Abstract: A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and a cationic dye-borate anion complex, said complex being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said compound; and photosensitive materials employing the composition where in one embodiment the composition is microencapsulated.

Abstract: A photohardenable composition comprising a free radical addition polymerizable or crosslinkable compound and an ionic dye-counter ion compound, said compound being capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of said compound; and photosensitive materials incorporating the same.

Abstract: Disclosed is a photopolymerizable composition which is very sensitive to visible light. The composition comprises a polymerizable compound and a photopolymerization initiator wherein the photopolymerization initiator comprises (a) a particular xanthene or thioxanthene dyestuff, (b) a photosensitizer selected from the group consisting of N-phenylglycine, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, and a mixture of p-dimethylaminobenzoic acid isopentyl ester and 2,4-diisopropylthioxanthone, and (c) a peroxide.

Abstract: Spectral sensitizing dyes which sensitize photoinitiators and disperse in aqueous solutions are desirable in photosensitive systems where precise color rendition is important.

Abstract: A photosolubilizable composition contains both a compound capable of producing an acid by irradiation with actinic rays and a compound which has at least one silyl ether or silyl ester group capable of being decomposed by an acid; optionally, a compound having at least one silyl ether group has at least one hydrophilic group, providing for increased solubility in a developing solution under the action of an acid, thus enhancing the photosensitivity and the development latitude of the composition.

Abstract: A free radical polymerizable composition comprising a free radical polymerizable material and a photoinitiator system therefor comprising appropriate amounts of an alpha-cleavage or homolytic bond cleavage, photoinitiator and a ferrocenium salt, said composition being suitable for use in the preparation of protective layers and photographic images.

Abstract: Disclosed herein is an optical recording medium which includes a recording layer composed of (a) an organometallic complex having an absorption maximum in the wavelength range of 600-1200 nm, (b) a resinous binder and (c) a sensitizer capable of generating radicals upon exposure to ultraviolet rays. The recording of information on the recording layer is effected with ease by exposure to ultraviolet rays. The reproduction of recorded information is effected by a laser beam having an oscillatory wavelength in the visible or near infrared wavelength range.

Abstract: Light-sensitive compounds are described which have the formula ##STR1## wherein R.sup.1 and R.sup.2 denote H or alkyl, R.sup.3 and R.sup.4 denote H or 4,6-bis-trichloromethyl-s-triazin-2-yl, R.sup.5 and R.sup.6 denote H or halogen, alkyl, alkenyl or alkoxy, and Ar denotes a mononuclear to trinuclear aromatic group.These compounds are suitable as photoinitiators for free-radical polymerizations or as photolytic acid donors for acid-cleavable compounds, and for cross-linking and color formation reactions. They are distinguished by a high sensitivity in various spectral ranges.

Abstract: A method and composition for increasing the cure depth of a solder mask coating at a low UV energy level. The stable composition, which includes a UV curable compound and a photoinitiator, is characterized by the presence of triphenylphosphite in the composition.

Abstract: Water soluble blends are provided of alkanolacrylamide, water soluble hydroxyl containing film forming organic oligomer and an effective amount of an onium salt photoinitiator. These photocurable compositions can be used as photoresists.

Abstract: A photopolymerizable mixture is described which contains the following: a binding agent which is soluble or at least capable of swelling in aqueous-alkaline solutions, a photoinitiator or a photoinitiator system and at least one ethylenically unsaturated monomer, whereby at least one monomer contains an aromatic hydroxyl-, mercapto-, sulfonamide- or a mono-N-substituted sulfonamide group, or combinations thereof.

Abstract: A photopolymerizable composition comprising an addition-polymerizable compound having at least one ethylenically unsaturated double bond and a photopolymerization initiator, characterized in that the initiator comprises (a) a compound of the formula: ##STR1## wherein R.sup.1 and R.sup.2 are alkyl group, n is 1, 2 or 3 and ring A is an aromatic ring containing nitrogen atom, and (b) hexaarylbiimidazole. The initiator may additionally contain a thiol of the formula: ##STR2## wherein Z is --O--,--S-- or --NH--. The composition is not only highly sensitive to ultraviolet ray but also highly stable in storage.

