MXPA00001004A - Rubber-based aqueous developable photopolymers and photocurable elements comprising same - Google Patents

Abstract

Photocurable compositions and methods for making the same are provided. The compositions comprise at least one ethylenically unsaturated monomer, at least one photoinitiator, and at least one water dispersible ethylenically unsaturated rubber. The ethylenically unsaturated rubber is tendered water dispersible by reaction of olefinic functionality therein with a hydrophilic diene. The resulting water-dispersible ethylenically unsaturated rubber is then blended with one or more ethylenically unsaturated monomers and one or more photoinitiators.

Description

AQUEOUS PHOTOPOLYMERS BASED ON H ULE REVELABLES AND FOTOCU RABLES ELEMENTS THAT UNDERSTAND THEMSELVES FIELD OF THE INVENTION The present invention is directed to discoverable aqueous-based rubber photopolymers, to synthetic techniques for preparing such photopolymers, and to the use of such photopolymers in photocurable elements.

BACKGROUND OF THE INVENTION Photocurable compositions are used to form printing plates and other photosensitive articles. In the field of photosensitive flexographic printing plates, the uncured plate typically includes a support and a photocurable surface or layer. Additional layers or surfaces may be included in the plate, for example, sliding films and / or release layers to protect the photocurable surface. Prior to processing the plate, the release layer is typically removed, and the photocurable layer is exposed to radiation in a manner like the image. The unexposed areas of the photocurable layer are then removed in developer baths. In the past, the unexposed areas of the photocurable layer were removed using developer baths comprising organic solvents. However, the toxicity, volatility, and low point of evaporation (flashing) of such solvents give rise to dangerous conditions and contamination problems. As a result, the need has been recognized to provide a photocurable composition that can be disclosed, for example, in aqueous solvents. A flexographic printing plate must possess not only a photocurable layer, but must also have sufficient flexibility to wrap around a printing cylinder and sufficient structural integrity to withstand the rigors experienced during typical printing processes. The printing plate should also be sufficiently smooth to facilitate ink transfer during printing, and should exhibit resistance to solvent for inks, including resistance to the various water-based and organic inks used in flexographic printing. Many of the revealable aqueous compositions reported to date have not had sufficient balance of these desired properties. Accordingly, a need remains for photocurable polymers that can be dispersed in aqueous solvents and exhibit an appropriate balance of the other properties required for the production of flexographic printing plates. The present invention is directed to these and other important purposes.

BRIEF DESCRIPTION OF THE INVENTION In one aspect, the present invention provides photocurable compositions and methods for making same. In general, the compositions comprise at least one ethylenically unsaturated monomer, at least one photoinitiator, and at least one unsaturated ethylenically dispersible rubber in water. The ethylenically unsaturated rubber becomes dispersible in water by reaction of the olefinic functionality therein with a hydrophilic diene. The resulting ethylenically dispersible unsaturated rubber in water is then mixed with one or more ethylenically unsaturated monomers and one or more photoinitiators. The present invention also provides photocurable elements that include a support layer and, in the support layer, a water-dispersible photocurable composition comprising an ethylenically unsaturated unsaturated rubber dispersible in water, at least one ethylenically unsaturated monomer, and minus a photoinitiator.

