US3697268A

US3697268A - Electrostatic printing method

Info

Publication number: US3697268A
Application number: US814547A
Authority: US
Inventors: Wasaburo Ohta
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1968-04-10
Filing date: 1969-04-09
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10
Also published as: DE1918303B2; US3795011A; GB1271561A; DE1918303A1; GB1271562A

Abstract

AN ELECTROSTATIC PRINTING METHOD AND DEVICE THEREFOR COMPRISING THE STEPS OF (1) FORMING AN ELECTROSTATIC LATENT IMAGE UPON A CONDUCTIVE PHOTORECEPTOR BY AN ELECTRONIC PHOTOGRAPHY, (2) DEVELOPING SAID IMAGE WITH AN ELECTRICALLY INSULATING AND WATER REPELLENT DEVELOPING AGENT AND FIXING THE DEVELOPED IMAGE IF NECESSARY, (3) RENDERING NON-IMAGE PORTIONS (THAT IS PORTIONS HAVING NO DEVELOPING AGENT ATTACHED THERETO) HYDROPHILIC WITH A HYDROPHILIC AGENT AFTER SAID FIXING, (4) RENDERING SAID HYDROPHILIC PORTIONS ELECTRICALLY CONDUCTIVE WITH A CONDUCTING AGENT, (5) ELECTRICALLY CHARGING THE ELECTROSTATIC PRINTING PLATE, THUS OBTAINED THEREBY BINDING THE CHARGE UPON THE ELECTRICALLY CHARGEABLE OR CHARGE RETAINABLE AND WATER REPELLENT IMAGE PORTION, (6) TRANSFERRING SAID CHARGE UPON AN ELECTRICALLY INSULATING BODY, THEREBY FORMING AN ELECTROSTATIC LATENT IMAGE, AND (7) DEVELOPING SAID ELECTROSTATIC LATENT IMAGE AND IF NECESSARY FIXING SAID IMAGE THUS DEVELOPED. REPRESENTATIVE FIGURES: FIGS. 6,7, AND 8.

Description

Oct. .10, 1972 WASABURO OHTA 3,597,253

ELECTROSTATIC PRINTING METHOD Filed April 9, 1969 3 Sheets-Sheet 1 FIG. 1

TNVENTOR WASABUQO OHTA ATTORNEYS Oct. 10, 1972 WASABURO OHTA 3,597,263

ELECTROSTATIC PRINTING METHOD Filed Anril 9, 1969 3 Sheets-Sheet 9 FIG. 10 a ai INVENTOR WASABURO OHTA ATTORNEYS Oct.-l0. 1972 WASABURO OHTA ELECTROSTATIC PRINTING METHOD 3 Sheets-Sheet 3 Filed April 9, 1969 FIG. 13

FIG. 14

INVENTOR WASABURO OHTA ji 6 iir ys United States Patent Ofiice 3,697,268 Patented Oct. 10, 1972 43/23 888 Int. Cl. G03g 5/04, 5/06, 5/08, 9/02, 13/06, 13/18 U.S. Cl. 96-1 R 2 Claims ABSTRACT OF THE DISCLOSURE An electrostatic printing method and device therefor comprising the steps of (1) forming an electrostatic latent image upon a conductive photoreceptor by an electronic photography, (2) developing said image with an electrically insulating and water repellent developing agent and fixing the developed image if necessary, (3) rendering non-image portions (that is the portions having no developing agent attached thereto) hydrophilic with a hydrophilic agent after said fixing, (4) rendering said hydrophilic portions electrically conductive with a conducting agent, (5) electrically charging the electrostatic printing plate, thus obtained thereby binding the charge upon the electrically chargeable or charge retainable and water repellent image portion, (6) transferring said charge upon an electrically insulating body, thereby forming an electrostatic latent image, and (7) developing said electrostatic latent image and if necessary fixing said image thus developed.

Representative figures: FIGS. 6, 7 and 8.

BACKGROUND OF THE INVENTION The present invention relates to an electrostatic printing method and device therefor and more particularly to an improved electrostatic printing method for providing a multiple number of prints or copies from one printing plate or original. The present invention relates more specifically to an electrostatic printing method comprising the steps of preparing an electrostatic printing plate by an electronic photographic method, rendering the nonimage portions of said printing plate electrically conductive thereby providing the difference in conductivity between the image portions and the non-image portions whereby a multiple number of prints or copies can be obtained from said printing plate.

The so-called electronic photography has been known, in which a photoreceptor having an insulating photoconductor formed upon a paper base or metallic plate base having a relatively lower electrical resistance is used. The photoreceptor is consisting of said electrically conductive paper base or metallic plate base upon which is formed by coating or vacuum evaporation coating a layer of an insulating photoconductor, which presents a high electric resistance in the dark but a low electric resistance, that is conductivity when lighted, such as an organic photoconductor represented typically by poly- N-vinylcarbazole, an inorganic photoconductor represented typically by selenium or a photoconductive layer consisting of photoconductor powder such as zinc oxide mixed with a special resin such as silicone resin. The photoreceptor of the type described above is electrically charged by the corona discharge of generally several kv./cm. or by pressing a pair of electrodes against the opposing surfaces of the photoreceptor and applying across said pair of electrodes a voltage higher than hundreds volts. An arbitrary light image is projected upon the photoreceptor imparted the charge, thereby dissipating the charge from the portions upon which are impinged the light image rays, whereby an electrostatic charge image (referred to as electrostatic latent image hereinafter) corresponding to said projected light image can be formed. Alternatively, the light image can be projected upon the photoreceptor without precharging, thereby forming an electrostatic latent image. In order to obtain visible images from these electrostatic latent images, charged powder developing agent or charged developing solution is used, in which solution charged particles or liquid are dispersed or suspended in a liquid having a high electrical resistance and a low dielectric constant sufficient to retain the charge imparted to the particles or liquid. If necessary, the developed image may be fixed upon the photoreceptor or transferred to a surface of a suitable image bearing plate.

