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
  • G03G13/06—Developing
  • G03G13/10—Developing using a liquid developer, e.g. liquid suspension
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers

Definitions

• the formation and development of images on the surface of photoconductor material by electrostatic means is well known.
• the basic xerographic process as taught by C. F. Carlson in U.S. Pat. No. 2,297,691 involves placing a uniform electrostatic charge on a photoconductive insulating layer exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer. exposed to the light and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic marking material referred to in the art as toner".
• the toner will normally be attracted to those areas of the layer which retain a charge thereby forming a toner image corresponding to the electrostatic latent image.
• the powder image may then be transferred to a support surface such as paper and permanently affixed to the support by any suitable means such as heat fixing or solvent fixing.
• the powder image may be fixed to the photoconductive layer if elimination of the powder transfer step is desired.
• the latent image instead of latent image formation by uniform charging followed by imagewise exposure, the latent image may be formed by directly charging the layer in image configuration.
• Other methods are known for applying electroscopic particles to the imaging surface. Ineluded within this group are the cascade development technique disclosed by E. N. Wise in U.S. Pat. No. 2,618,552; the powder cloud development technique disclosed by C. F. Carlson in U.S. Pat. No. 2,221,776; and the magnetic brush process disclosed for example, in U.S. Pat. No. 2,874,063.
• electrostatic latent image may also be achieved with liquid rather than dry developer materials.
• electrophoretic development an insulating liquid vehicle having finely divided solid material dispersed therein contacts the imaging surface in both charged and uncharged areas. Under the influence of the electric field associated with a charged image pattern, the suspended particles migrate toward the charged portions of the imaging surface separating out of the insulating liquid. This electrophoretic migration of charged particles results in the deposition of the charged particles on the imaging surface in image configuration.
• Electrophoretic development of an electrostatic latent image may, for example, be obtained by pouring the developer over the image bearing surface, by immersing the imaging surface in a pool of the developer or by presenting the liquid developer on a smooth surface roller and moving the roller against the imaging surface.
• the liquid development technique has been shown to provide developed images of excellent quality and to provide particular advantages over other development methods in offering ease in handling.
• the electrophotographic sheet prior to immersing the electrophotographic sheet in the liquid developer, the electrophotographic sheet may be prebathed or presoaked in a prebathing liquid which is retained on both sides of the sheet and in the fibrous construction of the base paper.
• the prebathing liquid is generally insulating, inert to the photoconductive material and miscible with the liquid developer in order to minimize any possibility of destruction of the imaging surface or contamination of the liquid developer.
• the prebathing liquid is typically very similar or identical to the carrier liquid employed in the liquid developer. Typically, these materials are nonpolar hydrocarbons and mineral oils.
• insulating, high-boiling liquids such as kerosene and Decalin have proved effective because they are less susceptible to loss due to vaporization within the copying machine and consequently provide reduced loss over a period of time and also provide little hazard due to fire.
• the prebathing liquid wets both the surface bearing the electrostatic latent image and simultaneously penetrates into the fibrous construction of the paper base through the opposite surface of the sheet. Since the openings in the fibrous construction of the paper are extremely small, the prebathing liquid which has penetrated into these openings cannot be very easily forced out. Thus, throughout the stage of development, the prebathing liquid, which is retained in the fibrous construction of the paper base intercepts the liquid developing agent and consequently prevents it from penetrating into the openings in the fiber and smearing the base of the sheet.
• the eleetrophotographic sheet is passed through a pair of squeezing rollers to remove any liquid developer that may adhere to the image bearing surface and the reverse surface of the sheet.
• this squeezing operation cannot remove the prebathing liquid which has been lodged deep within the fibrous construction of the paper. Consequently, the sheet thus obtained has a large volume of prebathing liquid penetrated inside the paper serving as the base for the electrophotographic sheet and therefore has a heavy, moist feeling.
• it is not desirable to have this sheet placed on top of another sheet because the prebath which has been retained within the sheet, gradually finds its way to the surface and wets the paper placed nearby or may dissolve the printing ink on the printed sheet of paper when placed adjacent to it.
• the prebathing liquid lodged deep within the construction of the paper base may be vaporized by means of a current of warm air.
• this drying operation involving the use of a current of warrn air, which must be of such a temperature as to have no adverse affect on the paper, becomes excessively time consuming.
