Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/26—Electrographic processes using a charge pattern for the production of printing plates for non-xerographic printing processes
  • G03G13/28—Planographic printing plates
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/02—Charge-receiving layers
  • G03G5/0202—Dielectric layers for electrography

Definitions

• This invention relates to a method for making a printing plate and a method of printing.
• PS presensitized
• printing plates of high sensitivity and high printing endurance those comprising an aluminum plate on which an organic photoconductive compound is coated are disclosed, for example, in Japanese Patent Examined Publication Nos. 17162/62, 6961/63, 2426/66 and 39405/71 and Japanese Patent Unexamined Publication Nos. 19509/75, 19510/75, 145538/79, 89801/79, 134632/79, 19803/79, 105254/80, 161863/82, 76843/83, 76844/83, 118658/83 and 244959/85.
• These printing plates are made through the steps of corona charging, camera exposure or laser exposure, wet or dry-type development, fixation and etching of non-image area with alkaline solution.
• the gist of this invention resides in a method for making a lithographic printing plate, characterized by forming a positive electrostatic latent image on a dielectric non-photosensitive layer provided on a conductive support of printing sheet for lithographic printing plate by the process mentioned hereinafter and then subjecting the latent image to at least development and fixation.
• the characteristics of the plate are stable to the changes of circumstances where the plate is made and further, uniform printed images can be obtained even if a printing plate of large size such as the whole kiku size (636 mm ⁇ 939 mm) is made by laser scanner exposure method.
• said non-photosensitive layer namely, printing layer can be made as thin as possible and thus resist property of the printing plate of which non-image area is removed by etching with alkaline solution can be improved and printing plates of high printing endurance can be obtained.
• photoreceptor which is separated from printing sheet is used and not only this photoreceptor can be repeatedly used, but printing sheet can also be reused by removing toner or printing layer of once used printing plate (in the latter case, only by coating a dielectric non-photosensitive layer on the support of the printing plate once used).
• economical advantage is great.
• a printing sheet comprising a conductive support having thereon a dielectric non-photosensitive layer and a photoreceptor having a conductive layer are placed opposite to each other and this assembly is subjected to imagewise exposure from a light transmitting side, generally, light transmitting photoreceptor side while applying a direct voltage between the conductive support of the printing sheet and the conductive layer of the photo­receptor from a direct current source, to thereby form a positive electrostatic latent image on said non-­photosensitive layer, which is then developed with a developer having polarity opposite to that of the latent image and is fixed.
• this positive electrostatic latent image is not necessarily clear, but some mechanism can be thought of. That is, one is that in the area irradiated with light, internal dis­charge occurs at the air-gap between the printing sheet and the photoreceptor where the voltage is above the break-down voltage due to the decrease in resistivity of photoreceptor, whereby charge is accumulated on said non-photosensitive layer resulting in formation of electrostatic latent image. Another one is that movable carrier formed in the area irradiated with light is injected and transferred into the dielectric surface by the action of external electrical field or charge is injected into said area from electrode surface and transfers to the dielectric surface, whereby an electrostatic image is formed thereon.
• This invention is not limited to the mechanism of image formation and forms a positive electrostatic image on the exposed area by laser exposure or exposure to a negative original through the above mentioned processes.
• Examples of the conductive supports used in the printing plate of this invention are preferably metal sheets such as aluminum sheet, zinc sheet, iron sheet, copper sheet, etc. Further, metal-deposited films, metal foil-laminated films or films subjected to conductive treatment may also be used.
• the non-photosensitive layer coated on the support comprises a resin which can trap the charge transferred from photoreceptor as dielectric or insulator and can be etched with alkaline solutions.
