CA1037103A - Method for preparing printing plate for use in lithography - Google Patents
Method for preparing printing plate for use in lithographyInfo
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- CA1037103A CA1037103A CA213,290A CA213290A CA1037103A CA 1037103 A CA1037103 A CA 1037103A CA 213290 A CA213290 A CA 213290A CA 1037103 A CA1037103 A CA 1037103A
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- layer
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Abstract
METHOD FOR PREPARING PRINTING PLATE
FOR USE IN LITHOGRAPHY
ABSTRACT OF THE DISCLOSURE
Printing masters of improved contrast are obtained by forming and developing an electrostatic latent image comprising a conductive substrate, an abhesive ink-releasing silicone surface layer and a photoconductive layer, said method of imaging comprising primary charging the master, selectively illuminating said master with an image pattern to effect charge migration, secondary charging said master, uniformly illuminating said master wherein a developable electrostatic latent image is formed on the exposed surface of said abhesive layer, and developing said image.
FOR USE IN LITHOGRAPHY
ABSTRACT OF THE DISCLOSURE
Printing masters of improved contrast are obtained by forming and developing an electrostatic latent image comprising a conductive substrate, an abhesive ink-releasing silicone surface layer and a photoconductive layer, said method of imaging comprising primary charging the master, selectively illuminating said master with an image pattern to effect charge migration, secondary charging said master, uniformly illuminating said master wherein a developable electrostatic latent image is formed on the exposed surface of said abhesive layer, and developing said image.
Description
~037~03 BACKGROUND OF THE INVENTION
This invention relates to a xerographic method for preparing a printing plate for use in lithography, and more particularly to a method for preparing a printing plate for use in lithography in which no fountain solutions or dampen-ing solutions are required in the non-image area in order to prevent adhesion of inX thereto.
In general, lithography is based on the principle that if an oily ink is applied to the surface of a printing plate having a non-imaged bearing area which has been dampened with a fountain solution, the non-imaged areas repel the oily ink while the oily ink adheres to the imaged area which is oleophilic and hydrophobic.
Heretofore, various methods for preparing a printing plate have been employed. These methods, however, involve special treatments and in order to produce a copy conforming to the quality of the original image and to sustain uniformity in the copies obtained, the balance between the ink and water required must be carefully controlled.
It has recently been discovered that if the non-imaged areas of the printing master are formed of an abhesive silicone elastomer, lithographic ink is readily released from said areas even in the absence of fountain solution or dampen-ing solution. This offers considerable simplification in process control and printing apparatus. This process has been called variously dry lithography, waterless lithography, or driography.
A particularly advantageous method for preparing printing plates for dry lithography takes advantage of the fact that xerographic toner which may be made of ink receptive materials, may be deposited in image patterns on a photocon-~,- . .
ductive plate whose surface comprises an ink releasing silicone elastomer. Typical of such photoconductive configurations are - zinc oxide dispersions in cured silicone elastomer binders.
~hile such photoconductive masters have good photosensitivity, they do not make very effective printing plates for waterless or dry lithography. This is apparently because a large portion (typically 20 - 40%) of the surface area comprises exposed (or only thinly covered) photoconductive pigment which is inherently ink~receptive. The bac~ground areas of the imaged plate accord-ingly tend to accept ink after the first thin surface coating of binder has been abraded and the underlying pigment becomes exposed to the ink. Typically this occurs after the first 10 -50 prints have been run, and contrast is rapidly degraded there-after. Accordingly conventional silicone elastomers with photoconductive materials do not offer satisfactory printing surfaces for long run waterless lithography. It is to this problem to which this invention is directed.
SUMMAR~ OF THE INVENTIO~
It has now been discovered that the aforesaid defects can be obviated and prints of excellent contrast obtained, employing masters having ink releasing abhesive surface layers of any desired thickness without the need for photosensitive particles dispersed therein.
