. 0 Benzophenone 3. 0 3. 0 - 3. 03; 0 3. 0 3 . 0 3~ 0 Be~zoin isobutyl ether 1. 0 1. 0 1. 01. 0 1. 0 1~ 0 1. 0 Pen~aerythritol tetrakis ~B-mercaptopropionate) 3, 0 3. 0 3, 03 . 0 3. 0 3. 0 3, o - ' : .

The formulations are coated onto aluminum panels at a wet film thickness of 20 1.~ mil. The thus-coated substrates are cured in air by exposure to ultraviolet light radiation (200 ~att/in. mercury'lamp) at line speeds of 50 feet per minute and 100 feet per minute. All formulations cure in air to a tack-free, mar-resistant surface in one pass at a rate of 50 feet per minute. At a cure rate of 100 feet per minute, all formulations require two passes to cure in air to a tack-free, mar-25 resistant~urface, .
- 2~

s~

. EXAMPLE VI
Employing Resins A, Bond L-N of E~ample I, formulatiorLs are prepared as fo~loT~vs:

. Formulation. A B _ C D E F G_ H
6 ResinA 70 70 Resin B - - 70 70 Resin L - - - - 80 80 70 7 Resin M
Resin N
2-ethylhexyl acrylate 35 35 35 35 25 25 35 3~
I?entaerythritol 1. ~ 1. 5 1~ i . 61. 5 1. 5 i~-3 triacrylate Acrylic acid 1.0 1.0 1.01~.0 1.0 loO 1~0 lqO
Benzophenone 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.~
Benzoin isobutyl 1.0 1.0 ~:~01.0 1.0 1.0 1.0 1.0 - ether Pentaerythritol 3.0 0.0 3.0 0.0 3.0 O.û 3,0 o.i~3 tetrakis ( G-mercaptopropionate) Viscosity,thousand cps 4 .4 4 4 30 4 30 - 27 . . ..

1513~

EXA~PLE VI - continued Formulation l _ J . L M N _ O_ Resin A
- Resin~B
Resin L
Resin M 80 80 70 70 - - ~ -Resin N ~ 80 80 70 70 2-ethylhexyl acrylate 25 25 35 ~ 25 2535 3 Pentaerythritol 1. 5 1. 5 1. 5 1. 5 1. 5 10 5 1. 5 1. 5 ~riacrylate ~ lic ac,id 1.0 1.0 1.0 t -O t,O 1.~
Benzophenone 3 . 03 . 0 3, 0 3 . 0 3 . 0 3~ 03 . 0 3 O
Benzoin isobutyl 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1;0 ether Pentaery~ritol 3. 0 0. 0 3. 0 0. 0 3 . O 0. 0 3. 0 0~ 0 tetrakis mercaptopropionate) Viscosity,thousand cps 30 4 30 4 30 . 430 4 T~e formulations are employed to coat alurninum Fanels ~.Q a wet film thickness of 20 1.5 mil. The thus-coated substrates are exposed in air to ultraviolet radiation (200 watt/in. mercury lamp) at a line speed of 100 feet per minute, The exposur2 time required in separate passes through the curing unit to obtain a tac~ ree, mar-- resistant surface is as follows:

, Formulation A B C D E F G H I J K L M N O P
Number of 5 9 g~6 2 1 2 2 2 1 2 2 1 1 2 2 passes ~? 100 fpm . .. . .

- , ' ' :~Z~58~

.
~ he data demonstrate that unsaturated urethane oligomer compositions derived from poly(alkylene oxide) polyols cure in air at a rate significantly greater than do such oligomer compositio~ derived from polyestPr pol~roLs~
The data further demonstrate the ~ster cure rate in air of oligomers prepared 5 from poly(tetramethylene oxide) polyoi in comparison to such oligomers prepared from poly(propylene oxide) polyol. The data also demo~strate that poly(tetra-meth~lene oxide) polyol~ased unsatur,ated urethane oligomer compositions, using a mixed photosensitizer-photoinitiator photocatalyst system without chain-transfer agent, cure in air at rates equivalent to, and in some instances, 10 . i~ster than, the same compositions employing the same photocatalyst system with chain-transfer agent.

.

'~ .

