US3930257A

US3930257A - Methods of and apparatus for electrostatic printing

Info

Publication number: US3930257A
Application number: US452346A
Authority: US
Inventors: Pham Kim Quang; Rene Gasdoue
Original assignee: Individual
Current assignee: Cellophane SA France
Priority date: 1973-04-03
Filing date: 1974-03-18
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30
Also published as: FR2224790B1; FR2224790A1

Abstract

Printed matter is recorded on dielectric paper by depositing an array of electrostatic charges on one surface of the paper at a potential level lower than the ionization potential and then raising the potential level of the charges higher than their ionization level according to a selected pattern with stylet-like electrodes. The selected pattern causes a developer to adhere to the dielectric paper in accordance with the pattern, thereby making the pattern visible.

Description

United States Patent Quang et al.

METHODS OF AND APPARATUS FOR ELECTROSTATIC PRINTING Inventors: Pham Kim Quang, Dieppe; Rene Gasdou, Neuville les Dieppe, both of France Assignee: La Cellophane, Paris, France Filed: Mar. 18, 1974 Appl. No.: 452,346

Foreign Application Priority Data Apr. 3, 1973 France 73.11867 US. Cl 346/74 ES Int. Cl. G03G 15/18 Field of Search 346/74 EL, 74 ES, 74 EB,

346/74 IB; l78/6.6 A

References Cited UNITED STATES PATENTS 3/1962 Schwertz 346/74 EW 51 Dec. 30, 1975 Lloyd 346/74 ES Gundlach et al 346/74 ES Primary ExaminerBernard Konick Assistant Examiner.lay P. Lucas Attorney, Agent, or FirmSherman & Shalloway [57] ABSTRACT Printed matter is recorded on dielectric paper by depositing an array of electrostatic charges on one surface of the paper at a potential level lower than the ionization potential and then raising the potential level of the charges higher than their ionization level according to a selected pattern with stylet-like electrodes. The selected pattern causes a developer to adhere to the dielectric paper in accordance with the pattern, thereby making the pattern visible.

12 Claims, 3 Drawing Figures CON TROL LER LOW VOLTAGE GENERATOR U.S. Patent Dec. 30, 1975 3,930,257

24 26 CONTROLLER 27 b LOW VOLTAGE GE NERATOR 32 CONTROLLER LOW VOLTAG E GEN ERATOR FIG? METHODS OF AND APPARATUS FOR ELECTROSTATIC PRINTING BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electrostatic printing. More particularly, the present invention relates to methods of and apparatus for arranging electrostatic charges in a selected configuration on a sheet of paper or other dielectric material to be subsequently developed by a liquid or powder developer.

2. Technical Considerations and Prior Art There are currently available several methods of and apparatus for electrostatic printing. However, each of these currently practiced approaches has disadvantages. For example, a system which is used in printers which record the output of computers deposits electrostatic charges on a sheet of paper having a coating of insulation by passing the sheet of paper between a pair of electrodes maintained at different potential levels. Generally, one of the electrodes is a mobile stylet which is brought to a predetermined potential by pulses generated therein with an electric signal generating device. This particular system presents problems because, in order to obtain sufficient line density after development, it is necessary that the insulating layer be supported by a very good electrical conductor, and that the potential difference developed between the electrodes be quite high. Accordingly, the potential difference between the electrodes must be between 400 and 500 volts, and often, depending on the nature of the insulating layer, support and spacing between the stylet and the dielectric sheet, the voltages may range from 600 to 1,000 volts. These high voltages require a good deal of electricity, and make it necessary to take certain precautions to ensure safety. In addition, the practical problems raised by utilizing this particular process are complicated due to the need for rapid switching devices.

In order to overcome the deficiencies of the aforementioned system or process, the prior art suggests placing two additional electrodes on opposite sides of the mobile stylet electrodes. These two electrodes amid voltages having a sign opposite to that of the stylet thereby raise the potential level of the conductive support over which the paper passes. By using this process, it is possible to operate with slightly lower voltages, but obviously this approach is merely remedial and adds to the complexity of the printer. In addition, as with the aforedescribed process, the use of the additional two electrodes still requires using a support for the paper or dielectric material which is a good electrical conductor. In addition, it is no mean task to easily modify the polarity of the charges deposited on the dielectric material without resorting to drastically increasing the complexity of the printer.