In accordance with one aspect of this invention there is provided a method of preparing a waterless lithographic master comprising forming an image on a non-imaged master comprising a photoconductive layer, a conductive substrate, and an abhesive ink xeleasing silicone surface layer, the imaging comprising primary charging the master, selectively illuminating said master with an image pattern to effect charge migration, secondary charging said master, uniformly illuminating said ~ _3_ master wherein a developable electrostatic latent image is formed on the exposed surface of said abhesive layer, and developing the image by deposition of marking material.
-3~-",~, - - \
~037103 DETAILED DESCRIPTION OF THE I~V~NTION
Methods of imaging, suitable ink releasing abhesive materials and other aspects of the invention will now be dis-cussed in detail.
The printing master consists essentially of a con-ductive supporting substrate, an abhesive ink releasing sili~
cone surface layer and a photoconductive layer. The substrate may be formed of a metal such as aluminum, a sheet of paper with a metallic foil bonded thereto, a sheet of paper rendered con-ductive by chemical treatment or other similar material.
The photoconductive layer may comprise any conven-tional photosensitive material optionally dispersed in a suit-able binder. Typical photosensitive materials include amorphous selenium, cadmium sulfide, cadmium sulfoselenide, zinc oxide, or an organic photoconductive material such as poly(vinyl car-bazole) complexed with trinitrofluorenone. Typical binders include dielectric polymeric materials such as polyesters, alkyd resins, silicone resins and copolymers of styrene and butadiene.
Conventional silicone elastomer gums can be employed in the invention. These include those having only methyl con-taining groups in the polymer chain such as polydimethylsil-oxane, gums having both methyl and phenyl containing groups in the polymer chain as well as gums having both methyl and vinyl groups, methyl and fluorine groups, or methyl, phenyl and vinyl groups in the polymer chain.
Exemplary of suitable room temperature vulcanizable gums which can be cured at ambient temperature and atmospheric conditions include RTV-108, 106, and 118 polydimethylsiloxane gums available from General Electric Company. Room tempera-ture vulcanizable gums can be cured by using poly-functional silanes and siloxanes as crosslinking agents together with certain catalysts. The preferred crosslinking agents are methoxy and ethoxy silanes or polysiloxanes because of their reactivity. Suitable catalysts are supplied by the manufac-turer of the gum.
Typical silicone gums which are curable at elevated A~ temperature and suitable for use in the invention are Syl Gard ~F
#182, Syl Off #22 and #23, manufactured by E~ow Corning Corpora-tion; Y-3557 and Y-3602 silicone gums supplied by Union Carbide Company and #4413 and #4427 heat curable silicone gums supplied by General Electric Company. Typical catalysts include diiso-cyanates such as toluene diisocyanate and peroxides such as dibenzoyl peroxide which are available from the manufacturer of the gum.
Ink releasable copolymers which can be employed and coalesced at elevated temperature comprise heterophase block copolymeric compositions consisting of an organopolysiloxane material and a non-silicone polymeric material. Polymeric materials which can be employed as the non-silicone component of the heterophase polymeric composition include materials such as poly ( ~C -methylstyrene), polycarbonate, polysulfone, polystyrene, polyester, polyamide, acrylic polymers, poly-urethané, and vinyl polymers. The present invention is not intended to be limited by the material for this non-silicone phase.
~037103 While not limiting, preferred proportions for the heterophase polymeric composition comprise a ratio by weight of between about 95 to 50 parts organopolysiloxane to 5 to 50 parts of the non-silicone polymeric phase. This ratio range of organopolysiloxane to non-silicone polymer, provides suitable ink release materials for the ink release layer of the instant printing master. Copolymers of the above type, could be typi-cally prepared in a manner as is illustrated by the procedure for preparation of an organopolysiloxane polystyrene block-copolymer as described in Macromolecules, Volume 3, January-February 1970, pages 1-4.
