GB1596827A - Radiation curing in the presence of steam - Google Patents

Description

(54) RADIATION CURING IN THE PRESENCE OF STEAM (71) We, DYNACHEM CORPORATION, a corporation organised and existing under the laws of the State of Delaware, United States of America, of Tustin, California, United States of America. do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is performed to be particularly described in and by the following statement: This invention relates to radiation-curable materials and more particularly, to the curing of radiation-curable materials comprising an ethylenically unsaturated substance in the presence of steam.

Reactions that occur during radiation curing of substances containing an ethylenically unsaturated group are free radical in nature and free radicals are inhibited by oxygen. The styryl radical, for example, will react 10 times more readily with oxygen than with a styrene monomer and an acrylate will react 400 times more readily with oxygen than with an acrylate monomer. The effect of oxygen in inhibiting free radical reactions in radiation curing is well known and two mechanisms are postulated. One is quenching or deactivation of the photo-activated sensitizer by oxygen; the other is reaction of oxygen with the polymer radicals.

By the quenching or deactivation mechanism, O quenching of the activated state competes with hydrogen abstraction:

Since reaction with R-H is necessary for generating the initiating species, quenching by oxygen clearly reduces the efficiency of the curing process.

The second mechanism, of oxygen inhibition reaction with the polymer radicals, impedes initiation and propagation. Reaction of growing polymers (P) with O, produces peroxy radicals (PO2) which are generally not effective in propagation, but rather undergo hydrogen abstraction from some H-donor (R-H) thereby terminating the chain.

The overall effect is the formation of short polymer chains resulting in a tacky or low gloss surface and poor coating characteristics.

Optimum cure conditions are presently obtained in an atmosphere of inert gas; the generally available inert gases are nitrogen and carbon dioxide with nitrogen being the most widely used inert gas and it is usual. in current commercial practice to replace oxygen on the surface of a coated substrate prior to and during exposure to radiation. While injection of nitrogen is acceptable in some applications, it would not be acceptable in a paper mill or a carpet mill, for example, where web widths run from 40 to 180 inches (about 4.5 meters) and more and where the cost of injecting nitrogen across such a width would be prohibitive.

The most common method of curing with ultra-violet (UV) radiation involves the use of medium pressure mercury vapor light sources which, in addition to UV light, produce considerable heat. The temperature at the surface of a 200 watt/inch mercury lamp is about 800"C. These lamps are generally located from 0.5 to 12 inches (1.3 to 31 cm.) above the surface of the substrate bearing the U.V.-curable material and it is clear that substantial quantities of this heat (that is, infra-red radiation) are transmitted to the substrate.

Attempts to cure U.V-curable ethylenically unsaturated compositions printed or coated on heat sensitive substrates such as thin paper, textiles and the like have not been successful because of the attendant damage (shrinking, warping, scorching, melting) to the substrate.

The present invention provides a method of curing a radiation curable material comprising a polymerisable ethylenically insaturated substance which comprises interposing between a radiating source of radiation which emits both U.V. and I.R. radiation and a material comprising said substance and curable by such radiation an atmosphere of superheated steam as hereinafter defined in order to reduce the amount of I.R. radiation incident upon such curable material.

It has been found that radiation polymerisable ethylenically unsaturated substances, particularly those that polymerize, crosslink or cure via a free radical mechanism, can be successfullv irradiated in the presence of steam to provide dry, high gloss, tack-free cured products; further, steam will transmit those forms of radiation effective to cure a variety of polymerizable, curable or crosslinkable ethylenically unsaturated substances while at the same time absorbing infra-red radiation. The invention is practiced most simply by blanketing a composition containing a radiation curable ethylenically unsaturated substance with steam prior to and during irradiation.

The steam can come from any convenient source: since low pressure steam at atmospheric or slightly elevated -- pressure i.e. up to 5 PSI -- can be used. the steam can be that available at most plants or can be easily produced by a conventional steam generator.

The use of steam injectors or one or more air knives to distribute the steam over the surface of the substrate being printed or coated is a conventional expedient and need not be discussed in detail.

The steam should be superheated: bv this it is meant that the steam should be heated to a temperature sufficiently high that it does not condense on the substrate under the conditions of use.

The use of steam thus provides three important advantages. First, it displaces or otherwise reduces the oxygen content of the atmosphere surrounding the radiation curable composition comprising an ethylenically unsaturated substance so that high gloss coatings can be obtained. Steam is thus an effective inerting medium. Second, it absorbs infra red radiation so that the temperature of the substrate being printed or coated remains at an acceptable level. Steam is thus an effective cooling medium. Finally, steam is readily available at virtually every industrial enterprise in the world. Steam is cheap.

This combination of inerting and cooling properties with ready availability and low cost represents a substantial improvement over the state of the art and makes such irradiation technology as UV-curing available to industries such as the paper, textile and printing-on plastics industries, where UV curing is not now utilized because of the disadvantages provided bv the high cost and heat associated with the present state of the art.

Radiation curable ethylenically unsaturated materials useful herein can be coated, printed or laminated to a greater variety of substrates than was previously possible.

