IMAGEABLE,COMPOSITE DRY-TRANSFER SHEET

Abstract: An imageable composite dry-transfer sheet that comprises (a) a cover sheet transmissive to actinic radiation that has at least one oleophilic surface, (b) a photopolymerizable layer on the oleophilic surface of the cover sheet that comprises a cationically polymerizable organic material, a cationic photopolymerization initiator, and, optionally, a thermoplastic hydrocarbon resin that is chemically inert to said organic material and said initiator and (c) a base sheet with an oleophobic surface on the photopolymerizable layer wherein, after image-wise exposure to activating radiation, the interfacial adhesion of the unexposed areas of the photopolymerizable layer is greater for the cover sheet than for the base sheet; the interfacial adhesion of the exposed areas of the photopolymerizable layer is greater for the base sheet than for the cover sheet; and wherein, after separation of the cover and base sheets, the unexposed areas of the photopolymerizable layer are rendered burnishable by subsequent exposure to activating radiation through the cover sheet.

Description: IMAGEABLE, COMPOSITE-DRY TRANSFER SHEET Cross Reference to Related Application This is a conti nuat on-in-part of copending appli cation Serial Number 67,322 filed October 18, 1978. Technical Field The present invention relates to image production and transfer. More particularly it relates to i ageable composite dry-transfer sheets and their method of use. In the present invention, an image is produced by exposing the composite dry-transfer sheet to activating radiation, e.g., ultraviolet light, in an image-wise manner. The image is then transferred to a suitable surface by burnishing (i .e. , the application of pressure to the backside of the transfer sheet in the image areas). To be transferable in this manner, the image must have a stronger affinity for the receptor surface than for the substrate surface after burnishing. Add tionally, the image must possess sufficient cohesive strength (i .e. , film character) so that it transfers completely from the substrate to the receptor after burnishing even though pressure may not have been applied evenly to all parts of the image. Pressure transfer of images from a substrate to a receptor has been previously described. For example, U.S. Patent 3,013,917 describes sheets that contain ink designs in the form of characters. A wax coating is pro¬ vided on the characters so as to make them pressure- transferable (i .e. , burn shabl e) . These sheets have not proven totally satisfactory, however, as it is necessary to maintain a large inventory of them in order to have sufficient quantities of all characters on hand. Moreover, non-standard characters are difficult to obtain and typically substantial lead times are required in order to make them available. Sheets that employ photopolymerizable layers for the formation of images that are then transferable by dry transfer techniques are also known. Thus, see British Patent 1 ,521 ,766 and U.S. Patent 4,041 ,204. The photo¬ polymerizable layer of these sheets must be image-wise exposed to activating radiation. The images are then developed by washing away the unexposed areas of the photopolymerizable layer. The exposed areas may then be burnished. These sheets are inconvenient to use because they require special developing equipment and solutions i order to wash away the unexposed areas of the photopolyme izable layer. Still other photopol merizable, image forming sheets are described in U.S. Patent 4,081 ,282. However, pressure-sensitive adhesive layer must be applied to the formed images of these sheets before they can be burnishe U.S. Patent 3,754,920 describes a sheet wherein the photopolymerizable layer utilizes a free radically polymerizable ethyl enical ly unsaturated monomer. The photopolymerizable layer is situated between a support an a cover layer. After these sheets are image-wise exposed to activating radiation, the support and cover layers are separated from the photopolymerizable layer. The unexpos portions of the photopolymerizable layer are said to be burnishable onto a receptor. However, the transfer of th unexposed portions cleanly and with high resolution is difficult to achieve. The present invention overcomes these disadvan¬ tages. It provides an imageable composite sheet material which permits the formation and ready transfer of images to a variety of receptors in a completely dry process. Consequently, the present invention permits the formation and transfer of images with conventional techniques thereby permitt ng simple and economical utilization. The present invention also permits the user to form the desired characters from a variety of original sources such as hand drawn masters, pre-printed masters, photographic positives, etc., and then transfer them to a receptor. This eliminates the need to maintain a large inventory of sheets bearing preformed characters. It als gives the user great flexibility in the design of the characters to be transferred. The present invention also ut l zes a photopol erizable material whose pol er zation is not inhibited by oxygen. Consequently, unexposed image areas can readily be either partially or completely polymerized if desired. Still other advantages of the present invention will be described hereinafter. The i ageable, composite dry-transfer sheets of the present invention may be employed in a number of ways. For example, they may be used as Do-It-Yoursel f transfer letter s.heets. Alternatively, they may be used to form and then apply decorative or informative decals to receptors that include glass and metal , Still further, they may be used to form burnishable images from artwork (e.g. , pictures, drawings, etc.) that may subsequently be trans¬ ferred to receptors. Other methods of use are also possible. Thus, the sheets of the nvention may be used to make s lk screen stencils and dry pr nting plates. Still other uses are possible as will be clear as a result of this disclosure. Disclosure of Invention In accordance th the present invent on there is provided an imageable composite dr -transfer sheet that comprises (a) a cover sheet that is transmissive to activating radiation and has at least one oleophil c surface, (b) a photopolymerizable layer on the oleophilic surface of said cover sheet that comprises a cationi cal ly polymerizable organic material , and from about 0,1 to 10 parts by weight per 100 parts by weight of said organic material of a cationic polymerization nitiator, and optionally, from about 1 to 100 parts by weight per 100 parts by we ght of said organic material of a thermoplastic hydrocarbon resin that has a ring and ball softening point of more than about 100°C and is chemically inert to said organic mate ial and said initiator, and (c) a base sheet that has an oleophobic surface in contact ith said photopol merizable layer; wherein said photopolymer zable layer has a complex shear modulus of, at most, 1 x 10 dynes/cm ; and OMPI wherein, after image-wise exposure to activatin radiation, the interfacial adhesion of the unexposed area of said layer is greater for said cover sheet than for sa base sheet; the interfacial adhesion of the exposed areas of said layer is greater for said base sheet than for sai cover sheet; and wherein, after separation of said cover and sai base sheets, the unexposed areas of said layer are render burnishable by subsequent exposure to activating radiatio through said cover sheet. The present invention combines peel-apart devel opment and burnish transferabi 1 i ty (burnishabi 1 ity) in achieving the foregoing results. These properties are th result of different