The silicone mixture can be applied to the photocon-ductive layer by conventional techniques such as solvent casting, dip coating or draw-bar coating after dissolution in organic solvents which typically may be solvents such as benzene, hexane, heptane, tetrahydrofuran, toluene, xylene, as well as other common aliphatic and aromatic solvents. Powdered photoconductors may be applied to the substrate by first coating a thin layer of oil thereover and then cascading the powder against the oiled surface. Vacuum evaporation is a desirable method for coating materials such as amorphous selenium.
In a preferred embodiment of the invention, the master is imaged by the Katsuragawa Process. This process comprises the steps of applying a first electric field across the photosensitive layer to deposit an electric charge of a first polarity on the surface of the silicone insulating layer, applying a second electric field across the photosensitive element to deposit an electric charge of a polarity opposite to the first charge on the surface of the insulatlng layer and projecting a light image concurrently with the application of the second field to form an electrostatic latent image on the surface of the insulating layer. The entire master is then subjected to blanket exposure by light and the latent image developed to produce the imaged printing master. This is the most photosensitive process and exhibits high electrostatic contrast. The Katsuragawa Process is described in more detail in an article titled, "Electrophotographic Processes Using a Dielectric Layer Bonded to a Photoconductive Layer as in the - Katsuragawa Process" by Nakamura ~IEEE Transactions on Electron Devices, Volume 19, ~4, April, 1972).
Another imaging process which can be employed is the Canon Process. In this process, the master is first given a primary charge followed by simultaneous image exposure and A.
C. corona discharge, and finally blanket light exposure.
During the primary charge, opposite polarity charge is formed at the interface between the insulating silicone layer and the photoconductive layer. In this step the charging polar-ity depends on the character of the photoconductor. That is, ~l positive charge is applied to n-type photoconductors and neg-`I ative charge to p-type photoconductors. During the second step of simultaneous image exposure and A.C. discharge, the primary charge on the top surface of the light-exposed ~ortion is eliminated by an A.C. corona discharge and the charge at I the interface of the light-exposed portion is also eliminated In the dark portion, the primary charge on the insulating layer is difficult to discharge and almost all charge remains without decay because the charged layer at the interface is not discharged but remains as it was. During the final step of blanket illumination, the electrostatic charge remaining at -103~103 the interface in the dark portion is partly eliminated and the latent image is formed by the primary charge remaining in the dark portion. The Canon Process is discussed in more datail in an article titled, "CanQgraphy (canon NP Process) in Elec-trophotography" by Mitsui (IEEE Transactions on Electron De-vice~, Volume 19, #4, April, 1972).
Finally, the Hall method of imaging may be employed (described in U.S. Patent 3,234,019), which is herein incor-porated by reference. By the Hall Process, the master is first sensitized by applying a uniform electrostatic charge to the exposed surface or primary charged, followed by a second stepof selectively illuminating the plate in accordance with an image pattern to effect charge migration. The plate is then subjected to a secondary charging to bring the exposed surface to a uniform potential and finally a blanket illumination whereby a developable latent electrostatic image is formed on the exposed surface of the master which is then developed.
Further, while the master has been described as having three .
layers, improved results may be obtained if one or more insu-lating layers are present such as for example a non-conductive plastic, resin or other film-forming member sandwiched between the photoconductive layer and the master substrate.
The thickness of the various layers will depend upon the particular materials employed, but generally the substrate will have a thickness between about 5 and about 50 microns.
The thickness of the silicone surface layer is based upon the relative thickness of the photoconductive intermediate layer.
It is generally advisable that the dielectric thickness ~ -8-~037~a3 (dielectric thickness being defined as the geometrical thick-ness/dielectric constant) of the silicone surface layer relative to the photoconductive layer be in the range of from about 0.1:1 to about 10:1 and preferably from about 0.5:1 to about 2:1. For example , :, ' :' ::, . .
:
.:
~03~7~03 the master might comprise a conductive substrate of aluminum 10 microns thick, a photoconductive layer of amorphous selenium approximately 0.5 microns in thickness and a silicone elastomer overcoating of about 10 microns.