• an electrostatographic imaging system of the liquid development type wherein prior to development of an electrostatic latent image present on electrophotographic sheet with a liquid developer having charged particles suspended in an insulating liquid at least the reverse or nonimage bearing surface of the electrophotographic sheet is contacted with a low-boiling, insulating liquid and subsequently, both surfaces of the electrophotographic sheet are brought into contact with a high-boiling insulating liquid.
• the present invention is based upon the principle that the electrophotographic sheet is first wetted with a low-boiling insulating liquid, hereinafter referred to as the first prebathing liquid, to allow it to penetrate sufiiciently into the paper serving as the base of the electrophotographic sheet, and the electrophotographic sheet is subsequently contacted with a high-boiling insulating liquid, hereinafter referred to as a second prebathing liquid to permit the formation of a film of the second prebathing liquid on the imaging surface. Thereafter, the electrophotographic sheet is immersed in the liquid developer to provide development of the electrostatic latent image.
• a low-boiling insulating liquid hereinafter referred to as the first prebathing liquid
• the second prebathing liquid cannot penetrate the paper. Furthermore, after application ofthe film of the second bathing liquid has been formed on the first prebathing liquid, the first prebathing liquid is prevented from mingling with the liquid developer and thus, deterioration by contamination of the liquid developer bath is prevented.
• the first prebathing liquid may be applied only to the opposite or nonimage bearing surface of the electrophotographic sheet instead of being applied to both surfaces.
• the electrophotographic sheet After treatment with the first prebathing liquid, the electrophotographic sheet may be subjected to the second prebathing treatment immediately.
• This practice is not desirable because the first prebathing liquid intermingles with the second prebathing liquid and eventually finds its way gradually into the liquid developer. No serious problem, however, is posed when the volume of the second prebathing liquid is so large that introduction of a relatively small volume of the first prebathing liquid would provide no noticable change in the composition. However, large differences in the relative volumes of the liquids are not normally encountered.
• the electrophotographic sheet subsequent to treatment of the electrophotographic sheet with a first prebathing liquid that the sheet be passed between insulating squeezing rollers to remove the portion of the first prebathing liquid which may adhere to the surfaces of the sheet. Thereafter, the electrophotographic sheet may be treated with the second prebathing liquid.
• the sheet after development of the electrostatic latent image present on the electrophotographic sheet with a liquid developer, the sheet may be passed through squeezing rollers to remove the residual liquid developer and may thereafter be easily dried because only the low-boiling liquid remains lodged inside the construction of the paper.
• partial replacement may occur between the first prebathing liquid lodged in the paper and the liquid developer.
• Any suitable cleaning liquid may be employed.
• the cleaning liquid may be one or more of the liquids used in the first prebathing treatment.
• the first prebathing liquid is selected to have such properties that it does not destroy the electrostatic latent image present on the electrophotographic layer, nor does it attack the structure of the electrophotographic sheet.
• these materials are selected from the group of nonpolar, highly insulating organic liquids having boiling points below about C.
• Typical specific materials useful as the first prebathing liquid include cyclohexane, n-hexane, n-heptane, isopentane, CCl FCCl F, CCl FCClF Any suitable liquid may be employed as the second prebathing liquid.
• the second prebathing liquids have boiling points in the range of from about to about 300 C., dielectric constants less than about 3.5, volume resistivities greater than 10 ohm-cm. and solubility parameters below 8.
• Typical specific materials include kerosene and lsopar H, an isoparaffinic hydrocarbon available from Humble Oil and Refining Company.
• Typical liquid developers contain electroscopic marking particles dispersed in an insulating liquid vehicle and may also contain control agents and suspending agents for their well-known functions.
• the liquid employed must have a relatively high insulating value, generally having a volume resistivity greater than about 10" ohm-cm. so as not to affect the electrostatic charge pattern on the insulating layer and low dielectric constants of less than about 3.5.
• Typical specific vehicles include hydrocarbons such as benzene, xylene, hexane, naptha, kerosene, halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene and chloroform.
• Typical electroscopic marking particles include among others, charcoal, carbon black, magnesium oxide, lithopone, cadmium yellow, chrome yellow, cobalt blue, cadmium red, burnt siena, Hansa yellow, rose bengal and phthalocyanine.
• the electroscopic marking particles are present in an amount of from about 4 to about grams per liter.
• the electroscopic marking particles are conventionally dispersed and suspended in the liquid by stirring or agitation and where a highly uniform and stable suspension is desired, the suspension may be passed through a colloid mill.
