US3657103A

US3657103A - Electrode imaging system

Info

Publication number: US3657103A
Application number: US821257A
Authority: US
Inventors: Donald J Fisher; Robert G Davies
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1969-05-02
Filing date: 1969-05-02
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: DE2021312A1; JPS4840095B1; GB1309663A

Abstract

Method and apparatus for improving imaging and eliminating corona arcing during imaging of an electrophoretic imaging system employing a blocking electrode having individually insulated electrical conductive portions behind a blocking layer and a commutating means to activate the conductive portions such that an electric field is generated in a manner preventing air ionization or corona arcing between electrodes of the imaging system.

Description

United States Patent Fisher et al.

[is] 3,657,103 [451 Apr. 18,1972

ELECTRODE IMAGING SYSTEM Donald J. Fisher, Fairport, N.Y.; Robert G. Davies, Clarksville, Va.

Xerox Corporation, Rochester, NY.

May 2, 1969 [72] Inventors:

Assignee:

Filed:

Appl. No.:

U.S. Cl ..204/299, 204/181, 204/300 Int. Cl ..B44c l/04, B0ld 59/42, BOld 5/00 Field of Search ..204/ l 8 PC, 299-302,

204/180481, 299 DE, l8l PE References Cited UNITED STATES PATENTS 3,477,934 11/1969 Carreira et al. ..204/300 PE Primary Examiner-John H. Mack Assistant Examiner-R. L. Andrews Attorney-James J. Ralabate, Barry J. Kesselman and David C. Petre [57] ABSTRACT Method and apparatus for improving imaging and eliminating corona'arcing during imaging of an electrophoretic imaging system employing a blocking electrode having individually insulated electrical conductive portions behind a blocking layer and a commutating means to activate the conductive portions such that an electric field is generated in a manner preventing air ionization or corona arcing between electrodes of the imaging system.

16 Claims, 5 Drawing Figures ELECTRODE IMAGING SYSTEM This invention relates in general to imaging systems and more specifically to an improved electrophoretic imaging system.

The system improved by this invention is of the type using photosensitive radiant energy absorbing particles believed to bear a'charge when suspended in a non-conductive liquid carrier and disposed in an electroded system tobe exposed to an image radiation configuration. For a detailed description of the operation of this system see Pat. Nos. 3,3 84,565 issued to V. Tulagin and L. M. Carreira, 3,384,566 to H. E. Clark and 3,383,993 to S. Yea issued on May 21, 1968. The particles of the system migrate in image configuration providing a visual image at one or both of the electrodes between which they are placed. The system employs particles which are photosensitive and which apparently undergo a net charge alteration upon exposure to activating radiation by interaction with one of the electrodes. Various mixtures of two or more different colored particles can be used to secure various colors of images and imaging mixes having different spectral responses. These colors can be used independently or in subtractive color synthesis. In a monochromatic system the particles will migrate if energy of any wavelength within the panchromatic spectrum of the particle response strikes the particle.

It has been found that images produced by the system broadly described above may on occasion exhibit uneven density or contrast. Further, the apparatus employed for imaging may be. damaged during imaging. It is thought that these dif' ficulties are caused by varying corona discharge or air ionization, referred to hereinafter as corona arcing, between the electrodes used for imaging within the system as one electrode approaches in proximity to the other electrode. The invention herein was developed to eliminate this electric arcing between electrodes. Other methods and apparatus having different operation and structure from the instant invention have been discovered for achieving similar results in eliminating arcing. For example, in copending application Ser. No. 519,034 filed on Jan! 6, 1968, now US. Pat. No. 3,485,738, in the name of L. M. Carreira and entitled Imaging Process, air ionization is prevented by filling the gap between approaching electrodes with aninsulating liquid. In copending application Ser. No. 821,202 filed May 2, 1969 in the names of John M. LaCagnina and Robert G. Davies and entitled Improved Electrode Imaging System, air ionization is prevented by placing a member which interfers with corona arcing near the interface between two electrodes so that any arcing still occurring interacts with the member rather than the two electrodes. In another copending application Ser. No. 821,255 filed May 2, 1969, in the name of Gerard T. Severynse and entitled Improved Imaging System, an electrode having a broad contact zone is moved relative to a second electrode in tractor-like fashion and the electric field betweenthe two is confined to a narrow area within the broad contact zone. Various electrical conductive means are shown therein but the invention is used primarily with broad contact zones between electrodes.

Therefore, an object of this invention is to improve electrophoretic imaging systems by eliminating corona arcing between electrodes. Another object of this invention is to improve systems using electrodes with self-contained commutating devices. Still another object is to provide circular cylindrical electrodes capable of eliminating corona arcing in imaging systems. 1

The foregoing objects and others are accomplished in accordance with this invention by providing an electrode for contact with another electrode within an electrophoretic imaging system wherein one electrode has a plurality of electrical conductive means insulated from each other and covered with a dielectric surface. A commutating means contacts a portion of the conductive means to provide a potential thereto. Corona arcing is prevented because the field is eliminated in areas where arcing is likely to occur. It may be that other systems exist or will be discovered orinvented that require improvements similar to those described herein and this invention can be used thereon to improve such a system and such use is contemplated hereby.