The thickness of the various layers will depend upon the particular materials employed but generally the substrate will have a thickness between about 5 and about 50 microns, the photosensitive layer between about 30 and about 50 microns, and the abhesive silicone layer between about 5 and about 40 microns.
Conventional particulate imaging materials, commonly referred to in the art as toner, can be employed as the marking material to develop the electrostatic latent image. Typical toners are finely divided thermoplastic polymers combined with a carrier such as glass and metal beads and a pigment such as }5 carbon black. Typical imaging polymers include styrene polymers such as poly(styrene), styrene-n-butyl/methacrylate copolymer, and styrene-butadiene copolymer. Other materials which can be employed include: poly(ethylene), poly(propylene), ethylene-vinyl acetate copolymers, acetals, acrylics, poly(amides), poly (imides), phenoxies, and vinyls.
Typical inks can be employed in the printing method of the invention to include inks of the oleophilic type having the vehicle component for the ink pigments derived from various oleophilic materials such as aromatic and aliphatic hydro-carbons, drying oil varnishes, lacquers and solvent type resins.
Other suitable inkg include the glycol and rubber based inks.
The imaged printing master can thereafter be employed in a planographic printing operation, including direct or offset lithography, with the dampening system removed to provide good quality prints over an extended period of operation.
_g_ ~0;~7103 The following examples will serve to illustrate the invention and embodiments thereof. All parts and percentages in said Examples a~d elsewhere in the specification and claims are by wei~ht unless otherwise specified.
EXAMPLE I
A printing master is prepared as follows~ An aluminum master substrate is coated with a xylene slurry of cadmium sulfide powder incorporated in a thermoplastic acrylic resin consisting of a copolymer of n-butyl and isobutyl meth-acrylate. The photoconductive powder and acrylic resin are present in equal volume amounts. The formed layer is then air dried and further dried at 80c for several hours. Several coatings are applied to obtain a dry film thickness of 40 microns. An insulating thermosetting acrylic resin is then coated on the photoconductive layer to a thickness of about 10 microns, the resin is cured by heat and then a silicone elastomer gum, curable at an elevated temperature, applied thereon to a thickness of about 30 microns and this layer cured by heat. The master is then imaged by primary charging the master to a positive polarity followed by a secondary charging of negative polarity which is effected simultaneously with the exposure of the image. The master is then subjected to blanket exposure whereby an electrostatic latent image is formed on the surface of the master. The image is developed by electrostatically depositing a toner comprising carbon black and a polyethylene thermoplastic polymer. The developed image is fixed to the master by heat, the master inked and prints made therefrom without prior application of a~ueous fountain solution. Prints of excellent contrast are obtained.
EXAMPLE II
The general procedure of Example I is repeated but for the exception that the insulating thermosetting acrylic resin layer is omitted. The total thickness of the photo-conductive layer is 40 microns and a 25 micron layer of General Electric silicone RTV 108 elastomer gum is coated over this and cured under ambient conditions. The photoreceptive master is then charge exposed and developed to provide a waterless lithographic master. The master is inked and excellent prints are obtained.
EXAMPLE III
, The general procedure of Example I is repeated but for the exception that the photoconductive composition employed is an equimolal complex of 2,4,7-trinitro-9-fluorenone with lS poly-N-vinylcarbazole. The coating is prepared by dissolving the polyvinylcarbazole in tetrahydrofuran, whereafter the trinitrofluorenone is added to the polymer sol~tion. The solution is coated on the aluminum substrate by using a :
doctor blade to a dry film thickness of 20 microns. The dried photoconductive film is overcoated with a 20 micron thick layer of silicone elastomer (General Electrlc RTV 108) and cured.
- The master is charged to a negative potential, imagewise-exposed, recharged to a zero potential while simultaneously ::~
subjecting the master to blanket exposure and the latent image developed with toner. The toner is fused, the master inked : ' and excellent prints are made therefrom.
Having described the invention with reference to these specific embodiments, it is to be understood that numerous variations can be made without departing from the spirit of t`ne invention and it is intended to encompass such reasonable variations or equivalents within its scope.