Abstract: The invention relates to photopolymerizable compositions comprising (a) a prepolymer containing photopolymerizable olefinic double bonds, (b) photoinitiator of the formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are as defined in claim 1, and optionally (c) an ester of acrylic or methacrylic acid or an allyl ether or allyl ester of a polyol.Owing to their excellent light sensitivity, these compositions are suitable for the economic production of high temperature resistant protective layers and relief structures having excellent resolution and good contours.

Abstract: A negative-acting photoresist imaging system is provided having a substrate, a metal layer, a latently sensitized, crosslinkable, negative-acting photoresist base layer, and a negative-acting photoresist layer. The system may further have an organic protective coat between the metal layer and the base layer, a matte top layer, and/or an antistatic layer on the back side of the substrate.

Abstract: Water soluble blends are provided of alkanolacrylamide, water soluble hydroxyl containing film forming organic oligomer and an effective amount of an onium salt photoinitiator. These photocurable compositions can be used as photoresists.

Abstract: Photopolymerizable compositions comprising(a) at least one ethylenically unsaturated compound,(b) at least one organic polymeric binder,(c) optionally at least one photoinitiator and(d) at least one constrained N-alkylamino aryl ketone compound as defined, e.g., bis(9-julolidyl ketone), bis-(N-ethyl-1,2,3,4-tetrahydro-6-quinolyl)ketone, etc. The compositions, in layer form, are useful in photoresists, including projection speed photoresists, printing plates, drafting and toning films, etc.

Abstract: An aqueous developable photopolymerizable element having improved rate of development consisting essentially of (a) an ethylenically unsaturated monomeric compound, (b) an organic acidic polymeric binder, (c) a photoinitiator or photoinitiator system and (d) at least 2% by weight based on weight of solids of an organic compound or salt of an organic compound as defined. The elements are useful as photoresists, printing plates and for preparation of proofs and litho masks.

Abstract: A water-soluble photopolymerizable composition which is suitable for forming the hydrophilic layer in a positive acting water-developable lithographic printing plate. The photopolymerizable composition comprises a mixture of:(a) an ethylenically-unsaturated dextrin oligomer,(b) at least one hydroxyfunctional acrylamide monomer,(c) inorganic solid particulate material, and(d) a photoinitiation system. Wetting agents and pH modifiers can also be added to the composition. The photopolymer formed from the composition is water-insoluble.

Abstract: Water-developable positive acting lithographic printing plate. The plate is prepared by first coating a substrate with an oleophilic composition, drying and curing the composition to form an insoluble adhering oleophilic layer and then overcoating said oleophilic layer with a water soluble photopolymerizable composition. Upon imagewise exposure of the plate, the photopolymerizable composition polymerizes in the non-image areas. Upon development with ordinary tap water, the unpolymerized image areas of the photopolymerizable composition are washed away, leaving an oleophilic surface in the image areas and a hydrophilic surface in the background.

Abstract: Peresters of the formula: ##STR1## wherein R is an alkyl group; and ##STR2## is a light-absorbing chromophore group; and use thereof as photoinitiators are provided.

Abstract: Abrasion resistant films formed by the copolymerization of epoxy-terminated silanes and limonene monoxide display water repellency that reduces damage to the integrity of the film.

Abstract: A radiation-polymerizable mixture comprising a binder which is insoluble in water, but soluble or at least swellable in aqueous alkaline solutions; a radiation-activatable polymerization initiator; and a polymerizable polypropylene glycol diester with acrylic or methacrylic acid corresponding to the formula: ##STR1## wherein R represents a hydrogen atom or a methyl group and n represents a number from 2 to 13; and a light-sensitive copying material comprising a support and a light-sensitive layer comprising a mixture of the foregoing type. The radiation-polymerizable mixture of the invention produces non-tacky layers which exhibit a low sensitivity to atmospheric oxygen and are useful as dry or liquid photoresists.

Abstract: An aqueous developable photopolymerizable element having improved rate of development consisting essentially of (a) an ethylenically unsaturated monomeric compound, (b) an organic acidic polymeric binder, (c) a photoinitiator or photoinitiator system and (d) at least 2% by weight based on weight of solids of an organic compound or salt of an organic compound as defined. The elements are useful as photoresists, printing plates and for preparation of proofs and litho masks.