Thus, there can be used the relatively heat-resistant substrates currently in use such as glass, ceramic and metal as well as the laminates used in the printed circuit board industry.

These substrates are used in a variety of forms including wires, rods, sheets, panels. films, fabrics, cylinders, bottles and containers.

There can also be used various plastics in the form of wires. rods. sheets, panels, films (including laminates of different plastics) fabrics (woven, non-woven and tufted) bottles and similar containers. These plastics include the thermoset plastics such as phenolic.

epoxy, polyester, polyurethane and polyimide as well as the well-known thermoplastic materials based on the homopolymers and copylymers of ethylene, propylene, butylene, butadiene, styrene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl methyl ether, allyl alcohol, vinyl pyrrolidone, vinyl alcohol, vinyl butyral, vinyl carbazole, acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, acrylamide, N,N-dimethyl acrylamide, methacrylamide, caprolactone, ethylene glycol, propylene glycol, terephthalic acid, adipic acid, caprolactam, ethylene oxide, propylene oxide, siloxane, isocyanate, sulfone, phenyl sulfone, pheylene sulfide, pheylene carbonate, pheylene ether, phenylene oxide, and acetal.

There can also be used as substrates the various natural and modified natural products such as gutta percha, silk, wool, cotton, cellulose acetate, methyl cellulose; there can be used wood and various woody materials and paper, including newsprint, tag stock, parchment, cardboard and bag stock.

The radiation curable material can be applied to the substrate in a thickness ranging from 0.01 to more than 100 mils; the thickness will depend on the ultimate use of the product.

Thicknesses of 0.2 to 2 mils are conventional.

The invention enables one to polymerize, cure or crosslink radiation curable compositions containing at least one monomer having an ethylenically unsaturated group capable of polymerization, curing or crosslinking via a free radical initiated mechanism.

In many instances the radiation curable compositions will produce solid, dry products upon exposure to suitable radiation with the addition of any photosensitizer, activator, catalyst or initiator. When it is desirable to use a photosensitizer, activator, catalyst or initiator, as is frequently the case with UV curable systems, they can be used singly or in admixture, with the total amount varying from 0.01 to 20 percent by weight of the composition; 0.1 to 5 percent is a preferred range. Synergistic effects are observed with some mixtures.

The general classes of photosensitizers include azo compounds, dyes, sulfur containing compounds, metallic salts and complexes, oximes, polynuclear compounds, peroxides, various halogen-containing compounds and carbonyls. For coatings and inks the benzoin ethers, benzophenone and benzophenone-Michlers ketone mixtures are widely used.

