Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/08—Damping; Neutralising or similar differentiation treatments for lithographic printing formes; Gumming or finishing solutions, fountain solutions, correction or deletion fluids, or on-press development
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/06—Preparing for use and conserving printing surfaces by use of detergents

Definitions

• the present invention relates to a plate cleaner for a lithographic printing plate which is made by an electrophotographic process.
• the printing plate can be easily made through only simple procedures of forming an image according to ordinary electrophotographic steps, and then wiping the copied surface of an electrophotographic photoreceptor with such a desensitizing solution (also called etching solution) as to render the non-image area hydrophilic, that is to say, only procedures requiring no special techniques.
• a desensitizing solution also called etching solution
• photoconductive zinc oxide is coated together with a binder on a base paper which has previously been so treated as to have a water resisting property.
• the thus-formed photoconductive layer is subjected to corona discharge or the like to gain charges electrostatically. Then, it is exposed to a light pattern in the dark, whereby charges in the exposed areas are dissipated and those in the non-exposed areas remain.
• electrostatic latent image is created on the photoconductive layer.
• the latent image is developed by then spraying charged toner particles onto the photoconductive layer or dipping the photoconductive layer in an insulating liquid in which charged particles are dispersed, thereby causing the charged toner particles to adhere thereto by Coulombic attraction in an imagewise pattern.
• toner particles used in a developer are coated with an oleophilic resin, and fixed to a photoconductive layer by a process of heat sealable adhesion or evaporation of solvent.
• the image part displays an oleophilic property due to the oleophilic resin coat of toner particles.
• the non-image part In order to convert an electrophotographic copy obtained thereby to a lithographic printing plate, it is necessary for the non-image part to be rendered hydrophilic. Such can be done, for example, in the following manner.
• the adhesion spots become ink-receptive, and are turned into stains. Also, it can be attributed to a similar cause, viz., fingerprints, which have been left on the hydrophilic layer before treatment for rendering the non-image part of the photoconductive layer hydrophilic, make their appearance at the background of printed matter.
• a typical PS plate which is the abbreviation of Pre-Sensitized printing plate, that is to say, a lithographic printing plate to which photosensitivity is imparted in advance
• the stains can be removed by wiping with dampening water or an etching solution and thereby the plate surface can be restored to the original state to some degree.
• an electrophoto-lithographic printing plate has a strong affinity for printing ink, and therefore the stains can hardly be changed for the better by wiping with an etching solution or a washing oil.
• a primary object of the present invention is to provide a plate cleaner for an electrophoto-lithographic printing plate which can restore the plate surface from stains generated in the course of printing operations, stains due to fingerprints or ink left on the plate surface before or after the treatment for rendering the non-image part of the photoconductive layer hydrophilic, or stains caused by scratches, and enables normal printing which is free from background contamination.
• the cleaner of the present invention may preferably additionally comprise the following components:
• Examples of compounds capable of producing hydrophilic substances by reacting with zinc oxide, which are employed as the component (1) in the present invention include ferrocyanide compounds such as potassium ferrocyanide, sodium ferrocyanide, etc.; ferricyanide compounds such as potassium ferricyanide, sodium ferricyanide, etc.; phosphoric acid compounds such as ammonium primary phosphate, ammonium secondary phosphate, etc.; phytic acid and the derivatives thereof, that is, phytic acid compounds, as described in Japanese Patent Application (OPI) No.
• polyvalent metal salts such as ferric chloride, cupric chloride, etc.
• hexamminecobalt salts such as hexamminenickel salts, EDTA (ethylenediaminetetraacetate) chelate compounds, and the like, as described in U.S. Patent 4,282,811
• polyacrylic acid sodium polyacrylate, polymethacrylic acid, sodium polymethacrylate, alginic acid, sodium alginate, cationic polymers such as melamine- formaldehyde resin, and so on.
• Compounds to be employed as the component (1) are not limited to any particular compounds, provided that they can react with zinc oxide to produce hydrophilic substances. Further, they can be used as a mixture of two or more thereof. It is preferred in the present invention to use these compounds in a condition of water solution.
• the water solution is preferably adjusted to a pH of from 2 to 6. It is advisable to use the above-described compounds in combination with an acid or a base such as ammonia, phosphoric acid, ammonium phosphate, citric acid, sodium citrate, or the like.
• the hydrocarbon solvent of the component (2) employed in the present invention is one which has an action of dissolving lithographic printing ink, and an especially useful hydrocarbon solvent is a petroleum fraction ranging in boiling point from 120°C to 320°C, which is conventionally used in washing for removal of ink.
• This hydrocarbon solvent is generally used in an amount corresponding to from 5 to 50%, and preferably from 10 to 40%, of the total weight of the cleaner composition.
• the component (1) and the component (2) are immiscible, they are thoroughly mingled and dispersed and put to use in such a dispersed condition.
• Preferred surface active agents forming the component (3) employed in the present invention are those having anionic or nonionic character, and have the function of enhancing dispersibility of the system.
• preferred anionic surface active agents include aliphatic salts, higher alcohol sulfate salts, aliphatic alcohol phosphate salts, sulfonic acid salts of dibasic fatty acid esters, fatty acid amide sulfonic acid salts, alkylarylsulfonic acid salts, and formaldehyde-condensed naphthalenesulfonic acid salts.
• nonionic surface active agents examples include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyox y- ethylene alkyl esters, sorbitan alkyl esters, polyox y- propylene, polyoxyethylene ethers and so on. These surface active agents may be used in combinations of two or more thereof.
• the quantity of such surface active agents used in the cleaner is, though not particularly limited, preferably in the range of not more than 10% of the total weight of the cleaner composition.