Abstract: A polymer composition comprising a urethane having terminal unsaturation and a terminal carboxyl group and which is capable of further free radical polymerization has been synthesized. This polymer can be a liquid or a solid depending on the molecular weight and backbone of the polymer. This polymer as a liquid has been found to be very useful in producing printed circuit boards by photo resist processes.

Abstract: A photo polymerization initiator composition is disclosed. The composition is comprised of an organic peroxide and a salt selected from the group consisting of pyrylium salts, thiapyrylium salts and selenopyrylium salts represented by the general formula (I): ##STR1## the substituents are defined within the specification. By utilizing the disclosed photo polymerization initiator composition, it is possible to obtain high sensitivity even in the visible range of light.

Abstract: Described are 1,3-diaza-9-thia-anthracene-2,4-diones of the general formula (II) ##STR1## wherein R.sup.1, R.sup.3 and R.sup.4 are identical or different and individually each denotes a hydrogen or halogen atom, an alkyl, alkoxy, carboxyl or alkoxy-carbonyl group,R.sup.2 denotes an alkoxy, carboxyl or alkoxy-carbonyl group, ortwo of the groups R.sup.1, R.sup.2, R.sup.3, and R.sup.4 together form a condensed aromatic radical.These compounds are used as photoinitiators in photopolymerizable recording materials and have an increased sensitivity in the spectral range between 425 and 480 nm.

Abstract: The present invention relates to novel 10-phenyl-1,3,9-triazaanthracenes and to a photopolymerizable mixture which contains, as the essential components,(a) a polymeric binder(b) a polymerizable compound having at least two terminal, ethylenically unsaturated groups and a boiling point of more than 100.degree. C., and(c) a 10-phenyl-1,3,9-triazaanthracene as the photoinitiator.

Abstract: A photosensitive resin composition which comprises (1) an ethylenically unsaturated compound which can be addition polymerized to form a high molecular compound, said addition polymerizaton being initiated by a free radical and of chain-propagation, (2) a 2-polycyclic aryl-4,5-diphenylimidazolyl dimer wherein the polycyclic aryl group comprises at least two benzene rings condensed each other and (3) at least one compound selected from the group consisting of dimedone, indolacetic acid, N-naphthylglycine, S-lower alkylthioglycollic acid, 4,4'-bis[di(lower)alkylamino]benzyl, p-di(lower)alkylaminobenzoic ester, leucocrystalviolet, indoxylic acid, rhodanine, 7-di(lower)alkylaminocumarine and diarylthiourea and their derivatives, the molar ratio of the component (2) and the component (3) being from 2:1 to 1:5.

Abstract: An electrical device coated with a polymerized polyimide structure resulting from a radiation-sensitive polyimide precursor composition which comprises a polymer of the formula ##STR1## wherein n is a positive integer corresponding to the number of units in the polymer and is sufficiently large to provide the polymer with a number average molecular weight of about 1500-15,000 as determined by vapor pressure osmometry, and wherein for any particular unit in the polymer:.fwdarw.denotes isomerism; R.sup.1 is a divalent aromatic, aliphatic or cycloaliphatic radical containing at least 2 carbon atoms; R.sup.2 and R.sup.3 are selected from the group consisting of a hydrogen radical and any organic radical containing a photopolymerizable olefinic double bond; and R.sup.4 and R.sup.5 are selected from the group consisting of perfluoro and perhalofluoro aliphatic hydrocarbons having 1 to 8 carbons.

Abstract: Photopolymerizable compositions comprising (a) at least one ethylenically unsaturated compound, (b) at least one photoinitiator or photoinitiator system, (c) sensitizing amount of an N-alkylindolylidene or N-alkylbenzothiazolylidene alkanone as defined, and optionally (d) at least one organic polymeric binder. The compositions, in layer form are useful in printing plates, litho films, photoresists, solder mask and for making image proofs. The products show sensitization to visible light.

Abstract: A photosensitive resin composition comprising (a) at least one compound selected from the group consisting of benzotriazole, benzimidazole, benzothiazole, derivatives thereof and salts thereof, (b) a phosphate compound having photopolymeric unsaturated bonds, (c), if necessary, an organic thermoplastic polymer, (d) a photopolymerizable unsaturated compound having at least one terminal ethylene group and (e) a sensitizer and/or a sensitizer system, and a photosensitive element comprising a layer of said photosensitive resin composition and a support film therefor, are provided. The photosensitive resin composition can form a protective coating film with excellent adhesiveness to the substrate surface, and such a protective coating film or, photosensitive element obtained therefrom can be advantageously used as a resist for soldering mask, etc.