interfacial adhesions of the base and cover sheets for the photopolymerizable layer. Thus, the photopolymer zable layer adheres more strongly to the cov sheet than to the base sheet prior to exposure to activat radiation. However, after the photopolymerizable layer h been exposed to activating radiation through the cover sheet, the now photopolymerized layer adheres more strongl to the base sheet than to the cover sheet. Consequently, when the photopolymerizable layer is exposed to activatin radiation in an image-wise manner through the cover sheet and the cover and base sheets are peeled apart, the expos areas adhere to the base sheet and the unexposed areas adhere to the cover sheet. The photopolymerizable layer demonstrates the following additional properties after image-wise exposure of the sheets to activating radiation: a) The cohesive strength of the unexposed area of the layer is greater than the strength of the adhesion of these areas to the base sheet. b) The cohesive strength of the unexposed area is ]ess than, or equal to, the adhesion of these areas to the cover sheet. c) The photopolymerizable layer has sufficient vertical cohesion and frangibility to fracture cleanly at the boundary between the exposed and unexposed areas. O PI IPO After the sheets of the invention have been image-wise exposed and peeled apart, the unexposed areas are rendered burnishable by being exposed to activating radiation through the cover layer or sheet. The now- burnishable areas possess sufficient cohesive strength, as opposed to particulate character, so that they transfer completely to the desired receptor even though not all of the coating has been subjected to the same degree of bur¬ nishing pressure. The areas to be transferred also possess a balanced adhesion/cohesion so that they transfer completely to the receptor. The foregoing characteristics of the invention are the result of the complex shear modulus of the photo- polymerizable layer. Thus, it has been found that if the 6 2 complex shear modulus exceeds 1 x 10 dyne/cm , both the unexposed and exposed areas of the photopolymerizable layer adhere more strongly to the base sheet than to the cover sheet. Consequently, when the cover and base sheets are peeled apart, there is nothing transferred to the cover sheet . The complex shear modulus may be measured according to the procedures described in "Viscoel astic Properties of Polymers", J. D. Ferry, 2d. Ed. , John Wiley & Sons, N.Y. (1970) at pages 121-124. Brief Description of Drawings The present invention is described in more detail hereinafter with reference to the accompanying drawings wherein like reference characters refer to the same elements throughout the several views and wherein Figure 1 shows an edge view of an imageable, composite dry-transfer sheet according to the invention; Figure 2 shows an edge view of the sheet of F gure 1 in contact with a graphic original being exposed through the original to activating radiation; Figure 3 shows the exposed sheet of Figure 2 being peeled apart; Figure 4 shows the previously unexposed portions of the sheet of Figure.3 being subjected to acti vati Figure 5 shows the exposed sheet of Figure 4 placed on a receptor and being burnished; Figure 6 shows the backing of the sheet of Figu 4 being removed from the burnished images so that the images transfer to the receptor. Detailed Description The cover sheet of the present invention must b transmissive to the activating radiation. While it may be oleophilic per se, it need have only one oleophilic s.urface for contact with the photopolymerizable layer. Thus, it may comprise a composite material that is made up of an oleophobic material that has been rendered oleophilic on at least one surface by coating or other surface treatment. Examples of materials which are oleophilic per or which may be rendered oleophilic, and which are, there fore, useful as the cover sheet include certain polyester sheeting, cellulose acetate sheeting, polypropylene sheet ing, polyethylene sheeting, vinyl chloride sheeting, etc. The base sheet may be either transmissive or opaque to the activating radiation and must possess at least one oleophobic surface for contact with the photo¬ polymerizable layer. Consequently, it may either be oleophobic per se or possess an oleophobic surface. Examples of materials useful as the base sheet include me sheets and foils, polyester, cellulose acetate, etc. Cationically polymerizable organic materials useful in the photopolymerizable layer include polymer¬ izable epoxide-contai ni ng and vinyl ether-containing materials. These materials undergo cationically induced polymerization to yield higher molecular weight products. They may be of the monomeric or polymeric type and can be aliphatic, cycl oal i phatic , aromatic or heterocycl ic . Useful epoxi de-coπtaini ng materials (hereinafte epoxides) are those having an average epoxide functionali of at least one. The epoxide functionality refers to an oxirane ring (i .e. , - - ) that is polymerizable by cationically induced ring opening mechanism. Preferably the epoxides have an average epoxide functional ty of at least two. The average epoxide functionality is determined by dividing the total number of epoxy groups in the epdxide by the total number of molecules of the epoxide. Polymeric epoxides useful in the invention in¬ clude linear polymers having terminal epoxy groups (e.g. , diglycidyl ether of a polyoxyal kyl ene glycol ), polymers having skeletal oxirane units (e.g. , polybutadiene poly- epoxide), and pol mers having pendent epoxy groups (e.g. , a glycidyl methacrylate polymer or copolymer). The epoxides may be pure compounds but are generally mixtures containing one, two, or more epoxy groups per molecule. The epoxides may vary from low molecular weig.ht monomeric materials to high molecular weight polymers and may vary greatly in the nature of their backbone and the substituent groups. For example, the backbone may be of any type and the substituent groups can be any group free of an active hydrogen atom which is reactive with an oxirane ring at room temperature. Illustrative of permissible substituent groups are halogens, ester groups, ether groups, sulfonate groups, siloxane groups, nitro groups, phosphate groups, etc. The molecular weight of the epoxides may vary from 58 to about 100,000 or more. Mixtures of various epoxides can be used in the compositions of this invention. Examples of useful epoxides include those which contain cyclohexane oxide groups, such as the epoxy- cycl ohexanecarboxyl ates typified by 3 ,4-epoxycycl ohexyl - methyl-3,4-epoxycyclohexanecarbox late; 3 ,4-epoxy-2-- ethyl - cycl ohexyl ethyl -3 ,4-epoxy-2-methyl cycl ohexane carboxylate; and bi s (3 ,4-epoxy-6-methyl cyclohexyl ethyl ) adipate. For a more detailed list of useful epoxides of this nature, reference is made to the U.S. Patent No. 3,117,099, incorporated herein by reference. Other epoxides which are useful in the practice of this nvention nclude glycidyl ether monomers of the formul a where R is alky! or aryl and n is an integer of 1 to 6. Examples of these epoxides include the glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phen with an excess of chlorohydrin such as epichl orohydrin (e.g., the diglycidyl ether of 2 ,2-bi s- (2 ,3-epoxypropoxy- phenol )propane) . Further examples of epoxides of this ty which can be used in the practice of this invention are described in U.S. Patent No. 3,018,262, incorporated here by reference, and in "Handbook of Epoxy Resins" by Lee an Neville, McGraw-Hill Book Company, New York (1967). There are many commercially available epoxides which can be used in this invention. In particular, such