The electronic photography of the type described above may be divided generally into Xerography and Electrofax. In Xerography, selenium is utilized as a photoconductive layer formed upon an electrically conductive backing metal. In practice, especially a single layer of amorphous selenium or selenium telluride or a lamination of said two layers are utilized as an insulating photoconductive layer. As a developing agent may be used dried and colored powder developing agent mixed with particles called carrier and electrically charged by rubbing electrification therebetween. The developing agent is attracted to and deposited upon said electrostatic latent image by the electrostatic force, thereby forming powder image, which may be further transferred to a copy paper in a high electric field, thus fixing the transferred image thereupon.

In Electrofax, a photoconductive layer is generally composed of a special zinc oxide powder in a synthetic resin which may be one of silicone resin, alkyd resin, vinyl resins, especially acrylic resins or mixtures thereof. A suitable solvent is used for dissolving a photoconductor such as zinc oxide into a resin and the mixture thus prepared is applied to a suitable base such as paper. The developing agent used in Electrofax is asimilar to that used in Xerography, that is dried and colored powder developing agent. The developing agent is applied to the photoreceptor, whereby forming a powder image corresponding to the electrostatic latent image. The powder image may be transferred to another copy paper or the like in a high electric field or in heating and fusing the powder before or after said powder image is fixed by a direct thermal fusion thereof or any other suitable manner, and further fixed by thermal fusion, if necessary. Another developing agent is such that charged particles or liquid particles are suspended or dispersed in a carrier liquid having a low dielectric constant and being electrically insulating. That is, the surface of the photoreceptor bearing thereupon an electrostatic latent image is made contact with such liquid developing agent, thereby developing the image and vaporizing the carrier liquid so as to fix the image. Alternatively, the developed image is electrostatically transferred to another copy paper.

The common defects in both of Xerography and Electrofax are that the above described steps of charging, exposure, development and if required transferring and fixing must be repeated for each copy when a multiple number of such copies are desired so that the long copying time will be required; that the photoreceptor comprising of an insulating photoconductor tends to be easily damaged and that the cost of the copy becomes expensive. Many attempts have been tried so far to eliminate such defects as described above. One attempt is to obtain a multiple number of prints from single copy obtained by an electronic photography. In this case, the copy obtained by this electronic photography is used as a printing plate for offset printing whereby multiple prints or copies are obtained by offset printing. In order to prepare a printing plate for offset printing from a copy obtained by an electronic photographic method, an image is transferred and fixed upon a paper base (that is an Offset printing plate) which has been previously rendered hydrophilic. If required, in order to render the non-image portion (corresponding to nonprinting portion) more hydrophilic, these portion is further processed so as to be rendered hydrophilic by use of a hydrophilic processing solution. Since the image portion is formed by the above described developing agent consisting of a pigment and a synthetic resin, only or fatty printing ink is readily retained by the image portion. On the other hand, the nonimage portions are rendered hydrophilic so that they readily retain tap Water used in offset printing. Therefore, offset printing can be made by use of a printing plate prepared in the manner as described above.

A printing plate for offset printing can be prepared by another electronic photographic method, that is Electrofax. This is a method for utilizing the copy obtained by Electrofax directly as a printing plate for offsetting printing. In this case, the image portion of the copy whether it is formed by a dry or wet type developing method is similar to that formed by Xerography generally consisting of a pigment or dye in a resin so that the image portion readily retains printing ink and is water repellent. Therefore, when the copy is further processed with a suitable hydrophilic processing agent or solution, the solution is repelled from the image portion and only the non-image portions are rendered hydrophilic so that the copy can be used as a printing plate for offset printing.

However, since the advent of printing, the printing efficiency is remarkably inferior when viscous printing ink is used not only in offset printing but also in other printing methods. Especially in case of offset printing, the viscosity of printing ink tends to vary remarkably due to the temperature variation so that highly refined techniques and skills are required in offset printing so as to adjust the printing pressure, impression pressure, the application of tap water, etc.

From the standpoint of the principle of offset printing, when the copies obtained by the above described electronic photographic methods are utilized as printing plates for offsetting printing, the copies must withstand the impression pressure and must be sufficiently wetted so that the copies must be sufliciently water-proofed. However, it is extremely difficult to improve a copy paper for electronic photography so as to be adapted to be used also as a printing plate for offset printing because of the requirements of the photoconductive layer of the copy paper for electronic photography. In other words, the copy paper can not satisfy both of the requirements as the copy paper for electronic photography and as the printing plate for offset printing at the same time. This is the major reason why an excellent photocopying machine can not be provided for this purpose.

The primary object of the present invention is therefore to provide an electrostatic printing method which can eliminate not only the above described detects which prevent from obtaining a multiple number of copies of prints by electrophotography and but also the defects encountered in offset printing and by which a multiple number of prints or copies can be obtained at higher speed and at an inexpensive cost.

It is therefore another object of the present invention to provide an improved method of the type described above for obtaining a multiple number of copies from a single original or printing plate.

A further object of the present invention is to provide a method of the type described by which a multiple of copies or prints can be obtained at a speed extremely higher than that of the conventional method from a single original or plate yet with expensive cost by a device simple in construction without the use of viscous printing ink.

The conventional method for attaining the similar ob- 4 jects of the present invention is generally comprisnig the steps of (a) forming an electrostatic latent image upon a photoconductive layer coated upon a base or backing material;

(b) developing said electrostatic latent image with an electrically insulating substance which can retain the charge even when the light rays are incident thereupon; and

(c) (l) imparting the charge to the whole surface of the printing plate thus obtained;

(2) exposing printing plate thus charged, thereby dissipating to the ground the charge upon the non-image portion;

(3) developing the remaining electrostatic charged imzlige with a toner mixed into an electrically insulating iquid.