' ` -11-
This invention relates to a xerographic method for preparing a printing plate for use in lithography, and more particularly to a method for preparing a printing plate for use in lithography in which no fountain solutions or dampen-ing solutions are required in the non-image area in order to prevent adhesion of inX thereto.
In general, lithography is based on the principle that if an oily ink is applied to the surface of a printing plate having a non-imaged bearing area which has been dampened with a fountain solution, the non-imaged areas repel the oily ink while the oily ink adheres to the imaged area which is oleophilic and hydrophobic.
Heretofore, various methods for preparing a printing plate have been employed. These methods, however, involve special treatments and in order to produce a copy conforming to the quality of the original image and to sustain uniformity in the copies obtained, the balance between the ink and water required must be carefully controlled.
It has recently been discovered that if the non-imaged areas of the printing master are formed of an abhesive silicone elastomer, lithographic ink is readily released from said areas even in the absence of fountain solution or dampen-ing solution. This offers considerable simplification in process control and printing apparatus. This process has been called variously dry lithography, waterless lithography, or driography.
A particularly advantageous method for preparing printing plates for dry lithography takes advantage of the fact that xerographic toner which may be made of ink receptive materials, may be deposited in image patterns on a photocon-~,- . .
ductive plate whose surface comprises an ink releasing silicone elastomer. Typical of such photoconductive configurations are - zinc oxide dispersions in cured silicone elastomer binders.
~hile such photoconductive masters have good photosensitivity, they do not make very effective printing plates for waterless or dry lithography. This is apparently because a large portion (typically 20 - 40%) of the surface area comprises exposed (or only thinly covered) photoconductive pigment which is inherently ink~receptive. The bac~ground areas of the imaged plate accord-ingly tend to accept ink after the first thin surface coating of binder has been abraded and the underlying pigment becomes exposed to the ink. Typically this occurs after the first 10 -50 prints have been run, and contrast is rapidly degraded there-after. Accordingly conventional silicone elastomers with photoconductive materials do not offer satisfactory printing surfaces for long run waterless lithography. It is to this problem to which this invention is directed.
SUMMAR~ OF THE INVENTIO~
It has now been discovered that the aforesaid defects can be obviated and prints of excellent contrast obtained, employing masters having ink releasing abhesive surface layers of any desired thickness without the need for photosensitive particles dispersed therein.
In accordance with one aspect of this invention there is provided a method of preparing a waterless lithographic master comprising forming an image on a non-imaged master comprising a photoconductive layer, a conductive substrate, and an abhesive ink xeleasing silicone surface layer, the imaging comprising primary charging the master, selectively illuminating said master with an image pattern to effect charge migration, secondary charging said master, uniformly illuminating said ~ _3_ master wherein a developable electrostatic latent image is formed on the exposed surface of said abhesive layer, and developing the image by deposition of marking material.
-3~-",~, - - \
~037103 DETAILED DESCRIPTION OF THE I~V~NTION
Methods of imaging, suitable ink releasing abhesive materials and other aspects of the invention will now be dis-cussed in detail.
The printing master consists essentially of a con-ductive supporting substrate, an abhesive ink releasing sili~
cone surface layer and a photoconductive layer. The substrate may be formed of a metal such as aluminum, a sheet of paper with a metallic foil bonded thereto, a sheet of paper rendered con-ductive by chemical treatment or other similar material.
The photoconductive layer may comprise any conven-tional photosensitive material optionally dispersed in a suit-able binder. Typical photosensitive materials include amorphous selenium, cadmium sulfide, cadmium sulfoselenide, zinc oxide, or an organic photoconductive material such as poly(vinyl car-bazole) complexed with trinitrofluorenone. Typical binders include dielectric polymeric materials such as polyesters, alkyd resins, silicone resins and copolymers of styrene and butadiene.
