PHOSPHINE ACTIVATED PHOTOSENSITIVE COMPOSITIONS AND PHOTOPOLYMER PRINTING PLATES MADE THEREFROM

Abstract: Photopolymerizable composition and photosensitive elements produced therefrom. The photopolymerizable composition includes: a) a monomer component, b) a polymer component, c) a photopolymerization initiator, and d) an activator. The monomer component contains at least one water-soluble, monofunctional unsaturated ethylenic monomer or the combination of such a monomer and at least one polyfunctional unsaturated ethylenic monomer. The polymer component includes a partially saponified watersoluble, polyvinyl acetate polymer compatible with the monomer components. The polyvinyl acetate polymer contains both acetyl and hydroxyl groups and has a polymerization degree of from 300 to 2,000. The degree of saponification of the polymer is desirably in the range of 65 to 99 percent. The preferred photopolymerization initiators are acetophenone derivatives such as 2,2-dimethoxy-2-phenyl acetophenone, 2,2-diethyoxy-2-phenyl acetophenone, 2,-2-diisopropoxy-2-phenyl acetophenone, benzoin alkyl, aryl, allyl or vinyl ethers, or benzophenone derivatives such as benzophenone, 2-methylbenzophenone, 2-methoxybenzophenone or 2,2'-dimethoxybenzophenone, which are compatible with the monomer component and the polyvinyl acetate polymer and are activatable by actinic light. Finally, the activator is a phosphine derivative generally described by the formula: (FORMULA) wherein any of X, Y and Z are hydrogen, halogen, alkyl, alkoxy, aryl, vinyl, or allyl, although not more than one of X, Y and Z may be hydrogen. It is especially preferred in the practice of the present invention that at least one of X, Y or Z in the phosphine derivative activator component be an aryl group.

Description: PHOSPHINE ACTIVATED PHOTOSENSITIVE COMPOSITIONS-- AND PHOTOPOLYMER PRINTING PLATES MADE THEREFROM_- DESCRIPTION ' Technical Field The present invention relates to a new class of water-developable photopolymerizable compositions, 5 and photosensitive elements and photopolymer printing \ plates that utilize such compositions. More speci¬ fically, the novel photopolymerizable compositions of the present invention can be used without any pre- exposure conditioning of the type that has become 0 ) customary with various prior art compositions. The present compositions thus provide photosensitive, ele¬ ments and photopolymer printing plates that not only / have vastly improved printing characteristics, but can be directly subjected to an imagewise exposure 5 and then developed with water without any costly or time consuming pre-exposure conditioning steps. Background Art Many photopolymerizable compositions and photo¬ sensitive elements that are useful in making printing 0 plates of one kind or another are known in the art. One, if not the most, commercially successful of all such prior art compositions is described in U.S. Patent No. 3,801,328 to Takimoto et al. Such compo¬ sitions, although they have met with enormous commer- 25 cial success, nevertheless require some form of pre- exposure conditioning before imagewise exposure in order to produce commercially satisfactory relief images on printing plates that employ such composi¬ tions. Two techniques for pre-exposure conditioning have evolved in the art. The first, commonly known as CO,, conditioning, requires the maintenance of the photosensitive, element or plate in a C0 2 atmosphere until just prior to the imagewise exposure of the element or plate. The second known technique, which has supplanted the CO^ conditioning technique and is commonly known as "bump exposure", requires that the photosensitive element or plate be subjected to a brief (typically 2 to 8 second) light exposure immediately prior to the longer duration imagewise exposure, in the presence of a negative. It has been recognized, of course, that both pre-exposure conditioning techniques require special, costly and time consuming additional handling of the photosensitive element or plate that, from a plate processing standpoint should desirably be eliminated. Moreover, both techniques make the design and oper¬ ation of automatic plate exposure and processing equipment unduly complicated and expensive. And perhaps even more importantly, both techniques, because of the necessity that imagewise exposure be carried out within a designated time period after pre-exposure conditioning occurs, introduce time controls in plate processing that are oftentimes difficult, if not impossible, to carefully maintain in the large quantity, commercial newspaper applica¬ tions for such plates. It has been determined by the applicants herein, for example, that a printing plate that has been "bump" exposed should desirably be subjected to an. imagewise exposure within approximately 30 seconds after the bump exposure is completed. Variations in this period of plate dormancy, between the completion of the bump exposure step and the ini¬ tiation of the imagewise exposure steps can, and often does, produce developed plates having vastly different printing quality characteristics. Thus, two plates utilizing the same photopolymer compo¬ sition and same negative can have different printing characteristics simply because the period of dormancy between bump and imagewise exposure varies. Moreover, photosensitive elements and plates, * which are subjected to bump exposure, must typically be exposed under high intensity point sources of actinic light, such as carbon arc lamps or high pressure mercury vapor lamps. Such lamps not only have extremely high current demands and short lives, but in normal operation produce unwanted heat, which can cause or contribute to the degradation of the photopolymerizable compositions or cause negatives to stick to the plate photopolymer surface. As a result of the many inconveniences, the added expenses and variations in product quality inherent in the use of plates requiring some form of pre-conditioning, either through CO- conditioning or bump exposure, a need has developed for water- developable photopolymerizable compositions (and resultant elements and plates) that entirely eliminat the