Abstract: A radiation-sensitive polyimide precursor composition, comprising a polymer of the formula ##STR1## wherein n is a positive integer corresponding to the number of units in the polymer and is sufficiently large to provide the polymer with a number average molecular weight of about 1500-15,000 as determined by vapor pressure osmometry, and wherein for any particular unit in the polymer:.fwdarw.denotes isomerism;R.sup.1 is a tetravalent aromatic non-halogen containing organic radical containing at least one ring of six carbon atoms, said ring characterized by benzenoid unsaturation, the four carbonyl groups being attached directly to separate carbon atoms in a ring of the R.sup.1 radical;R.sup.2 and R.sup.3 are selected from the group consisting of a hydrogen radical and any organic radical containing a photopolymerizable olefinic double bond, at least one of R.sup.2 and R.sup.3 being said organic radical;R.sup.4 and R.sup.

Abstract: Photocurable resin compositions result from a mixture of polymerizable entities containing both terminal olefinic unsaturation and oxirane groups and a bifunctional curing system capable of initiating free radical and cationic polymerization.

Abstract: Photographic material comprising a supported or self-supporting binder layer incorporating a photoradical precursor compound in operative relationship with an image-forming precursor compound which is capable of taking part in image formation by reaction with the photoradicals formed by photoexposing said photoradical precursor, wherein the image-forming compound is a reducing compound containing Zerewitinoff active hydrogen for forming a print-out image or an ethylenically unsaturated compound capable of free-radical addition polymerization, and the photoradical precursor compound is a di- or tri(2,3-aryl substituted indolyl) compound free of Zerewitinoff active hydrogen.

Abstract: An image reproducing material comprising a supporting sheet bearing a metal or metallic compound layer having a thickness of 100 to 1000 .ANG. and a photosensitive resin layer, which is characterized in that said photosensitive resin layer contains (1) an ethylenically unsaturated compound which is polymerizable by the action of free radical and chain propagative, (2) a compound showing photochromism by radical mechanism, (3) a free radical producing agent and (4) an acitinic light absorber. There is also provided an image formed (reproduced) material obtained by patterned exposing the above image reproducing material and then processing the same, a method for obtaining such image formed material and also a method for dot-etching such image formed material. By the use of these materials and methods, dot-etching can be effected easily and there are obtained sharp images without the formation of pin holes.

Abstract: A radiation-sensitive polyimide precursor composition comprises a polymer of the formula ##STR1## wherein n is a positive integer corresponding to the number of units in the polymer and is sufficiently large to provide the polymer with a number average molecular weight of about 1500-15,000 as determined by vapor pressure osmometry, and wherein for any particular unit in the polymer:.fwdarw.denotes isomerism; R.sup.1 is a divalent aromatic, aliphatic or cycloaliphatic radical containing at least 2 carbon atoms; R.sup.2 and R.sup.3 are selected from the group consisting of a hydrogen radical and any organic radical containing a photopolymerizable olefinic double bond; and R.sup.4 and R.sup.5 are selected from the group consisting of perfluoro and perhalofluoro aliphatic hydrocarbons having 1 to 8 carbons.

Abstract: In a photopolymerizable composition comprising, as essential components, (A) a compound having at least one ethylenically unsaturated double bond capable of undergoing addition polymerization and (B) a photopolymerization initiator, the improvement which comprises that the photopolymerization initiator comprising a combination of (a) a 5-[(arenooxazol-2-ylidene)ethylidene]-2-thiohydantoin compound represented by the general formula (I) (a 5-[(substituted benzoxazol-2'-ylidene)ethylidene]-2-thiohydantoin compound) or (II) (a 5-[substituted naphthol(1,2-D)oxazol-2-ylidene)ethylidene]-2-thiohydantoin compound) and (b) a 2,4,6-substituted-1,3,5-triazine compound represented by the formula (III): ##STR1## wherein X represents a hydrogen atom, an alkyl group, a substituted alkyl group, an alkoxy group, an aryl group, a substituted aryl group, an aryloxy group, an aralkyl group or a halogen atom; R.sup.1, R.sup.2 and R.sup.