An additional approach which has been envisioned is to deposit on an insulating layer a prior electric charge having a level lower than the critical voltage necessary for good production of images. This process, however, results in print-outs which have a poor background after development.

SUMMARY OF THE INVENTION In view of the afore-mentioned deficiencies of prior art devices, it is an object ofthe instant invention to for electrostatic printing wherein printing is applied on dielectric materials mounted on supports which are not electrical conductors.

It is still an additional object of the instant invention to provide new and improvedmethods of and apparatus for electrostatic printing wherein the printing is applied to dielectric materials mounted on supports which are only slightly conductive of electricity.

It is still a further object of the instant invention to provide new and improveed methods of and apparatus for electrostatic printing wherein supports for the dielectric materials being printed on easily accept electrostatic charges, the polarity of which can be easily reversed.

It is an additional object of the instant invention to provide new and improved methods of and apparatus for electrostatic printers wherein printers have stylets that use relatively low inscription voltages which are capable of response times that are considerably shorter than the response times of prior art devices.

It is still a further object of the instant invention to provide new and improved methods of and apparatus for creating an external field in the support for a dielectric layer being printed on by using tribe-electricity or, rather, friction-induced electricity.

It is still another object of the instant invention to provide new and improved methods of and apparatus for electrostatic printing wherein said methods and apparatus are relatively non-complex and relatively inexpensive to manufacture and use.

It is a further object of the instant invention to provide new and improved methods of and apparatus for electrostatic printing wherein the methods and apparatus utilize voltages levels in a way which is relatively safe and, therefore, does not require extensive safety equipment.

Still a further object of the instant invention is to provide new and improved methods of and apparatus for electrostatic printing wherein the dielectric layer which is printed upon may be composed of readily available, inexpensive paper having a conventional, readily available, dielectric surface.

In view of these and other objects, the instant invention is directed to methods of and apparatus for electrostatic printing which include the concepts of advancing a strip of dielectric material past a charging station in order to distribute an array of electrostatic charges thereon, and then re-arranging the array of electrostatic charges to correspond to a selected image by advancing the dielectric material past an electrode means maintained at a potential level different from the potential level of the array. The resulting image is then developed by fixing it permanently on the dielectric material.

BRIEEDES CRIPTION OF THE DRAWINGS 3 of dielectric material prior to arranging the charges with a stylet type electrode;

FIG. 2 is a schematic view of a second embodiment of the invention wherein electrostatic charges are placed directly on a strip of dielectric material without first utilizing a belt of insulating material as an intermediary to deposit the charges; and

FIG. 3 is an enlarged cross-section of the type of paper being printed upon in accordance with the principles of the invention.

DETAILED DESCRIPTION Referring now to FIG. '1, there is shown one embodiment of a printer in accordance with the instant invention, wherein negative charges are deposited on a belt 1 1 of insulating material, such as polyester film, by a corona-charging device 12. The belt 11 is trained around three rollers l3, l4 and 15, one of which is driven and all of which are positively engaged by the belt. The belt is driven by the powered roller to travel in the direction of the arrow 16 so as to pass through a printing station, designated generally by the numeral 17.

A supply of dielectric paper 18 is dispensed from a supply reel 19 and passes over a roller 21 positioned opposite the roller 13, and a roller 22 positioned opposite the roller 14, so as to travel in a parallel direction with the belt 11 while in the printing station 17. The paper 18 is positively driven by the

rollers

21 and 22 at the same linear speed that the belt 11 is driven. This may be accomplished by any convenient means, such as gearing the

rollers

21 and 13 together and the

rollers

14 and 22 together so that these rollers each rotate at the same speed.

While the dielectric paper 18 and belt 11 are advancing through the printing station 17, the electrostatic charges 10 are transferred in a selected manner so as to record intelligence on the paper 18 by raising the level of potential of the charges to their ionization level according to a selected pattern. When the ionization level is reached, the charges so raised will, in effect, transfer to the paper 18 in the selected pattern to record intelligence on the paper in the form of letters, numbers and the like.