Among the sensitizers, the aromatic carbonyl compounds are quite important; there are included benzoin and the benzoin ethers including benzoin methyl ether; benzoin ethyl ether; benzoin allyl ether; benzoin propyl ether; benzoin isopropyl ether; benzoin butyl ether; benzoin isobutyl ether; benzoin sec-butyl ether; benzoin thiophenyl ether; benzoin amyl ether; benzoin hexyl ether; benzoin octyl ether; benzoin 2-ethylhexyl ether; benzoin nonyl ether; benzoin trimethyhexyl ether; benzoin diethyl ether; benzoin phenyl ether; hydroxyethyl benzoin ether; ethylene glycol benzoin ether; 2-chloroethyl-benzoin ether; benzoin isobutoxymethyl ether; a-alkoxybenaoin ethers; and benzoin carbamates; benzophenone and derivatives of benzophenone including "Michler's Ketone" 4,4' Bis(dimethylamino)benzophenone; p,p'-diaminobenzophenone; 4-(dimethylamino) ben zophenone; p-dichloromethylbenzophenone; p-chlorobenzophenone; 4,4' bis(bromomethyl) benzophenone; p-hydroxybenzophenone; 2-hydroxy-4 methoxybenzophenone-5-sulfonic acid; p-acryloxybenzophenone; o- methoxybenzophenone- p-methoxybenzophenone; glycidyl ethers of benzophenone; vinyl substituted benzophenone; 2-isopropenylbenzophenone; monocarboxyl-substituted ben zophenone; polycarboxyl-substituted benzophenone; p-nitrobenzophenone; m benzophenonesulfonyl chloride; p-p-'-bis (dimethylamino) thio-benzophenone; pheny lthiomethylbenzophenone; benzylthiomethylbenzophenone; benzopinacolone; anthrone; benzanthrone; benzathronesulfonyl chloride; 9-fluorenone; hydroxy-fluorenones; aminof luorenones; 2-bromoethyl-9-fluorenonesulfonyl chloride; dibenzosuberone; 1 chloromethyl-6-chlorosulfonyl-2-naphthylphenyl ketone; n-methylacridone; and poly(vinyl benzophenone; monoaryl ketones including acetophenone; chloroalkylphenyl ketones; o methylacetophenone; a-bromoacetophenone; ortho-bromoacetophenone; trichloroace tophenone; trichloroethylidineacetophenone; 2-2-dichloro-4'-tertiary-butylacetophenone; 2,2,2-trichloro-4'-tertiary-butylacetophenone; a-bromoisobutyrophenone; 2,2-dibromo 2(phenylsulfonyl) acetophenone: a ,a-dialkoxyacetophenone; 2,2-dimethoxyacetophenone; 2,2-dimethoxy-2-phenylacetophenone; 2,2-diethoxyacetophenone; o- methoxyacetophenone; m-methoxyacetophenone; p-methoxyacetophenone; 2-butoxy-2 phenylacetophenone 2-phenylthio-2-phenylacetophenone- ethyl benzoylacetate; para aminophenyl ketones; cyclohexylphenyl ketone; pivalophenone; valerophenone; and acetonaphthone; diketones including biacetyl; benzil dimethyl ketal; 2,3-dibenzoyl-2-norbornene; ben zoylbenzal chloride; 2,2-dibromo-2-(phenylsulfonyl) propanedione; a-naphthil; 2,3 butanedione; benzil; pentanedione; 1-aryl-1 ,2-propanediones; 2,3-bornanedione; pheny lpyruvic acid; and 2,4-pentanedione; xanthone and thioxanthenones including 3,6-bis(dimethylamino) thioxanthenone; and 2-chlorothioxanthenone; thioketones including thiobenzophenone; p,p'-dimethoxythiobenzophenone; and p,p'bis(dimethylamino)thiobenzophenone; sulfur-containing compounds such as n-dodecyl mercaptan; 2-mercaptobenzimidazole; diphenyl sulfide, cyclohexylphenylsulfide; benzoin thioethers; benzoin thiophenyl ether; phenylthiomethylbenzophenone; s,s' -diphenyl dithiocarbonate; calcium sulfide; metallic selenides; metallic tellurides; diaryl disulfides; diphenyl disulfide; dithiolane; dibenzoyldisulfide; dixanthate; benzothiazoles; 2,2'-dithiobis(benzothiazole); 2mercaptobenzothiazole; thiazolines; thiocarbamates; dithiocarbamic esters; dithiocarbamic anhydrides; thiurams; toluene sulfonic acid; sulfonyl chlorides; m-(chlorosulfonyl)benzyl chloride; naphthalenesulfonyl chloride; 2-bromoethyl-9-fluorenonesulfonyl chloride; 2,2dibromo-2(phenylsulfonyl) acetophenone; 2,2-dibromo-2(phenylsulfonyl) propanedione; benzophenoesulfonyl chloride; and diphenyl disulfone; oximes including o-acyloximes; 1-phenyl-1 ,2-propanedione-2-o-benzoyl oxime; oxidooxazole; benzylmonooime; and biacetyl monooxime phenylcarbamate; azo and azido compounds including 2,2'-azobisisopropane; azobia-isobutyronitrile; 2-phenylazobisisobutyronitrile; azobisisobutyramide; azobis (isobutyl acetate); di-(2,4,6- tribromophenyl)-4,4'-azobis(4-cyanovalerate); p-azidobenzaldehyde; bnaphthalenesulfonyl azide; diazomethane; bis(phenylsulfonyl) diazomethane; diazonaphthalenes; diazothioethers; quinone diazides; and m,m'-azoxystyrene; imidazoles including benzimidazoles; 2-methylbenzimidazole; 2-mercaptobenzimidazole; and triphenyl-imidazolyl dimers; amines including triethylamine; n,n-dimethylbenzylamine; methyldiethanolamine; ethyldiethanolamine; triethanolamine; p-nitro aniline; n-acetyl-4-nitro-1-naphthylamine; and aminoanthraquinone; ammonium salts such as bipyridylium salt; benzyltrimethylammonium chloride; and diazonium salts; halogenated organic compounds such as chloroform; bromoform; iodoform; carbon tetrachloride; carbon tetrabromide; ethylene dichloride; trichloroethylene; trichloroethane; bromotrichloroethane; vinyl bromide; 1.2-dibromotetrafluoroethane; iodoethane; diacylhalomethane; hexachloroethane; tetrachloroethane; hexachlorobenzene; and o-dichlorobenzene; polynuclear compounds including napththalene; halogenated naphthalenes; 2,3,6- trimethylnaphthalene; a-naphthol; 1-aminonaphthalene; 1 -methoxynaphthalene; 2,3- diphenylquinoxaline; anthracene; aminoanthraquinone; phenanthrene; naphthacene; fluorene; 9-fluorenone; stilbene; trinitrofluorenone; and polynuclear quinones; useful quinones include p-benzoquinone; o-benzoquinonediazide; anthraquinone; alkylanthraquinones; 2-methylanthraquinone; 2-ethylanthraquinone; 2-tertiary butylanthraquinone; 2-chloroanthraquinone; aminoanthraquinone; 1,5 diaminoanthraquinone; piperidino-anthraquinones; anthraquinonesulfonyl chloride; benzanthraquinone; 1-4-napthoquinone derivatives; phenanthrenequinones; and achloranthraquinone; the metal salts and complexes include zinc chloride; zinc bromide; zinc sulfide; ferric chloride; chromium chloride; nickel chloride; tin chloride; stannous chloride; vanadium tetrachloride; vanadium oxychloride; vanadium naphthenate; aluminium chloride; aluminium bromide; aluminium iodide; silver halides; gold salts; sodium chloraurate; mercury salts; mercury iodosulfide; titanium tetrachloride; cadmium sulfide; boron trifluoride; boron trichloride; ceric salts; thallium salts; uranyl salts; cobalt octoate; cobalt naphthenate; magnesium oxide; zinc oxide; titanium dioxide: alumina; cupric oxide; chromium oxide; silver oxide compounds: metal chelates; metal amine complexes; cobalt edta complexes; iron deta complexes; metal acetylacetonate; manganese tris (acetylacetonate); metal salt-saccharide complexes; metal oxalato complexes; p-benzoquinone complexes; copper (I) complexes; manganese carbonyl; rhenium carbonyl; osmium carbonyl; iron carbonyls; metal thiocarbonyls; trialkylaluminium; diethylaluminium chloride; tripheny lmethyldiethvltitanium chloride; bis(2-chloroethyl) diethyltitanium; tetrabenzyltitanium; ferrocene; and cyclopentadienylmanganese tricarbonyls; useful peroxides include hydrogen peroxide; benzoylperoxide, tertiary-butyl peroctoate; t-butvl a-cyanoperacetate; t-butyl hydroperoxide; di-t-butyl peroxide; cumene hydroperoxide; a-cumyl peroxide; ergosterol peroxide; fluorenone hydroperoxide; and acetyl peroxide; dyes that are useful include acridines; benzacridine; benzidines; b-carotene; chlorophyll; crystal violet; eosin; erythrosine; fluorescein; indanthrene yellow; irgazin yellow; methyl violet; methylene blue; pyronine-G; rhodamines; riboflavin; rose bengal; thiazine dyes; thionine; xanthene dyes; xanthophyll; and iodoeosine; The radiation curable materials that can be polymerized, cured or cross-linked in accordance with this invention are those having at least one polymerizable ethylenically unsaturated group of the structure C=C Of these materials, on eimportant class is characterized by the presence of at least one acrylyl or methacrylyl group of the general formula