epoxides include octadecylene oxide, epichl orohydrin , styrene oxide, vinyl cyclohexene dioxide, glycidol , glycidyl ethacrylate , diglycidyl ether of Bisphenol A (e.g. , those available under the trade designations "Epon 828", "Epon 1004" and "Epon 1010" from Shell Chemical Com pany, "DER-331", "DER-332", and "DER-334", from Dow Chemical Company), vinyl cycl ohexene dioxide (e.g. , "ERL- 4206" from Union Carbide Corporation), 3 ,4-epoxycyclo- hexylmethyl -3 ,4-epoxycycl ohexane carboxylate (.e.g. , "ERL- 4221" from Union Carbide Corporation), 3,4-epoxy-6- methyl cycl ohexylmethyl -3,4-epoxy-6-methyl cycl ohexane carboxylate (e.g. , "ERL-4201" from Union Carbide Corpora- tion) , bi s (3 ,4-epoxy-6-methyl cycl ohexylmethyl ) adipate (e.g. , "ERL-4299" from Union Carbide Corporation), bis(2, epoxycycl opentyl ) ether (e.g., "ERL-0400" from Union Carbide Corporation), aliphatic epoxy modified with polypropylene glycol (e.g. , "ERL-4050" and "ERL-4052" fro Union Carbide Corporation), dipentene dioxide (e.g., "ERL-4269" from Union Carbide Corporation) , epoxidized polybutadi ene (e.g. , "oxiron 2001" from FMC Corporation), silicone resin containing epoxy functionality, flame retardant epoxy resins (e.g. , "DER-580", a brominated bisphenol type epoxy resin available from Dow Chemical Company), 1 ,4-butanediol diglycidyl ether of phenolformaldehyde novolak (e.g. , "DEN-431" and "DEN-438" from Dow Chemical Company), and resorcinol diglycidyl eth (e.g. , "Kopoxite" from oppers Company, Incorporated) . ( OMP WIP Still other useful epoxides are copolymers of acrylic acid esters of glycidol such as glycidyl acrylate and glycidyl methacrylate with one or more copolymerizabl e vinyl compounds. Examples of such copolymers are 1 :1 styrene : glycidyl methacrylate, 1 :1 methyl methacrylate: glycidyl acrylate and a 62.5:24:13.5 methyl methacrylate: ethyl acryl ate : glycidyl methacrylate terpoly er, Other useful epoxides are well known and include epichl orohydri ns , e.g. , epichl orohydrin ; alkene oxides, e.g., propylene oxide, styrene oxide; al kenyl oxides, e.g. , butadiene dioxide; and glycidyl esters, e.g, , ethyl glycidate. Useful vinyl ether-containing materials (.herein¬ after vinyl ethers) are those containing at least one vinyl ether group (i.e. , CH 2 =CH0-). These materials are known and include the alkyl vinyl ethers represented by q the formula (H 2 C=CH0) R wherein m is an integer of 1 to 4 and R is an organic group (either polymeric or low mole¬ cular wieght) that is free from groups that are reactive with the vinyl ether group. Representative of useful vinyl ethers is divinyl ether of diethylene glycol . Combinations of two or more vinyl ethers are useful in the present invention as are combinations of epoxides with vinyl ethers. Cationic photopolymeri zation initiators useful in polymerizing the epoxides and vinyl ethers include aromatic iodonium and sulfonium complex salts. Halogen-containing organic compounds are also useful as cationic polymeriza¬ tion initiators for the vinyl ethers. The iniators com- prise from about 0.1 to 10 parts by weight per 100 parts by weight of the cationically polymerizable organic material . Preferably they comprise from about 0.5 to 7 parts by weight. The exact quantity of initiator employed is influenced by the polymerizable material and the initiator utilized, and the transmissivity of the polymerizable layer to activating radiation. Useful aromatic iodonium and sulfonium complex salts have formulae selected from f OMPI 1 2 In these formulae, Ar and Ar are the same or different substituted and unsubstituted divalent aromatic 3 groups that have from about 6 to 20 carbon atoms; Ar 4 and Ar are the same or different substituted or unsub¬ stituted monovalent aromatic groups that have from about 1 2 6 to 20 carbon atoms; R and R are selected from substi¬ tuted and unsubstituted divalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted or unsubstituted alkylene groups that contain from about 1 to 3 4 5 about 20 carbon atoms; and R , R and R are each selected from substituted and unsubstituted monovalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted and unsubstituted alky! groups that contain from 1 to 20 carbon atoms, provided that at least one of 1 5 the R through R groups is aromatic. Preferably, each 1 5 of the R through R groups is aromatic. In formulae A and C, Z is selected from a carbon-to-carbon bond; oxygen, sulfur, S=0, C=0, 0=S=0, ~ f*. 7 ~ 7 J-. R -N wherein R is aryl or acyl , R -C-R wherein R and R are selected from hydrogen, alkyl groups that contain from about 1 to 4 carbon atoms, and alkenyl groups that contain from about 2 to 4 car.bon atoms. In all formulae X is a halogen-containing complex ani on . 1 2 Representative examples of useful Ar , Ar and 1 2 aromatic R and R groups include phenyleπe, thienylene, furanylene, and pyrazolylene groups. 3 4 Representative examples of useful Ar , Ar and 3 4 5 aromatic R , R and R groups include phenyl , thienyl , furanyl , and pyrazol groups. The divalent and monovalent groups may also have one or more fused benzo rings [e.g. , naphthyl , naphthylene and the like; benzothienyl , benzoth enylene, benzofuranyl , benzofuranyl ene , di benzofuranyl ; etc.). The divalent and monovalent aromatic groups may also be substituted, if desired, by one or more of the following groups: halogen, nitro, hydroxyl , ester groups (e.g. , al oxycarboxyl such as methoxycarbonyl and ethoxyca bonyl , phenoxycarbony! and acyloxy such as acetoxy and propi onyl ox ) , sulfo ester groups (e.g. , al koxysul fonyl such as methoxysul fonyl and butoxysul fonyl , phenoxysul fonyl , and the like), alkoxy groups (.e.g. , methoxy, ethoxy, butoxy, and the like), aryl groups (e.g. , phenyl ), alkyl groups (e.g. , phenoxy), thioaryloxy groups (e.g. , thiophenoxy) , al kyl sul fonyl (e.g., methyl sul fonyl , ethyl sul fonyl , and the like), arylsulfonyl groups (e.g. , phenyl sul fonyl groups), perf1 uoroal kyl groups (e.g. , tri fl uoromethyl , perf1 uoroethyl , and the like) , and perf1 uoroal kyl sul fonyl groups (e.g. , tri fl uoromethyl sul fonyl perfl uorobutyl sul fonyl , and the like). Halogen-containing anions (X ) useful in the invention include tetraf1 uoroborate , hexaf1 uoroarsenate , hexafl uorophospha te and hexaf1 uoroanti onate . The aromat c iodonium cat ons are known and recognized in the art. See for example, U.S. Patents 3,565,906; 3,712,920; 3,759,989; and 3,763,187; F, Beringer, et al . , Diaryl odoni urn Salts IX , J, Am, Chem. Soc, 81 , 34 (1959) and F. Beringer, et al . , Diar l iodonium Salts XXIII J. Chem. Soc. 1964, 442-51 ; F. Beringer, et al . , Iodonium Salts Containing Heterocyclic Iodine, J, Org. C em. 30 1141-8 (1965). Representative examples of useful aromatic iodonium complex salts include di phenyl iodonium tetrafluoroborate di (4-methyl phenyl )iodonium tetrafluoroborate phenyl -4-methyl phenyl iodonium tetrafluoroborate di(4-heptyl phenyl ) iodonium tetrafluoroborate di [3-ni trophenyl )iodon urn hexaf1 uorophosphate i(4-chlorophenyl) odoniurn hexafl uorophosphate di(naphthyl ) iodoni urn tetrafluoroborate di (4-tri fl uoromethyl phenyl )iodonium tetrafluoro¬ borate di phenyl iodonium hexaf! uorophosphate di (4-methyl phenyl ) iodoni urn hexaf! uorophosphate di phenyl iodonium hexafluoroarsenate d (4-phenoxyphenyl ) i odon urn tetrafluoroborate phenyl -2-thienyl iodonium hexafl uorophosphate 3,5-di ethylpyrazolyl-4-phenyl iodoniurn hexa- f1 uorophosphate b s- ( . 