necessity of pre-exposure conditioning, yet at th same time provide all of the advantageous properties of the commercially desirable compositions of the type described .in the Takimoto 3,801,328 patent. One such effort to solve the pre-exposure condition¬ ing problem is described in U.S. Patent No. 4,042,386 to Okai and Kimoto, wherein the selection and use of specific components, in certain ratios and amounts, and intensified exposure of the resulting photo¬ sensitive element or plate, are disclosed as means of eliminating the need for pre-exposure conditioning This approach, however, suffers from the disadvantage that only carefully selected components and ratios amounts of such components can be used, and from the additional disadvantage that only costly high inten¬ sity light sources (which have shortened lamp lives and generate excessive amounts of undesired heat) can be used. Moreover, it has been determined that the photopolymerizable compositions disclosed in the Okai and Kimoto patent work best with lower reflectiv ity substrates (e.g., a high degree of antihalation) in order to provide developed photopolymerizable elements having the desired dot depth characteris- tics in hi-light, middle tone and shadow image areas. Disclosure of Invention The photopolymerizable compositions of the present invention not only eliminate the need for any pre-exposure or C0 2 ' conditioning ' of the resultant photosensitive elements and plates that employ such compositions, but provide water-developable elements and plates that can utilize a wide range of monomer and polymer components, require shortened exposure times and less antihalation conditioning of the plate substrate, can be exposed with less intense light sources, and yet still provide consistently improved printing characteristics; e.g., improved dot depth in hi-light, middle tone and shadow image areas, and improved minimum line width and shapes in reverse areas. Furthermore, the photopolymerizable composi¬ tions of the present invention can be applied to ultra-shallow relief plates, such as 4 mils to 8 mils in relief thickness, because such compositions are not adversely affected by oxygen exposure. The surprising and unexpected .properties of the photopolymerizable compositions (and resulting<- photopolymer elements and plates) of the present invention are the result of the selection and use of a unique combination of components, including a de- fined class of phosphine derivative activator com¬ ponents, which interact with the remaining photo¬ polymerizable composition components to provide the heretofore unrecognizable and unachievable advantages of the present invention. It is, therefore, an object of the present invention to provide a new photopolymerizable compo¬ sition and a new photosensitive element which do not require pre-exposure conditioning. It is another object of the present invention to provide a photopolymerizable composition and a photosensitive'element which require shorter exposure times than is required with prior compositions. OAΪPI It is still a further object of the present invention to provide a photopolymerizable composition and a photosensitive .element which can be processed more quickly and more efficiently than was hitherto possible. These and other objects of the present inven¬ tion together with its various advantages will become apparent to those skilled in the art from a consider¬ ation of the following detailed description of variou embodiments of the invention. Best Mode for Carrying Out the Invention The photopolymerizable composition of the present invention generally includes the following four components: A. A monomer component including at least one water-soluble, monofunctional unsaturated ethylenic monomer, or the combination of such a monomer and at least one polyfunctional unsaturated ethylenic mono¬ mer, said monomers being capable of forming a polymer by photoinitiated polymerization in the presence of a polymerization initiator activatable by actinic light B. A polymer component including a partially saponified, water-soluble, polyvinyl acetate polymer compatible with said monomer component, containing both acetyl and hydroxy groups, and having a poly¬ merization degree of about 300 to 2,000, and a saponification degree of about 65 to 99 mole percent; C. A photopolymerization' initiator compatible with said monomer component'and said 1 polyvinyl acetat polymer, and activatable by actinic light; and D. An activator component including a phos¬ phine derivative described by the formula: TjU OiV. P-Y z •wherein any of X, Y and Z are hydrogen, halogen, alkyl, alkoxy, aryl, vinyl, or allyl, and wherein not more than one of X, Y and Z may be hydrogen. It has been found especially desirable in the practice of the present invention that at least one of X, Y or Z in the phosphine derivative activator com¬ ponent be an aryl group. Indeed, in those instances in which a phosphine derivative without at least one aryl group have been used- (such as tri-n-butyl- phosphine) the resultant photopolymer plates have unacceptable properties. Thus, the phosphine deriv¬ ative is preferably selected from among the following compounds: triphenyl phosphine, o-tolyl diphenyl phosphine, di-(o-tolyl) * phenyl phosphine, tri-(o- tolyl) phosphine, o-methoxyphenyl diphenyl phosphine, o-ethylphenyl diphenyl phosphine, and o-chlorophenyl diphenyl phosphine. Most preferable among those phos- phine derivatives is triphenyl phosphine because of its improved sensitivity, cost and air stability. As noted above, the absence of at least one phenyl group in the phosphine activator component of the present invention does not eliminate the pre-exposure conditioning step. Similarly, the presence of at least one phenyl group (and preferably two or more phenyl groups) , especially in an air stable form pro¬ vide the correct balance of printing plate proper¬ ties, the elimination of any pre-exppsure condition- ing and the reduced exposure time and other advan¬ tages of the present invention. - 8 - The monomer component A found useful in the practice of this invention generally comprises; (1 .a monofunctional acrylic