Abstract: Permanent records of X rays or radiations of shorter wavelengths are formed on a film substrate by direct exposure to the radiation and heat development. The process is not sensitive to visible radiation and can therefore be carried on in daylight. An X ray photosensitive film containing a halogenated photodegradable polymer and an aryl dye promoter reacting to free radicals is exposed to an X ray image and then heated under conditions which allow the free radical generated by the photodegradation of the polymer to migrate and react with the aryl dye promoter to provide the imaging dye. The X ray photosensitive layer of the X ray photosensitive film or paper includes, in addition to the photodegradable polymer and the aryl dye promoter, a heat activable complexing agent and an organic binder. The process can be carried out using currently available X ray equipment with the advantage of handling the film in daylight and eliminating chemical development.

Abstract: A photopolymerizable recording composition which comprises a mixture, containing a photoinitiator, of (a) a photopolymerizable olefinically unsaturated monomer and (b) an organic polymeric binder, wherein the photoinitiator is an acylphosphine oxide compound of the formula R.sup.1 R.sup.2 PO--CO--R.sup.3, where R.sup.1 and R.sup.2 are certain organic radicals and R.sup.3 is tert.-alkyl or a cyclic radical with two substituents in the ortho-position to the carbonyl group. The recording compositions have a high reactivity when irradiated with UV light and are used in particular for the preparation of printing plates, relief plates and photo-resists.

Abstract: This invention relates to a novel 4-halogeno-5-(halogenomethyl-phenyl)-oxazole derivative; to a radiation-sensitive composition which, as the radiation-sensitive compound, contains a 4-halogeno-5-(halogenomethyl-phenyl)-oxazole derivative; and to a process for the preparation of the novel 4-halogeno-5-(halogenomethyl-phenyl)-oxazole derivatives.

Abstract: This invention relates to a novel 2-(halogenomethyl-phenyl)-4-halogeno-oxazole derivative; to a radiation-sensitive composition which, as the radiation-sensitive compound, contains a 2-halogenomethyl-phenyl)-4-halogeno-oxazole derivative; and to a process for the preparation of the novel 2-(halogenomethyl-phenyl)-4-halogeno-oxazole derivatives.

Abstract: A photopolymerizable composition, element and method of photopolymerizing the composition or element are disclosed wherein the composition comprises an addition polymerizable compound containing ethylenic unsaturation and a co-initiator including a photopolymerization activator and photosensitizer.In one aspect of the invention, the photosensitizer is selected to be a coumarin having an absorption maximum between about 250 and about 550 nm, and a ##STR1## substituent in the 3-position wherein R.sup.1 is alkyl or alkenyl having 1-12 carbon atoms, or a carboxylic or heterocyclic group having 5-20 nuclear carbon and hetero atoms, the coumarin and the activator being present in an amount sufficient to provide, when the compound is coated, dried and exposed to a medium-pressure mercury light source, a speed which is at least about one-fifth that of the same composition coated, dried and exposed identically except with a co-initiator consisting of Michler's ketone and benzophenone.

Abstract: Photoimaging compositions comprising (A) a cyclohexadienone compound as defined, and at least one of (B.sub.1) a leuco dye or (B.sub.2) addition polymerizable ethylenically unsaturated monomer. A polymer binder can be present in the compositions. The new imaging compositions are useful in photoimaging products such as proofing papers, printout papers, overlay films and photopolymerizable elements useful for printing and photoresist purposes. The compositions have improved thermal stability.

Abstract: Aromatic-aliphatic ketones of the formulae I, II, III or IV ##STR1## wherein n is 1 or 2, Ar is an aryl radical, R.sup.1 and R.sup.2 are monovalent aliphatic, cycloaliphatic or araliphatic radicals, R.sup.3 is a direct bond or a divalent organic radical, X is a hydroxyl or amino group or the monovalent etherification or silylation products thereof, and X' is a divalent amino, ether or silyloxy group, Y is a direct bond or CH.sub.2 and Z is O, S, SO.sub.2, CH.sub.2 or C(CH.sub.3).sub.2, are suitable sensitizers for the photopolymerization of unsaturated compounds and for the photochemical crosslinking of polyolefins. Some of these compounds are novel and can be obtained by methods analogous to those for obtaining the known compounds of this type.