where R is hydrogen or methyl. Monomers, polymers, oligomers and compositions whose functionality is attributable to the presence of acrylate and/or methacrylate groups include acrylic acid, methacrylic acid, acrylamide, methacrylamide, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hexyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl acrylate, butoxyethoxyethyl acrylate, bicyclo [2.2.1J hept-2-yl acrylate, dicyclopentenyl acrylate, isodecyl acrylate, ethylene diacrylate, diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, ethylene dimethacrylate; ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 1,4benzenediol dimethacrylate, 1,4-cyclohexanediol diacrylate, neopentyl glycol diacrylate, triethylene glycol diacrylate, tetraethyleneglycol diacrylate, pentaerythritol mono-, di-, tri or tetracrylate or mixtures thereof, pentaerythritol tri- or tetramethacrylate, 1,5pentanediol dimethacrylate trimethylol propane mono. -di-, or triacrylate or mixtures thereof, 2-phenoxyethyl acrylate, glycidyl acrylate, 2-ethoxyethyl acrylate, 2-methoxyethyl acrylate. 2-(n ,n-diethylamino) ethyl acrylate. omega-methoxyethyl (hendecaoxyethylene) acrylate, omega-tridecoxyethyl (hendecaoxyethylene) acrylate, trimethoxyallyloxymethyl acrylate, bicyclo 12.2.11 hept-2-en-5-ylmethyl acrylate, bicyclo 12.2.11 hept-2-en-5,6-diyl diacrylate, vinyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl acrylate, (methyl carbamyl) ethyl acrylate and the bis-acrylates and methacrylates of polyethylene glycols of molecular weight 200-1500.

One group of acrylyl and methacrylyl esters that are particularly useful have the general formula

Where the acrylyl compound has the general formula

in which M is H or Cl M' is cycloalkyl having 5 to 12 carbon atoms (such as cyclopentyl, dicyclopentyl, methyclyclopentyl and dimethylcyclopentyl) cycloalkenyl having 5 to 12 carbon atoms (such as cyclopentenyl, methylcyclopentenyl, dicyclopentenyl or bicyclo 12.2.1! hept-2-en-yl).

CpH2pM" or (C9H2q O)s Cq H2q+1; where p is an integer from 1 to 10 q is 2,3, or 4, s is 0,1,2,3, or 4, M" is hydrogen, hydroxyl, phenoxy, alkoxy of 1 to 8 carbon atoms; and where the acrylyl compound has the general formula

G is a polyvalent alkylene group of the formula --C,H2x~y in which x is an integer from 2 to 8 y is 0,1 or 2, (for example, divalent alkylene when y= 0 such as -C2H4-, C3H6isC,H6, C5H10- and neC6H12; trivalent alkylene when y=1 such as

or tetravalent alkylene when y is 2, such as

or G is a divalent ether or ester group of the formula (Cq H2q O)t Cq H2q or (Cq H2q COO)t Cq H2q where t is an integer from 1 to 5 and q is 2,3 or 4 (such as oxyethylene, oxpropylene, oxybutylene, polyoxyethylene, polyoxypropylene or polyoxybutylene) and r is the valence of G and may be 2,3 or 4.