or, methacrylic ester of a lower alkanol having one or more hydroxy groups, o 5 (2) the combination of such a monofunctional monome and a polyfunctional acrylic or methacrylic ester o polyethylene glycol [HOtCH-CB O) H] which is etheri fied or esterified at one end thereof and wherein n is desirably between one and twenty-three. Examples 10 of the monofunctional unsaturated ethylenic compoun are B-hydroxyethyl acrylate, B-hydroxyethyl metha- cryla e and B-hydroxypropyl acrylate. Examples of the polyfunctional monomer are polyethylene glycold esters (e.g., polyethylene glycol diacrylate or 15 polyethylene glycol dimethacrylate) . In the-said polyethylene glycol derivatives, n is one to twenty three. In addition, other monomer components such as pentaerythritol dimethacrylate, trimethylolpropa trimethacrylate, tetramethylolmethane tetrameth- 20 acrylate, and trimethylolethane trimethacrylate may used solely or in combination. It should be recognized that the ethylenic unsaturated monomer component includes mixtures of both mono- and polyfunctional compounds, the mono- 25 functional compounds serving as solubilizing mater¬ ials for the initiator component, and the polyfunc¬ tional compounds enhancing the adhesive characteris tics of the resultant photopolymerizable compositio Thus, by using both the water-soluble monofunctiona 30 ethylene unsaturated compound and polyfunctional ethylenic unsaturated compound, the highly desirabl balance of properties, e.g., water-washability and high adhesion, can be imparted to the photopolymeri able composition. The polymer component B used in the practice of this invention is a partially saponified poly¬ vinyl acetate, preferably having an average degree of polymerization of 300 to 2,000 and a saponification degree of 65 to 99 mole percent. If a suitable par¬ tially saponified polyvinyl acetate cannot be obtained by saponifying polyvinyl acetate having a low sapon- - ification degree as a homopolymer, a copolymer ob¬ tained, for example, by copolymerizing vinyl acetate with maleic anhydride can be partially saponified to give the desired polymer. Saponification as used herein is intended to mean the conversion of ester groups or the like into alcohol groups and the sapon- ification degree represents the extent to which ester groups or the like have been converted to alcohol or hydroxy groups. The hardness of the obtained printing plate as well as the speed of washing out in the developing procedure depends directly on the degree of saponi- fication. Thus to accomplish the desirable balance of properties in a finished developed plate, it is preferred that the partially saponified polyvinyl acetate have a degree of saponification within the stated range in saponifying polyvinyl acetate. There are some cases, for example, wherein a certain degree of saponification is required for compatibility with certain monomer components. Thus, it has been recog¬ nized that the required degree of saponification may be obtained by mixing two or more partially saponified polyvinyl acetate polymers having different degrees of saponification and calculating the arithmetic average of the different degrees of saponification. Mixtures of two or more polymers can be used, there¬ fore, each having a different saponification degree, to obtain the desired average saponification degree for any given monomer component. This feature of the present invention adds significant flexibility t the formulation process and contributes significantl to the balance of properties that are desired for th photopolymerizable composition. As the initiator component C, acetophenone, benzophenone or benzoin derivatives are used. Ben¬ zoin derivatives are soluble in the ethylenic unsat¬ urated monomer component and are highly compatible with the other components in the aqueous composition Moreover, since benzoin derivatives are not decom¬ posed thermally below about 100°C, they do not harde or become insoluble with heating during the prepara¬ tion of the photopolymerizable composition. Specifi examples of the benzoin derivatives found useful in the practice of this invention are methyl, ethyl, isopropyl, isobutyl, octyl, vinyl, aryl and allyl ethers of benzoin, i.e., benzoin methyl ether, benzo ethyl ether, benzoin vinyl ether, benzoin allyl ethe etc. The benzophenone derivatives found useful in t practice of the present invention include benzopheno and the like. The presently preferred initiators, however, are acetophenone derivatives, such as 2,2- dimethoxy-2-phenyl acetophenone, 2,2-diethoxy-2- phenyl acetophenone, 2,2-diisopr ' opoxy-2-phenyl ace- tophenone, and 2,2-di-h-but * oxy-2-phenyl acetophenone because of their unexpectedly high solubility in the monomer component of the photopolymerizable composi¬ tions and their excellent photoinitiation properties Although ordinarily photopolymerization re¬ quires a photoinitiator such as an anthraquinone com¬ pound in addition to the polymerization initiators discussed above, a high photosensitivity can be attained in the present invention by using aceto¬ phenone or benzoin derivative initiators alone. The amounts of the various components of the photopolymerizable composition of the present inven¬ tion should preferably lie within the following v/eight ratios based on the total weight of the composition; a) about 0.1 to 3.0 parts by weight of the monomer component, b) about 0.1 to 3.0 parts by weight of the polymer component, c) about 0.001 to 0.3 parts by weight of the polymerization initiator, and d) about 0.001 to 0.3 parts by weight of the activator compon¬ ent. It should be recognized, however, that these are suggested ratios which have been experimentally determined to be desirable and preferred. These ratios can nonetheless be altered depending on the particular uses contemplated for the printing ele¬ ments to be made using the compositions of the present invention. It has been found, however, that when the concentration of the phosphine derivatives used in the present invention exceeds the broad concentration ranges set forth above, the light sensitivity of the photopolymerizable composition is so enhanced as to make it