~ 29 ~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Unsaturated addition-polymerizable urethane resins characterized by the presence of at least one ethylenically unsaturated group having the structure - CH = C ? , said resins being further characterized by the presence of a principal carbon-to-carbon chain consisting essentially of at least one poly(alkylene oxide) polyol, said principal chain being separated from said un-saturated group by at least two urethane groups, said resins consisting essentially of the reaction product of i) at least one organic isocyanate compound having at least two isocyanate groups;
ii) at least one poly(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkylene group separating each pair of oxygen atoms;
and iii) at least one unsaturated addition-polymerizable monomeric com-pound having a single isocyanate-reactive active hydrogen group;
There being present an excess of isocyanate compound with respect to the hydroxyl groups of said poly(alkylene oxide) polyol;
said unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive hydrogen group being present in an amount sufficient to provide at least one molar equivalent of active hydrogen group with respect to isocyanate reactivity.

2. Unsaturated urethane resins according to claim 1 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

3. Unsaturated urethane resins according to claim 2 wherein said poly(tetramethylene oxide) glycol has a molecular weight in the range from about 250 to about 4000.

4. Unsaturated urethane resins according to claim 1 comprising the reaction product of A) at least one isocyanate-functional prepolymer, said prepolymer comprising the reaction product of a) at least one organic isocyanate compound having at least two isocyanate groups; and B) at least one poly(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkylene group separating each pair of oxygen atoms;
the amount of such isocyanate compound being sufficient to provide an excess of isocyanate groups with respect to hydroxyl groups of such poly(alkylene oxide) polyol; and C) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group;
the amount of such unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being sufficient to provide at least one molar equivalent of active hydrogen group with respect to the isocyanate groups of such prepolymer.

5. Unsaturated urethane resins according to claim 4 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

6. Unsaturated urethane resins according to claim 5 wherein said poly(tetramethylene oxide) glycol has a molecular weight in the range from about 250 to about 4000.

7. Unsaturated urethane resins according to claim 4 wherein such isocyanate compound is present in an amount sufficient to provide an NCC:CH
ratio of at least 2.3:1, with respect to the hydroxyl groups of such poly(alkylene oxide) polyols.

8. Unsaturated urethane resins according to claim 7 wherein at least one of said polyalkylene ether polyols is poly(tetramethylene oxide) glycol.

9. Unsaturated urethane resins according to claim 8 wherein said poly-(tetramethylene oxide) glycol has a molecular weight in the range from about 250 to about 4000.

10. Unsaturated urethane resins according to claim 8 wherein said NCO:OH ratio is in the range of about 2.3-4:1.

11. A coating composition comprising A) at least one unsaturated urethane resin comprising the reaction product of i) at least one organic isocyanate compound having at least two isocyanate groups;
ii) at least one poly(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkyelen group separating each pair of oxygen atoms;
iii) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group;

there being present an excess of isocyanate compound with respect to the hydroxyl groups of said poly(alkylene oxide) polyol;
said unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being present in an amount sufficient to provide at least one molar equivalent of active hydrogen group with respect to isocyanate reactivity; and B) A reactive diluent system comprising at least one unsaturated addition-polymerizable monomeric compound which is copolymerizable with said unsaturated urethane resin;
the amount of unsaturated urethane resin being in the range from about 30 to about 90 weight percent, based on total weight of unsaturated ure-thane resin and reactive diluent system.

12. A coating composition according to claim 11 wherein said diluent system contains at least one unsaturated addition-polymerizable monofunctional monomeric compound selected from the group consisting of esters having the general formula ;

wherein R0 is hydrogen or methyl and R is an aliphatic or cyclo-aliphatic group having from 4 to 18 carbon atoms.

13. A coating composition according to claim 12 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

14. A composition according to claim 11 wherein said unsaturated urethane resin comprises the reaction product of A) at least one isocyanate-functional prepolymer, said prepolymer comprising the reaction product of a) at least one organic isocyanate compound having at least two isocyanate groups; and B) at least one poly(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkylene group separating each pair of oxygen atoms;
the amount of such isocyanate compound being sufficient to provide an excess of isocyanate groups with respect to hydroxyl groups of such poly(alkylene oxide) polyol; and C) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group;
the amount of such unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being sufficient to provide at least one molar equivalent of active hydrogen group with respect to the isocyanate groups of such prepolymer.

15. A coating composition according to claim 14 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

16. A coating composition according to claim 14 wherein said diluent system contains at least one unsaturated addition-polymerizable monofunctional monomeric compound selected from the group consisting of esters having the general formula ;

wherein R is hydrogen or methyl and R is an aliphatic or cyclo-aliphatic group having from 4 to 18 carbon atoms.

