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

Definitions

• the solution is oppositely charged from the area configuration it is attracted to the charged areas and converts them while the noncharged areas remain unconverted. If the solution is of the same charge as the charged areas, it will be repelled by them and they will remain unconverted and the noncharged areas, after a period of time, will be converted.
• This invention relates generally to the making of printing masters, and more particularly to a process of making a printing master wherein a material which is normally oleophilic/hydrophobic is selectively electrostatically charged and the material is then contacted with a fluid which will be attracted to, and will convert only the areas to be altered in oleophilic nature. Usually it will be preferred to render the larger background area hydrophobic to reject ink and produce a printed image on an unaltered stock background.
• One common prior art practice utilized an electrostatic process for making printing masters.
• material which is normally oleophilic/ hydrophobic but which can be converted to hydrophilic/oleophobic condition is charged on the surface thereof and then selectively discharged leaving a charge only in the desired printing areas.
• the material is then contacted with a toner which itself is oleophilic/hydrophobic and which is not converted to hydrophilic/oleophobic condition.
• the toner is then fused by heat and/or pressure. Thereafter the material is immersed in a conversion solution which converts the nonimaged untoned area to a hydrophilic/oleophobic condition while the toner and the material underlying the toner and protected thereby remain oleophilic/hydrophobic.
• the master is then able to print using a grease or oil base ink in a conventional manner.
• a method of producing a printing master wherein the oleophilic/ hydrophobic material is selectively charged to the desired image configuration and the material is then contacted with an emulsion of electrically conducting conversion fluid droplets in a non-conducting non-converting fluid which will selectively convert the desired area by electrical interaction of the charged area with conversion fluid particles.
• the present invention is directed toward a simplified process of making a printing master by electrostatic processing.
• a material is provided which is normally oleophilic/hydrophobic in nature but which can be converted to hydrophilic/oleophobic in nature.
• the material also must be capable of being charged on the surface thereof and selectively discharged to provide a desired configuration of electrically charged and noncharged areas.
• Zinc oxide is the most common material which meets these requirements and hence constitutes the preferred base material. However, other materials can also be used.
• the zinc oxide material is provided on a substrate which can either be in the form of a drum or a sheet or strip of material.
• the zinc oxide is imaged in a conventional manner by first electrostatically charging the entire surface thereof and then exposing the areas which it is not desired to convert to a light source which will discharge the surface which is struck by the light. This will then provide a surface configuration of electrically charged and uncharged areas.
• the zinc oxide is then contacted with an emulsion of a conversion solution emulsified and dispersed in a nonconverting non-conducting liquid with a low dielectric constant.
• an emulsion of this nature the fine droplets of the conversion solution are attracted by the electrical charge to those areas which have an electrical charge thereon and the conversion solution when contacting these areas converts the material from oleophilic/hydrophobic to hydrophilic/oleophobic in nature.
• the fine droplets are not attracted electrically to the non-imaged, i.e. non-charged, areas since there is no charge thereon to cause such attraction. Thus there will be very little contact of the fine droplets with the non-charged area. Hence the non-charged areas will not be converted whereas the charged area will be.
• the material After the conversion of the charged area the material is removed from the conversion solution and it is ready for printing. If conventional oil base or grease base inks are used the ink will cause the non-converted areas to print, whereas the converted areas will not print. However, if conventional exposure techniques are utilized it is the background areas which are remaining oleophilic/hydrophobic and with conventional printing techniques using conventional grease or oil base inks the background areas would therefore print leaving the imaged areas unprinted.
• One such technique is to provide a fountain of oil, rather than water against the conventional material and utilize a water base ink. This would cause the imaged areas to print, but the oil in the background would prevent the background area from pickup of ink and printing.
• Such oils should be non-destructive to the material and have a high enough flash point to be safe. There are various hydrocarbons and mineral oils which are satisfactory.