BRIEF DESCRIPTION OF THE DIAMETERS The numerous objects and advantages of the present invention can be better understood by those skilled in the art by reference to the attached non-scale figures, in which: Figure 1 is a cross-sectional view of an element photocurable according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The photocurable compositions of the present invention are developable in water and dispersible in water. Dispersibility in water is mainly achieved by the use of an ethylenically unsaturated rubber which has been chemically modified through reaction with a diene having a hydrophilic portion that is incorporated into the rubber. The reaction product is also referred to herein as an ethylenically unsaturated rubber dispersible in water. Ethylenically unsaturated rubbers suitable for use in the present invention include polyisoprene, ethylene elastomer terpolymers, propylene and diene monomers (EPDM), isobutylene / isoprene copolymer neoprene, butadiene-derived rubbers including styrene-butadiene rubber (SBR), and nitrile rubbers. Preferred dienes are those having hydrophilic groups which are anionic (i.e., bear a negative charge or have substantial anionic character due, for example, to the electron withdrawing nature of constituent atoms). Preferred hydrophilic anionic groups contain a group C = O, S = O, P = O, OH, and / or amine. The diene may be a cyclic diene or a linear 1, 3-cis. Exemplary cyclic dienes suitable for use in the present invention include substituted pyrroles, furans, thiophenes and carbocycles. Particularly preferred dienes include carboxy furans, amino furans, and alkyl pyrroles. The reaction between the rubber and the diene can be carried out using methods known to those skilled in the art, such as, for example, mixing, rotomilling, or extrusion. Typically, the reaction is carried out at a temperature that is within about 20 degrees of the Tg of the rubber. Although the present invention is not intended to be limited by any particular theory, it is believed that the rubber and the diene undergo a cyclization reaction from Diels-Alder. As those skilled in the art know, a Diels-Alder reaction is a cycloaddition reaction in which a diene and an unsaturated dienophile react to form a 6-membered ring. The cyclization reactions present can be seen as "inverse" reactions of Diels-Alder because the dienes used are relatively rich in electrons. Following the reaction of the rubber with the diene, one or more monomers are added. The monomers preferably produce salts by base treatment, whereby the solubility in water of materials to which the monomers are incorporated is increased. If more than one monomer is added, the monomers are preferably added sequentially. The monomers for use in the present invention may be monofunctional or polyfunctional, and include, for example, alkyl acrylates and alkyl methacrylates.; N-alkyl acrylamide, N, N-dialkyl amino monoalkyl (meth) acrylates, N-alkyl aminoalkyl (meth) acrylate, N, N, N-trialkylamino alkyl (meth) acrylates, and cationic salts thereof; unsaturated monocarboxylic acids; unsaturated polycarboxylic acids and anhydrides; substituted and unsubstituted unsaturated esters and amides of carboxylic acids and anhydrides; nitriles; vinyl monomers; vinylidene monomers; monoolefin and polyolefin monomers; and unsaturated heterocyclic monomers. "Alkyl", as used herein, refers to hydrocarbon chains having from 1 to about 30 carbon atoms, preferably up to about 18 carbon atoms, more preferably up to 10 carbon atoms, and even more preferably up to about 8 carbon atoms, and most preferably up to about 6 carbon atoms.

Exemplary monofunctional monomers include alkyl acrylates and alkyl methacrylates, monomers containing carboxylic acid groups, monomers containing hydroxyl groups, aliphatic monomers with conjugated dienes, polymerizable amides, vinyl ethers, vinyl esters, styrenes, vinyl ketones, olefins, nitriles polymerizable, and monomers having sulfonic or phosphoric groups. Particular examples of suitable alkyl acrylates and methacrylates, also collectively referred to herein as (meth) acrylates, include methyl (meth) acrylates, ethyl (meth) acrylate, n-butyl (meth) acrylate, (meth) acrylate. of propyl, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, acyl (meth) acrylate, cyclohexyl (meth) acrylate, dimethylaminoethyl (meth) acrylate. Other useful acrylates include octyl acrylate and 2-chloroethyl acrylate. Particular examples of aliphatic monomers of conjugated dienes include 1,3-butadiene, isoprene, dimethylbutadiene, 1,3-pentadiene, and chloroprene. Monomers containing exemplary carboxylic acid groups include acrylic acid, methacrylic acid, maleic acid, fumaric acid, tetracosanoic acid, and crotonic acid. Anhydrides include maleic anhydride. Exemplary monomers containing hydroxyl groups include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, metal alcohol, N- (4-hydroxyphenyl) acrylamide, N- (4) -hydroxyphenyl) methacrylamide, o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, and o-, m-, or p-hydroxyphenyl (meth) acrylate. Exemplary polymerizable amides include acrylamide, methacrylamide, N-methylolacrylamide, N-ethylacrylamide, N-hexylacrylamide, N-cyclohexyl acrylamide, N-hydroxyethylacrylamide, N-phenylacrylamide, N-nitrophenylacrylamide, and N-ethylphenylacrylamide. Exemplary vinyl ethers include ethyl vinyl ether, 2-chloroethyl vinyl ether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, butyl vinyl ether, octyl vinyl ether, and phenyl vinyl ether. Exemplary styrenics include styrene, α-methylstyrene, methylstyrene, and chloromethylstyrene. Exemplary vinyl ketones include methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, and phenyl vinyl ketone. Exemplary olefins include ethylene, propylene, isobutylene, and glycidyl (meth) acrylate. Exemplary polymerizable nitriles include acrylonitrile, methacrylonitrile, N-vinylpyrrolidone, N-vinylcarbazole, and 4-vinylpyridine. Exemplary monomers having sulfonic or phosphonic groups include vinyl sulfonic acid, styrene-p-sulfonic acid, 2-sulfoxyethyl methacrylate, and 2-acrylamide-2-methylpropansulfonic acid. The polyfunctional monomers have more than one potential polymerization site, and can therefore be incorporated into more than one polymer chain and thus facilitate the entanglement between the polymer chains. Polyfunctional monomers include polyethylenically unsaturated monomers in which the ethylenically unsaturated groups preferably have about equal reactivity, such as divinyl benzene, polyethylenically unsaturated monomers in which the ethylenically unsaturated groups have different reactivities, and ethylenically unsaturated monomers containing carboxyl groups or groups epoxy.