17. A coating composition according to claim 16 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol,

18. A coating composition according to claim 18 wherein said isocyanate compound is present in an amount sufficient to provide an NCO:OH ratio of at least 2.3:1, with respect to the hydroxyl groups of said polyalkylene ether polyol.

19. A coating composition according to claim 18 wherein at least one of such poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

20. A coating composition according to claim 19. wherein said NCO:OH
ratio is in the range of about 2.3-4:1.

21. A coating composition according to claim 21 wherein the molecular weight of said poly(tetramethylene oxide) glycol is in the range from about 250 to about 4000.

22. A coating composition comprising A) at least one unsaturated urethane resin comprising the reaction product of i) at least one organic isocyanate compound having at least two isocyanate groups;
ii) at least one poly(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkylene group separating each pair of oxygen atoms, and iii) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group;
there being present an excess of isocyanate compound with respect to the hydroxyl groups of said poly(alkylene oxide) polyol;
said unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being present in an amount sufficient to provide at least one molar equivalent of active hydrogen group with respect to isocyanate reactivity;
B) A reactive diluent system comprising at least one unsaturated addition-polymerizable monomeric compound which is copolymerizable with said unsaturated urethane resin;
the amount of unsaturated urethane resin being in the range from about 30 to about 90 weight percent, based on total weight of unsaturated ure-thane resin and reactive diluent system;
C) At least one aromatic ketone or aromatic aldehyde photo-sensitizer which promotes photopolymerization through bimolecular photochemical reactions of the energy donor type or hydrogen abstraction type; and D) At least one aromatic ketone photoinitiator which generates a radical pair by way of unimolecular homolysis resulting from photoexcitation.

23. A coating composition according to claim 22 wherein at least one of said poly(alkylene oxide) polyols is poly)tetramethylene oxide) glycol.

24. A coating composition according to claim 22 wherein said isocyanate compound is present in an amount sufficient to provide an NCO:CH ratio of at least 2.3:1, with respect to the hydroxyl groups of said polyalkylene ether polyol.

25. A coating composition according to claim 24 wherein said photosensitizer is present in an amount in the range from about 0.01 to about 50 parts by weight, and said photoinitiator is present in an amount in the range from about 0.01 to about 10 parts by weight, said parts by weight being per 100 parts by combined weight of said unsaturated urethane resin and said re-active diluent system.

26. A coating composition according to claim 25 wherein at least one of said poly(alkylene oxide)polyols is poly(tetra-methylene oxide)glycol.

27. A coating composition according to claim 26 wherein said photosensitizer is benzophenone and said photoinitiator comprises benzoin isobutyl ether.

28. A coating composition according to claim 22 con-taining from about 0.01 to about 5 parts by weight, per 100 parts by combined weight of said urethane resin and said reactive diluent system, of at least one thiol selected from the group consisting of monothiols and polythiols, said polythiols having a molecular weight in the range from about 95 to about 20,000 and having the general formula R9(SH)m , wherein R is a polyvalent organic moiety and m is at least 2.

29. A coating composition according to claim 28 where-in at least one of said poly(alkylene oxide)polyols is poly(tetra-methylene oxide)glycol.

30. A coating composition according to claim 28 where-in such isocyanate compound is present in an amount sufficient to provide an NCO:OH ratio of at least 2.3:1, with respect to hydroxyl groups of such poly(alkylene oxide)polyols.

31. A coating composition according to claim 30 wherein said photo-sensitizer is present in an amount in the range from about 0. 01 to about 50 parts by weight, and said photoinitiator is present in an amount in the range from about 0. 01 to about 10 parts by weight, said parts by weight being per 100 parts by combined weight of said unsaturated urethane resin and said reactive diluent system.

32. A coating composition according to claim 31 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

33. A coating composition according to claim 32 wherein said photo-sensitizer is benzophenone, said photoinitiator is benzoin isobutyl ether, and said thiol compound is pentaerythritol tetrakis (.beta.-mercaptopropionate).

34. A coating composition according to claim 33 wherein said diluent system contains at least one unsaturated addition-polymerizable monofunctional monomeric compound selected from the group consisting of esters having the general formula ;

wherein Ro is hydrogen or methyl and R is an aliphatic or cyclo-aliphatic group having from 4 to 18 carbon atoms.