2,4-dimethyl phenyl ) iodoni urn hexafluoro- anti onate di phenyl odon urn hexafl uoroant monate 2 '2-di phenyl iodoniurn tetrafluorobora e di(2,4-dichlorophenyl )iodon um hexafl uorophospha di (4-bromophenyl ) iodonium hexafl uorophosphate di (4-methoxyphenyl ) iodonium hexaf1 uorophosphate di(3-methoxycarbonyl phenyl) odoni urn hexafl uoro¬ phosphate di (3-methoxysul fonyl phenyl ) iodonium hexafl uoro¬ phosphate di (2-benzothienyl )iodonium hexaf1 uorophosphate The aromatic iodonium complex salts preferred in the present invention are the diaryl iodonium hexafluoro- phosphate and the diaryl iodon urn hexaf1 uoroantimonate sal ts . The aromatic iodonium complex salts may be pre¬ pared by metathesis of corresponding aromatic iodonium simple salts (such as, for example, the di phenyl iodonium bisulfate) in accordance with the teachings of Beringer et a! . , J. Am. Chem, Soc. 81 , 342 (1959). Alternatively, they may be pre¬ pared in accordance with Beringer et al , , above, by various methods including 0 ) coupling of two aromatic compounds with iodyl sulfate in sulfuric acid, (2) coupling of two aromatic compounds with an iodate in acetic acid-acetic anhydride-sul furi c acid, ( . 3) coupling of two aromatic com¬ pounds with an iodine acylate in the presence of an acid, and (4) condensation of an iodoso compound, an iodoso diacetate, or an iodoxy compound with another aromatic compound in the presence of an acid . More specif cally, aromatic iodonium complex salts may be prepared by reacting an appropriate aromatic iodine salt (e.g. , 316.5 g 0 2 I Cl " ) with a desired complex salt (e.g. , 252.8 g AgPF β ) in a polar solvent such as methyl alcohol . Reaction may be conveniently carried out at room temperature. Aromatic sulfonium salts are known and recognized in the art. Triaryl -substi tuted sulfonium compounds, for example, can be prepared by the procedures described in G. H, Wiegand, et a! ., Synthesis and Reactions of Triaryl -sul fonium Halides, J. Org. Chem. !3i > 2671-75 (1968). Aromatic sulfonium salts also having al yl -substitution can be prepared by the procedures described in K. Ohkubo et al , , J. Org, Chem. 36 , 3149-55 (1971 ). Yet another method for making tri aryl - substituted sulfonium compounds is described in U.S. 2,807,648 incorporated herein by reference, from which the complex sulfonium salts can be made. The complex sulfonium salts can be prepared from the corresponding simple salts, such as the halide salts, by metathesis with a eta! or ammonium salt of the complex anion desired. Examples of useful aromatic sulfonium complex salt photoinitiators include: tri phenyl sul fonium tetrafluoroborate methyl di phenyl sul foni urn tetrafluoroborate di ethyl phenyl sul foni urn hexafl uorophosphate triphenyl sul foni urn hexaf1 uorophosphate tri pheny sul foni urn hexafl uoroantimonate tri phenyl sul fonium hexafl* uoroarsenate di phenyl naphthyl sul foni urn hexafl uoroarsenate OMPI 5-methylthianthrenium hexafl uorophosphate) (10-phenylthioxanthenium hexafl uorophosphate) ylthioxantheni.um hexafl uorophosphate) m tetrafl uoroborate) (5-methyl-lO-oxothianthrenium tetrafl uoroborate) tri phenyl sul fonium hexafl uoroarsenate tr tolysul fonium hexafl uorophosphate am " s Idi phen l sul fonium hexafl uoroantimonate 4-butoxyphenyldi phenyl sul foni um tetrafl uorobora 4-chlorophenyldi phenyl sul foni um hexafl uoro¬ antimonate 4-chlorophenyldi phenyl sul fonium hexafl uoro¬ arsenate tris (4-phenoxyphenyl )sulfonium hexaf1 uorophosph 10 di(4-ethox phenyl )methy! sul fonium hexafl uoro¬ arsenate 4-acetoxy-phenyldi phenyl sul fonium tetrafl uoro¬ borate tri s (4-thiomethox phenyl )sul fonium hexafl uoro¬ 15 phosphate di(methox sul fon l phenyl )methyl sul fonium hexafl uoroantimonate di(methoxynaphthyl )methyl sul fonium tetrafluoro¬ borate 20 4-phenylthiophenyldi phen l sul foni um hexafl uoro¬ antimonate 4-phenylthiophenyldi phen l sul foni um hexafluoro¬ arsenate di(carbomethoxyphenyl)methyl sul fonium 25 hexafl uorophosphate di ethyl naphthyl sul foni um hexafl uorophosphate tri fl uoromethyldi phenyl sul fon um tetrafl uoro¬ borate methyl (N-methylphenothiazinyl )sul fonium 30 hexaf1 uoroantimonate phenylmethyl benzyl sul fon um hexafl uorophosphate (10-methylphenoxathiinium hexafl uorophosphate) strongly basic. Examples of useful halogen-conta ning compounds include 1 -methyl -3 ,5-bi strichl oromethyl triazine, 1 ,3,5-tristrichloro ethyl tr azine, 1 ,3,5-t ist i romoethyl triazine, hexabromoethane, carbon tetrabromide, X__ ~ζ •*■ dibromo-o-xylene. ring softening point of at least 100°C and are chemically inert to the cationically polymerizable organic material and the photopoly erization initiator in the absence of activating radiation. Additionally, they do not ncrease the cohesive nature of the unpolymerized photo¬ polymerizable layer beyond the limits described above and do not alter the adhesion balance of the exposed and unex¬ posed areas of the photopolymerizable layer to the base and cover sheets beyond the limits previously described. Representative examples of useful thermoplastic resins include block copolymers, polyolefin resins, and acrylic resins. Representative examples of useful block copolymers are raton 1101 , a block copolymer having- terminal blocks of styrene and central blocks of butadiene groups, and Kraton 1650 having terminal blocks of styrene groups and central blocks of combinations of ethylene and butylene groups. The Kraton resins are available from Shell Chemical Company. Representative examples of useful polyolefin resins include polystyrene resins such as Piccol astic-^ Cl 25 , a modified, low molecular weight resin produced largely from styrene monomer and having a ring and hall softening point in the range of 122-128°C, available from Hercules Incor¬ porated; and Styroit- 685 , a polystyrene resin available from Dow Chemical Company. Representative examples of useful acrylic resins include El vaci te--' 2041 (a methyl methacrylate polymer, glass transition temperature of 95°C), available from DuPont. Various other ingredients may be included in the photopolymerizable layer of the present invention. For example, tackifying agents, plasticizing agents, sensitizers, colorants, fillers, viscosity modifiers, and so forth, may be included. Tackifying agents typically comprise up to 200 parts by weight per 100 parts by weight of the organic cationically polymerizable material . Useful tackifying agents have a ring and ball softening point below about 100°C and preferably below about 60°C and include rosin and rosin derivatives, low molecular weight styrene resins, cycl ohexanone resins, coumarone resins, indene resins, terpene resins, coumarone- ndene resin, etc. Specific examples of useful tack fying resins include polystyrene w such as Piccolasti -^ A series of resins having ring and ball softening points below about 100°C such as A-25 (ring and ball softening point in the range of 24-27°C available from Hercules Chemical Company) a nd polymerized mixed " olefins such as the Sta-Tac and Super Sta-Tac series of resins from Reichold Chemical Company. Other specific examples include Foral 85, a hydrogenated ester resins available from Hercules Incorporated. Representat ve examples of useful plasticizing agents are solid phthalate esters, e.g. , dicycl ohexyl phthal ate , and para-tol uene-sul fonami de and its derivatives, etc. Other materials that may be employed as plasticizing agents include heavy mineral oils such as Drakeol 35 a white mineral oil available from Pennsylvania Refining Company; Shellmax 500, a microcrystal 1 i ne wax (R) available from Shell Chemical Company and Elvax 150, an ethyl ene/vi nyl acetate copolymer available from DuPont. The use of tackifying resins and plasticizing agents n the present invention is particularly preferred. Thus, without at least one of these materials present in the photopolymerizable layer, the