Conventional silicone elastomer gums can be employed in the invention. These include those having only methyl con-taining groups in the polymer chain such as polydimethylsil-oxane, gums having both methyl and phenyl containing groups in the polymer chain as well as gums having both methyl and vinyl groups, methyl and fluorine groups, or methyl, phenyl and vinyl groups in the polymer chain.
Exemplary of suitable room temperature vulcanizable gums which can be cured at ambient temperature and atmospheric conditions include RTV-108, 106, and 118 polydimethylsiloxane gums available from General Electric Company. Room tempera-ture vulcanizable gums can be cured by using poly-functional silanes and siloxanes as crosslinking agents together with certain catalysts. The preferred crosslinking agents are methoxy and ethoxy silanes or polysiloxanes because of their reactivity. Suitable catalysts are supplied by the manufac-turer of the gum.
Typical silicone gums which are curable at elevated A~ temperature and suitable for use in the invention are Syl Gard ~F
#182, Syl Off #22 and #23, manufactured by E~ow Corning Corpora-tion; Y-3557 and Y-3602 silicone gums supplied by Union Carbide Company and #4413 and #4427 heat curable silicone gums supplied by General Electric Company. Typical catalysts include diiso-cyanates such as toluene diisocyanate and peroxides such as dibenzoyl peroxide which are available from the manufacturer of the gum.
Ink releasable copolymers which can be employed and coalesced at elevated temperature comprise heterophase block copolymeric compositions consisting of an organopolysiloxane material and a non-silicone polymeric material. Polymeric materials which can be employed as the non-silicone component of the heterophase polymeric composition include materials such as poly ( ~C -methylstyrene), polycarbonate, polysulfone, polystyrene, polyester, polyamide, acrylic polymers, poly-urethané, and vinyl polymers. The present invention is not intended to be limited by the material for this non-silicone phase.
~037103 While not limiting, preferred proportions for the heterophase polymeric composition comprise a ratio by weight of between about 95 to 50 parts organopolysiloxane to 5 to 50 parts of the non-silicone polymeric phase. This ratio range of organopolysiloxane to non-silicone polymer, provides suitable ink release materials for the ink release layer of the instant printing master. Copolymers of the above type, could be typi-cally prepared in a manner as is illustrated by the procedure for preparation of an organopolysiloxane polystyrene block-copolymer as described in Macromolecules, Volume 3, January-February 1970, pages 1-4.
The silicone mixture can be applied to the photocon-ductive layer by conventional techniques such as solvent casting, dip coating or draw-bar coating after dissolution in organic solvents which typically may be solvents such as benzene, hexane, heptane, tetrahydrofuran, toluene, xylene, as well as other common aliphatic and aromatic solvents. Powdered photoconductors may be applied to the substrate by first coating a thin layer of oil thereover and then cascading the powder against the oiled surface. Vacuum evaporation is a desirable method for coating materials such as amorphous selenium.
In a preferred embodiment of the invention, the master is imaged by the Katsuragawa Process. This process comprises the steps of applying a first electric field across the photosensitive layer to deposit an electric charge of a first polarity on the surface of the silicone insulating layer, applying a second electric field across the photosensitive element to deposit an electric charge of a polarity opposite to the first charge on the surface of the insulatlng layer and projecting a light image concurrently with the application of the second field to form an electrostatic latent image on the surface of the insulating layer. The entire master is then subjected to blanket exposure by light and the latent image developed to produce the imaged printing master. This is the most photosensitive process and exhibits high electrostatic contrast. The Katsuragawa Process is described in more detail in an article titled, "Electrophotographic Processes Using a Dielectric Layer Bonded to a Photoconductive Layer as in the - Katsuragawa Process" by Nakamura ~IEEE Transactions on Electron Devices, Volume 19, ~4, April, 1972).
Another imaging process which can be employed is the Canon Process. In this process, the master is first given a primary charge followed by simultaneous image exposure and A.