35. A coating composition according to claim 34 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

36. A coating composition according to claim 35 wherein said photo-sensitizer is benzophenone, said photoinitiator is benzoin isobutyl ether, and said thiol compound is pentaerythritol tetrakis (.beta.-mercaptopropionate).

37. A coating composition according to claim 22 wherein said unsaturated urethane resin comprises the reaction product of A) at least one isocyanate-functional prepolymer, said prepolymer comprising the reaction product of a) at least one organic isocyanate compound having at least two isocyanate groups; and b) at least one poty(alkylene oxide) polyol, said polyol having from 1 to 9 carbon atoms in the alkylene group separating each pair of oxygen atoms;
the amount of such is ocyanate compound being sufficient to provide an excess of isocyanate groups with respect to hydroxyl groups of such poly(alkylene oxide) polyol; and B) at least one unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group;
the amount of such unsaturated addition-polymerizable monomeric compound having a single isocyanate-reactive active hydrogen group being sufficient to provide at least one molar equivalent of active hydrogen group with respect to the isocyanate groups of such prepolymer.

38. A coating composition according to claim 37 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

39. A coating composition according to claim 37 wherein said isocyanate compound is present in an amount sufficient to provide an NCO:OH ratio of at least 2.3:1, with respect to the hydroxyl groups of said poly(alkylene oxide) polyol.

40. A coating composition according to claim 39 wherein said photo-sensitizer is present in an amount in the range from about 0.01 to about 50 parts by weight, and said photoinitiator is present in an amount in the range from about 0.01 to about 10 parts by weight, said parts by weight being per 100 parts by combined weight of said unsaturated urethane resin and said reactive diluent system.

41. A coating composition according to claim 40 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

42. A coating composition according to claim 41 wherein said photo-sensitizer is benzophenone and said photoinitiator is benzoin isotutyl ether.

43. A composition according to claim 37 containing from about 0.01 to about 5 parts by weight, per 100 parts by combined weight of said urethane resin and said reactive diluent system of at least one thiol selected from the group consisting of monothiols and polythiols, said polythiols having a molecular weight in the range from about 95 to about 20,000 and having the general formula R9(SH)m, wherein R9 is a polyvalent organic moiety and m is at least 2.

44. A coating composition according to claim 43 wherein at least one of said poly(alkylene oxide) polyols is poly(tetramethylene oxide) glycol.

45. A coating composition according to claim 43 wherein such, isocyanate compound is present in an amount sufficient to provide an NCO:OH ratio of at least 2.3:1, with respect to the hydroxyl groups of such poly(alkylene oxide) polyols.

46. A coating composition according to claim 45 wherein said photo-sensitizer is present in an amount in the range from about 0.01 to about 50 parts by weight and said photoinitiator is present in an amount in the range from about 0. 01 to about 10 parts by weight, said parts by weight being per 100 parts by combined weight of said unsaturated urethane resin and said reactive diluent system.

47. A coating composition according to claim 46 wherein at least one of said poly(alkylens oxide) polyols is poly(tetramethylene oxide) glycol.

48. A coating composition according to claim 47 wherein said photo-sensitizer is benzophenone, said photoinitiator is benzoin isobutyl ether, and said thiol is pentaerythritol tetrakis (.beta.-mercaptopropionate).

49. A coating composition according to claim 45 wherein said diluent system contains at least one unsaturated addition-polymerizable monofunctional monomeric compound selected from the group consisting of esters having the general formula ;

wherein R° is hydrogen or methyl and R is an aliphatic or cyclo-aliphatic group having from 4 to 18 carbon atoms.

50. A coating composition according to claim 49 where-in at least one of said poly(alkylene oxide)polyols is poly(tetra-methylene oxide)glycol.

51. A coating composition according to claim 50 where-in said photosensitizer is benzophenone, said photoinitiator is benzoin butyl ether, and said thiol is pentaerythritol tetrakis (.beta.-mercaptopropionate).

52. A coating composition according to claim 51 wherein said poly(tetramethylene oxide)glycol has a molecular weight in the range from about 250 to about 4000.

53. A method for coating a substrate comprising apply-ing to said substrate a coating composition according to claim 22, and exposing such coated substrate to actinic radiation in the presence of oxygen for a period of time sufficient to cure said coating to a hard mar-resistant surface.