unphotopolymerized areas to be transferred can be only partially polymerized before burnishing. However, when either or both of these materials are present in the unphotopoly erized areas to be transferred, they can be completely polymerized before burnishing. These ingredients are apparently unaffected by exposure to the activating radiation. In any event, the images transferred are resistant to abrasion and smeartng. The photopolymerization initiators useful in the present invention are of themselves photosensitive only in the ultraviolet. They, however, can be sensitized to the near ultraviolet and the visable range of the spectrum by a variety of sensitizers. Typically, the sensitizers comprise up to about 10 parts by weight per 100 parts by weight of cationically polymerizable material . Examples of useful sensitizers may be found in the following categories: (1) Aromat the formula C c • where Ar , Ar and Ar are aromat c groups aving 6 to 20 carbon atoms and may be the same or different. The aromatic groups may be substituted, if desired, with groups or radicals such as hydroxyl , alkoxy, acyl or alkyl, Q may 9 9 be oxygen; sulfur; S=0; C=0; 0=S=0; R -N where R is aryl (of 6 to 20 carbons, such as phenyl , naphthyl , etc.); a 7 8 carbon-to-carbon bond or R 7 -C-R 8 where R and R are selected from hydrogen, alkyl radicals of 1 to 4 carbons, and alkenyl radicals of 2 to 4 carbons, and wherein a is zero or 1. (2) Aromatic tertiary dia ines having the formul a where Y is a divalent radical selected from arylene and 12 13 Ar -Z-Ar , where Q is as described above for aromatic 8 13 tertiary amines; Ar , through Ar are aromatic groups having 6 to 20 carbon atoms and may be the same or different; and each a is, individually, zero or 1. The aromatic groups may be substituted, if desired, with groups or radicals such as hydroxyl , alkoxy, acyl or alkyl , (3) Aromatic polycyclic compounds having at leas three fused benzene rings and having an ionization energy less than about 7.5 ev. , as calculated by the method of F. A. Matsen, J. Chem. Physics, 24, 602 (1956), incorporate herein by reference. Other useful classes of sensitizers are xanthenes thiazoles, polymethi nes , methines, acridines, C PI di phenylmethanes , thiazines, azines, ami noketones , porphyrins, aromatic polycyclic hydrocarbons, p-substi tuted ami nostyryl s , aminotriaryl methanes, non-basic propenone compounds described in U.S. Patent 3,617,288. Representative examples of sensitizers coming within the above useful classes include: tri phenyl ami ne di naphthyl phen l ami ne N, N-diphenyl-N-p-methox phenyl amine 9-(N,N-d phen lamino)-anthracene N,N,N' ,N'-tetraphenyl-p-phenylenediamine N,N,N' ,N'-tetraphen lbenzidine N-phenylphenothiazine N-phenylphenoxazine N, N ' -di phenyl dibenzopiperazine N-phenyl-9,10-dihydroacridine N-naphthylacridine 4,4'-diρheπylaminodiphenylether anthracene 2-ethyl-9,10-dimethoxyanthracene 9, 10-di thox anthracene 1 ,2-benzanthracene peryl ene rubrεne tetraphenylpyrene 9, 10-di phenyl anthracene tetracene pentacene anthanttirene Rhodamine 6G (C.I. 45160) Acridine Orange (C.I. 52015) Hematoporphyrin Protoporphyrin Benzoflavin The above classes of sensitizers, together with additional examples of each, may be found in U.S. Patent Numbers 3,515,552; 3,617,288; 3,640,718; 3,729,313 and 4,069,054. Colorants, fillers, viscosity modifiers, extenders, and so forth may also be incorporated into the photopoly¬ merizable layer. Typically these ingredients to about 75 parts by weight per 100 parts by weight of the cationically polymerizable material . Useful colorants include pigments such as carbon black (e.g. , Raven 22 available from Cities Service) and dyes. They may be opaque and may be conductive or resisti materials. Such materials may include fine metal powders. Useful fillers and viscosity modifiers include talc, clay, aluminum oxide, silica (e.g., Cab-0-Sil U-5 from Cabot Corporation), etc. Useful ■ extenders include organic resins such as segmented polyester resins prepared as described in U.S. Patent 4,049,483, and hydroxy terminated polyester resins such as Multron R-18 available from Mobay Chemical Company. Still other useful polyesters include the aliphatic polyesters of sebacic acid and 1 ,4-cycl ohexane dimethanol . The formation and transfer of images according to the present invention is achieved in a surprisingly simple manner. Thus, referring to the drawings, Figure 1 illustrates an imageable, composite dry-transfer sheet 1 comprising a cover sheet 2 that has an oleophilic surface, a base sheet 4 that has an oleophobic surface, and a photopolymerizable layer 6 interposed between the oleo¬ philic surface of cover sheet 2 and the oleophobic surface of base sheet 4. In use, as illustrated in Figures 2-6 , images are formed in sheet 1 by placing an original 10 in contact with cover sheet 2. Preferably original 10 is in intimate conta with cover sheet 2. Original 10 has areas 11 which are non-trans ssive to activating radiation 14 and areas 12 that are transmissive to activating radiation 14. Sheet 1 is exposed to activating radiation 14 (Se Figure 2) through original 10 for a time and at an intensit sufficient to cause the formation of polymerized areas 6a i photopolymerizable layer 6. Areas 6a correspond directly to the transmissive areas 12 of original 10.. Areas 6b n photopol merizable layer 6 are not exposed to radiation 14 and therefore do not polymerize. Areas 6b correspond directly to non-transmi ssi ve areas 11 of original 10. The photopolymerizable layer is generally exposed to ultraviolet light for a short period of time, e.g. , three minutes, to bring about image-wise polymerization of the exposed areas of layer 6. The resultant areas 6a and 6b represent a negative and a positive, respectively, of the image on original 10. After exposure to radiation 14, sheet 1 is peeled apart (see Figure 3) to provide component A bearing unpolymeri zed areas 6b and component B bearing polymerized areas 6a. Component A is then exposed to activating radiation 15 through cover sheet 2 for a time and at an intensity to at least partially polymerize areas 6b. See Figure 4. After exposure, component A is' placed in contact with a receptor 16 such that the now at least partially exposed areas 6b contact the receptor. See Figure 5, Pressure is then applied to the backside 3 of component A, for example by a burnishing tool 18, over the areas 6b to be transferred. After burnishing, component A is peeled off of receptor 16. See Figure 6. In so doing, areas 6b release from cover sheet 2 of component A and adhere to receptor 16. The transferred image areas are non-tacky and resistant to smearing and abrasion. Typically the exposure of component A is to ultraviolet light and requires only about 30 seconds to achieve transferabi 1 i ty for partially polymerized areas 6b. Slightly longer times (e.g. , 3 minutes or more) are normally required to effect complete polymer zation of areas 6b, Component B cannot be burnished but can serve as an original to make a negative image that is burnishable. Thus, the negative image produced with another sheet of the invention thereon may be transferred to a receptor in a similar manner as employed to transfer a positive image. Component B may also be used as a sign or label . Although the activating radiation has been described only with reference to ultraviolet light, the photopolymerizable layer will also polymerize upon exposure to a source of radiation of other wavelengths, e,g,, visible light. Suitable sources of radiation include mercury, xenon, carbon arc, tungsten filament lamps, sunlight, etc. Exposures may be from less than 30 seconds to more than 15 minutes