Triethyleneglycol diacrylate, tetraethylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate and pentaerythritol tetraacrylate are especially useful Acrylate or methacrylate functionality can be incorporated in polymers and oligomers having carboxyl, hydroxyl, oxirane or isocyanate groups via reaction with acrylic monomers. Addition reactions of isocyanates to form urethanes or oxiranes to form esters are relatively straightforward. Other methods of acrylation involving condensation or ester interchange reactions are well known.

Thus, there can be used epoxy acrylates obtained by reacting an epoxy resin with acrylic or methacrylic acid or obtained by reacting a hydroxyalkyl acrylate with an acid anhydride and reacting that product with a diepoxide. Oils. such as soyabean oil and linseed oil, can be epoxidized and acrylated.

Polyester resins, for example from a glycol-dibasic acid condensation, can be acrylated by using acrylic or methacrylic acid to complete the esterification. Another method uses the reaction of an anhydride with a mixture of propylene oxide and glycidyl acrylate to obtain an acrylated polyester.

Acrylated alkyd resins are obtained by the reaction of, for example, a triol, dibasic acid, phthalic anhydride and a fatty acid such as hydrogenated castor oil fatty acids. After reaction is complete acrylation is achieved by direct esterification with acrylic acid.

Urethane acrylates can be prepared directly by the reaction of a diisocyanate with an hydroxyalkyl acrylate, such as 2-hydroxyethyl acrylate. Oligomers are obtained by using an isocyanate-terminated urethane prepolymer for reaction with the hydroxyalkyl acrylate.

The urethane prepolymer can be of the polyether or polyester type.

Acrylate functionality can be incorporated in a variety of polymer backbones by incorporating glycidyl methacrylate into the polymer chain and then reacting the pendant oxirane groups with acrylic or methacrylic acid.

Other radiation curable systems are based on unsaturated polyesters such as are obtained from fumaric acid. 4,4'-stilbenedicarboxylic acid, maleic acid, and diallyl ether.

Cinnamate ester groups are also useful, for example in a polyvinyl alcohol--cinnamate ester combination and in conjunction with a variety of polymer materials: polycarbonate cinnamate; polyurethane cinnamate: cinnamylidene-malonate copolyesters; bisphenol A-fumarate polyester-cinnamate; cinnamyl-modified poly(meth) acrylates; polyepichlorohydrin/cinnamate; poly(cinnamyl methacrylate); epoxy cinnamylidene acetate; carboxycinnamate modified polyesters; Radiation curable ethylenically unsaturated substances are also obtainable from the 2-phenylmaleimido group, allyl ester-maleimide combinations, allylthioether polymers, chalcones, sorbic acid derivatives, itaconic acid derivatives and mixtures containing itaconic acid; polyvinyl alcohol, polyvinyl acetate or polyvinyl butyral.

Another radiation curable ethylenically unsaturated polymer system is based on the free-radical addition of a thiol to an olefinic double bond: R-SH + CH2=CHR' yR-S-CH2-CH2-R' When a polyene and a polythiol are admixed and a source of free-radicals is present, rapid curing occurs by simultaneous chain extending and crosslinking reactions.

Other crosslinkable, polymerizable or curable ethylenically unsaturated substances include the nitriles such as acrylonitrile and methacrylonitrile; the olefins such as dodecene, styrene, 4-methylstyrene, alphamethylstyrene, cyclopentadiene, dicyclopentadiene, butadiene, 1,4-hexadiene, 4-methyl-1-pentene, bicyclo 12.2.1] hept-2-ene, bicyclo[2.2.1J hept2,5-diene, cyclohexene; the vinyl halides such as vinyl chloride, vinylidene chloride; the vinyl esters such as vinyl acetate, vinyl butyrate, vinyl benzoate, vinyl butyral, vinyl methacrylate, vinyl hepto, vinyl crotonate; the vinyl ketones such as vinyl methyl ketone, vinyl phenyl ketone, isopropenyl methyl ketone, divinyl ketone, alphachloro-vinyl methyl ketone, vinyl phenyl ketone; acrolein and methacrolein; the vinyl ethers and thioethers such as methyl vinyl ether, ethyl vinyl ether, divinyl ether, isopropyl vinyl ether, the butyl vinyl ethers, 2-ethylexyl vinyl ether, vinyl 2-chloroethyl ether, vinyl 2-methoxyethyl ether, n-hexadecyl vinyl ether, vinyl methyl sulfide, vinyl ethylsulfide, divinyl sulfide, 1chloroethyl vinyl sulfide, vinyl octadecyl sulfide, vinyl 2-ethoxyethyl sulfide, vinyl phenyl sulfide, diallyl sulfide; the miscellaneous sulfur and nitrogen containing monomers such as divinyl sulfone, vinyl ethyl sulfone, vinyl sulfonic acid, vinyl ethyl sulfoxide, sodium vinyl sulfonate, vinyl sulfonamide, vinyl pyridine, N-vinyl pyrollidone and N-vinyl carbazole.