(4) moving in an electric field the printing plate together with a copy sheet while the developed image is still wet, thereby transferring the image to the copy sheet;

((15) separating the copy sheet from the printing plate; an

(6) fixing the transferred image upon the copy sheet.

The most fundamental principle upon which the above described method depends is the steps of (c)-(1), (2) and (3).

However, this method has the following defects. Even though the method described above offers the advantage that the cop obtained may be directly used as a printing plate for offset printing, when the non-image portion is exposed, the photoconductor constituting the photosensitive layer has to reduce its resistance; the whole surface of the photoreceptor must be electrically charged by the corona discharge; and the above steps must be repeated many times. These steps are essential to the method described above. However, generally, when the photoconductor is once exposed, its electrical characteristics can not be restored immediately to its normal conditions. That is the fatigue phenomenon is observed due to the previous exposures. Once this phenomenon occurs, it will take a long time for the once exposed electronic-photographically sensitized layer to reach a predetermined charged potential by the next charging and exposure. Furthermore, as compared with the photoconductor layer which has been stored in a dark room for a long time, the degree of dissipation of the charge due to the light exposure is less. That is, when the sensitized layer is exposed, the charge is not dissipated immediately and in some cases it takes a few hours before the charge is dissipated completely to the ground. It is therefore obvious that it is not feasible to repeat the charging and exposure steps within a short time in order to obtain a multiple number of prints or copies, and that it is impossible to obtain a multiple number of prints or copies in a true sense of a multiple.

The present invention contemplates also eliminating the defects encountered in the conventional method of the type described above and is to provide an improved method based upon a novel technical concept and quite different from the invention which will be described hereinafter. This invention is such that by an electronic photographic method an image is formed upon a photoconductive layer coated upon a backing metal and the photoconductive layer except the image portion is removed, thereby exposing the metal surface. Furthermore, the exposed metal surface is rendered hydrophilic, thereby providing a plate for offset printing. By this conventional method, an electrostatic printing plate of the present invention could be prepared, but by the conventional method now in practice it is extremely difiicult to remove completely the unexposed photoconductive layer without damaging the metal surface. If the photoconductor remains or the binding material thereof is left, the non-image portion will not act as a uniform conductor so that the nonprinting portions of the print or copy will be contaminated, thereby making it difficult to obtain a better quality print.

SUMMARY OF THE INVENTION In brief, the present invention relates to an electrostatic printing method and device therefor comprising the steps of (l) forming an electrostatic image upon a conductive photoreceptor by an electronic photography,

(2) developing said image with an electrically insulating and waterrepellent developing agent and fixing the developed image if necessary,

(3) rendering the non-image portion, that is the portion to which has not attached the developing agent after developing and fixing, hydrophilic with a hydrophilic agent,

(4) rendering further electrically conductive said nonimage portion which has been rendered hydrophilic in steps (3),

electrically charging the electrostatic printing plate thus obtained, thereby binding the charge upon the charge retainable and waterrepellent image portion,

(6) transferring thus bound charge to an electrically insulating body, thereby forming another electrostatic latent image, and

(7) developing said another electrostatic latent image and if necessary fixing said image thus developed.

According to the present invention, both of the socalled dry and wet type developing steps may be utilized in developing the electrostatic latent image transferred from the printing plate.

According to the present invention, in order to obtain a multiple number of prints from the electrostatic printing plate of the present invention prepared as described above, the following alternative steps may be utilized. That is, the steps (6) and (7) above are modified as follows:

(6) developing the printing plate binding thereupon said charge; and

(7') transferring the image thus developed to a transferred image bearing plate or base and if necessary fixing the image thus transferred upon said plate or base.

In this case, the better results will be attained by interposing a transferring solution between said printing plate and said base.

The above and other objects, features and advantages of the present invention will become more clear from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 illustrates the formation of an electrostatic latent image upon a recording base comprising a plate having a relatively low electrical resistance and an electrically insulating photoconductive layer formed thereupon;

FIG. 2 illustrates the state in which the electrostatic latent image shown in FIG. 1 is developed by a developing agent, thereby forming an image corresponding to the electrostatic latent image;

FIG. 3 illustrates the state in which the portions or areas having no developing agent affixed thereto have been rendered hydrophilic;

FIG. 4 illustrates the state in which the portions or areas having been rendered hydrophillic (portions or areas having no developing agent affixed thereto) have been rendered electrically conductive by an aqueous electrically conductive agent;

FIG. 5 is an explanatory view of the charge applied to the areas having the developing agent aifixed thereto and being electrically insulating;

FIG. 6 is an explanatory view of transferring the charge applied to said image areas to a base to which is transferred the image;

FIG. 7 illustrates the formation of a secondary electrostatic latent image upon said copy base;

FIG. 8 illustrates the state in which said secondary electrostatic latent image has been developed;

QTI

FIG. 9 illustrates the state in which the charge image obtained by the step of FIG. 5 has been developed, thereby forming an image to be transferred;

FIG. 10 is an explanatory view of means for use in transferring said image to be transferred shown in FIG. 9 to a copy base;

FIG. 11 is an explanatory view of another image transferring means;

FIG. 12 is an explanatory view of still another image transferring means;

FIG. 13 is a schematic view illustrating one embodiment of an electrostatic printing device according to the present invention;

FIG. 14 is a sectional view illustrating a wet type developing device; and

FIG. 15 is schematic view illustrating another embodiment of an electrostatic printing device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, upon an insulating photoconductive layer 2 formed a support or base 1 having a relatively low electrical resistance is formed an electrostatic image by the electronic photographic method described hereinabove. In this case, the electrostatic latent image 3 is shown as consisting of negative charge but it will be obvious that the electrostatic latent image 3 consisting of positive charge may be formed in view of the principal of the electronic photography. Electrostatic latent image 3 thus formed is developed by either dry or wet developing process, thereby forming a (visible) image 4 as shown in FIG. 2. In this case, a developing agent used must be electrically charged and water repellent at least for some time after development. In case of the dry process, developing agents are colored or not colored natural or synthetic resin powder or inorganic resin capable of being electrically charged upon mixing into and being rubbed with finely divided glass or iron powder. For example, they are finely divided thermoplastic phenol resin, ethylcellulose, acrylic resin, ebonite, shellac, cellulose acetate, polystyrene, polyethylene, fluorine-contained resins, cellulose, nitrate, selenium, sulphur and mixtures of one or more than one of said compounds with organic or inorganic pigments or dyes. In addition to the above compounds, may be used any compound which can be electrically charged and which is water repellent after development.