very difficult to handle the photosensitive element prior to imagewise exposure. Also, excessive amounts of the' phosphine derivatives cause the photo- polymerizabie composition to become heat sensitive which further -interferes with the practical use of the photosensitive elements and reduces their useful shelf life. When, on the other hand, the concentration o the phosphine derivative used is less than that spec fied in the broad concentration range described abov the sensitivity of the photosensitive element will generally be too low to be practically used without the undesired pre-exposure conditioning. It is also desirable in some instances to ad to the photopolymerizable composition of this invent about 0.01 to 0.3 percent, based upon the amount of monomer component, of a thermal polymerization inhi¬ bitor. Among the thermal polymerization inhibitors found useful in the practice of this invention are 2,6-di-t-butyl-p-cresol, hydro quinone, and p-meth- oxyphenol. The preferred inhibitor is 2,6-di-t- butyl-p-cresol because of its compatibility with the other components. The novel photopolymerizable composition of t invention can be cast directly on a metallic and/or plastic supporting adhesive layer. Small amounts of dyestuffs may be added to the photopolymerizable composition to provide antihalation properties. Gen erally, sufficient amounts are added to the photo¬ polymerizable composition just below that at which the composition becomes hazy. Examples of an effec¬ tive dyestuff are rose bengal, eosine, methylene blu and malachite green. These dyestuffs may be used solely or in combination in a ratio of 20 and to 150 ppm based on the amount of the photopolymerizable co position. The metallic and/or plastic substrate used ca be either chemically or physically treated prior to coating with the photopolymerizable material in orde to insure strong adhesion with the photopolymerizable composition. This roughening or grating of the sub¬ strate surface eliminates the need for a separate ad¬ hesive layer although such may be used, where desired, in certain instances. The preferred substrate is a metallic plate and preferably an aluminum or tin plate. As described in U.S. Patent No. 3,877,939, the use of a dispersed an¬ tihalation material can be eliminated by treating the substrate with an aqueous solution of a chromic com¬ pound. Thus, for example, an aluminum plate would first be abraded and then chemically treated to im¬ part the desired antihalation properties. The pre¬ ferred chemical treatment for obtaining these anti- halation properties is a chemical solution of a chromic compound which includes, for example, chromic acid, water soluble salts of chromic acid and ferri- ~ cyanic or ferrocyanic acid and water soluble salts thereof. Generally, the useful treating compositions contain either chromic acid or sodium bichromate, as a required component, and mixtures of potassium ferri- cyanide, barium fluosilicate, sodium ferrocyanide, sodium fluoborate, potassium fluozirconate and related compositions. The presently preferred treating com¬ positions is 2 percent aqueous solution of "Alodine 1200" manufactured by Amchem Products, Inc. , Ambler, Pennsylvania. The treating composition is typically first placed in a bath and then the aluminum or tin support plate is immersed * in the bath for approximate¬ ly 40 second ' s. After the support plate has been treated in this fashion, it generally changes its color from the metallic aluminum or tin color to an to an orange colo * r. In this way, the orange-colored aluminum or tin support plate itself provides the ant halation function for the resultant photopolymer printing plate. As discussed above, however, the degree of antihalation required in the photopolymer plates made from the photopolymerizable plates made from the photopolymerizable compositions of the present inven¬ tion is reduced, since the presence of the phosphine derivative activator component in the composition min imizes the need for lower reflectivity substrates, an thus reduces the manufacturing cost of the photopoly¬ merizable compositions. Moreover, the exposure of a photosensitive ele ment, including a layer of the water-developable photopolymerizable composition described herein upon substrate involves the step of subjecting the element to a single imagewise exposure of actinic light. Al¬ though prior photosensitive elements required the use of high intensity point sources such as carbon arc lamps and/or high pressure mercury lamps, exposure of the photopolymerizable composition of the present invention may be carried out under diffusion light sources such as black light tubes, otherwise known as chemical lamps. These chemical lamps are far less expensive than the prior high intensity point sources use considerably less energy, and generate less heat. Such chemical lamps give off actinic light with wave¬ lengths in the desired range of 300-400 nanometers, and provide the further advantage of generating bette shoulders in the final relief image which results in improved resolution and highlight reproduction. By eliminating the previously required pre- exposure conditioning that is characteristic of prior art photopolymerizable compositions, the compositions of the present invention shorten plate processing time, and are more readily useable in automatic plate devel¬ oping equipment. It is no longer found necessary, for example, to engage in the time consuming task of first bump exposing a plate, and then placing a negative on the plate for imagewise exposure. Instead, a nega- tive can be immediately placed on the plate (without bump exposure) and then exposed for a shorter period of time with less intense light, without sacrificing printing plate quality in terms of dot depth or mini¬ mum line size. It should be understood that printing plates having varying degrees of photopolymer thickness 'can employ the photpolymerizable compositions of the present invention, including relief plates having photopolymer thicknesses greater than .020 inch and shallow relief plates having photopolymer layers between .004 and .020 inch in thicknesses. When such shallow