depending upon the amounts of particular polymerizable materials and complex salts being utilized, the absence or presence of sensitizers, the radiation source and distance from the source, the transmissi vi ty of the photopolymerizable layer to the activating radiation, and the thickness of the photopolymerizable layer to be polymerized. The compositions may also be polymerized by exposure to electron beam irradiation. Generally speaking the dosage necessary is from less than 1 megarad to 100 megarad or more. The imageable sheets of the invention may be readily prepared using conventional processing techniques. Thus the photopolymerizable composition is first prepared by combining the cationically polymerizable material and any colorants to be employed. The remaining components of the photopolymerizable layer are mixed together and then combined with the cationically polymerizable material and the colorant. Conventional mixing techniques are utilized. The combination of ingredients is mixed until uniform and then applied to the non-polar surface of the oleophilic cover sheet by, for example, knife, reverse roll , or Meyer bar coating. The coated cover sheet is then typically dried at less than 70°C for one half to five minutes. The resulting photopolymerizable layer is typically 2.5 to 25 micrometers thick. The base sheet is then laminated to the photopoly¬ merizable layer by, for example, conventional techniques so that an oleophobic surface contacts the photopolymerizabl layer. The preparation of the imageable sheet is carried out in the absence of activating radiation. The present invention is further illustrated with reference to the following examples wherein the term parts refers to parts by weight unless otherwise noted. Example 1 Imageable composite dry-transfer sheets according to the invention were prepared. The cover sheet comprised a section of biaxially oriented pol ( ethyl ene terephthal ate) _OHPI_ * ' PET) film which had an oleophilic coating of a silicone surface-acti e agent on one surface. This film was obtained from Akrosil Corporation as type 2C-5459. It was 35 micrometers thick. The cationically polymerizable photopolymerizable layer was applied from a composition that contained the following ingredients: Ingred ent Parts 3 ,4-epox cycl ohexylmethyl -3,4-epoxycyclo- hexane carboxylate (Bakelite ERL-4221 from Union Carbide Corporation) 15,4 Carbon black (Raven 22, a furnace carbon black from the Columbian Division of Cities Service Company) 4.3 Triaryl sul fonium hexaf1 uoroantimonate (10% by weight solution in methyl ethyl ketone) (TASHFA)* 7,7 2-ethyl -9 ,1 O-dimethoxyanthracene (5% by weight solution in methyl ethyl ketone) CEDMA) Pyrogenic silica ( . Cab-0-Sil M-5 from Cabot Corporation) Segmented polyester resin (25% by weight in methyl ethyl ketone) prepared according to Example 1 of U.S. Patent 4,049,483, col lines 53-68 19.7 Thermoplastic rubber ( . 25% by weight in toluene. A block copolymer available as Kraton 1101 from Shell Chemical Company). 9.9 Methyl ethyl ketone (MEK) 34.1 * 50% by weight 4-phenyl thiophenyl di phenyl sul fonium hexafl uoroantimonate 45% by weight triphenyl sul fonium hexaf1uoroantimonate 5% by weight 4-chl orophenyl di phenyl sul foni um hexafluoroantimonate The composition was coated onto the oleophilic surface of the PET with a No. 22 Meyer bar and then dried at 65°C for 2 m nutes in an air circulating oven. An oleophobic base sheet of PET film was then laminated to the dried photopolymerizable layer. The resultant imageable, composite dry-transfer sheet was image-wise exposed to ultraviolet (UV) light in a model EU 8000 Ultraviolet Exposure unit from 3M. Exposure was achieved by placing a stencil on the cover ■ ^ sheet and exposing the transfer sheet through the stencil to ultraviolet light from General Electric fluorescent lamps (model number F15T8-BL) for three minutes. Intimate contact was maintained between the stencil and the transfer sheet by placing a glass plate over the stencil and pressing the stenci 1 /sheet combination onto a sponge with the oleophobic base sheet of the transfer sheet in contact with the sponge. After exposure, the cover sheet was stripped away from the base sheet. The cover sheet had an unpolymerized positive image on it while the base sheet had a polymerized negative image on it. The positive and negative images separated cleanly from each other. The cover sheet (with positive image) was placed in the exposure unit with the imaged side in contact with a sheet of plain bond paper which had been folded in an accordion-li e fashion so that the image areas had minimal contact therewith. The image areas were then exposed through the cover sheet to ultraviolet light for 30 seconds. The cover sheet (with the partially cured positive image) was then placed upon a receptor (a sheet of bond paper) so that the partially cured images were in contact with the receptor. The images were then transferred to the paper receptor by applying pressure to the back of the cover sheet with a burnishing tool . When the cover sheet was separated from the bond paper, the burnished image was completely transferred to and adhered on the paper. The surface of the image was non-tacky and resistant to smearing and abrasion. Sheets prepared according to this example were also found useful in transferring images to other receptors such as cardboard, acetate film, poly( . ethyl ene terephthal ate) film and metal foil . Exampl e 2 Example 1 was repeated except that the photo¬ polymerizable layer was applied to the cover sheet from the following composition: '.hΛ i Ingredient Parts ERL-4221 (Union Carbide Corporation) 17.2 Raven-22 (Cities Service Company) 4.8 TASHFA (10% by weight in MEK) 8.5 EDMA (5% by weight in MEK) 8.5 Cab-0-Sil -5 (Cabot Corporation) 1.3 Acrylic resin (Elvacite 2041 from E, I. DuPont 25% by weight in MEK) 10.9 Hydroxy terminated polyester (Multron R-18 from Mobay Chemical Company) 10 MEK 37 The dry transfer sheet was imaged as described in Example 1 and the base sheet and the cover sheet stripped away from each other. Separate portions of the cover sheet, bearing an unpolymerized positive image, were post exposed for various lengths of time as described in Example 1 to partially cure the image. The positive images were then transferred to a piece of bond paper by burnishing as described in Example 1. The results of the tests are set forth below in Table 1 Table 1 Post Exposure (Min) Comments Compl ete transfer. Images non-tacky and resistant to abrasion and s earing. Complete transfer. Images non-tacky and resistant to abrasion and smearing . Complete transfer. Images non-tacky and resistant to abrasion and smearing . 12 Some loss in burni shabi 1 i ty in that additional pressure needed to burnish, Images less re*- sistant to abrasi on . 15 Some loss in burn shabi 1 i ty n that more pressure needed than requ red in 12 min. exposure sa pl e . Images less res stant to abrasion, 27 Exampl es 3-1 A series of imageable composite dry-transfer sheets according to the invention were prepared according to the procedures described in Example 1 except that the photopolymerizable layer of each was different. In each example the cover sheet comprised a section of biaxially oriented PET that had been coated with a silicone surface- active agent to render one surface oleophilic. The silico treated cover sheet was UBL 110-1 available from Akrosil Corporation. The oleophobic base sheet in each example was a biaxially oriented PET film. Each sheet was imaged and used in a burnishing process as described in Example 1 except that the positive image, which was transferred by burnishing, was burnishabl even though it was completely polymerized by the post exposure. Post exposures of up to 15 minutes were used. all cases the transferred images were non-tacky and re¬ sistant to abrasion and smearing. The components used in the photopolymer zable compositions are set forth below in Table 2. O V IP Divinylether of diethylene glycol (2) 24 24 Raven 22 6 5,4 6,8 6.8 6.8 6.8 6.8 6.8 TASHFA 1 1.2 1.5 1.7 1.5 di phenyl i odonium hexafluorophosphate 1.5 Bis- (2 ,4-dimethy! phenyl ) iodonium hexaf1 uoroantimonate 1.5 Triaryl sul fonium 00 hexafl uoroarsenate X ~ ) 1.5 l-methyl-3,5- istrichloromethyl triazine 1.5 (1) bis (3 ,4-epoxy-6-methylcycl ohexylmethyl )adi pate available from Union Carbide Corporation (2) Available from GAF. (3) 50% by weight 4-phenyl hiophenyl di phenyl sul foni um hexafl uoroarsenate . 