In case of the wet process, particle type or fluid type developing agents may be utilized which are composed of one or more than one compounds selected from the group of consisting polyethylene, silicone resin, vinyl resins, acrylic resins, alkyd resins, rubber denatured polystyrenes, polystylens, ethyl cellulose, hydroxyethyl cellulose, chlorinated rubbers, rubber latex, bitumen (asphalt), damma rubber, rosin, bees wax, natural rubbers, mixed with varnish, oil, polarity control agents, one or more than one pigments and dyes or mixed, fused or combined with organic or inorganic pigments or dyes and metallic powder. The above developing agents are electrically charged when passing through an nozzle applied with a voltage higher than hundreds volts and then dispersed and suspended in an electrically insulating liquid such a hydrocarbons, hydrogenated hydrocarbons, halogenated hydrocarbons or the like having a dielectric constant less than 3 and a resistivity higher than 10 ohm-cm. Other compounds may be used as wet-type process developing agents as far as they can be suspended in the above described insulating liquid while maintaining the water repellency and a property of being electrically charged after the image has been developed.

By use of one of the above described developing agents, the image 4 (which may be invisible) having water repellency and capable of being electrically charged is formed as shown in FIG. 2. Thereafter, the non-image portions as shown in FIG. 3 by 5 (the portions to which have not afiixed the developing agent) is rendered hydrophilic by a suitable processing solution depending upon the layers, upon which are formed electrostatic latent images, such as organic semiconductor photosensitive layer, the layers further including a photoconductor inorganic photoconductor.

Next the copy having water repellent image portions and hydrophilic non-image portions is processed by a processing method as will be described in more detail hereinafter so that the non-image portion shown in FIG. 4, that is hydrophilic portions shown in FIG. 3 are rendered electrically conductive as shown by 6. The processing solution used in this step is composed of aqueous or hydrophilic solvent such as alcohols and an electrically conductive substance mixed and suspended in said solvent. The conductive substance must be absorbed or retained to the hydrophilic portions thereby preferably forming a thin film thereupon having a electric resistance less than of the surface resistance of the image forming compound and a surface resistivity less than 10 ohm, preferably less than 10 ohm. They are, for example, conductive substance of QX-261l series manufactured by Dow Chemical Co., U.S.A., conductive polymer 261 manufactured by Calgon Co., U.S.A., high molecular compounds including at least vinylpyridine, antistatic agents having at least hydrophilic groups, anionic, cationic and nonionic surface active agents available in the market, organic and inorganic salts and mixture thereof with surface active agents, acrylic resin emulsion, synthetic rubber latex emulsion, soidum acrylate, polyvinyl alcohols, etc. It is obvious that other compounds may be used in addition to the above described compounds as far as they can satisfy the requirements described above. The above aqueous or hydrophilic conducting solution is applied to the copy having hydrophilic non-image portions and water repllent image portions, thereby selectively retaining said solution only to the hydrophilic portions, whereby the conductive non-image portions designated by 6 in FIG. 4 can be obtained.

The present invention is characterized by obtaining from the copy having the electrically charged image portions and conductive non-image portions formed by the above described steps an electrostatic printing plate from which a multitude of copies can be obtained. The plate is electrically charged as shown in FIG. 5 by a corona discharge or contact electrode methods as described hereinabove. In this case, since the image portions 4 are formed from the above described highly resistant, charge retainable compound, the charge 7 is trapped thereupon. On the other hand, since the non'image portions are formed from the conductive compound 6, no charge can be bound thereupon. That is, only the image portions 4 bind the charge. In this case, the charge trapped is shown as being negative, but it is obvious that the positive charge may be bound thereupon.

The above described steps may be summarized as follows:

(1) a step for forming an electrostatic latent image upon the conductive photoreceptor by an electronic photography .(FIG. 1);

(2) a step of developing said image by an insulating and water repellent developing agent and if desired fixing it (FIG. 2);

(3) a step of rendering the non-image portions hydrophilic, that is the portion to which are not affixed the developing agent (FIG. 3);

(4) a step of rendering conductive the hydrophilic portions by a conducting agent .(FIG. 4); and

(5) a step of electrically charging the electrostatic printing plate thus obtained thereby trapping charge upon the electrically chargeable water repellent image portions (FIG. 5).

Through the above steps, the printing plate for electrostatic printing according to the present invention can be provided. In the course of provision of such plate, an electronic photographic process is utilized, but it is not necessary in some cases that the printing plate itself is an electronic photoreceptor. That is, the printing plate is a direct contact master made of a specially treated paper for use in offset printing. In some cases, the surface of a direct contact master for oifset printing has been previously treated so as to be hydrophilic, but generally, the surface is not hydrophilic. The copy prepared by the above described Xerography or Electrofax proces and having an image formed by a developing agent, is superposed upon the master in direct contact relation therebetween, and is electrically charged by a corona discharge of kv./cm. or by contact electrodes across which is applied several a voltage higher than hundreds volts, thereby transferring the image to be copied directly upon the surface of the master. If necessary, the master is further heated and fixed. Thereafter when the master thus provided undergoes the above described hydrophilic and conducting treatments of the present invention, the electrostatic printing plate according to the present invention will be provided as will be described in more detail in examples hereinafter. In this case, the steps from (3) to (5) of the steps from (1) to (5) described above, remains unchanged but the steps (1) and .(2) are modified as follows:

(l) a step of providing a copy by use of an electrically insulating and water repellent developing agent after formation of an image according to an electronic photographic method; and

(2) a step of transferring under the action of electric field said copy image to a paper sheet having one surface thereof rendered hydrophilic or not.