relief plates are desired a binder composi¬ tion is interposed between the substrate and photo¬ polymer layer. The binder composition contains dis- persed within it particles which are present in a size and concentration sufficient to create a plural¬ ity of protuberances in the background areas of the photosensitive element after its exposure and devel¬ opment to create a relief image. Useful binders in- elude polyesters, polyurethanes, polyethylene- butadiene copolymers, polyvinyl acetate derivatives, polyamides, epoxy resins, styrene-butadiene copolymers, mixtures of such copolymers and partially hydrolyzed polyvinyl acetate, unsaturated polyesters made, for example, from diethylene glycol, maleic anhydride and phthalic anhydride, mixtures of such polyesters and partially hydrolyzed polyvinyl acetate, and mix¬ tures of flyoxal and partially hydrolyzed polyvinyl acetate. The dispersed particles suitable for use in such plates include glass, "Teflon" polytetrafluro- ethylene, and alumina beads. Particle size and con¬ centration will of course be chosen on a case by case basis depending on the printing parameters such as th thickness of the relief image, printing pressures, number of repetitions, etc. Presently preferred " nd practical embodiments of the present invention are illustrated in the fol¬ lowing examples wherein all percentages and parts are by weight unless otherwise indicated. EXAMPLE 1 Substrates for the photosensitive elements use below are prepared as follows: Method A: An aluminum plate is immersed in a surface treating agent comprising sodium bichromate (1.0 part) concentrated sulfuric acid (10 parts) and water (30 parts) at 70 to 80°C for about 20 minutes. Then, the palte is washed with water and dried. Method B: A " tin plate is immersed in a detergent comprising Ridoline (1.0 part; manufactured by Amchem Products, Inc.) and water (30 parts) at 65°C for abou 20 minutes. Then, the plate is washed with water and dried. Method C: The solution (70 parts") which consists of 14 parts of partially saponified polyvinyl acetate (average polymerization degree, 500; saponification degree, 7.0 mole %) and 86 parts of water, and the well-ground pigment paste (10 parts) which consists o 14 parts of the above-mentioned polyvinyl acetate, 56 parts of water and 30 parts of red iron oxide pigment (RO-5097 manufactured by Pfizer) are mixed together. The latex of carboxylated styrene/butadiene copolymer (20 parts) (XD-655 manufactured by Dow Chemical Co.) is added into the resulted solution gradually under stirring. The solution is cast on the plate which is described in Method B and dried for 2 minutes at 190°C to form the layer 15 u in thickness. Method D: The solution (60 parts) which consists of 14 parts of partially saponified polyvinyl acetate (average polymerization degree, 500; saponification degree, 78.0 mole %) and 86 parts of water, and the well-ground pigment paste (15 parts) which consists of 14 parts of above-mentioned polyvinyl acetate, 56 parts of water and 30 parts of red iron oxide pigment (RO-5097 manufactured by Pfizer) are mixed together. The latex of carboxylated styrene/butadiene copolymer (20 parts) (XD-655 manufactured by Dow Chemical Co.) is poured into the resulted solution gradually under stirring, and 5 parts of Teflon power (TL-115 by LNP Co.) is added into the solution. The solution is cast on the plate which is described in Method B and dried for 2 minutes at 190°C to form the layer 20 microns in thickness. EXAMPLE 2 A mixture of partially saponified polyvinyl ace¬ tate (average polymerization degree * , 500; saponifica¬ tion degree, 82.0 mole %) (35 parts), water (30 parts) and Rose bengal (30 ppm of all components by weight) is kneaded in a ' kneader at 80 to 90°C for 30 minutes. _ ___ * * • . * Then, this mixture is cooled to 60°C and a mixture of diethylene glycol dimethacrylate (5 parts) , B- hydroxyethyl ethacrylate (28 parts) , hydroquinone (0.1% of total monomer by weight), benzoin iso-propyl ether (0.5 part) and triphenyl phosphine (1.5 parts) is added and stirred for 30 minutes. The resulted photopolymerizable composition is case on the plate which is described in Example 1, Method C. A poly¬ ester sheet is placed thereon and the resulted piled product is passed between two roils. After cooling, the polyester sheet is peeled off and the plate is dried in a dryer at 75°C for 40 minutes to form phot sensitive layer 20 mils in thickness. EXAMPLE 3 A mixture of partially saponified polyvinyl acetate (average polymerization degree, 500; saponi¬ fication degree 77.0 mole %) (5 parts), partially saponified polyvinyl acetate (average polymerization degree, 500; saponification degree 82.0 mole %) (30 parts) , water (30 parts) and Eosin (30 ppm of all co ponents by weight) is kneaded in a kneader at -80 to 90°C for 30 minutes. Then, this mixture is cooled * t 60°C and a mixture of ethylene glycol dimethacrylate (8 parts) , B-hydroxypropyl methacrylate (25 parts) , hydro-quinone (0.1% of total monomer by weight), 2,2 dimethoxy-2-phenyl acetophenone (1.0 part) and tri¬ phenyl phosphine (1.0 part) is added and stirred for 30 minutes. The resulted photopolymerizable composi tion is cast on the plate which is described in Exam ple 1, Method C. The photosensitive plate is obtain by the same method as described in Example 2, and th photosensitive layer is 20 mils. EXAMPLE 4 A mixture of partially saponified polyvinyl acetate (average polymerization degree, 500; saponi- fication degree 82.0 mole %)' (35 parts ' ), water (30 parts) and Rose- bengal (30 ppm of all components ' by weight) is kneaded in a kneader at 80 to 90°C for 30 minutes. Then, this mixture is cooled to 60°C and a mixture of ethylene glycol dimethacrylate (5 parts) , B-hydroxypropyl methacrylate (28 parts) , hydroquinon " BU O (0.1% of total monomer by weight), benzoin iso-propyl ether (1.0 parts) and o-tolyl diphenyl phosphine (1.0 part) is added and stirred for 30 minutes. The result¬ ed photopolymerizable composition is cast on the plate which is described in Example 1, Method A. The photo¬ sensitive plate is obtained by the same method as described in Example 2, and the