Other ethylenically unsaturated curable materials are readily apparent to one skilled in the art of polymerization chemistry. The specific compounds mentioned are illustrative only and not all-inclusive. They can be polymerized alone or in mixtures of two or more thereof with the proportions thereof dependent upon the desire of the individual. They can also be blended with polymers.

Among the polymers that can be used one can include, for example, the polyolefins and modified polyefins, the vinyl polymers, the polyesters the polyesters, the polylactones, the polyamides, the polyurethanes, the polyureas, the polysiloxanes, the polysulfides, the polysulfones, the polyformaldchydes, the phenolformaldehyde polymers, the natural and modified natural polymers and the heterocyclic polymers.

The term polymer as used herein includes the homopolymers and copolymers and includes the olefin polymers and copylymers such as polyethylene, poly(ethylene/ propylene), poly-(ethylene/norbornadiene) poly(ethylene/vinyl acetate), poly(ethylene/ vinyl chloride), poly(ethylene/ethyl acrylate), poly(ethylene/acrylonitrile), poly(ethylene/ acrylic acid), poly(ethylene/styrene), poly(ethylene/vinyl ethyl ether), polyfethylene/vinyl methyl ketone), polybutadiene, poly(butadiene/styrene/acrylonitrile), poly(vinylchloride) poly(vinylidene chloride), poly(vinyl acetate), poly(vinyl methyl ether), poly(vinyl butyr al), polystyrene, poly(N-vinyl-carbazole), poly(acrylic acid), poly(methyl acrylate), poly (ethyl acrylate), polyacrylonitrile, polyacrylamide, poly(methacrylic acid), poly(methyl methacrylate), poly(ethyl methacrylate). poly(N,N-dimethyl acrylamide), poly(methacry lamide). polycaprolactone, poly(caprolactone/vinyl chloride), poly(ethylene glycol tereph thalate), poly(caprolactam), poly(ethylene oxide), poly(propylene oxide), copolymers of ethylene oxide and propylene oxide with starters containing reactive hydrogen atoms such as the mixed copolymer using ethylene glycol or glycerol or sucrose, etc., as starter, the natural and modified natural polymers such as gutta percha, cellulose, methyl cellulose, starch, silk, wool, and the siloxane polymers and copolymers, the polysulfides and polysulfones, the formaldehyde polymers such as polyformaldehyde, formaldehyde resins such as phenol-formaldehyde, melamineformaldehyde, urea-formaldehyde, aniline formaldehyde and acetone-formaldehyde.

The materials that are treated by the method of this invejtion can contain any of the known pigments, fillers, stabilizers polymers or other additives conventionally added to coating compostions in the quantities usually employed; provided, however, that they are not employed in such quantities as will unduly interfere with or prevent the curing or crosslinking and that the polymers are dissolved or dispersed therein. It is known tha that can be used is less than usual in order that the filler or colorant should not unduly interfere with the ability of the ultraviolet radiation to penetrate below the surface of the coating and prevent curing or crosslinking from occurring. These principles are known to those skilled in the art of radiation chemistry and do not require extensive discussion or elaboration, the same is true for the particular materials that can be used.

The following Examples illustrate the nature of the invention and the manner in which it may be performed. The words "Modaflow", "Pluracol", "Aroclor" and "Santolite" are Registered Trade Marks.

EXAMPLE I A metal hood was constructed containing sixteen 1.000-watt mercury vapor lamps; the lamps were provided with aluminium reflectors. Superheated steam (atmospheric pressure) was injected into the hood. A web of paper, 2 mils thick (.002" or 5.080 x 10-3 cm) was coated with a UV-curable composition, as indicated below, to a thickness of about 0.2 mil (.0002" or 5.08 x 104cm) and introduced into the hood; the distance between the paper and UV lamps was about 3/4 inches (1.91 cm). The paper and coating were run at a speed to provide an exposure time to the UV lamps of 6 seconds. The paper emerged from the hood with the UV curable composition fully cured to a hard, dry, tack-free, glossy coating; the paper showed no sign of curling, warping or shrinking.

Component Parts by Weight Polyester Binder (l) 30 1,6-hexanediol diacrylate 1,6-hexanediol diacrylat 65 Diethoxyacetophenone 4 Modaflow(2' 1 (l) a condensation polymer of propylene glycol and 1:1 molar mixture of maleic and isophthalic acids having a molecular weight of about 5,000 and an acid number of about 10; (2) a resinous hydrocarbon flow control agent from Monsanto Chemical Co.