45% by weight tri phenyl sul fonium hexaf1 uoroarsenate . 5% by weight 4-chlorophenyl i phenyl sul fonium hexaf1 uoroarsenate . * TABLE 2 (Cont'd) ' co • ** σ- COMPOSITION Exampl es © © 8 9_ 1_0 © 1 i i 7 CO O EDMA 1.5 1.2 1.5 1.5 1.5 1.5 1 ,7 1.5 1.5 H Aliphatic polyester of sebacic U acid and 1 ,4-cyclohexane dimethanol (50% by weight in toluene) 18,3 • Foral 85 ( ' 75% by weight in MEK) . 4 ) 10 16.1 15.4 15.4 15.4 15.4 16,5 15,4 15.4 Elvacite 2044 (25% by weight in MEK) v 5 - 1 14.6 12.4 15.4 15.4 15.4 15.4 16.5 15.4 15.4 Kraton 1101 (25% by weight in MEK) 22 Kraton 1650 (20% by eighty in 50/50 toluene/heptane) L ' 18,6 23.1 23.1 23,1 23.1 24.7 23,1 23.1 (4) A hydrogenated ester resin from Hercules, Inc. (.5) An n-butyl methacrylate polymer from DuPont. (6) A thermoplastic rubber/styrene block copolymer, availble from Shell Chemical Co r- < SO © © CO O Etha nol 2,9 [(6)] (7) A white mineral oil available from Pennsylvania Refining Co. [(7)] (8) A microcrystal 1 ine wax available from Shell Chemical Co. [(9)] (9) An ethylene/vi nyl acetate copolymer available from E. I. du Pont de Nemours © «*•"> - - Example 12 Imageable composite dry-transfer sheets according to the invention were prepared. The cover sheet comprised a section of biaxially oriented PET film which had been coated with a silicone surface-acti e agent to render its surface oleophilic. The film was UBL 110-1 available from Akrosil Corporation. A sheet of PET film was employed as the oleophobic base sheet. The cationically polymerizable layer was applied from a composition that contained the following ingredients: Ingredient Part ERL 4299 19.5 Raven 22 5.5 Elvacite 2044 (25% in MEK) 12.4 TASHFA 1.2 9,10-Diethoxyanthracene (DEA) 1.2 Kraton 1650 3.7 Shellmax 500 2.5 Piccolastic A-25 (polystyrene resin from Hercules Chemical Co.) 6.8 Toluene/Heptane (1 :1) 19,6 MEK 27.6 The Kraton 1650, Shellmax 50Q and Piccolastic A-25 were mixed together under high shear using a laboratory Dispersator with a Hi-Vis^ head. Mixing was carried out at a temperature of about 150°C for 30 min. The mixture was then cooled below room temperature with dry ice, ground into small chunks and solubilized with a 1:1 by weight blend of to! uene : heptane to a final solids content of 40%, The remaining ingredients were then added to the solution and th entire formulation was run through a Manton Gaulin laborator 2 homogenizer at 8,000 PSI (581 kg/cm ) . The resulting formulation was coated onto the oleophilic surface of the co sheet to a thickness of 0.00125 cm. It was then oven dried for two minutes at about 65°C and the base sheet was then laminated thereover. The resulting sheet was then image-wis exposed, the base and cover sheets separated and the unexposed areas post exposed and used in a burnishing proces as described in examples 3-11. The positive images were burnishable even though they had been completely po1ymg ή 7 p . by the post exposure. The transferred images were non-tacky and resistant to abrasion and smearing. Example 13 Example 1 was repeated except that the photopoly- merizable layer was applied to the oleophilic surface of the cover sheet from the following composition: Ingredient Parts ERL-4221 78 Raven 22 22 TASHFA (10% by weight in MEK) 39 EDMA (10% by weight in MEK) 39 Cab-0-Sil M-5 6 Solid polystyrene resin (Dow- 685 from Dow Chem. 12-1/2% by weight in MEK) 50 MEK 173 The dry transfer sheet was imaged as described in Example 1 and the base sheet and the cover sheet stripped away from each other. The cover sheet (with positive image) was then exposed to ultraviolet light for a brief time as described in Example 1 and the images were then burnished onto bond paper. The surface of the image was non-tacky and resistant to smearing and abrasion. Exampl e 14 Example 1 was repeated except that the photo¬ polymerizable layer was applied to the oleophilic surface of the cover sheet from the following composition: Ingredient Parts ERL-4221 78 Raven 22 22 TASHFA (10% by weight in MEK) 39 EDMA (10% by weight in MEK) 39 Cab-0-Sil M-5 6 Dow 685 (12.5% by weight in MEK) 20 MEK 173 o. :rτ • The dry transfer sheet was imaged as described in Example 1 and the base sheet and the cover sheet stripped away from each other. The cover sheet (with positive image was then exposed to ultraviolet, light for a brief time as described in Example 1 and the images were then burnished onto bond paper. The surface of the image was non-tacky an resistant to smearing and abrasion. Exampl e 15 Example 1 was repeated except that the photopoly¬ merizable layer was applied to the oleophilic surface of th sheet from the following composition: Ingredi ents Parts ERL-4221 78 Raven 22 22 TASHFA ( . 10% by weight in MEK) 39 EDMA (10% by weight in MEK) 39 Cab-0-Sil M-5 6 Acrylic resin (Elvacite 2044 from E. I. DuPont deNemours and Company, 25% by weight in MEK) 20 MEK 173 The dry transfer sheet was imaged as described in Example 1 and the base sheet and the cover sheet stripped away from each other. The cover sheet (with positive image was then exposed to ultraviolet light for a brief time as described in Example 1 and the images were then burnished onto bond paper. The surface of the image was non-tacky and resistant to smearing and abrasion. Example 16 Example 1 was repeated except that the photopoly¬ merizable layer was applied to the oleophilic cover sheet from the following composition: Ingredients Parts ERL-4221 78 Raven 22 22 TASHFA (10% by weight in MEK) 39 EDMA (10% by weight in MEK) 39 Cab-0-Sil M-5 6 Kraton 1101 (.25% by weight in MEK) 50 The dry transfer sheet was imaged as described in Example 1 and the base sheet and the cover sheet stripped away from each other. The cover sheet (with positive image) was then exposed to ultraviolet light for a brief time as described in Example 1 and the images were then burnished onto bond paper. The surface of the image was non-tacky and resistant to smearing and abrasion. Examples 17-18 . Imageable composite dry-transfer sheets were prepared as described in Example 1 using the following compositions as the photopolymer zable layer. Inqredi ents - Parts 17 18 "Epon" 836 (softening point of 4Q-45°C available from Shell Chemical Company) 45.4 "Epon" 10Q1 (softening point of 65-75°C available from Shell Chemical Company) 45 TASHFA -2.3 2 DEA 2.3 2.3 MEK 50 50 Modulus of Photopolymerizable Layer (.dynes/cm^ ) 8 x 10 J 1 x 10 ,10 The dry transfer sheets were imaged as described in Example 1 and the base and cover sheets stripped away from each other. In Example 17, the positive image released from the base sheet and adhered to the cover sheet while the negative image did the opposite, thereby exhibiting the desired adhesion/cohesion relationships among the base sheet, the cover sheet and the photopolymerizable layer. In Example 18, neither the positive nor the negative image released from the base sheet but rather both adhered to the cover sheet.