photosensitive layer is 20 mils. EXAMPLE 5 The photosensitive resin which is obtained by the method in Example 3, is cast on the plate which is , described in Example 1, Method D, and the photosensi¬ tive layer is 5 mils after dried. EXAMPLE 6 A mixture of partially saponified polyvinyl acetate (average polymerization degree, 500; saponi¬ fication degree, 82.0 mole %) (35 parts), water (30 parts) and Rose bengal (50 ppm of all components by weight) is kneaded in a kneader at 80 to 90°C for 30 minutes. Then, this mixture is cooled to 60°C and a mixture of ethylene glycol dimethacrylate (2 parts) , B-hydroxyethyl methacrylate (32 parts) , hydroquinone (0.1% of total monomer by weight) and benzoin iso- propyl ether (1.0 part) is added and stirred for 30 minutes. The resulted photopolymerizable composition is cast on the plate which is described in Example 1, Method A. The photosensitive plate is obtained by the same method as described in Example 2, and the photosensitive layer is 20 mils. ' EXAMPLE 7 The photosensitive resin which is obtained by the method in Example 6, is cast on the plate which is described in Example 1, Method C, and the photosensi¬ tive layer is 20 mils after dried, EXAMPLE 8 The photopolymer plate made according to Example 3 is placed in a vacuum frame and the photo¬ polymerizable surface is brought into contact with a line negative or a half tone negative. It is expose to a 3,000 watt high pressure mercury arc for 50 seconds from a distance of 20 inches. After exposur the negative is stripped from the plate and the unex posed polymer is removed by spray washing with water (temperature, 120°F) under the pressure of 40 psi fo 3 minutes. The printing plate is dried at 230°F for 3 minutes. The printing plates thus prepared show excellent image quality and long press life when use for direct printing and also are utilizable as ori- ginal plates for a paper mache. Table I demonstrates the comparison in qualit between the photosensitive plates with (Examples 3 a 4) and without (Examples 6 and 7) phosphine deriva¬ tives. TABLE I As shown in Table I above, photopolymer plate made with the photopolymerizable compositions of the present invention have improved dot depth characteris¬ tics in hi-light, middle tone and shadow areas. Dot depths that are less than 200 microns in hi-light areas, 80 microns in middle tone areas and 35 microns in shadow areas, (as in the case in Examples 6 and 7) provide dark, unacceptable half tone areas. Moreover, line widths above 50 to 60 microns are generally re¬ garded as unacceptable in newspaper printing applica¬ tions. The significance of component selection in the present invention can be demonstrated through a series of tests in which (1) derivatives employing Group V elements other than phosphorus are substituted for the phosphine derivatives of the present invention, (2) phosphine derivatives with no phenyl groups are substituted for the preferred phosphine derivatives having 1, 2 or 3 phenyl groups, and (3) halogenated compounds such as pentachlorobenzene are used as an additional component in the present invention. Table II set forth on the following page shows the results of such tests: TABLE II *TPP Triphehylphosphine BDP n-Bu-tyldiphenylphosphine CPP Dic l orophenylplxisphine TBP • l^i-n-butylphosphine TPA Triphenylarsine TPS Triphenylantimony BPP Dibutylpheny-Lbisπiithine TPN Triphenylamine TEA Triet_hanol__m_Lr_e O * » 22/2 TSBLE II (continued) *TPP: -rχip ehylphθ-_ph-lne BDP: n-Bu-tyldiphenylphosphine CPP: Dichlorophenylp- * _osphine TBP: Tri-n-butylphosphine TPA: Triphenylarsine IPS: Triphenyl-mtirrony BPP: Dibui^lphenylbisrt_a * t_r_ine TPN: Triphenylamine TEA: Triethanolamine OMPI fa IPO Λ 22/3 TfiE E II (continued) *TPP : Triphenylphosphine BDP: n-Bu * t_yldiphehylphosphine CPP: DicMorophenylptosphine TBP: Tri-n-bu * tylp_rasp_-ine TPA: Tciphenylarsine TPS: Triphenylantirrony BPP: D__bu * tylpheny3±iisrr_a * t±___ne TPN: Triphenylamine TEA: Trie * i±-_molam_lne OMPI Λ. WIPO TABLE A U (continued) *TPP: Triphehylphosphine BDP: n-I-Utyldiphenylphosphine CPP: DicMorophenylphosphine TBP: Tri-n-butylphosphine TPA: Triphenylarsine TPS: Triphenylantiirony BPP : Dibu tylphenylbisrr. ithine TPN: TriphenylaiTiine TEA: Triethanolairdne - 23 - Examples 1, 2 and 3 demonstrate that the use phosphine derivatives having 3 (triphenyl phosphine) 2 (n-butyldiphenyl phosphine) and 1 (dichlorophenyl phosphine) phenyl groups in the phosphine activator component of the present invention all produce print plates with satisfactory properties. Surprisingly, however, the degree of acceptance decreases as the number of phenyl groups is decreased from 3 to 1, e.g., exposure time increases, dot depth decreases, and gray step values decrease, but all within accep able limits. Example 4 demonstrates that the use of a phos phine derivative with no phenyl groups (tri-n-butyl phosphine) , with all other parameters remaining * the same, does not result in a printing plate having satisfactory conditions for newspaper printing appli cations. Likewise when derivatives of Group V elements such as nitrogen, arsenic, antimony and bismuth are used in place of phosphorous, the resultant printing plate has unsatisfactory properties (Examples 6-10) . Surprisingly, this is the case even when three pheny groups are used (triphenylarsine, triphenylantimony and triphenylamine) , or when two phenyl groups are used (dibutylphenylbismithine) . Finally, the presence of a halogenated compou such as pentachlorobenzene neither improves the prop ties of the resultant plate (compare Examples 1 and nor renders the resultant plate ' satisfactory when a phosphine derivative w'ith at least one phenyl group is not present, (compare Examples 4 and 12) . It, of course, should be understood that vari changes and modifications to the preferred embodimen described herein will be apparent to those skilled i the art. Such changes and modifications can be made IJ - 24 - without departing from the spirit and scope of the present invention and without diminishing its attend¬ ant advantages. It is therefore, intended that such changes and modifications be covered by the following claims.