• resins mention may be made of, for example, those which contain, as at least one component of copolymer, a monomer containing acidic group such as acrylic acid, methacrylic acid, crotonic acid or the like, for example, styrene-maleic anhydride copolymer, maleic ester resin, vinyl acetate-crotonic acid copolymer, vinyl acetate-­maleic anhydride copolymer, (meth)acrylic ester-(meth)­acrylic acid copolymer, acrylic acid half ester, etc. and furthermore, phenolic resin, etc.
• a monomer containing acidic group such as acrylic acid, methacrylic acid, crotonic acid or the like
• styrene-maleic anhydride copolymer maleic ester resin
• vinyl acetate-crotonic acid copolymer vinyl acetate-­maleic anhydride copolymer
• layer of these resins can be made as thin as 5 ⁇ m or less, sometimes as thin as 2 ⁇ m or less, even a tough film required for printing plate can be easily etched.
• Another example of the printing plate of this invention is anodized aluminum sheet and in this case aluminum oxide layer constitutes the dielectric non-­photosensitive layer, which also serves as hydrophilic surface. That is, according to this invention, when the dielectric non-photosensitive layer on the con­ductive support per se has a sufficient hydrophilicity or can be converted to hydrophilic layer, printing plate can be made without removing the non-image area by etching.
• An example of capable of rendering the non-image area hydrophilic after development and fixation is to use a non-photosensitive layer comprising an insulating resin having dispersed therein zinc oxide which undergoes substantially no exposure due to difference in sensitivity or sensitive wavelength when photoreceptor is exposed and to hydrophilize this layer, for example, with a hydrophilizing solution containing, for example, potassium ferrocyanide.
• a printing sheet comprising a conductive support on which a compound or a web such as film which is per se hydro­philic and insulating is coated or laminated.
• photoreceptors in this invention there may be used those which are generally used for electro­photographic system, but since non-light transmitting printing sheets are often used, light transmitting support such as film or glass is used as support for photoreceptor and besides this support for photoreceptor must have conductivity for forming electrode with the printing sheet.
• Photoconductive compound sensitive to laser beam as mentioned before is preferred as the photoreceptor component.
• organic photoconductors such as azo pigments, copper-­phthalocyanine, PVK-TNF, etc. or inorganic photo­conductors such as non-crystalline selenium, cadmium sulfide, etc. These may be of function-separated type.
• a printing sheet and a photoreceptor placed opposite to each other are subjected to imagewise exposure while applying a suitable voltage (generally 400 V or higher) between the printing sheet and the photoreceptor.
• the printing sheet and the photoreceptor may be brought into close contact with each other or they may be positioned with providing a suitable air space therebetween (generally, about 1-20 ⁇ m) when voltage of latent image is to be increased.
• the air space can be provided by forming uniform irregularity on the surface of the printing sheet or the photoreceptor. Specifically, the air space can be provided by allowing fine particles of suitable particle size to be present exposed on the surface of the printing sheet or the photoreceptor and bringing them in contact with each other.
• the surface of non-photosensitive layer namely, the printing sheet is roughened by fine particles
• resist property or etching speed at etching of non-image area with alkaline solution and a printing plate of high resolving power and high alkaline endurance can be obtained.
• non-photosensitive layer having surface roughened by fine particles forms uniform space with the photoreceptor placed opposite to the roughened surface of the non-image layer at the time of exposure, whereby applied voltage can be made uniform and reproducibility can be enhanced.
• the fine particles used for the above purpose are of organic or inorganic compound and of about 1-about 20 ⁇ m, preferably about 3-about 15 ⁇ m in average particle size.
• These fine particles are dispersed in the dielectric and alkali-soluble non-photosensitive layer and must not be those which are dissolved or molten during preparation of coating liquid for the non-­photosensitive layer and formation of coating film to become miscible with the alkali-soluble resin.
