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

• One method of producing a lithographic printing master is by the electrostatic process.
• a master sheet coated with a photoconductive material is charged, then exposed to dissipate the charge in the non-image areas, to provide the desired latent image thereon.
• a toner is then applied to the surface, which toner will adhere to the charged surface where the latent image is formed.
• Such toner when held on the surface only by electrostatic charge, is easily removed. According to conventional prior art practice, therefore, this toner is then fixed at elevated temperatures, i.e. the toner is heated to such a degree that it firmly adheres to the paper which thus sets the toner on the surface.
• This fixing has conventionally been done with high wattage lamps, utilized to generate radiant energy, or by ovens.
• the entire surface of the master is then treated with a conversion solution.
• the conversion solution chemically converts the non-image areas, i.e. the background photoconductive material, to a water insoluble hydrophilic material.
• the fixed toner in the form of the image, is and remains oleophilic.
• the master will receive ink in the image area and reject it in the background. All of this in well known in the art.
• a master has the latent image formed thereon in the conventional manner. and toner applied in a conventional manner.
• a conversion solution is maintained at, or above, the temperature. required to fix the toner.
• the master is contacted by the solution for a sufficient period of time to simultaneously fix the toner and convert the background.
• any master. sheet having photoconductive material which can be converted to a water insoluble hydrophilic material can be utilized.
• potential materials include metal oxides and sulphides. Of these, zinc oxide is by far the most commonly used material and hence is preferred for this invention.
• the coated master is first given a uniform surface charge, and then selectively discharged by exposure to a pattern of light and shadow.
• the light struck area will discharge, leaving a charged area latent image thereon in the desired shape to be printed.
• Toner is then applied which will adhere to the charged latent image.
• toners There are various formulations of toners which can be utilized. Basically, all
• the temperature required to fix these toners varies, and is determined by their composition.
• the preferred toner is a mixture of natural and synthetic resins with suitable dyes, and carbon black. This toner must be heated to approximately C., or above, to obtain the required degree of fixing. When the toner is heated to or above this temperature, it will firmly adhere to the sheet, forming a relatively permanent image configuration thereon. This is sometimes referred to as fusing the toner, although it is doubtful that complete or even any appreciable melting is required to obtain satisfactory adherence to the sheet.
• This toner is oleophilic and will accept grease ink for printing.
• the master When the toner has been applied, the master is then brought into contact with a conversion solution heated to a temperature above the temperature required to fix the toner. Usually, with most conventional toners, the solution must be heated to at least 80 C. While there are many solutions or compounds which are suitable for converting the zinc oxide to a hydrophilic-oleophobic form, such as oxalates, citrates, and tartrates, the preferred solution of 10% mono-ammonium phosphate, with 5% glycerin, and 0.03% sorbic acid added thereto.
• the phosphate is the converting agent, the glycerin is a humectant and wetting agent, and the sorbic acid a mold inhibitor. This solution is quite stable at temperatures of 80 C. and above, and has a virtually indefinite shelf life.
• Other phosphates, such as monosodium phosphate are also well adapted for conversion purposes.
• the imaged and toned master is maintained in contact with the liquid solution at the elevated temperature a sufficient period of time to fix the image and convert the background to a water insoluble hydrophilic material.
• the fixing process is a time-temperature dependent relationship; the, higher the temperature, the less time required. to complete the fixing process.
• the upperlimit for the temperature is controlled only by the characteristics of the conversion solution and the material of the components of the master; i.e. the temperature cannot be too high to degrade or impair the conversion reac tion or to degrade any of the components of the master or solution. With aqueous solutions, the upper limit'is therefore,-about 100 C., the boiling point of water.
• temperatures of 81 to 84 C. are satisfactory, and adequate fixing is completed within about 0.3 second. Conversion is also completewithin this same time, andthe master is then ready for printing.
• the fixing of the toner and converting of the background is accomplished in a single step, rather than in two steps, therebyeliminating one processing step.
• the energy requirements to maintain the solution in the 81 to 84 C. range are substantially less than the energy requirement to operate the heat lamps or ovens in the prior art devices. Further, the elimination of the heat lamp or ovens eliminates potential fire hazards.
• phosphate conversion solutions are commercially practicable. These solutions are desirable since they are stable and have virtually indefinite shelf life. However, when phosphate solutions are used at ambient temperatures, i.e. about 20 C., the rate of the conversion reaction is so slow that they are not convenient in a machine copier. Hence, other converting agents, such as ferrocyanides have been used since they react rapidly enough at ambient temperatures. However, these agents are comparatively unstable, with a resulting short shelf life. Thus, by operating at temperatures of 80 C., and above, the rate of the conversion reaction of the phosphates with the zinc oxide is sufiiciently rapid to be commercial, thereby permitting their use and, hence, avoiding the undesirable characteristics of the ferrocyanide solutions.
• the improvement which comprises, providing a conversion liquid which will convert the non-imaged material at a temperature above that required to fix the toner, and contacting the surface having the unfixed toner thereon with said liquid at a temperature at least as high'as the temperature required to fix said toner and lower than that which would degrade any of the components of the master and liquid for a suflicient time to fix the toner and convert the non-imaged areas, whereby to simultaneously convert the background and fix the image.
• the liquid is an aqueous solution.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fixing For Electrophotography (AREA)
• Printing Plates And Materials Therefor (AREA)
• Printing Methods (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22320918

Family Applications (1)

Country Status (8)

Cited By (1)

• 1971
  • 1971-01-20 US US108214A patent/US3701673A/en not_active Expired - Lifetime
  • 1971-09-16 CA CA122,971A patent/CA941244A/en not_active Expired
  • 1971-09-24 IT IT29038/71A patent/IT951591B/it active
  • 1971-10-06 DE DE2149920A patent/DE2149920C3/de not_active Expired
  • 1971-10-25 FR FR7138272A patent/FR2122845A5/fr not_active Expired
  • 1971-10-29 BE BE774702A patent/BE774702A/xx unknown
  • 1971-12-21 JP JP46103327A patent/JPS5021883B1/ja active Pending
• 1972
  • 1972-01-19 GB GB265972A patent/GB1378721A/en not_active Expired

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