The selected transfer of the charges 10 from the belt 11 to the paper 18 is accomplished by stylets 24 (only one of which is shown). These stylets are electrodes which are connected by leads 26 to a pole 27 of a low voltage generator 28. The pole 27 is opposite in polarity from the charges 10 deposited by coronacharging device 12. In other words, if the charges 10 are negative, the pole 27 will be positive, and it the charges 10 are positive, then the pole 27 will be negative. The generator 28 has another pole 30 which is grounded through lead 31, and is controlled by signals from a controller 32 impressed over a lead 34. Controller 32 lies outside the scope of the present invention, but may be assumed to be the type that is used to control the prior art electrostatic printers. Since the stylet 24 has an opposite polarity from the charges 10 due to the pole 27, when the charges 10 located opposite the stylet advance past the stylet, their level of potential is raised. If the potential level of the charges 10 are quite close to their ionization threshold, then the electric field at the tip of the stylet 24 will cause the charges to ionize if the potential level of the stylet, when added to the potential level of the charges, exceeds the ioniza- 4 tion threshold. This phenomenon may be expressed as follows:

V Potential level of charges;

V Potential level of stylet;

V,-,,,, Potential level of ionization threshold;

Then V V s V (no transfer of charge 10 from belt 11 to paper 18). However,

V V V (results in a transfer of charges 10 from belt 11 to paper 18).

It should be understood that the stylets 24 may be arranged in any manner which is convenient to cause transfer of the charges 10 from the belt 11 to the paper 18 according to a selected pattern of intelligence.

There are known teachings in the prior art showing just how the stylets 24 may be arranged, which include arranging the electrode in parallel batteries to conform to various configurations, such as combs or the like. Each electrode 24 may be connected to an associated generator by a suitable switching system of a conventional, well-known type. These aspects lie outside the scope of the present invention.

After the charges 10 have been transferred from the belt 11 to the paper 18 in a selected manner, the intelligence recorded on the paper 18 is not yet visible. In order to make the intelligence visible, the paper 18 is carried around a conductive roller 36 and passed between the conductive roller and a developing roller 37. The developing roller 37 rotates through a bath 38 of liquid developer which is transferred to the paper 18 and fixed to the paper by a heater 39 before being accumulated on a take-up roll 40.

The conductive roller 36 serves to short-circuit the backside of the paper 18 so that charges deposited thereon are removed from the backside before the liquid developer 38 is deposited by the developing roller 37. Although the charges are removed from the backside of the paper 18, they remain on the front side of the paper so that the intelligence recorded on the front side of the paper is not confused by developer which is adhered to the paper due to charges on the back of the paper. Consequently, the background is not darkened, and print on the front of the paper is clearly developed.

One of the objects of this invention is to have the stylets 24 operate with a relatively low potential. In practice, this potential is on the order of 50V. However, this potential may be regulated to be as high or low as desired so long as, when added to the potential of the charges 10 on the belt 11, the ionization thresh old of the charges will be exceeded.

Generally, the paper 18 may be considered a dielectric system in which paper forming an insulating layer 45 is coated with a standard dielectric layer or coating 46 of, for example, butadiene-styrene pigmented with zinc sulfide. The resin, of course, may be any other sufficiently dielectric polymer, such as one of the vinyl copolymers, acrylic resins, silicones, cellulose esters, etc. In order to pigment the resin, titanium, zinc, tin oxide, silica and/or any other know pigment may be used. The most suitable dielectric paper are those which have volume resistances equal to or in excess of l0 ohms/cm /cm. Since, in this process, the charges are not placed on the paper by passage of current between two electrodes, but rather by injection through the supporting paper or insulating layer 45, the paper 18 does not have to be a good conductor of electricity. Consequently, ordinary paper may be used.

In practice, the potential level developed at the tip of the stylet 24 is achieved by pulsing the stylet with pulses having a period of to 50 micro seconds at a level, as mentioned previously, of 50V; whereas, in the prior art, the pulses were for a period of a millisecond at a potential level of 600 to 1,000 V.