The advantages of this improved electrophoretic imaging system will become further apparent upon consideration of the following detailed disclosure of the invention; especially when taken in conjunction with accompanying drawings; wherein:

FIG. 1 is a side view schematic of an electrophoretic imaging system employing one embodiment of this invention;

FIGS. 2, 3 and 4 are side view schematic illustrations of other embodiments; and

FIG. 5 is a front view partially sectional along line 5-5 of FIG. 4.

Referring to the drawings, shown in FIG. 1 is a photoelectrophoretic imaging system having an injecting electrode 10 composed of a transparent glass substrate 12 and an overcoated electrical conducting layer 14. The injecting electrode may have a layer of tin oxide coating on glass which forms a 0 composite commercially available under the name of NESA from Pittsburgh Plate Glass Co. Any other suitable structure usable with the electrophoretic imaging system as described in U.S. Pat. Nos. 3,383,993; 3,384,566 and 3,384,567 the disclosures of which are incorporated herein, is acceptable with this invention.

Deposited on the electrical conducting layer 14 of the injecting electrode 10 is a thin layer of finely divided photosensitive particles dispersed in an insulating liquid carrier. This is the imaging suspension 16 from which a final image is formed.

Adjacent to the electrode 10 and the suspension 16 coated thereon is a blocking electrode generally referred to by the numeral 18. The blocking electrode" has a layer 20 of blocking material, that is, material which once contacted by photosensitive particles will not inject a sufficient charge into them to cause them to migrate from the blocking electrode.

The term photosensitive for the purposesof this inven tion refers to the properties of a particle which, once attracted to the injecting electrode, will reverse its polarity of charge and migrate away from it under the influence-of an applied electric field when exposed to activating electromagnetic radiation. The term suspension" may be defined as a system having solid particles dispersed in a solid, liquid or gas. Nevertheless, the suspension described in the embodiments herein is of the general type including those having a solid suspended in a liquid carrier. The term injecting electrode refers to the electrode the properties of which apparently inject charges into photosensitive particles activated by electromagnetic radiation while under the influence of an electric field.

The photosensitive suspension 16 is subjected to electromagnetic radiation in image configuration by, for example, shining a light source 22 through an object such as a transparency 24 which is imaged through lens 26 to the photosensitive suspension 16 on the upper surface of the injecting electrode 10. More or less simultaneously with the projection of the object 24 to the suspension 16, an electric field is applied between the

electrodes

10 and 18. The blocking electrode is given shape by the support member 21 and the shaft 23 which is suitably joumaled for rotation over the imaging electrode. Shown schematically in FIG. 1 is an electrical energy source 28 connected through a switch 30 to a connector mechanism 32 internal to the surface 20 of the blocking electrode 18. The connector member 32 extends the length of the electrode. The mechanism functions such that when the electrode 18 traverses the surface of the injecting electrode 10, the switch 30 is closed forming an electric field at the interface of the two electrodes. The surface 20 of blocking electrode 18 is preferably negative relative to the surface 14 of the injecting electrode 10.

The particles within the suspension are non-conductive unless they are struck with activating radiation. Under the influence of the applied electric field, as shown in this embodiment, the negative particles come into contact with or are closely adjacent to the injecting electrode 10 and remain there. When activating radiation strikes the photosensitive particles, it makes the particles conductive creating" holeelectron pairs of charge carriers which may be considered mobile in nature. These newly created hole-electron pairs within the particles are thought to remain separated before they can re-combine due to the electrical field surrounding the particle between the two electrodes. The negative charge carriers of these hole-electron pairs move toward the positive electrode 10 while the positive charge carriers move toward the negative blocking electrode 18. The negative charge carriers near the particle-electrode interface at electrode 10 can move across the very short distance between the particles and the surface 14 leaving the particles with a net positive charge after sufficient charge transfer. These net positively charged particles are now repelled away from the positive surface of the electrode l and are attracted toward the negative blocking electrode 18. The particles struck by activating radiation of a wavelength to which they are sensitive, i.e., one which will cause the formation of hole-electron pairs within the particles, move away from the electrode to the electrode 18 leaving behind only particles which are not exposed to sufficient electromagnetic radiation in their responsive range to undergo this change. Those particles remaining function to form the image sought by the imaging system.