• a water-soluble colloidal substance as a component (4) for the purpose of further enhancing the dispersing stability of the cleaner.
• preferred water-soluble colloidal substances which can be preferably used in the present invention include natural resins or modified resins thereof such as dextrin, gum arabic, shellac, alginic acid salts, cellulose deriva-tives (e.g., carboxymethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, methyl cellulose, etc.), and so on; and synthetic resins such as polyvinyl alcohol and the derivatives thereof, polyvinyl pyrrolidone, polyacrylamide and copolymers thereof, acrylic acid copolymers, vinyl methyl ether/maleic anhydride copolymers, vinyl acetate maleic anhydride copolymers, styrene/maleic anhydride copolymers, and so on. These substances can be used alone or as a mixture.
• wetting agents are also useful as a component (5) in the plate cleaner for the purpose of imparting an excellent spread characteristic and retarding the progress of drying and thereby making an improvement in using facility.
• Suitable wetting agents are compounds of the formula HO( ⁇ R-O) ⁇ m H [wherein R is C n H 2n (n is an integer from 2 to 6) and m is from 1 to 500].
• R is C n H 2n (n is an integer from 2 to 6) and m is from 1 to 500].
• ethylene glycol, propylene glycol, butylene glycol, pentanediol, hexylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, and the like are preferably used.
• Other wetting agents which can be used advantageously are glycerin, sorbitol, and pentaerythritol.
• the characteristics of the plate cleaner of the present invention are that they can exert a very strong action preventing background contamination due t6 scratches the hydrophilic layer received, and perform a powerful function in maintaining or reinforcing the recovered hydrophilic property. Said characteristics are further intensified by using as the component (6) at least one compound selected from the group consisting of molybdic acid, boric acid, nitric acid, phosphoric acid or polyphosphoric acid, and water-soluble alkali metal salts thereof together with the foregoing components. Such a compound as described above is typically used in a range of from 0.1 to 10%, and preferably from 0.2 to 5%, of the total weight of the cleaner composition.
• the plate cleaner of the present invention may also contain in itsm composition granular powders such as pumice, alumina powder, silica powder and the like, colloidal silica, colloidal alumina, dyes and so on in addition to the above-described ingredients.
• granular powders such as pumice, alumina powder, silica powder and the like, colloidal silica, colloidal alumina, dyes and so on in addition to the above-described ingredients.
• Solution A In 70 parts of distilled water were dissolved 10 parts of glycerine, 10 parts of ammonium primary phosphate, 5 parts of potassium ferrocyanide, 2 parts of gum arabic and 3 parts of polyethylene glycol oleyl ether (Noigen ET-120, produced by Dai-ichi Kogyo Seiyaku Co., Ltd.), and the resulting solution was named Solution A.
• Solution B was slowly added dropwise to Solution A with stirring, and dispersed into Solution A.
• the resulting dispersion was made into a yellow emulsion by means of a homogenizer.
• a lithographic printing plate was prepared by means of a commercially available offset master-making machine, ELP-280 (made by F uji Photo Film Co., Ltd.).
• the electrophotographic light-sensitive material used in the production of the printing plate was produced by coating the following composition on a waterproof paper rendered electroconductive to obtain a photoconductive layer having a dry thickness of 10 ⁇ .
• the developer used hereinabove had the following formulation.
• a desensitizing solution having the following composition was applied to the whole surface of the printing plate.
• a lithographic printing plate was made in the same manner as employed in Example 1 and finger marks were formed thereon with ink-stained fingers, followed by subjecting it to the same treatment for acquiring hydrophilic property with the desensitizing solution used in Example 1.
• Printing was carried out using the resulting printing plate, and stains of a fingerprint pattern were observed in the printed matter. After 100 copies had been printed, the operation of the printing machine was suspended, and the finger marks (to which ink had already been sticked) were wiped with the above-described plate cleaner, and thereafter the printing machine was operated again. Thus, not less than 10,000 copies which had good quality and no finger marks were obtained. Furthermore, these copies showed no abnormality in the image part, e.g., no deterioration in inking.
• a lithographic printing plate made in the same manner as employed in Example 1 was placed in a printing machine, Hamadastar 700 CD, and ink was put on a part of the plate surface using an inking roller. Then, the resulting plate was rendered hydrophilic using the etching solution used in Example 1. As a result of printing, intense printing stain was generated in the part where the inking had been carried out before the treatment for rendering hydrophilic. The operation of the printing machine was suspended, and the plate surface was wiped with the above-described cleaner. Thereafter, the operation was started again, and more than 10,000 copies which had good quality and no stain were obtained. Furthermore, these copies showed no abnormality in the image part.
• a lithographic printing plate made in the same manner as employed in Example 1 was treated as to acquire an affinity for water, and printing was carried out using the resulting printing plate. Then, the printing operation was suspended, and the plate surface got scratches by being rubbed with sandpaper. Thereafter, the printing machine was operated again. As a result, the scratching marks remained as stains on the prints. Therefore, the printing operation was suspended again, and the plate surface was wiped with the plate cleaner prepared in Example 1. Thereafter, more than 10,000 copies having good quality and no scratch stain were obtained. In addition, it was recognized similarly that the plate cleaner prepared in Example 2 and Example 3, respectively, had an improving effect (i.e., minimized) on scratch stain.

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Cited By (6)

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Citations (5)

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• 1983
  • 1983-11-25 JP JP22058783A patent/JPS60112495A/ja active Granted
• 1984
  • 1984-11-23 EP EP19840308150 patent/EP0144201B1/de not_active Expired
  • 1984-11-23 DE DE8484308150T patent/DE3481981D1/de not_active Expired - Lifetime

Patent Citations (5)

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