It should be noted that an exposure period of 6 seconds is quite slow by paper industry standards, where speeds in excess of 1.000 feet per minute (305 meters/min) are realized in printing ink on newsprint. In paper mills, line speeds of the order of 40() feet/min. (122 meters/min) are more common. Thus exposure periods to the UV source can be from a fraction of a second to several seconds. Other factors to be considered in determining the exposure time include the thickness of the coating being used (typical thickness are from 0.1 mil to 1 mil or even more) and the reactivity of the curable compostion. In this latter respect, it might be noted that UV curable ethylenically unsaturated compositions formulated to cure in air will cure faster in an atmosphere of steam.

While a 2 mil paper substrate and a 0.2 mil coating were not affected by the heat produced, from sixteen 1,000-watt mercury vapor lamps, at a distance of 0.75 inch (1.91 cm) for 6 seconds because of the effects of the steam, a question was raised concerning extended exposure of a heat sensitive substrate to the heat produced by the UV lamps; for example, could a line be stopped for extended periods without injury to the substrate caused bv the heat from the UV lamps. The paper web of Example 1, after being coated with the curable composition of that Example. was introduced to the hood and stopped under the UV lamps while the steam flow continued. After a period of ten minutes of continuous exposure the paper was removed and examined: there was no discoloration, charring or other evidence of an adverse effect from the heat of the UV lamps.

EXAMPLE 2 UV curable ethylenically unsaturated compositions prepared according to the following formulations, coated on thin paper and cured according to the procedure of example 1.

provide high gloss, tack-free coatings.

Components Composition, Parts by Weight I II III IV V PCP(a) 36.2 - - - - EPOA(b) 4.8 4.5 - - - E.D.(C) 16.2 57.0 54.5 59.5 47.6 NPGDA(d) 14.2 18.1 17.3 19.0 19.0 HEA(e) 14.2 9.0 8.7 9.5 9.5 DCPA(f) 9.6 6.9 15.2 7.2 19.0 Sensitizer(g) 4.8 4.5 4.3 4.8 4.9 (a) 80% solution of Union Carbide PCP-0300 polycaprolactone/toluene diisocyanate oligomer in 20sic hydroxyethyl acrylate (b) polyacrylate of epoxidized soya bean oil available from Union Carbide (c) epoxy diacrylate-reaction product of an epichlorohydrin/bisphenol A-type epoxy resin with a stoichimetric amount of acrylic acid.

(d) neopentyl glycol diacrylate (e) hydroxyethyl acrylate (f) dicylopentenyl acrylate (g) 4.5 parts benzophenone/0.5 parts Michlers Ketone EXAMPLE 3 When the following ethylenically unsaturated ink composition is applied to a paper substrate and cured in the presence of steam in accordance with the conditions described in Example 1. there is obtained dry, tack free printed paper.

Parts by Weight EPDA (see Example 2) 55.3 Ultraflex Microcrystalline Wax 3.1 Pentaerythritol Tetraacrylate 27.4 Benzophenone 4.5 Michler's Ketone .50 Phthalocyanine Blue Pigment 9.2 EXAMPLE 4 A UV curable composition of the ene/thiol type is prepared as follows: 751 g. (0.38 mole) of a commercially available poly-(propylene ether) glycol sold under the Registered Trade Mark iiPluracol P 2010" by Wyandotte Chemical Co. is degassed at room temperature for 3 hours and then charged to a dry resin kettle maintained under a nitrogen atmosphere and equipped with a condenser, stirrer, thermometer and gas inlet and outlet. 132 g (0.76 mole) of tolylene -2,4 - diisocyanate are charged to the kettle and the kettle is heated for 2 hours at 1200C. with stirring under nitrogen. After cooling 58 g. (1.0 mole) of allyl alcohol are added and the mixture refluxed at 1200C. overnight. Excess allyl alcohol is stripped under vacuum overnight at 120 C. The thus formed allyl-terminated liquid prepolymer is representative of the ene component of an ene-thiol system.

A UV-curable ethylenically unsaturated composition has the following formulation Parts by Weight Allyl-terminated prepolymer 79.4 Pentaerythritol tetrakis (p-mercaptopropionate) 15.9 Acetophenone 4.7 When coated on paper and cured according to Example 1 in the presence of steam a dry coating is obtained. Tough coatings are similarly obtained using Parts by Weight 1 .2,4-trivinylcyclohexane 38.08 Pentaerythritol tetrakis (ss-mercaptopropionate) 56.07 Benzophenone 5.85 EXAMPLE 5 The composition of Example 3 is screened onto thin white knit cotton jersey and cured in the apparatus used in Example 1 in the presence of steam. Tack free, decorated jersey is obtained, with no damage to the substrate.

EXAMPLE 6 A red ink is prepared from Parts by Weight Pentaerythritol triacrylate 67 Aroclor 1260(1) 9.75 Santolite MHP(2) 3.25 Lithol Rubine Red pigment 20 (l) Monsanto Chemical Company's biphenyl containing 60% by weight of chlorine (2) Monsanto Chemical Company's p-toluene sulfonamide-formaldehyde resin A glass bottle is printed with this ink and exposed to UV light under the conditions described in Example 1. A cured ink is obtained.