Next the method for obtaining a multiple number of copies from a printing plate prepared by the process described hereinabove will be described in detail. The electrostatic printing plate having charge 7 trapped upon the image portions thereof as shown in FIG. 5 is placed in contact with or in closely spaced-apart relation with a transferred copy bearing support 8 such as paper, plastic sheet, cloth and so on in the electric field or is passed through the field in the above described state. This field of about several kv./cm. may be created by a corona discharge device having a pair of corona discharge electrodes 9 and an earth plate 10 as shown in FIG. 6 so that the charge 7 is transferred to the copy bearing support 8. Besides the single corona discharge method as shown in FIG. 6, the so-called double corona discharge method, the contact electrode method of a voltage higher than hundreds volts and so on may be used. It is not necessary to produce a complete electrostatic field only in the direction for moving the charge 7 toward the copy bearing support 8 if the charge 7 is finally transferred to the bearing support 8. Thus, the transferred copy bearing support 8 trapping the charge 7 thereupon is obtained as shown in FIG. 7. Next the copy bearing support 8 is developed by either of the dry or wet process described hereinabove. thereby obtaining a print having a visible image 11 formed thereupon as shown in FIG. 8. In this development, the above described developing agents may be used, but it is not necessary that the developing agents are electrically chargeable and water repellent after formation of the image.

Another method for transferring the charge 7 shown in FIG. 5 is based upon the principle of contact charging or electrification, in which the charge is induced upon the surface of a dielectric by contacting this dielectric with the charged body. In this case when an electrode is attached to the surface of the dielectric opposed to the contact surface with the charged body, an electric field is produced between the electrode and the charged body and if the direction of this field is the direction for causing the movement of the charge of the charged body toward the dielectric, then the charge of the charged body is transferred toward the dielectric. In this case, it is not necesary to apply a voltage to the electrode. The electrode may be grounded. A support 8 shown in FIG. 12, which is adapted to be charged or electrified when contacted with the original or plate, may be a sheet made of polyethylene, polyacetate, cellulose acetate, vinyl resins, etc. or a sheet impregnated with one of the above compounds, a sheet having a layer made thereof, etc. The support 8 is interposed between a pair of

pressure members

13 and 14 in order to ensure the close contact of the support 8 with the plate, thereby transferring the charge thereto. In this case, the pair of

pressure members

13 and 14 are preferably made of metal and more preferably grounded. In FIG. 12, the

pressure members

13 and 14 are shown as being in the form of a pair of rollers which serve also as a pair of feed rollers, but it is obvious that the pair of

pressure members

13 and 14 need not be of the roller form for charge transferring purpose.

The support 8 which has now the transferred charge bound thereupon is developed by either of the above described dry or wet developing process of an electronic photography, whereby a print having a visible image can be obtained as shown in FIG. 8.

In order to obtain a multiple number of same prints through the above described steps, the step of electrically charging the printing plate so as to bind the charge upon the image portions (FIG. the steps of transferring the charge to a support (printing paper) as shown in FIGS. 6 and 12 and the step of developing the printing paper or support may be repeated as many times as desired. An embodiment of a device for obtaining a multiple number of prints in a short time by the repetition of the above described steps will be described hereinafter with reference to FIG. 13.

In FIG. 13, upon the peripheral surface of a rotatable drum 28 is set by means of for example a clamp 36 an electrostatic printing plate of the present invention having a support 1 having relatively low electric resistance, a photoconductive layer 2 formed thereupon, water repellen image portions 4 and electrically conductive non-image portions 6. This drum 28 may serve as one of the pair of corona discharge electrodes in FIG. 6 and as the opposing electrode of a corona discharge section (H.V. stands for High Voltage) for imparting the charge 7 to the image portions 4. The drum 28 is driven through a transmission device from a prime mover (not shown).

From a paper feed section 37 in which a multiple of printing papers are stocked are picked up printing paper sheets one by one by a roller 16 and fed toward a pair of

feed rollers

17 and 18 from which the paper sheet is directed toward the lower side of the drum 28. The paper sheet 8 is made in contact with the electrostatic printing plate having the charge 7 by means of a roller 19 and advanced together with the rotation of the drum 28 so as to pass through the corona discharge section 9. In the corona discharge section 9. In the corona discharge section 9, the charge 7 is transferred to the paper sheet 8 and the paper sheet 8 is separated from the drum 28 by a separation roller 20. In order to ensure the smooth separation of the paper sheet 8 from the drum 28, the separation roller 20 may be comprised of a pipe having perforations through which can pass the air having a negative pressure produced by a pump. In this case, the simultaneous use of a transportation a pump. In this case, the simultaneous use of a transportation belt 38 will further facilitate the separation.

Thereafter, the paper sheet 8 is advanced toward the magnet brush developing section 23 by a pair of

feed rollers

21 and 22 is developed by dry type magnet brush process developing agent 24, thereby forming an image 11. In this case, the magnet brush process developing agent 24 may be a mixture of magnetic substance powder with one of the above described developing agents. Thereafter, the paper sheet 8 is advanced into a heating and fixing section 25 where the developing agent is heated and fused upon the paper sheet 8 and therefrom the paper sheet 8 is discharged through a pair of

rollers

26 and 27 whereby a print may be obtained.

Alternatively in the developing section may be used a conventional wet type developing device as shown in FIG. 14. In this case, a pair of

rollers

29 and 30 serve instead of the

feed rollers

21 and 22 shown in FIG. 13 and the paper sheet 8 is fed into the developing agent container 32 and is developed when passing through the developing solution 31 under a guide plate 33. The developed paper sheet 8 is discharged and squeezed by a pair of discharge rollers 34 and 3S and is obtained in almost dried state. If necessary, the developed paper sheet 8 may be further heated and dried in a heating and fixing section.