An additional embodiment of the present invention is shown in FIG. 2 where the use of a belt of insulating material, such as the belt 11 of FIG. 1, is dispensed with. In the embodiment of FIG. 2, a strip of dielectric paper 18 is advanced from a supply roll 19' around a first roller 21 and a second roller 22. A printing station 17' is disposed between the first roller 21' and the second roller 22. Instead of depositing charges first on an insulating belt, a corona-charging device 12 is positioned in the printing station 17' at a location just opposite the stylet 24'.

The corona-charging device 12 deposits charges on the paper 18 while the stylet 24' raises certain of these charges past their ionization level at selected locations across the paper 18 to thereby record intelligence on the paper 18'. As with the embodiment of FIG. 1, the stylet 24' is connected to a pole 27 on a low voltage generator 28 which is opposite in polarity to the polarity of the charges deposited on the paper 18 by the corona-charging device 12'. The low voltage generator 28 is controlled in the same way as the low voltage generator of the FIG. 1 embodiment by using a controller 32. Downstream of the roller 22', a conductive roller 36' and development roller 37' cooperate with a heat-fixing device 39 to form an image on the paper 18' in the same way as done with the embodiment of FIG. 1.

In practicing the invention according to the embodiment of FIG. 2, the corona-charging device 12' may be placed at the back of the supporting layer of the dielectric paper 18' at a distance ranging from 10 to 100 mm. It has been found that a distance of to mm gives good results, and that it is not necessary to place the corona-charging device 12' exactly opposite the stylet 24. The corona-charging device 12' may be shifted around, provided that no metallic portion thereof comes into contact with the back of the paper 18 in the zone located between the corona-charging device and the stylet 24.

Depending on the characteristics of the dielectric layer coating the paper 18 (which is similar to the dielectric layer coating the paper 18 in the embodiment of FIG. 1) and the nature of the supporting paper layer, the wires of the corona-charging device 12-12 are elevated to a potential of between 1,000 to 15,000 V. Generally, in practice a potential ofl ,000 to 6,000 V is used. It is found that potential must be increased as the distance between the corona 12 and the paper support 18 is increased. The value of this potential, of course, must be regulated as a function of this distance between the corona and the paper to produce an electric field which is less than the field necessary to reach the ionization potential, but is as close to the threshold of ionization potential as possible. Accordingly, the voltage that must be applied to the stylet may be reduced to a range of 25 to V. In order to simplify the equipment of the control circuits as much as possible, it is to ones advantage to use as low voltages as possible which are of a sufficient level to elevate the voltage of the charges deposited by the corona past the ionization potential threshold.

In another embodiment of the invention, the external field may be created by applying an insulating sheet of a film, such as polyester film, which is uniformly charged to the backside of the dielectric support or paper. This dielectric sheet may be uniformly charged beforehand by a corona-charging device, such as those disclosed.

Instead of using a corona-charging device, such as 12 or 12', it is possible to deposit charges on the paper by using tribo-electricity or, rather, friction-induced electricity. This may be accomplished by a convenient tribo-electricity generating device which, for example, may be a nylon brush applied against the back of the supporting layer of the paper 18 and rotated at high speed in a direction opposite the advance of the paper 18.

Another approach within the spirit of this invention is to raise the value of the field of charges deposited on the dielectric paper to a level sufficient to produce a deposit of charges on the dielectric paper as soon as stylet 24' or 24 is brought close to the opposite surface of the paper. The distance between the stylet and paper may be reduced, in this case, hundreds of millimeters. In this situation, the level of the field in the paper should be higher than the ionization threshold for the distance considered. With this embodiment, it is possible to transmit a document by telecopy, wherein the printing is formed at a distant station by advancing and retracting printing keys which have printing characters thereupon as instructed by remotely controlled electric signals. Once transferred onto the dielectric surface, the deposited charges may be developed by a liquid or powder developer, such as in the embodiments of FIGS. 1 and 2, and then thermally fixed by well known methods.