C. corona discharge, and finally blanket light exposure.
During the primary charge, opposite polarity charge is formed at the interface between the insulating silicone layer and the photoconductive layer. In this step the charging polar-ity depends on the character of the photoconductor. That is, ~l positive charge is applied to n-type photoconductors and neg-`I ative charge to p-type photoconductors. During the second step of simultaneous image exposure and A.C. discharge, the primary charge on the top surface of the light-exposed ~ortion is eliminated by an A.C. corona discharge and the charge at I the interface of the light-exposed portion is also eliminated In the dark portion, the primary charge on the insulating layer is difficult to discharge and almost all charge remains without decay because the charged layer at the interface is not discharged but remains as it was. During the final step of blanket illumination, the electrostatic charge remaining at -103~103 the interface in the dark portion is partly eliminated and the latent image is formed by the primary charge remaining in the dark portion. The Canon Process is discussed in more datail in an article titled, "CanQgraphy (canon NP Process) in Elec-trophotography" by Mitsui (IEEE Transactions on Electron De-vice~, Volume 19, #4, April, 1972).
Finally, the Hall method of imaging may be employed (described in U.S. Patent 3,234,019), which is herein incor-porated by reference. By the Hall Process, the master is first sensitized by applying a uniform electrostatic charge to the exposed surface or primary charged, followed by a second stepof selectively illuminating the plate in accordance with an image pattern to effect charge migration. The plate is then subjected to a secondary charging to bring the exposed surface to a uniform potential and finally a blanket illumination whereby a developable latent electrostatic image is formed on the exposed surface of the master which is then developed.
Further, while the master has been described as having three .
layers, improved results may be obtained if one or more insu-lating layers are present such as for example a non-conductive plastic, resin or other film-forming member sandwiched between the photoconductive layer and the master substrate.
The thickness of the various layers will depend upon the particular materials employed, but generally the substrate will have a thickness between about 5 and about 50 microns.
The thickness of the silicone surface layer is based upon the relative thickness of the photoconductive intermediate layer.
It is generally advisable that the dielectric thickness ~ -8-~037~a3 (dielectric thickness being defined as the geometrical thick-ness/dielectric constant) of the silicone surface layer relative to the photoconductive layer be in the range of from about 0.1:1 to about 10:1 and preferably from about 0.5:1 to about 2:1. For example , :, ' :' ::, . .
:
.:
~03~7~03 the master might comprise a conductive substrate of aluminum 10 microns thick, a photoconductive layer of amorphous selenium approximately 0.5 microns in thickness and a silicone elastomer overcoating of about 10 microns.
The thickness of the various layers will depend upon the particular materials employed but generally the substrate will have a thickness between about 5 and about 50 microns, the photosensitive layer between about 30 and about 50 microns, and the abhesive silicone layer between about 5 and about 40 microns.
Conventional particulate imaging materials, commonly referred to in the art as toner, can be employed as the marking material to develop the electrostatic latent image. Typical toners are finely divided thermoplastic polymers combined with a carrier such as glass and metal beads and a pigment such as }5 carbon black. Typical imaging polymers include styrene polymers such as poly(styrene), styrene-n-butyl/methacrylate copolymer, and styrene-butadiene copolymer. Other materials which can be employed include: poly(ethylene), poly(propylene), ethylene-vinyl acetate copolymers, acetals, acrylics, poly(amides), poly (imides), phenoxies, and vinyls.
Typical inks can be employed in the printing method of the invention to include inks of the oleophilic type having the vehicle component for the ink pigments derived from various oleophilic materials such as aromatic and aliphatic hydro-carbons, drying oil varnishes, lacquers and solvent type resins.
Other suitable inkg include the glycol and rubber based inks.
The imaged printing master can thereafter be employed in a planographic printing operation, including direct or offset lithography, with the dampening system removed to provide good quality prints over an extended period of operation.
_g_ ~0;~7103 The following examples will serve to illustrate the invention and embodiments thereof. All parts and percentages in said Examples a~d elsewhere in the specification and claims are by wei~ht unless otherwise specified.