Next another method of obtaining a multiple number of prints from an electrostatic printing late prepared according to the present invention will be described hereinafter. The electrostatic printing plate having the charge 7 bound upon the image portion 4 as shown in FIG. 5 is developed by either dry or wet type developing process so that the developing agent is attracted by the charge upon the image portions 4 shown in FIG. 5 and the new developed image 11. In the electric field the electrostatic printing plate thus prepared is set in contact with or in closely spaced apart relation with a transferred copy bearing support 8 such as the papers of the type described above, plastic sheets, cloth and so on so that the image 11 is transferred to the copy bearing support, whereby the prints may be obtained as shown in FIG. 8. Thereafter, the prints may be fixed by heating if required. In this case, when the image 11 is formed by the wet type developing process, the better effect can be attained by interposing a transferring solution 12 between the electrostatic printing plate and a copy bearing support or paper sheet 8 as shown in FIG. 11. The transferring solution 12 is saturated or unsaturated hydrocarbons, hydrogenated hydrocarbons, halogenated hydrocarbons or mixture thereof and must have an electric resistivity higher than 10" ohm-cm. and a dielectric constant less than 5. The electrostatic printing plate and the paper sheet 8 with the transferring solution being interposed therebetween is placed in the electric field or passed through the field so that the image is transferred, whereby the print as shown in FIG. 8 can be obtained.

Another advantage obtained by the use of such transferring solution is that the image transfer or impression may be elfected not only at the time when the developed image is still wet but also as the time when the developed image has been once dried. That is, the transferring solution according to the present invention is characterized by the fact that it is prepared so as to swell or dissolve the wet type developing agent after drying and fixing.

The method for transferring the image by use of a transferring solution has been used generally only in case where the image 11 is formed or developed by the wet type developing process. However, according to the present invention, When the mixture of saturated or unsaturated hydrocarbons, hydrogenated hydrocarbons and halogenated hydrocarbons is used as transferring solution (see FIG. 11), it becomes possible to transfer the image formed or developed by the dry type developing process. That is, the synthetic or natural resin surface which is one composition of the dry type developing agent of the type described hereinabove is dissolved or swelled by the transferring solution so that the electrophoresis is caused by the transferring electric field. Furthermore, when this transferring solution is used, the image 11 of FIG. 8 which is the image after transfer, is fixed to the paper sheet 8 as the transferring solution is dried. Consequently, the fixing step by heating or other method can be advantageously eliminated.

In either method for transferring the image 11 shown in FIG. 10 or the method for transferring the image 11 by use of the transferring solution 12 shown in FIG. 11, a multiple of prints may be obtained by repeating the steps of electrically charging the image portions of an electrostatic printing plate, of developing with a developing 1 1 agent, of transferring the image thus developed to a transferred copy or impression bearing support in the electric field and, if required, fixing.

Next an embodiment of a device adapted to accomplish the above described steps will be described hereinafter with reference to FIG. 15.

Around the peripheral surface of the drum 28 is attached by means of for example a clamp 36 an electrostatic printing plate having electrically chargeable or charge retaining water repellent image portions and electrically conductive non-image portions 6 both of which are formed upon the photoconductive layer 2 formed upon the support 1 having a relatively low electric resistance. The rotating drum 28 serves as an opposing electrode 10 of the corona discharge section shown in FIG, 10 and as an opposing electrode of a contact electrode 42 for use in the above described contact electrode transferring method for transferring the developing agent image 11 to the paper sheet 8. In the corona discharge section 15, the charge 7 is imparted upon the image portions 4 and the rolled paper sheet 8 is advanced by a pair of feed rolls 17 and 18 in synchronism with the rotation of the drum 28 which is rotated by a prime mover through a transmission device not shown and is cut into a predetermined length by a cutter 43. The cut-off paper sheet 8 is advanced toward the lower side of the drum 28 and is closely contacted by a rotary roller 19 with the electrostatic printnig plate having the developing agent image 11. Thereafter the paper sheet 8 is advanced together with the drum 28 so that the image 11 is transferred to the paper sheet 8 when it passes through the contact electrode 42 which is used for image or impression transfer. Thereafter, the paper sheet 8 is separated from the rotary drum 28 by a separating roller 20 and is advanced into the heating and fixing section 25 so that the image 11 is fused upon the paper sheet 8 and the paper sheet 8 is discharged by a pair of

discharge rollers

26 and 27, whereby the print can be obtained.

Next the advantages of the present invention will be briefiy described. As compared with the conventional electrostatic printing plate in which the portions of the photoconductive layer bearing no image are illuminated by the light rays as they are so as to converting them into electrically conductive state, the conductive portions 6 shown in FIG. 4 are electrically conductive and are not made of a photoconductor whose light sensitivity is remarkably subject to secular variation so that the state shown in FIG. 4 can be maintained for a long time. Therefore, it is not necessary to carry out the steps following that shown in FIG. immediately after the step shown in FIG. 4. That is several printing plates are sequentially processed up to the steps of FIG. 1 and thereafter they can be processed simultaneously in the following steps.

Secondly, as compared with the conventional electrostatic printing plate in which the photoconductor layer is used as it is, the electrostatic printing plate according to the present invention presents no variation in printing effect due to deterioration of the photoconductor photosensitive layer so that staining of non-image portions of prints can be reduced to the minimum after a multiple number of prints are made in a long use of the plate. That is a multiple number of sharp prints can be obtained.

Thirdly, as compared with the olfset printing in which the printing plate tends to be damaged by tap water applied in the course of printing and to be damaged by the mechanical forces applied thereto such as the impression transferring force, the electrostatic printing plate of the present invention is completely free from such defects. Therefore, as compared with the method for preparing a printing plate for offset printing which is directly prepared from the copy obtained by an electronic photography, the electrostatic printing plate of the present invention affords to print sharp prints far larger in number.