Alkyl acrylates and polyfunctional alkyl methacrylates useful in the present invention include trimethylolpropane di (meth) acrylate, trimethylolpropane di (meth) acrylate, ethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, tetra (meth) ) pentaerythritol acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, di (meth) ) polyethylene glycol acrylate, pentaerythritol di (meth) acrylate, glycerol dimethacrylate, glyceroalkyloxy di (meth) acrylate, 1, 1, 1-trishydroxymethylethane di (meth) acrylate, 1, 1, 1-trishydroxy methylethane tri (meth) acrylate, 1,1-trisydroxymethylpropane di (meth) acrylate, tri (meth) acrylate, 1, 1, 1 -trishydroxymethylpropane, triallyl cyanurate, triallyl isocyanurate, glycidyl (meth) acrylate, allyl methacrylate, diallyl maleate, allyl acryloxy propionate, triallyl cyanurate, triallyl isocyanurate, diallyl terephthalate, phthalate diallyl, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, and citraconic acid. Other suitable monomers for forming the entangled polymer will be readily apparent to one skilled in the art once armed with the present disclosure. Following the addition of the ethylenically unsaturated monomer to the rubber, a photoinitiator is added, as well as any optional additives. The additives that can be used are well known to those skilled in the art, including antioxidants, fillers, binders, and plasticizers. Suitable photoinitiators include polymerization initiators which are activated by actinic radiation, usually ultraviolet or visible radiation. As used herein, "actinic" radiation is radiation which is capable of effecting a chemical change in an exposed portion of the composition. Actinic radiation includes, for example, amplified (v. G., Laser) and non-amplified light, particularly in the ultraviolet and infrared wavelength regions. Actinic radiation for use in the present invention is preferably in the wavelength region from about 250 nm to about 450 nm, more preferably from about 300 nm to about 400 nm, and most preferably from about 320 nm to about 380 nm. Photoinitiators for use in the present invention may be soluble or insoluble in aqueous medium. Exemplary suitable photoinitiators include benzophenones (eg, p-aminobenzophenone), acetophenones (eg, 2,2-dimethoxy-2-phenylacetophenone), anthraquinones (eg, 9, 10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone), xanthones and benzoin ethers. The photocurable compositions of the invention can be prepared by mixing from about 2 percent to about 30 percent by weight (preferably from about 8 percent to about 15 percent by weight) of the ethylenically unsaturated monomer, from about 0.25 percent to about 2. percent by weight (preferably from about 0.5 percent to about 1.5 percent by weight) of the photoinitiator, and from 60 percent to about 98 percent by weight (preferably from about 85 percent to about 92 percent) by weight) of the ethylenically unsaturated rubber dispersible in water, based on the total composition. Unsaturated ethylene-dispersible rubber in water, in turn, is formed by reacting from about 6 percent to about 20 percent by weight (preferably from about 8 percent to about 12 percent by weight) of the diene with from 80 percent by weight. percent to about 94 weight percent (preferably from about 88 percent to about 92 weight percent) of the ethylenically unsaturated rubber, based on the reaction product. The optional additives can be formed from about 2 to about 30 percent of the photocurable compositions. The photocurable compositions of the present invention are useful for forming photocurable elements. A photocurable element is generally formed by placing a plate of the photocurable composition 14 on a suitable support, or backing, layer 12, as shown in Figure 1. The support layer may be formed of a transparent or opaque material such as paper, cellulose film, plastic, rubber or metal. In preferred embodiments, the support layer is formed of polyethylene terephthalate film having a thickness of about 0.127 millimeters. The thickness of the photocurable layer can vary, but is generally from about 0.508 to about 8.89 millimeters. If necessary, an adhesive can be applied to the support material.