Claims: - 25 - CLAIMS 1. A water developable photopolymerizable composition comprising: a. at least 0.1 parts by weight of the total composition of a monomer component including at least one water-soluble, monofunctional unsatur¬ ated ethylenic monomer, or the combination of said moncfunctional monomer and at least one polyfunction unsaturated ethylenic monomer, said monomers capable of forming a polymer by photoinitiated polymerizatio in the presence of a polymerization initiator acti¬ vatable by actinic light; b. at least 0.1 parts by weight of the total composition of a polymer component including a partially saponified, water-soluble, polyvinyl ace". tate polymer compatible with said monomer component containing both acetyl and hydroxy groups, and havin a polymerization degree of about 300 to 2,000 and a saponification degree of about 65 to 99 mole percent c. at least about 0.001 parts by weight of the total composition of a photopolymerization initiator compatible with said monomer component and said polyvinyl acetate polymer, and activatable by actinic light; and, d. at least 0.001 parts by weight of the total composition of an activator including a phos¬ phine derivative described by the formula: ✓X ' P-Y * N z wherein any of X, Y and Z are hydrogen, halogen, alk alkoxy, aryl, vinyl or allyl and at least one of X, and Z is aryl. fU O 26 - 2. A photopolymerizable composition according to claim 1 wherein said polymerization initiator is an acetophenone derivative selected from the group consisting of 2,2-dimethoxy-2-phenyl acetophenone, 2,2-diethoxy-2-phenyl acetophenone, 2,2-diisopropoxy- 2-phenyl acetophenone, and 2,2-di-n-butoxy-2-phenyl acetophenone. 3. A water-developable photopolymerizable com¬ position which can be exposed and developed without pre-exposure conditioning comprising: a. a monomer component constituting at least about 0.1 parts by weight of the total compo¬ sition and including at least one water-soluble mono¬ functional unsaturated ethylenic monomer, or the com¬ bination of said monofunctional monomer and at least one polyfunctional unsaturated ethylenic monomer, said monomers capable of forming a polymer by photoinitiated polymerization in the presence of a polymerization initiator by actinic light; b. a polymer component constituting at least about 0.1 parts by weight of the total composi- tion and including a partially saponified, " water- soluble, polyvinyl acetate polymer compatible with said monomer component containing both acetyl and hy- droxy groups, and having a polymerization degree of about 300 to 2,000 and a saponification degree of about 65 to 99 mole percent; c. a photopolymerization initiator con- stitutmg at least about 0.001 parts by weight of the total composition and said initiator being com¬ patible with said monomer component and said poly- vinyl acetate polymer, and activatable by actinic - 27 - light; and d. an activator constituting at least about 0.001 parts by weight of the total composition and including a phosphine derivative described by the 30 formula: ✓X P-Y N Z wherein any of X, Y and Z are hydrogen, halogen, alkyl, alkoxy, aryl, or vinyl, but not more than one 3.5 of the X, Y and Z is hydrogen, and at least one of X, Y and Z is aryl. 4. A photopolymerizable composition accqrdin to claim 3 wherein said activator is selected from t group consisting of triphenyl phosphine, o-tolyl diphenyl phosphine, di-(o-tolyl) phenyl phosphine, * 5 tri-(o-tolyl) phosphine, o-methoxyphenyl diphenyl phosphine, o-ethylphenyl diphenyl phosphine, and 0- chlorophenyl diphenyl phosphine. 5. A photopolymerizable composition accordin to claim 3 wherein said initiator is selected from t group consisting of benzoin, acetophenone and benzo¬ phenone derivatives. 6. A photopolymerizable composition accordin to claim 5 wherein said photopolymerization initiato is selected from the group consisting of benzoin iso propyl ether, .benzoin isobutyl ether, benzoin vinyl 5 ether, benzoin aryl ether, benzoin allyl ether, 2,2- dimethoxy-2-phe " nyl acetophenone, 2,2-diethoxy-2-phen acetophenone, 2,2-diiso propoxy-2-phenyl-acetophenon 2,2-di-n-butoxy-2-phenyl acetophenone, benzophenone, 2-methoxybenzophenone, 2--methylbenzophenone and 2,2' 10 dimethoxybenzophenone, " BU O - 28 - 7. The photopolymerizable composition of claim 3 wherein said partially saponified polyvinyl acetate polymer comprises one or more partially saponified polyvinyl acetate polymers having different degrees of saponification, where the arithmetic average of the different saponification degrees, based upon the weight percent of each polymer, is within the range of about 65 to 99 mole percent. 8. The photopolymerizable composition according to claim 7 wherein said polyvinyl acetate polymers have different degrees of polymerization, said degrees of polymerization ranging from about 300 to about 2,000. 9. A photopolymerizable composition of claim 3 wherein said monomer component is monofunctional ^ monomer selected from the group consisting of an acryl-" ic or methacrylic ester of a lower alkanol having at least one hydroxy group. 10. The photopolymerizable composition of claim 3 wherein said monomer component includes at least one water-soluble monofunctional unsaturated ethylenic monomer and at least one polyfunctional monomer se¬ lected from the group consisting of acrylic or meth¬ acrylic esters of a polyethylene glycol having the structural formula [HO(CH_CH 2 0)nH] and, n. the number of ethylene oxide units in said polyethylene glycol ester, being between one and twenty-three. - 29 - 11. A photopolymerizable composition accordin to claim 10, wherein said monofunctional monomer is selected from the group consisting of B-hydroxyethyl acrylate, B-hydroxypropyl methacrylate, and said polyfunctional monomer is selected from the group consisting of polyethylene glycol diacrylate, poly¬ ethylene glycol dimethacrylate, glycol dimethacrylat pentaerythritol dimethacrylate, trimethylolethane trimethacrylate and tetramethylolmethane tetrameth- acrylate. 12. A photopolymerizable composition accordin to claim 3 wherein said monomer component includes o more of the following monomer components either alon or in combination: pentaerythritol dimethacrylate-, trimethylolpropane trimethacrylate, tetramethylol- methane tetramethacrylate, and trimethylolethane tri methacrylate. 13. A photopolymerizable composition accordin to claim 3 further characterized by having the follo ing ratios by weight of the respective components based on the total weight of the composition: about 0.1 to 3.0 parts by weight of said monomer component about 0.1 to 3.0 parts by weight of said polymer component, about 0.001 to 0.3 parts by weight of sai polymerization initiator and about . 