Fourthly, as compared with the electronic photography,

especially with Electrofax process in which the photoconductive layers of the copies are made of very expensive photoconductor, the ordinary papers may be used as copy or printing papers so that the cost per copy or print can be made remarkably inexpensive.

Fifthly, in the conventional electronic photography, especially in Xerography process, each copy must be processed in all of the steps of electrically charging, exposure, development, transfer and fixing so that the copying speed is limited by the sensitivity of the photoconductive layer of the copy paper. However, in the method of the present invention, the repetitive steps can be reduced to the steps of electrically charging, transfer and development (or development and transfer) and if necessary fixing so that the printing speed will not be restricted by the sensitivity of the photoreceptor, whereby the high-speed copying or printing is feasible.

Next some examples of the present invention will be described hereinafter, but it will be understood that the present invention is not limited thereto because as described above various materials may be used in various combinations.

EXAMPLE 1 The following materials were previously prepared:

(1) Remington Offset Master B4, product of Kabushiki Kaisha Ricoh.

(2) Ricoh Offset Fixing agent, type T.

(3) Ricoh Electronic Printer Paper.

(4) Ricoh Fax Developing agent.

(5) QX2611.7 (conducting agent), product of Dow Chemical Co., U.S.A.

The copy of the document was obtained on a Ricoh Electronic Printer Paper by the Ricoh Electronic Printer S-l, an electronic photographic copying machine incorporating therein a dry type developing section. Ricoh Fax Developing agent, dry type developing agent, was used. Without being heated and fixed, the copy was superposed on a Ricoh Offset Master B4 and was moved through the electric field produced by the corona discharge by applying 6 kv. to tungsten wires, thereby transferring the mage of the copy to the Master B4 whereby the negative image was obtained. Next the negative image was heated and fixed by the fuser attached to the above mentioned copying machine. The whole surface of the master thus prepared was applied with Ricoh Offset Fixing agent, Type T impregnated in absorbent cotton so that the non-image portions were rendered hydrophilic. The conducting agent, QX-261l.7, product of Dow Chemical Co., USA. was diluted with water about 10 times that of the agent and then applied to the whole surface of the master which has been half-dried so that the non-image portions were rendered conductive. The surface resistance was 2X 10'' at a temperature of 20 C. and a humidity of 65%. Thereafter, without turning on the light source lamp of the Ricoh Electronic Printer, the master was applied with the corona discharge and developed so that new developing agent was attached to the fixed image. A better quality paper sheet was superposed upon this master and moved through the electric field produced by the corona discharge of 6 kv. and the paper sheet was separated from the master. A sharp positive image was obtained and then heated and fixed by the fuser for Ricoh electronic printer, thereby obtaining the copy having the fixed image.

By using the same master, the transfer of the image was repeated many times through the corona discharge and development described above, thus obtaining a multiple number of same copies (or prints).

EXAMPLE 2 The same copy as Example 1 was obtained by the Ricoh Electronic Printer S-l upon Ricoh electronic printer paper in which the mixture of zinc oxide with a resin is applied upon the surface of a sheet of paper which was used in Example 1.

The whole surface of the copy was applied with Ricoh Fax H solution, so that the non-image portions were rendered hydrophilic. An aqueous solution of Conductive Polymer 261, product of Calgon Co., U.S.A. was applied to the copy (master) so that the non-image portions were rendered conductive. The surface resistance was about 7X10 ohms at a temperature of 20 C. and at a humidity of 65%. In the similar manner as described in Example 1, the master was electrically charged and developed and a good quality paper was superposed upon this master and applied with the corona discharge, thereby obtaining a better copy.

EXAMPLE 3 The photoconductive layer had the following composimixture was applied to one surface of a sheet of art paper whose the other surface was applied with aqueous solution of QX26-ll, Dow Chemical Co. diluted in water 10 times that of QX-26l1. The art paper was dried for ten minutes in the air at about 100 C. and left for twentyfour hours in the dark room at 20 C. and at 60% RH.

The photoconductive sensitized paper thus prepared was electrically charged by corona discharge of -6.5 kv. and the charged surface was projected by a photographic enlarger so as to provide a negative image. Non-image portions were exposed for one second with light rays of approx. 200 lux and then developed by use of the following developing agent.

Developing solution A Carbon black (Elftex-S, product of Caphot Co.,

U.S.A.) gr l Alkyd resin (Super Beckosol 1352, product of Del Nippon Ink KK., Japan) gr l0- Mineral turpentine cc 30 They were mixed in a ball mill for 20 hours and an amount of gr. of paste toner thus obtained was dispersed into 1 l. of saturated hydrocarbon (Isobar H, product of Esso Standard Oil Co.)

Developing solution B Parts by weight Hydrogenated resin 2 Polymerized linseed oil 8 They were mixed and heated for 30 minutes at about 150 C. After cooling, about 40 gr. of this mixture was taken and mixed with gr. of carbon black (of the type described above) in a ball mill for 20 hours, thereby obtainin the paste-like toner. An amount of 5 gr. of this toner was dispersed into 1 l. of n-heptane, an aliphatic hydrocarbon.

With both of the above developing solutions, the solutions were filled into metallic developing trays and the copies were immersed therein and therafter dried.

The copy or printing plate thus obtained had its whole surface thereof wetted by the hydrophilic agent having the following composition:

Sodium ferrocyanide (Na,,Fe(CN )-10H,0 gr 45 Ammonium phosphate (NH HPO gr 90 Oxalic acid (COOH) -2H O cc 5 Ethylene glycol (CHgOH)g cc 20 Ammonium chromate (NHJCrO; cc 10 They were added in water, thus preparing 1 l. of aqueous solution. The non-image portions were rendered by the above hydrophilic agent and the whole surface of the printing plate was applied with 10% aqueous solution of sodium polyacrylate. The surface resistance of the nonimage portion was 2x10 ohms at a temperature of 20 C. and at a relative humidity of 65%.