Abstract: Aromatic-aliphatic ketones of the formulae I, II, III or IV ##STR1## wherein n is 1 or 2, Ar is an aryl radical, R.sup.1 and R.sup.2 are monovalent aliphatic, cycloaliphatic or araliphatic radicals, R.sup.3 is a direct bond or a divalent organic radical, X is a hydroxyl or amino group or the monovalent etherification or silylation products thereof, and X' is a divalent amino, ether or silyloxy group, Y is a direct bond or CH.sub.2 and Z is O, S, SO.sub.2, CH.sub.2 or C(CH.sub.3).sub.2, are suitable sensitizers for the photopolymerization of unsaturated compounds and for the photochemical crosslinking of polyolefins. Some of these compounds are novel and can be obtained by methods analogous to those for obtaining the known compounds of this type.

Abstract: Aromatic-aliphatic ketones of the formulae I, II, III or IV ##STR1## wherein n is 1 or 2, Ar is an aryl radical, R.sup.1 and R.sup.2 are monovalent aliphatic, cycloaliphatic or araliphatic radicals, R.sup.3 is a direct bond or a divalent organic radical, X is a hydroxyl or amino group or the monovalent etherification or silylation products thereof, and X' is a divalent amino, ether or silyloxy group, Y is a direct bond or CH.sub.2 and Z is O, S, SO.sub.2, CH.sub.2 or C(CH.sub.3).sub.2, are suitable sensitizers for the photopolymerization of unsaturated compounds and for the photochemical crosslinking of polyolefins. Some of these compounds are novel and can be obtained by methods analogous to those for obtaining the known compounds of this type.

Abstract: Photoimaging compositions comprising (A) 2,4,5-triphenylimidazolyl dimer having selected substituents on the 2,4 and 5 phenyl rings and an extinction coefficient determined in methylene chloride at 10.sup.-5 to 10.sup.-3 mol/liter at 350 nm of at least 4000 liters/mol-cm and at 400 nm of at least 250 liters/mol-cm; and at least one of (B1) leuco dye or (B2) addition polymerizable ethylenically unsaturated monomeric compound. The new imaging compositions are useful in preparing dual response photoimaging products such as proofing papers, printout paper, overlay films and photopolymerizable elements. Improved imaging speed is achieved at equal concentration levels when compared with conventional 2,4,5-triphenylimidazolyl dimers.

Abstract: There are disclosed light-sensitive compounds and a composition comprising (a) such compounds and (b) a compound having at least one reactive site capable of stepwise photo-reaction with the light-sensitive compounds. The light-sensitive compounds have the structural formula, ##STR1## wherein Z.sup.1 and Z.sup.2 are each independently the number of non-metallic atoms necessary to complete 1, 2, 3, or 4 unsaturated carbocyclic or heterocyclic rings of from 6 to 18 nuclear atoms;Z.sup.3 is either a carbon-to-carbon bond or vinylene;and X is a linking group.The composition can be applied to a variety of supports and photoreacted by exposure to activating radiation.

Abstract: Stable print-out dye systems are provided for photopolymerizable compositions, finding particular use as photoresists. The dye compositions comprise a triarylmethane leuco dye in combination with a high-boiling, relatively thermally-insensitive polyhalo alicyclic compound having at least five bromines. The print-out dye system is incorporated with an addition polymerizable composition, a light-sensitive initiator, and minor amounts of other additives.

Abstract: A photopolymerizable composition, element and method of photopolymerizing the composition or element are disclosed wherein the composition comprises an addition polymerizable compound containing ethylenic unsaturation and a co-initiator including a photopolymerization activator and a photosensitizer.In one aspect of the invention, the photosensitizer is selected to be a coumarin having an absorption maximum between about 250 and about 550 nm, and a ##STR1## substituent in the 3-position wherein R.sup.1 is alkyl or alkenyl having 1-12 carbon atoms, or a carbocyclic or heterocyclic group having 5-20 nuclear carbon and hetero atoms, the coumarin and the activator being present in an amount sufficient to provide, when the composition is coated, dried and exposed to a medium-pressure mercury light source, a speed which is at least about one-fifth that of the same composition coated, dried and exposed identically except with a co-initiator consisting of Michler's ketone and benzophenone.