• the electrophotographic sheet may be treated with the first or second prebathing liquid at any suitable time. It may, for example, be treated sequentially immediately following formation of the electrostatic latent image. Alternatively, the electrophotographic sheet may be treated first with the first prebathing liquid and may even be treated with a second prebathing liquid prior to the formation of the electrostatic latent image.
• the prebathing liquid may be applied to the electrophotographic sheet in any suitable manner.
• the sheet may, for example, be immersed in the prebath or may be brought into contact with a sponge or felt impregnated with a prebathing liquid.
• the sheet may also be sprayed with the prebathing liquid.
• a particularly preferred means of applying the prebathing liquid is by means of a spongy roller impregnated with the liquid which is rolled across the electrophotographic sheet and transfers theliquid to the sheet on contact.
• EXAMPLE 1 An electrophotographic sheet is prepared by coating a sheet of art paper about 150 microns in thickness which is undercoated with a conductive material such as conductive polymer 261 (available from Calgon Corporation) with a mixture of photoconductive zinc oxide powder in an insulating resin which when dry has a thickness of about 7 microns.
• the electrophotographic sheet is charged negatively in the dark to a surface potential of about 200 volts.
• the charged sheet is exposed to light projected through an original to form an electrostatic latent image.
• the image bearing sheet is then immersed for about 5 seconds in lsopar E, a low-boiling, insulating, isoparaffinic hydrocarbon availablefrom Humble Oil and Refining Company and subsequently passes through a pair of squeezing rollers made of silicon rubber to remove the lsopar E adhering to both surfaces of the sheet.
• lsopar E a low-boiling, insulating, isoparaffinic hydrocarbon availablefrom Humble Oil and Refining Company
• the electrophotographic sheet is soaked for about 5 seconds in the second prebathing liquid or lsopar H, a high-boiling, insulating, iosparaffinic hydrocarbon also available from Humble Oil and Refining Company, removed from the bath, held up to allow the second prebath to trickle down and immersed in the liquid developer.
• the liquid developer is prepared by dispersing carbon black, ranging in particle size of from about 0.1 to about 1 micron in lsopar H with a small quantity of varnish dispersion stabilizer, also being present.
• the sheet is removed and passed through a pair of squeezing rollers to remove liquid developer adhering to both surfaces of the sheet.
• the squeezing roller which contacts the surface carrying the toner image is a hard, smooth metallic roller with a mirror finish surface and the squeezing roller that contacts the reverse soft surface is a soft, resilient rubber roller.
• Example ll The procedure of Example 1 is repeated except that immediately following development of the electrostatic latent image on the electrophotographic layer, both surfaces of the electrophotographic sheet are sprayed with a cleaning liquid of lsopar E to remove the liquid developer which has adhered to both surfaces.
• the electrophotographic sheet is then passed through the squeezing rollers to remove the cleaning liquid followed by drying. Complete drying is obtained in several tens of seconds when the sheet is allowed to stand at normal room temperature. When exposed to a current of warm air at 50 C., drying is obtained in less than about 10 seconds. Dry prints of similar quality to those obtained in Example I are produced.
• Example I in The procedure of Example I is repeated except that prior to formation of the electrostatic latent image on the electrophotographic sheet, the sheet is first contacted with a sponge roller which is impregnated with the first prebathing liquid, lsopar E. Thereafter, the formation of the electrostatic latent image, the second prebathing treatment and the remaining procedure of Example 1 are repeated. Prints of quality similar to those obtained in Example I are produced.
• an electrostatographic imaging method comprising forming an electrostatic latent image on an electrostatographic imaging member comprising an image layer capable of receiving an electrostatic latent image coated on a fibrous substrate, developing said electrostatic latent image by contacting said imaging layer with a liquid developer comprising marking particles dispersed in an insulating liquid and drying said imaging member, the improvement comprising prior to development of the electrostatic latent image, contacting at least the side of said imaging member opposite and imaging layer with a first prebathing liquid comprising an insulating nonpolar organic liquid having a boiling point no greater than about C. and subsequently, contacting both surfaces of said imaging member with a second prebathing liquid comprising an insulating organic liquid having a boiling point between about and 300 C.
• said imaging layer comprises photoconductive pigment particles substantially unifonnly dispersed in an insulating material.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Wet Developing In Electrophotography (AREA)
• Liquid Developers In Electrophotography (AREA)
• Cleaning In Electrography (AREA)

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Citations (2)

• 1969
  • 1969-09-19 JP JP44074406A patent/JPS4912429B1/ja active Pending
• 1970
  • 1970-09-08 US US70551A patent/US3642471A/en not_active Expired - Lifetime
  • 1970-09-18 CA CA093497A patent/CA936034A/en not_active Expired
  • 1970-09-18 DE DE19702046219 patent/DE2046219A1/de active Pending

Patent Citations (2)

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