Next the printing plate was electrically charged by the corona discharge of -6 kv. and developed by being immersed in the developing solution A. After the printing plate had been dried, a good quality paper having a weight of 60 gr./m. was superposed upon the printing plate and immersed into the transferring solution having the following composition:

Parts by volume Halogenated hydrocarbon (CCIgF-CClgF) 50 Naphtha (specific gravity: 0.79 and aniline point: 45) 50 The paper superposed upon the printing plate was passed through a pair of rollers, one being applied with 2 kv. while the other, ground in such a manner the back surface of the paper was in contact with the roller applied with 2 kv. Thereafter, the paper was separated from the printing plate, thus obtaining a sharp copy or print.

EXAMPLE 4 The photoconductive sensitized layer was provided electrically charged and exposed in the similar manner as described in Example 3.

The magnetic brush developing method was utilized with the dry type developing agent having the following composition and being mixed with magnetic iron powder having a particle size from 200 to 300 mesh and after development the image was heated and fixed.

The composition of the dry type developing agent was consisting of Gr. Carbon black (of the type described) l0 Polystyrene 70 Methyl methacrylate 20 and they were added into toluene, providing 1 l. of solution. The solution was ejected at a rate of about 20 cc./ min. The particle size of the toner thus obtained was almost about 3 1 through an observation of electronic microscope.

Thereafter, the copy was processed by the hydrophilic agent similar to that used in Example 3 so that the nonimage portions were rendered hydrophilic. Next, the whole surface was applied with 10% aqueous solution of conductive polymer 261, product of Cargon Co., U.S.A. so that the non-image portions were rendered conductive. The surface resistance was 7x10 ohms at a temperature of 20 C. and at a humidity of 65%.

The printing plate thus obtained was electrically charged by the corona discharge of 6 kv. A sheet of good quality paper was superposed upon the printing plate and electrically charged with the corona charge of +6 kv. After separation of the paper, it was developed with the dry type developing agent of the type described above, so that the sharp image was obtained. The copy or print was further heated and fixed.

EXAMPLE 5 The photoconductive sensitized paper was prepared electrically charged, exposed and developed in the similar manner as described in Example 3. In this case, the development was made with the use of the developing solution B described above and the non-image portions were rendered hydrophilic and electrically conductive. That is, the electrostatic printing plate similar to that obtained in Example 3 was prepared.

The whole surface of the printing plate was electrically charged by the corona discharge of 6 kv. and thereafter a good quality paper sheet was superposed thereupon. The

superposed paper and printing plate were made to pass through a pair of rollers shown in FIG. 3 in such a manner that the paper sheet was made in contact with the roller to which was applied +2 kv. After separation, the paper sheet was developed by use of the wet type developing solution A described in Example 3, thereby obtaining the copy of print.

Both of the devices shown in FIGS. 13 and 15 are such that a printing plate previously prepared is set around the peripheral surface of the rotating drum. It is however possible according one aspect of the present invention that a printing plate may be attached to the rotary drum before the plate is prepared and may be prepared while being retained by the drum and then used continuously for printing or copying without removing the plate from the drum. In this case, the hydrophilic agent and conducting agent used in preparing this printing plate must be removed after the plate has been completely prepared.

Furthermore, it is also possible to mix the hydrophilic agent of the type described in Example 3 with the electrically conducting agent described in Example 1 into a single processing solution, so that the printing plate may be selectively rendered conductive through one step of operation.

The present invention has been so far described with particular embodiments and examples thereof, but it will be understood that variations and modifications can be effected without departing the true spirit of the present invention as described hereinabove and as defined in the appended claims.

I claim:

1. An electrostatic printing method comprising the steps of (a) forming an electrostatic latent image upon a photoconcluctive layer comprising zinc oxide (b) developing said electrostatic latent image with a developing agent selected from the group consisting of a finely divided thermoplastic phenol resin, ethy cellulose, an acrylic resin, ebonite, shellac, cellulose acetate polystyrene, polyethylene, a flourine-containing resin, cellulose nitrate, selenium, sulfur, a silicone resin, an alkyd resin, a rubber denatured polystyrene, hydroxyethylcellulose, a chlorinated rubber, rubber latex, asphalt, damma rubber, rosin, bees wax, natural rubbers, or mixtures thereof (c) rendering the non-image portion hydrophilic by treating said photoconductive layer with a hydrophilic processing solution, (d) rendering said non-image portion electrically conductive by treating the photoconductive layer with a solution comprising an electrically conductive substance which is capable of forming a thin film upon said photoconductive layer, (e) electrically charging the resulting photo-conductive layer and (f) transferring the electrostatic latent image obtained to a insulative print support and developing said support to obtain the desired print.

2. A method according to claim 1 wherein said developing agent is dispersed in an electrically insulating liquid selected from the group consisting of a hydrocarbon, a hydrogenated hydrocarbon, a halogenated hydrocarbon, said insulating liquid having a dielectric constant of less than 3 and a resistivity higher than 10 ohm.

References Cited UNITED STATES PATENTS 2,637,651 5/1953 Copley 96-1.4 3,005,726 10/1961 Olson 117-37 L X 3,106,157 10/1963 Rcithel 101-1492 3,147,679 9/1964 Schaffer -1.! 3,196,013 7/1965 Walkup 117-376 X 3,417,819 12/1968 Beyes 254-621 3,451,336 6/1969 Mignone 101-450 3,426,678 2/1969 Carger et al 101-132.5 3,253,913 5/1966 Smith et a1. 96-1 3,131,630 5/1964 Spencer 101-465 3,242,857 3/ 1966 Noclean 101-465 2,965,868 12/ 1960 Fichles 96-1 OTHER REFERENCES Electrophotography, 1965, R. M. Schatfert, pp. 88-96.

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner US. Cl. X.R.