What we claim:

1. An apparatus for electrostatic printing on a strip of material, wherein said material includes an insulating support layer with a dielectric layer thereupon, the dielectric layer having an interior surface and an exterior surface, said apparatus comprising:

means for locating the material at a printing station;

means for depositing a uniform field of electrostatic charges in the insulating support layer, wherein the charges have a level of potential which is below a threshold ionization level;

stylet means for creating the charge image, said stylet means being located in said printing station, wherein said stylet means is brought to a predetermined level of potential substantially lower than that of the electrostatic charges and of opposite polarity, but high enough to cause ionization when added to the potential level of said charges to thereby transfer a charge image to the exterior surface of the dielectric layer; and

means for developing said charge image to make the image visible.

2. The apparatus of claim I, wherein the means for depositing the electrostatic charges is located in the printing station at a position generally opposite the stylet.

3. The apparatus of claim 1, wherein the means for depositing the electrostatic charges deposits the charges on a belt of insulating material which transfers the charges upon subsequently passing through the printing station while positioned adjacent the dielectric material.

4. The apparatus of claim 1, wherein the stylet means includes a plurality of electrodes, each of which is selectively pulsed to the predetermined level of potential by a low voltage generator.

5. A process of electrostatic printing on a strip of material, wherein said material includes an insulating support layer with a dielectric layer thereupon, the dielectric layer having an interior surface and an exterior surface, comprising the steps of:

creating a uniform field of electrostatic charges within the support layer; ionizing a selected portion of the field of electrostatic charges with a potential of opposite polarity to the charges to transfer the selected portion of the field to the exterior surface of the dielectric layer to thereby form a charge image thereupon; and

applying an electrostatic developer to the exterior surface of the dielectric layer to render the charge image visible.

6. The process of claim 5, wherein the electrostatic field within the support layer has a potential approaching the ionization potential thereof and wherein the ionizing step is accomplished by elevating the potential of only the selected portion above the ionization potential.

7. The process of claim 6, wherein the uniform field of electrostatic charges is produced from charges previously deposited on an insulating surface.

8. The process of claim 6, wherein the uniform field of electrostatic charges is deposited within the support layer by triboelectricity.

9. The process of claim 6, wherein the uniform field of electrostatic charges is created by a corona charging device and the ionizing step is performed by an electrode.

10. The process of claim 9, wherein the electrode is placed at a fixed distance from the dielectric layer and is pulsed with low voltage signals to effect ionization of the charges.

11. The process of claim 9, wherein the electrode is kept at zero potential with respect to ground and wherein ionization of the charges is effected by bringing the electrode into proximity with the exterior surface of the dielectric layer.

12. The process of claim 9, wherein the uniform field of electrostatic charges is created in the support layer by positioning the corona charging device adjacent to the support layer in opposed relation with the electrode which is positioned adjacent to the exterior surface of the dielectric layer.

Claims

1. An apparatus for electrostatic printing on a strip of material, wherein said material includes an insulating support layer with a dielectric layer thereupon, the dielectric layer having an interior surface and an exterior surface, said apparatus comprising: means for locating the material at a printing station; means for depositing a uniform field of electrostatic charges in the insulating support layer, wherein the charges have a level of potential which is below a threshold ionization level; stylet means for creating the charge image, said stylet means being located in said printing station, wherein said stylet means is brought to a predetermined level of potential substantially lower than that of the electrostatic charges and of opposite polarity, but high enough to cause ionization when added to the potential level of said charges to thereby transfer a charge image to the exterior surface of the dielectric layer; and means for developing said charge image to make the image visible.

2. The apparatus of claim 1, wherein the means for depositing the electrostatic charges is located in the printing station at a position generally opposite the stylet.

5. A process of electrostatic printing on a strip of material, wherein said material includes an insulating support layer with a dielectric layer thereupon, the dielectric layer having an interior surface and an exterior surface, comprising the steps of: creating a uniform field of electrostatic charges within the support layer; ionizing a selected portion of the field of electrostatic charges with a potential of opposite polarity to the charges to transfer the selected portion of the field to the exterior surface of the dielectric layer to thereby form a charge image thereupon; and applying an electrostatic developer to the exterior surface of the dielectric layer to render the charge image visible.