• Still another technique is the so called reversal process in converting the selectively charged photoconductive material.
• a conversion fluid which is electrically repelled by the charged area is utilized in the emulsion.
• the conversion fluid will contact and convert the non-charged areas while the charged areas repel the conversion fiuid and remain unconverted.
• Another technique is to first form a reverse image negative and then use such negative as the imaging device for selectively charging the zinc oxide.
• the thus imaged zinc oxide would then provide charged background and an uncharged image area, which would cause the background to be converted and the image area to be non-converted resulting in printing of the image and nonprinting of the background.
• liquid emulsion which will selectively convert the charged areas according to this invention.
• the requirements are that a conversion solution be capable of being attracted to an electrical charge while the liquid in which it is immersed be essentially non-conductive with a low dielectric constant.
• the electrical resistance of the non-conducting fluid should be ohm-cm. or greater and the dielectric constant should be lower than 3.4.
• the conversion solution is either an aqueous ferrocyanide type or an aqueous phosphate type and the insulating liquid is a hydrocarbon.
• a typical formulation for the ferrocyanide type of conversion is as follows:
• the size of the droplets of the conversion solution in the emulsion should be between .5 and 500 microns, ideally about 10 microns.
• Such an emulsion can be satisfactorily formed and maintained using ultrasonic vibration. It has been found when utilizing a ferrocyanide or phosphate type conversion solution in either Isopar H or Sovasol 35 power generation of 400 watts at kilocycles is sufiicient for establishing and maintaining the emulsion.
• a non-conducting surface active agent such as Span 85, manufactured by Atlas Powder Company, can be added in the amount of about 1 part per 1000 of emulsion to aid in stabilizing the dispersion although such agents are not necessary.
• the exact proportions of the conversion solution and the insulating liquid may vary widely.
• the basic requirement in this respect is merely that the drops be sufficiently fine and sufficiently dispersed so that they will be attracted to the charged areas of the zinc oxide but they will not be in sufficient quantity to substantially convert any of the non-charged areas.
• the electrical resistance of the resulting emulsion should be about 10 ohm-cm. or greater.
• ferrocyanide or phosphate type conversion solutions in either Isopar H or Savasol 35 it has been found 1 to 10 parts conversion solution to 100 parts of insulating liquid by volume provides very satisfactory results.
• This formulation is merely illustrative and is not intended to be a limitation.
• a method for preparing a lithographic printing master on an electrically insulating, oleophilic/hydrophobic surface comprising the steps of electrostatically charging portions of said surface in accordance with a predetermined pattern to provide a surface having charged and uncharged areas, and converting one of said charged and uncharged areas to provide it with an oleophobic/hydrophilic surface, the improvement comprising contacting said charged and uncharged areas with an emulsion in which (a) the discontinuous phase is a liquid which selectively is deposited on one of said charged and uncharged areas, depending on whether it is attracted to or repelled by the electrostatic charge carried by said charged area, and converts the selected area to provide it with an oleophobic/hydrophilic surface, and
• the continuous phase is an insulating liquid having an electrical resistance of at least 10 ohm-cm, and a dielectric constant of less than about 3.4.
• the active ingredient in said discontinuous phase liquid is selected from the group consisting of aqueous ferrocyanides and aqueous phosphates and said continuous phase liquid is a hydrocarbon.
• discontinuous phase liquid is in the form of droplets measuring within the range of about 0.5 to about 500 microns in diameter.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Printing Plates And Materials Therefor (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22710284

Family Applications (1)

Country Status (9)

Cited By (4)

Families Citing this family (1)

• 0
  • BE BE790464D patent/BE790464A/fr unknown
• 1971
  • 1971-10-26 US US00192584A patent/US3758330A/en not_active Expired - Lifetime
• 1972
  • 1972-09-26 CA CA152,546A patent/CA958458A/en not_active Expired
  • 1972-10-04 AU AU47378/72A patent/AU461627B2/en not_active Expired
  • 1972-10-20 FR FR7237380A patent/FR2158907A5/fr not_active Expired
  • 1972-10-23 GB GB4879672A patent/GB1413526A/en not_active Expired
  • 1972-10-24 JP JP47105887A patent/JPS5134762B2/ja not_active Expired
  • 1972-10-25 BR BR7485/72A patent/BR7207485D0/pt unknown
  • 1972-10-25 DE DE2252397A patent/DE2252397A1/de active Pending

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