EXAMPLE I
A printing master is prepared as follows~ An aluminum master substrate is coated with a xylene slurry of cadmium sulfide powder incorporated in a thermoplastic acrylic resin consisting of a copolymer of n-butyl and isobutyl meth-acrylate. The photoconductive powder and acrylic resin are present in equal volume amounts. The formed layer is then air dried and further dried at 80c for several hours. Several coatings are applied to obtain a dry film thickness of 40 microns. An insulating thermosetting acrylic resin is then coated on the photoconductive layer to a thickness of about 10 microns, the resin is cured by heat and then a silicone elastomer gum, curable at an elevated temperature, applied thereon to a thickness of about 30 microns and this layer cured by heat. The master is then imaged by primary charging the master to a positive polarity followed by a secondary charging of negative polarity which is effected simultaneously with the exposure of the image. The master is then subjected to blanket exposure whereby an electrostatic latent image is formed on the surface of the master. The image is developed by electrostatically depositing a toner comprising carbon black and a polyethylene thermoplastic polymer. The developed image is fixed to the master by heat, the master inked and prints made therefrom without prior application of a~ueous fountain solution. Prints of excellent contrast are obtained.
EXAMPLE II
The general procedure of Example I is repeated but for the exception that the insulating thermosetting acrylic resin layer is omitted. The total thickness of the photo-conductive layer is 40 microns and a 25 micron layer of General Electric silicone RTV 108 elastomer gum is coated over this and cured under ambient conditions. The photoreceptive master is then charge exposed and developed to provide a waterless lithographic master. The master is inked and excellent prints are obtained.
EXAMPLE III
, The general procedure of Example I is repeated but for the exception that the photoconductive composition employed is an equimolal complex of 2,4,7-trinitro-9-fluorenone with lS poly-N-vinylcarbazole. The coating is prepared by dissolving the polyvinylcarbazole in tetrahydrofuran, whereafter the trinitrofluorenone is added to the polymer sol~tion. The solution is coated on the aluminum substrate by using a :
doctor blade to a dry film thickness of 20 microns. The dried photoconductive film is overcoated with a 20 micron thick layer of silicone elastomer (General Electrlc RTV 108) and cured.
- The master is charged to a negative potential, imagewise-exposed, recharged to a zero potential while simultaneously ::~
subjecting the master to blanket exposure and the latent image developed with toner. The toner is fused, the master inked : ' and excellent prints are made therefrom.
Having described the invention with reference to these specific embodiments, it is to be understood that numerous variations can be made without departing from the spirit of t`ne invention and it is intended to encompass such reasonable variations or equivalents within its scope.
' ` -11-
Claims (2)
1. A method of preparing a waterless lithographic master comprising forming an image on a non-imaged master comprising a photoconductive layer, a conductive substrate, and an abhesive ink releasing silicone surface layer, the imaging comprising primary charging the master, selectively illuminating said master with an image pattern to effect charge migration, secondary charging said master, uniformly illuminating said master wherein a developable electrostatic latent image is formed on the exposed surface of said abhesive layer, and developing the image by deposition of marking material.
2. The method of Claim 1 wherein the image is developed with an ink accepting particulate toner.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12917273A JPS5146443B2 (en) | 1973-11-19 | 1973-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1037103A true CA1037103A (en) | 1978-08-22 |
Family
ID=15002911
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA213,290A Expired CA1037103A (en) | 1973-11-19 | 1974-11-06 | Method for preparing printing plate for use in lithography |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5146443B2 (en) |
| CA (1) | CA1037103A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57195251A (en) * | 1981-05-26 | 1982-11-30 | Dainippon Printing Co Ltd | Formation of picture |
-
1973
- 1973-11-19 JP JP12917273A patent/JPS5146443B2/ja not_active Expired
-
1974
- 1974-11-06 CA CA213,290A patent/CA1037103A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5078403A (en) | 1975-06-26 |
| JPS5146443B2 (en) | 1976-12-09 |
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