Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
2001-11-28
2004-10-19
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C101S457000, C101S462000
Reexamination Certificate
active
06805052
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a printing system for on-press development making use of a negative working thermal plate, which has been made sensitive to infrared radiation.
More specifically the present invention is related to the use of a lithographic printing plate showing an improved chemical resistance and lithographic performance, and, more particularly, a higher run length, a broader lithographic latitude and a better scratch resistance, wherein the effects are related with the use of particular hydrophobic polymer particles in an image-forming layer of the heat sensitive imaging element.
BACKGROUND OF THE INVENTION
Lithographic printing plates making use of polymer binders containing nitrogen atoms have been described in various patent applications, as being particularly suitable for use in order to increase the chemical resistance or print durability.
Toyo Gosei Kogyo KK e.g. in the Japanese patent application JP-A 07-036186 makes use of polymers with heterocyclic ring residues containing nitrogen and copolymers of acrylonitrile-butylacrylate-methyl methacrylate and triallyl isocyanurate. Toyo Gosei makes use of photosensitive vinyl acetate emulsion copolymers in combination with an hydrophilic binder, i.e. polyvinyl alcohol. In this application the photsensitive resin compositions are used for an emulsion screen printing plate.
Kodak Polychrome Graphics GMBH, in the PCT patent application filing WO 99/64930, discloses offset printing plates having a high durability. Said plates are composed of a suitable support coated with a positive- or negative-working, or electrophotographic-working radiation-sensitive composition containing an alkali soluble/insoluble thermoplastic polymer that is incorporated into the composition, making use of a solvent in which both the radiation-sensitive polymer and the thermoplastic polymer are soluble and, if required, a second solvent, less volatile than the first solvent, wherein the radiation-sensitive polymer is soluble but wherein the thermoplastic polymer is insoluble. Upon drying the photosensitive layer contains homogeneously distributed polymer particles, providing improved printing durability for the resulting exposed and developed plate. No significant coalescence of particles occurs during imaging. Moreover the photosensitive layer contains a solvent for the employed thermoplastic polymer. Thermoplastics useful in the process are e.g. acrylonitrile-styrene polymers. Just as in the present application styrene-acrylonitrile copolymers were most preferable.
Acidic vinyl copolymers containing acrylonitrile in combination with triazines as a photopolymerization initiator have been described by Mitsubishi Chemical Industries in JP-A 11-249298. Konica, in JP-A 10-207056, makes use of acrylonitrile-benzyl methacrylate-4-hydroxyphenyl-methacrylate-methyl-methacrylate copolymers in order to prepare a lithographic printing plate with improved sensitivity, cleaner resistance and writability. A similar copolymer has been used by Konishiroku Photo Industries in JP-A 08-220766. Okamoto Kagaku Kogyo, in JP-A 05-088369, makes use of alkali-soluble copolymers of N-(4-hydroxyphenyl)maleimide, acrylonitrile, and mono(2-methacryloxyethyl)hexahydrophthalate. The corresponding plates wherein the copolymers are present, show a high photosensitivity, a wide development latitude, and good printing durability, even when using UV-inks. Thus, an anodized aluminum substrate was coated with a component containing naphthoquinon(1,2)-diazido-5-sulfonic acid ester of acetone-pyrogallol resin and acrylonitrile copolymer in order to give a presensitized lithographic plate.
Konica further describes photosensitive compositions comprising naphtoquinone diazide sulphonates and phenolic resins having a good resistance towards cleaners and oils. In JP-A's 63-183441 and 10-207056 Konica makes use of a N-(4-hydroxyphenyl)acrylamide-acrylonitrile-ethyl acrylate-methyl methacrylate copolymer binder.
In JP-A 63-066558 a similar polymer is used in a photosensitive composition containing o-quinone diazide compounds. In JP-A 10-207056 Konica describes a composition comprising (A) a compound generating an acid or a radical under irradiation of light, activated radiation or electron beams and (B) a polymer containing at least one monomer unit (a) with a dipole moment of at least 3.0 D and at least one monomer unit (b) with a dipole moment of less than 3.0 D and having Y=1.800-2.300 (wherein Y is based on an equation, regarding the dipole moment of the monomers and the molar ratio of the monomers, as specified by the author. In JP-A 04-062556 Konica describes a nitrogen-containing polymer in a chemically resistant positive-working resist for presensitized lithographic plates.
Otherwise in JP-A 59-002045 DuPont de Nemours describes the solvent resistance of flexographic plates prepared by making use of a photosensitive elastomer composition containing an acrylonitrile-butadiene copolymer type resin.
A polymer having onium group containing structural components containing one or more onium group(s) is further used in a positive-working presensitized lithographic plate, as disclosed by Fuji in JP-A 10-301262. The lithographic plate shows good performance in erasure of unnecessary image portions, low residual color stain, and high printing durability as well as chemical resistance. In another patent application by Fuji N-containing polymers like Acrylonitrile-N-(p-Aminosulfonylphenyl)-methacrylamide-ethyl methacrylate copolymers are used. The positive-working photosensitive composition for the manufacture of a lithographic plate comprises a polymer with a sulfonamido-group, an alkali-soluble novolak and a positive-working photosensitive compound.
For use of polymer binders in an application such as a negative working lithographic printing plate, improvement of chemical resistance and lithographic performance, and, more particularly, provision of a higher run length, a broader lithographic latitude and a better scratch resistance, is highly desired as it remains an ever lasting demand.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide printing system making use of a negative working lithographic printing plate material, wherein the printing plate material shows an improved chemical resistance and lithographic performance, and, in particular, a higher run length, a lithographic latitude and scratch resistance.
It is a further object to avoid environmentally unfriendly measures in the manufacturing of the printing plate suitable for use in the system, more particularly with respect to the properties of the hydrophobic thermoplastic polymer particles in combination with the hydrophilic polymer binders used therein.
More particularly it is an object of the present invention to provide required solvent resistance on the exposed image areas, while unexposed areas may still give a fast clean-up during the on-press processing of the printing plate in the printing system.
Further advantages and embodiments of the present invention will become apparent from the following description.
SUMMARY OF THE INVENTION
The above mentioned objects are realized by providing in a printing system a heat sensitive imaging element comprising, on a lithographic base with a hydrophilic surface thereupon, an image-forming layer including hydrophobic thermoplastic polymer particles and a hydrophilic (water-soluble, water-dispersable, alkali-dispersable or alkali-soluble) polymer binder, and, optionally, an infrared absorbing compound, characterized in that the hydrophobic polymer particles are containing structural chemical groups selected from the group consisting of amide, urethane, methacrylonitrile, crotononitrile, vinylidene cyanide, isocytosine, pyrrolidone, piperazine, cyanomethyl, cyanoethyl, cyanopropyl, cyanoaryl, cyanoacrylate, primary amines, mono- or di-n-alkyl substituted amines, urea, imide, imine, triazine, sulfonamide, onium, melamine, pyrimidine, ureido-pyrimidone, pyridine, barbiturate, isocyanurate or imidazole.
The printing syst
Aert Huub Van
Kokkelenberg Dirk
Vermeersch Joan
AGFA-Gevaert
Funk Stephen R.
Guy Joseph T.
Nexsen Pruet , LLC
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