Claims: What is claimed is: 1. An imageable composite dry-transfer sheet that comprises (a) a cover sheet that is transmissive to activating radiation and has at least one oleophilic surface, (b) a photopolymerizable layer on the oleophilic surface of said cover sheet that comprises a cationically polymerizable organic material , and from about 0.1 to 10 parts by weight per 100 parts by weight of said organic material of a cationic photopolymerization initiator, and (c) a base sheet that has an oleophobic surface in contact with said photopolymerizable layer; wherein said photopolymerizable layer has a complex shear modulus of, at most, 1 x 10 dyne/cm ; and wherein, after image-wise exposure to activating radiation, the interfacial adhesion of the unexposed areas of said photopolymerizable layer is greater for said cover sheet than for said base sheet; the interfacial adhesion of the exposed areas of said photopolymerizable layer is greater for said base sheet than for said cover sheet; and wherein, after separation of said cover and said base sheets, the unexposed areas of said layer are rendered burnishable by subsequent exposure to activating radiation through said cover sheet. 2. An imageable sheet according to claim 1 where- in said photopolymerizable layer further comprises from about 1 to 100 parts by weight per 100 parts by weight of said organic material of a thermoplastic hydrocarbon resin that has a ring and ball softening point of more than about 100°C and thermoplastic hydrocarbon resin being chemically inert to said organic resin and said initiator. 3. An imageable sheet according to claim 1 wherein said cationically polymerizable organic material is selected from epoxides that have an epoxide functionality of at least one, and materials that have at least one vinyl ether group. 4. An imageable sheet according to claim 3 wherein said cationically polymerizable organic material is an epoxide having an epoxide functionality of at least one. ^\J i.Λ " 7 OMPI v . V IPO &: 5. An imageable sheet according to claim 4 wherein said initiator is an aromatic onium salt that has a formula selected from 1 2 wherein Ar and Ar are the same or different substituted and unsubstituted divalent aromatic groups that contain from about 6 to 20 carbon atoms; 3 4 Ar and Ar are the same or different substituted or unsubstituted monovalent aromatic groups that contain from about 7 to 20 carbon atoms; 1 2 R and R are selected from substi tuted' and un¬ substituted divalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted and unsubstituted alkylene groups that contain from 1 to about 20 carbon atoms; 3 4 5 R , R , and R are each selected from- substituted and unsubstituted monovalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted and unsubstituted alkyl groups that contain from 1 to about 20 1 2 3 carbon atoms; provided that at least one of R , R . and R is 3 4 5 aromatic in formula C and at least one of R , R , and R is aromatic in formula D; carbon-to wherein R selected from ydrogen, alkyl groups that contain from abou 1 to 4 carbon atoms, and alkenyl groups that contain from about 2 to 4 carbon atoms; and X is a halogen-containing complex anion, - 6. An imageable sheet according to claim 3 wherein said organic material contains at least one vinyl ether group, 7, An imageable sheet according to claim 6 wherein said initiator is selected from a) halogen-containing organic compounds which conta n halogen attached to carbon and which, upon exposure to radiation of suitable wavelength, is dissociable with formation of halogen-free radicals, the bond dissociation energy for the carbon-to- halogen bond being in the range of about 40 to 70 kilogram calories per mole; and b) an aromatic onium salt that has a formula selected from - JRE OMPI wherein Ar and Ar are the same or different substituted and unsubstituted divalent aromatic groups that contain from about 6 to 20 carbon atoms; 3 4 Ar and Ar are the same or different substituted or unsubst tuted monovalent aromatic groups that contain from about 6 to 20 carbon atoms; 1 2 R and R are selected from substituted and unsubstituted divalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted or unsubstituted alkylene groups that contain from 1 to about 20 carbon atoms ; 3 4 5 R , R ,and R are each selected from substituted and unsubstituted monovalent aromatic groups that contain from about 6 to 20 carbon atoms and substituted and unsubst tuted alkyl groups that contain from 1 to about 20 1 2 3 carbon atoms; provided that at least one of R , R ,and R is aromatic in formula C and at least one of R , R , and R is ur oiii a Lie in foπιιul.1 D; nd, oxygen, s s aryl or acyl , R 7 - hydrogen, alkyl gro atoms, and alkenyl groups that contain from abυut 2 to 4 carbon atoms ; and X is a hal ogen-conta i ni •- . complex anion. 8 - An imageable sheet according to claim 19 wherein said initiator is selected from triaryl sul fonium hexaf1 uoroan imonate and tri a rγl sul fon um hexaf1 uoroa rsenate - 39 9. An imageable sheet according to claim 1 wherein said photopolymerizable layer further includes at least one material selected from plasticizing agents, tackifiers, extenders, colorants, fillers, and viscosity modi fi ers . 10. A process for image production and transfer that comprises the steps of image-wise exposing the dry-transfer sheet of claim 1 to activating radiation through the cover sheet to provide photopolymerized areas in said dry transfer sheet; separating the base sheet and cover sheet of the exposed dry-transfer sheet, wherein the photopolymerized areas of the photopolymerizable layer adhere to said base sheet and the non-photopolymeri zed areas of the photopoly- merizable layer adhere to said cover sheet; irradiating the non-photopolymerized areas throu said cover sheet with activating radiation for a time sufficient to at least partially photopolymeri ze said non- photopolymerized areas; and transferring the at least partially photopoly¬ merized areas from said base sheet to a receptor by burnishing.

Inventors: BERGGREN W, BROWNLEY S
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING & MFG CO
Application year: 1980
Main classification: G03C11
IPC codes: G03F7