0.001 to 0.3 part by weight of said activator. - 30 - 14. A photopolymerizable composition according to claim 13 further comprising about 0.01 to 0.3 per¬ cent by weight of a thermal polymerization inhibitor, based upon the , weight of said unsaturated ethylenic monomers. 15. The photopolymerizable composition according to claim 14 further containing small amounts of dye¬ stuffs. 16. A photosensitive element comprising a substrate and a layer of water-developable photo¬ polymerizable composition including: a. about 0.1 to 3.0 parts by weight of a monomer component including at least one water- =. soluble, monofunctional unsaturated ethylenic monomer, or the combination of said monofunctional monomer and at least one polyfunctional unsaturated ethylenic mon¬ omer, said monomers capable of forming a polymer by photoinitiated polymerization in the presence of a polymerization initiator activatable by actinic light; b. about 0.1 to 3.0 parts by weight of a polymer component including a partially saponified, water-soluble, polyvinyl acetate polymer compatible with said monomer component containing both acetyl and hydroxy groups, and having a polymerization degree of about 300 to 2,000 and a saponification degree of about 65 to 99 mole percent; c.~ about 0.001 to 0.3 parts by weight of a photopolymerization initiator compatible with said monomer component and said polyvinyl acetate polymer, and activatable by actinic light; and, - 31 - d. about 0.001 to 0.3 parts by weight o an activator including a phosphine derivative des¬ cribed by the formula: ✓X . P-Y S Z wherein any of X, Y and Z are hydrogen, halogen, alkyl, alkoxy, aryl, or vinyl, but not more than on of the X, Y and Z is hydrogen, and wherein at least of X, Y and Z is aryl. 17. A photopolymerizable composition accordi to claim 16 wherein said activator is selected from the group consisting of triphenyl phosphine, o-toly diphenyl phosphine, di-(o-tolyl)- phenyl phosphine, (o-tolyl) phosphine, o-methoxyphenyl diphenyl phosp o-ethylphenyl diphenyl phosphine, and o-chloropheny diphenyl phosphine. 18. The photosensitive element of claim 16 wherein said substrate is a chemically or mechanica braded metallic and/or plastic plate. 19. The photosensitive element of claim 16 further having a binder composition carrying a plur ality of dispersed particles interposed between sai substrate and said layer of photopolymerizable comp sition, said dispersed particles being present in a size and concentration sufficient to create a plura of protuberances in the background areas of said ph sensitive element after exposure and development of said photopolymerizable composition to create a relief image. - 32 - 20. The photosensitive element of claim 19 wherein said dispersed particles are selected from the group consisting of (a) glass beads, (b) poly- tetrafluorethylene and (c) alumina powder and said binder layer is selected from the group consisting of styrene-butadiene copolymers, polyesters, glyoxal, and mixtures of (a) , (b) or (c) and partially hy¬ drolyzed polyvinyl acetate. 21. The photosensitive element of claim 19 wherein said photopolymerized layer has a " thickness between about 0.004 and 0.035 inch. 22. A water-developable photopolymerizable composition which can be exposed and developed without pre-exposure conditioning comprising (a) at least one unsaturated ethylenic monomer polymerizable by actinic light in the presence of a photopolymerization initia¬ tor, (b) a photopolymerization initiator and (c) a partially saponified polyvinyl acetate having both acetyl groups and hydroxy groups produced by sapon¬ ification, said polyvinyl acetate having a saponifi- cation degree of about 65 to 99 mole percent and a ■ polymerization degree of about 300 to 2,000, and (d) a phosphine derivative described by the formula: ✓X P-Y N z wherein any of X, Y and Z are hydrogen., halogen, alkyl, alkoxy, aryl or vinyl, but not more than one of X, Y or Z is hydrogen. - 33 - 23. The photopolymerizable composition of cla 22 wherein said initiator is an acetophenone deriva¬ tive, and said phosphine derivative is selected fro the group consisting of a photopolymerizable composi tion having: a. a monomer component constituting at least about 0.1 parts by weight of the total compo¬ sition and including at least one water-soluble, mon functional unsaturated ethylenic monomer, or the com ■ bination of said monofunctional monomer and at least one polyfunctional unsaturated ethylenic monomer, said monomers capable of forming a polymer by photo¬ initiated polymerization in the presence of a poly¬ merization initiator activatable by actinic light; b. a polymer component constituting at., least about 0.1 parts by weight of the total compo¬ sition and including a partially saponified, water- soluble, polyvinyl acetate polymer compatible with said monomer component containing both acetyl and hydroxy groups, and having a polymerization degree of about 300 to 2,000 and a saponification degree of about 65 to 99 mole percent; c. a photopolymerization initiator con¬ stituting at least about 0.001 parts by weight of th total composition and said initiator being compatibl with said monomer component and said polyvinyl aceta polymer, and activatable by actinic light; and, d. * an activator selected from the group consisting of * triphenyl pho'sphine, ό-'tolyl diphenyl phosphine, di ' —(o-tolyl) phenyl phosphine, tri-(o-tol phosphine, o-methoxyphenyl diphenyl phosphine, o-eth phenyl diphenyl phosphine, and o-chlorophenyl diphen phosphine. " B _ - 34 - 24. A process for developing a photosensitive element which includes a layer of water-developable photopolymerizable composition comprising at least one unsaturated ethylenic monomer polymerizable by actinic light in the presence of a photopolymerization initia¬ tor, a photopolymerization initiator, a partially saponified polyvinyl acetate having -both acetyl groups and hydroxy groups produced by saponification, and a phosphine derivative described by the formula: X P-Y Z wherein any of X, Y and Z are hydrogen, halogen, alkyl, alkoxy, aryl, vinyl or allyl, but not more than one of X, Y or Z is hydrogen, said process comprising the steps of: a. subjecting said element to a single exposure of actinic light having an effective wave¬ length of less than 400 nm. b. removing the unexposed photopolymeri- zable composition from said element by washing with water; and, c. drying said element.

Inventors: KIMOTO K, OKAI S
Applicants: NAPP SYSTEMS INC
Application year: 1979
Main classification: G03C1
IPC codes: G03F7