While glass is not normally considered to be heat sensitive in the same way as thin paper and textiles, glass bottles that have been screen printed with UV curable inks and kept in close proximity to a UV source and the intense heat generated thereby, as could happen as the result of a breakdown in some part of a bottling plant, will begin to break. Here again, the use of steam interposed between the UV source and the glass substrate will absorb the infra-red radiation and prevent damage.

It is noted that this invention. contemplating the use of steam to absorb infra-red radiation and as an atmosphere in which UV curable ethylenically unsaturated compositions are cured, is independent of the specific composition of the UV curable composition or the substrate.

WHAT WE CLAIM IS: 1. A method of curing a radiation curable material comprising a polymerizable ethylenically unsaturated substance which comprises interposing between a radiating source of radiation which emits both U.V. and I.R. radiation and a material comprising said substance and curable by such radiation an atmosphere of superheated steam as hereinbefore defined in order to reduce the amount of I.R. radiation incident upon such curable material.

2. A method according to claim 1 in which said steam is supplied at atmospheric pressure or up to 5 p.s.i. superatmospheric pressure.

3. A method according to either of claims 1 or 2 in which said ethylenically unsaturated substance is present in a coating or printing of curable material upon a substrate.

4. A method according to any of the preceding claims is which said substrate is of glass, ceramic, metal or laminated board.

5. A method according to any of claims 1-3 in which said substrate is a thermoplastic material.

6. A method according to any of claims 1-3 in which said substrate is gutta percha. silk, wool, cotton, cellulose acetate or methyl cellulose.

7. A method according to any of claims 1-3 in which said substrate is wood, paper. tag stock, parchment, cardboard or bag stock.

8. A method according to any of the preceding claims in which said curable material polymerises, undergoes cross-linking or cures by a free radical mechanism.

9. A method according to claim 8 in which said ethylenically unsaturated substance comprises an acrylic or methacrylic ester.

10. A method according to any of the preceding claims in which said curable material further comprises at least one component which yields free radicals under the influence of U.V. radiation.

11. A method of curing a radiation curable material according to claim 1 and substantially as hereinbefore described with reference to any one of the Examples.

12. Radiation cured material which has been produced by the method of any of claims 1-11.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. EXAMPLE 5 The composition of Example 3 is screened onto thin white knit cotton jersey and cured in the apparatus used in Example 1 in the presence of steam. Tack free, decorated jersey is obtained, with no damage to the substrate. EXAMPLE 6 A red ink is prepared from Parts by Weight Pentaerythritol triacrylate 67 Aroclor 1260(1) 9.75 Santolite MHP(2) 3.25 Lithol Rubine Red pigment 20 (l) Monsanto Chemical Company's biphenyl containing 60% by weight of chlorine (2) Monsanto Chemical Company's p-toluene sulfonamide-formaldehyde resin A glass bottle is printed with this ink and exposed to UV light under the conditions described in Example 1. A cured ink is obtained. While glass is not normally considered to be heat sensitive in the same way as thin paper and textiles, glass bottles that have been screen printed with UV curable inks and kept in close proximity to a UV source and the intense heat generated thereby, as could happen as the result of a breakdown in some part of a bottling plant, will begin to break. Here again, the use of steam interposed between the UV source and the glass substrate will absorb the infra-red radiation and prevent damage. It is noted that this invention. contemplating the use of steam to absorb infra-red radiation and as an atmosphere in which UV curable ethylenically unsaturated compositions are cured, is independent of the specific composition of the UV curable composition or the substrate. WHAT WE CLAIM IS:

1. A method of curing a radiation curable material comprising a polymerizable ethylenically unsaturated substance which comprises interposing between a radiating source of radiation which emits both U.V. and I.R. radiation and a material comprising said substance and curable by such radiation an atmosphere of superheated steam as hereinbefore defined in order to reduce the amount of I.R. radiation incident upon such curable material.

2. A method according to claim 1 in which said steam is supplied at atmospheric pressure or up to 5 p.s.i. superatmospheric pressure.

3. A method according to either of claims 1 or 2 in which said ethylenically unsaturated substance is present in a coating or printing of curable material upon a substrate.

4. A method according to any of the preceding claims is which said substrate is of glass, ceramic, metal or laminated board.

5. A method according to any of claims 1-3 in which said substrate is a thermoplastic material.

6. A method according to any of claims 1-3 in which said substrate is gutta percha. silk, wool, cotton, cellulose acetate or methyl cellulose.

7. A method according to any of claims 1-3 in which said substrate is wood, paper. tag stock, parchment, cardboard or bag stock.

8. A method according to any of the preceding claims in which said curable material polymerises, undergoes cross-linking or cures by a free radical mechanism.

9. A method according to claim 8 in which said ethylenically unsaturated substance comprises an acrylic or methacrylic ester.

10. A method according to any of the preceding claims in which said curable material further comprises at least one component which yields free radicals under the influence of U.V. radiation.

11. A method of curing a radiation curable material according to claim 1 and substantially as hereinbefore described with reference to any one of the Examples.

12. Radiation cured material which has been produced by the method of any of claims 1-11.