A photocurable element according to the present invention can be, for example, in the form of a cylinder or a sheet or rectilinear plate. If desired, a photocurable element may further comprise a second layer of photocurable material, a cover sheet, and a protective layer. If a second photocurable layer is used, it is typically disposed over the first and is similar in composition, but considerably thinner, generally less than about 0.254 millimeters. The protective layer, if used, is typically from about 0.0254 to about 0.254 millimeters thick. The protective layer protects the photocurable element from contamination, increases the ease of handling, and acts as a layer that accepts ink. The cover sheet, if used, forms the final layer and can be formed of any suitable material which protects the damage element until it is ready to be used. As will be recognized by one skilled in the art, exposure of the photocurable composition to actinic radiation should be avoided prior to the development of the photocurable element to which the composition is incorporated. In a typical development process, a plate formed from the composition of the present invention is exposed to actinic radiation through a negative and polymerized in the portions exposed to light to form latent images. The exposed plate is then rinsed with water to produce freed images, dried and then post-exposed to radiation to form a flexographic printing plate.

The following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention in any way. These examples and their equivalents will become more apparent to those skilled in the art in light of the present disclosure and the appended claims.

Example 1 In a Haake rotary mixer, 200 grams (g) of polyisoprene (pmol 800,000, cis 97%, from Aldrich Chemical Co.) and 22.2 g of 2-carboxifuran were reacted at 132 ° C for 30 minutes. After cooling to 60 ° C, 36.7 g of diethylaminoethyl methacrylate (from CPS Chemical) and 23.2 g of 1,6-hexanediol diarylate (from Sartomer) were added, followed by 5.8 g of Irgacure 651 photoinitiator (from Ciba Geigy) and 2.9 g of butylated hydroxytoluene. A printing plate was formed from the mixture according to the following procedure. A layer of approximately 1.7018 millimeters thick was sprayed on a polyethylene terephthalate support. The layer was then exposed to UVA radiation (within the wavelength region of about 350-400 nm) through a negative for about six minutes. The exposed portions hardened, while the unexposed portions did not harden. The negative was removed and the plate was washed with 2 weight percent Na2CO3. The printing plate was clear and had a wash rate of 2.6 ml / min. in 2% of Na2 CO3 and 2% of RW140 at 62.7 ° C. The resilience was > 50% and Shore A durometer was 46.

Example 2 In a Haake rotary mixer, 200 (g) of polyisoprene and 22.2 g of 1-methyl pyrrole (from Aldrich) were reacted at 120 ° C for 30 minutes. After cooling to 60 ° C, 23.6 g of methacrylic acid (from Huís America) and 23.2 g of 1,6-hexanediol diarylate (from Sartomer) were added, followed by 5.8 g of Irgacure 651 photoinitiator and 2.9 g of butylated hydroxytoluene. . A printing plate was formed from the mixture as in Example 1. The printing plate was clear, and had a wash rate of 2.2 ml / min. in 2% of Na2 CO3 and 2% of RW140 at 62.7 ° C. Resilience was > 50% and 50 smoothness in Shore A.

Example 3 In a Haake rotary mixer, two hundred grams of polyisoprene / polystyrene triblock (Kraton D1 107, Shell Chemical) and 22.2 g of dimethylaminomethylfurfuryl alcohol hydrochloride (Aldrich) were reacted at 132 ° C for 0.5 hours. The reaction mixture was then allowed to cool to 60 ° C. The monomers were then added dimethylaminopropyl methacrylamide (39.5 g, Aldrich) and 1,6-hexanediol diarylate (20.4 g, Sartomer). Irgacure 651 photoinitiator (5.8 g, Ciba-Geigy) and butylated hydroxytoluene (2.9 g) were also added. A printing plate was formed from the mixture as in Example 1. The resulting plate was clear, resilient (>50%), mild (46 Shore A) and had a wash rate of 2.0 ml / min. in 2% lactic acid at 62.7 ° C.

Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. It is intended that such modifications fall within the scope of the appended claims.

Claims (23)

1. REVIVAL NAMES 1. A photocurable composition comprising: at least one ethylenically unsaturated monomer; at least one photoinitiator; and the reaction product formed by reacting an ethylenically unsaturated rubber with a diene comprising at least one hydrophilic moiety which is a group C = O, S = O, P = O, OH, or amine. The composition of claim 1 wherein said ethylenically unsaturated rubber is selected from the group consisting of polyisoprene, neoprene, isobutylene / isoprene copolymers, butadiene-derived rubber, nitrate rubber, and elastomeric terpolymers of ethylene, propylene, and monomers diene 3. The composition of claim 1 wherein said ethylenically unsaturated monomer is selected from the group consisting of alkyl acrylates and alkyl methacrylates; N-alkyl acrylamide, N, N-dialkylamino monoalkyl (meth) acrylates, N-alkylamino alkyl (meth) acrylate, N, N, N-trialkylamino alkyl (meth) acrylates, and cationic salts thereof; unsaturated monocarboxylic acids, acids and unsaturated polycarboxylic anhydrides; nitriles; vinyl monomers; vinylidene monomers; monoolefin and polyolefin monomers; and unsaturated heterocyclic monomers. The composition of claim 1 wherein said ethylenically unsaturated monomer constitutes from about 2 percent to about 30 percent by weight of said composition. 5. The composition of claim 1 wherein said hydrophilic portion is anionic. 6. The composition of claim 1 wherein said diene is cyclic. The composition of claim 1 wherein said diene is a furan, thiophene, pyrrole, or carbocycle. The composition of claim 1 wherein said diene is a carboxy furan, an amino furan, or an alkyl pyrroline. The composition of claim 1 wherein said reaction product constitutes from about 60 percent to about 98 percent by weight of said composition. 10. A synthetic method comprising reacting an ethylenically unsaturated rubber with a diene comprising at least one hydrophilic moiety which is a group C = O, S = O, P = O, OH, or amine. eleven . The method of claim 1 wherein said ethylenically unsaturated rubber is selected from the group consisting of polyisoprene, neoprene, isobutylene / isoprene copolymers, butadiene rubber, nitrile rubber; and elastomeric terpolymers of ethylene, propylene, and diene monomers 12. The method of claim 1 wherein said hydrophilic portion is anionic. The method of claim 1 wherein said diene is cyclic. The method of claim 1 wherein said diene is a furan, thiophene, pyrrole, or carbocycle. 15. The method of claim 1 wherein said diene is a carboxy furan, an amino furan, or an alkyl pyrrone. 16. A method for forming a photocurable water dispersible composition comprising: providing an ethylenically unsaturated rubber; reacting said rubber with a diene comprising at least one hydrophilic portion which is a group C = O, S = O, P = O, OH, or amine, whereby an unsaturated ethylenically dispersible rubber is formed in water; and mixing said ethylenically dispersed unsaturated rubber in water with at least one ethylenically unsaturated monomer and at least one photoinitiator. The method of claim 16 wherein said ethylenically unsaturated rubber is selected from the group consisting of polyisoprene, neoprene, isobutylene / isoprene copolymers, butadiene rubber, nitrile rubber, and elastomeric terpolymers of ethylene, propylene, and monomers diene 18. The method of claim 16 wherein said hydrophilic portion is anionic. 19. The method of claim 16 wherein said diene is cyclic. The method of claim 16 wherein said diene is a furan, thiophene, pyrrole, or carbocycle. 21. The method of claim 16 wherein said diene is a carboxy furan, an amino furan, or an alkyl pyrrole. 22. The composition of claim 16 wherein said ethylenically unsaturated monomer is selected from the group consisting of alkyl acrylates and alkyl methacrylates; N-alkyl acrylamide, N, N-dialkylamino monoalkyl (meth) acrylates, N-alkylamino alkyl (meth) acrylate, N, N, N-trialkylamino alkyl (meth) acrylates, and cationic salts thereof; unsaturated polycarboxylic unsaturated monocarboxylic acids, acids and anhydrides; nitriles; vinyl monomers; vinylidene monomers; monoolefin and polyolefin monomers; and unsaturated heterocyclic monomers. 23. A photocurable element comprising a support layer and a photocurable composition according to claim 1 disposed on said support layer.