• organic fine particles such as of polystyrene; crosslinked copolymers of styrene and divinylbenzene, etc; copolymers of styrene and unsaturated carboxylic acids such as acrylic acid; copolymers of styrene and (meth)acrylic acid lower alkyl esters or styrene, (meth)acrylic acid lower alkyl esters and unsaturated carboxylic acid such as acrylic acid; polymethyl methacrylate; copolymers of methyl methacrylate and (meth)acrylic acid lower alkyl esters or methyl methacrylate, (meth)acrylic acid lower alkyl ester and unsaturated carboxylic acid such as acrylic acid, etc., inorganic fine particles such as of silicon dioxide, titanium dioxide, zinc oxide, calcium carbonate, etc., composite fine particles of organic and inorganic materials, crosslinked organic fine particles, etc.
• inorganic fine particles such as of silicon dioxide, titanium dioxide, zinc oxide, calcium carbonate,
• one or more kinds of these fine particles are contained in non-photosensitive layer in an amount of about 0.1-about 5% by weight, but they may be used in an amount outside said range.
• Height of irregularity on the roughened surface is preferably about 0.5-about 10 ⁇ m, but it may be outside this range.
• Toner used for image formation may be either dry or wet toner, but wet toner for liquid developing is far preferable to dry toner for obtaining printing plate of superior resolving power. Further, toner is required to be hydrophobic and ink receptive and have enough adhesiveness to stand printing. The toner is further required to have resist property when etching with alkali and/or alcohol solution is carried out.
• alkalis used for etching solution mention may be made of, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, potassium phosphate, ammonia, etc.
• alcohols mention may be made of, for example, lower alcohols or aromatic alcohols such as menthanol, ethanol, propanol, benzyl alcohol, etc., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, cellosolve, etc.
• the etching treatment can also be effected with aqueous alkali solution alone or alcohol alone.
• etching solution which can be used in this invention.
• Monoethanolamine 40 ml Diethanolamine 10 ml Ethanol 250 ml
• Polyethylene glycol (molecular weight 600) 400 ml
• a dispersion of copper-phthalocyanine in an acrylic resin was coated on a transparent conductive film (IP-001 of Mitsubishi Chemical Industries, Ltd.) and dried to obtain a photoreceptor.
• phenolic resin was coated on an anodized aluminum sheet at 2 g/m2 and dried to obtain a printing sheet.
• Said photoreceptor and printing sheet (both in B5 size) were put together so that the coated sides contacted with each other and imagewise exposure was effected from backside of the photoreceptor through a transparent negative original while applying externally a voltage of 400 V between the photoreceptor and printing sheet from a direct current source.
• this printing sheet was subjected to development with liquid toner and fixation to obtain a positive image having a maximum image density of 1.5 and free from fog. Further, this printing sheet was subjected to etching with the above etching solution resulting in removal of non-image area in 15 seconds to obtain a printing plate having a resist image of good resolving power. A lot of prints could be made on a printing machine by this printing plate.
• This example was repeated using this printing sheet and the same photoreceptor used above to obtain a printing plate of similarly high printing endurance.
• a printing plate was made by exposure, development and fixation in the same manner as in Example 1 except that fine particles were dispersed in the photoreceptor and an anodized aluminum sheet per se was used as the printing sheet.
• This printing plate had maximum image density of 0.7 and was free from fog.
• This printing plate can be used again as a printing sheet by removing only the toner image with a solvent after used for printing.
• a dispersion of copper-phthalocyanine in acrylic resin was coated on a transparent conductive film (IP-001 of Mitsubishi Chemical Industries, Ltd.) and dried to make a photoreceptor.
• Example 3 was repeated except that 5 g/m2 of styrene-butyl methacrylate-acrylic acid (60:20:20 by weight) copolymer was used in place of phenolic resin and 0.1 g/m2 of polymethyl acrylate of 10 ⁇ m in average particle size was used in place of polystyrene fine particles. Photoreceptor used in Example 3 was reused here.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Photoreceptors In Electrophotography (AREA)
• Printing Plates And Materials Therefor (AREA)

Applications Claiming Priority (4)

Publications (3)

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Family Applications (1)

Country Status (2)

Cited By (3)

Citations (1)

• 1988
  • 1988-01-14 EP EP19880100453 patent/EP0281727B1/fr not_active Expired - Lifetime
  • 1988-01-14 DE DE19883883811 patent/DE3883811T2/de not_active Expired - Fee Related

Patent Citations (1)

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