The electric field formed by this apparatus is deliberately limited in area. A contact means such as the connector bar 32 contacts only a selected portion of the conductive segments formed in this embodiment as pins 34. Each of the pins are held separated from each other by an electrical insulating material 36 such as glass or a suitable plastic or the like having a requisite high insulating ability to prevent conduction of electricity to pins not directly contacted by the connector bar 32. This insulating material 36 extends beyond the outer extremes of the pins 34 forming a complete insulating surface around the periphera of the blocking electrode 18. The conductive means, here formed as pins 34, are generally complete conductors such as aluminum or copper, but semiconductors may also be used to form the conductive means. The insulating material 36 should have a specific dielectric constant greater than 5 and a bulk resistivity of at least 10 ohm-cm. The connector bar 32 extends across the entire rear portion of the surface housing the pins.

As the electrode 18 is moved across the surface 14 of the electrode 10 by a suitable drive means such as motor M-l, a field is maintained at the interface since the connector bar 32 slides along the inside surface of the electrode 18 on the contact ends of pins 34. When this field coincides with the activating electromagnetic radiation at any given position of contact, the particles of the suspension react as described hereinabove to form an image on the surface 14 while non-image photosensitive particles are attracted to the electrode 18 for removal from the system. Those unused photosensitive particles remaining on the electrode 18 are removed therefrom by any suitable means such as a brush 38. The portion of the pins 34 contacted by the connector bar 32 is sufficiently small to locate within the area at the interface of the two electrodes which is filled with suspension. By limiting the conductive segments causing an electric field, there is no air to be ionized in the area of the electric field. A second contact means such as connector bar 40 may be provided next to the connector bar 32 on the trailing side thereof. The connector bar 40 creates a contact with a different portion of the pins 34 from those contacted by the connector 32. The potential connected to these pins is of limited strength being merely sufficient to hold the photosensitive particles that have migrated to the blocking electrode 18 during the imaging process ensuring that they are removed from the electrode 10. The electrical source for connector 40 can be a separate source from the main supply.

FIG. 2 represents a second embodiment similar to that shown in FIG. 1. The electrode shell is suitably bracketed (not shown) to the shaft 41 for rotation thereabout in when moving in rolling contact over the injecting electrode. The connector mechanism here is a bead 42 of conducting liquid such as mercury which will ride on the electrode pins 44 held by insulating material 46 separating each pin from the others electrically. The bead maintains itself within the area near the interface of the

electrodes

18 and 10 so that corona arcing and air ionization is prevented as discussed above. Here, the pins 44 extend through the outer surface of the insulating material 46 and into the dielectric blocking material 48 which forms the outer surface of the blocking electrode 18. In this manner, highly insulating material designated 46 may be used to separate the conductive pins 44 from each other while another suitable material 48 forms the blocking electrode surface. The surface material 48 can be wrapped around or molded to the extended conductive pins 44 to provide excellent imaging within the system. A drive means, motor M-2, moves the blocking electrode 18 across the injecting electrode 10.

The pins in the insulating carrier can be spaced on 4 mil centers so that there is a density of 62,500 conductors per square inch. Devices of this sort have been made by the Corning Glass Works of Coming, New York. The spreading of the field at the surface of the dielectric material 48 can be such as to give a relatively uniform field thereat for attracting photosensitive particles during the imaging of the photoelectrophoretic imaging system. This occurs because of overlapping of the spreading fields through the dielectric surface. The field can be limited in its spreading effect by the proper geometry of the pin matrix or by pin spacing to provide a nonuniform field at the interface of the surface 48 with the surface 14 of the injecting electrode. This would tend to give a half-tone type screen affect to the image formed by the imaging system. This may have certain benefits for later uses of the images such as lithographic masters or the like. The spacing of the dots on the half-tone screen are determined by the spacing of the pins 44 within the electrode 18 as well as the thickness of the dielectric blocking layer 48 extending beyond the tips of the pins of the electrode.

FIG. 3 represents another modification of an electrode to achieve the results desired by preventing air ionization around the electrode during the imaging of a photoelectrophoretic imaging suspension. Here, the injecting electrode remains structurally the same as in the preceding figures but the blocking electrode 18 is divided into conductive segments formed as sectors 50 separated by electrically insulating dividers 52. The connector mechanism shown is designed to contact at least one and, in the embodiment shown, as many as two separate sectors as the blocking electrode 18 rolls across the injecting electrode 10. Of course, more than two sectors can be activated if desired in a particular embodiment or situation. The connector mechanism translates across the injecting electrode 10 such that the bottom most sectors of the blocking electrode are always activated while the remainder of the sectors are at the same relative potential as the injecting electrode 10.

The connectors 54 do not rotate but maintain the sectors they contact at the same potential, shown as ground, as the surface 14 of the injecting electrode. The only electrically active connection is from connector member 58 shown here contacting two

sectors

60 and 62 of the blocking electrode. These sectors are maintained at a sufficiently high negative potential to create a field across the suspension maintained between the blocking electrode 18 and injecting electrode 10 such that when the particles of the suspension are struck by activating electromagnetic radiation those particles so struck will migrate to the surface 64 of the blocking electrode 18. The surface 64 is a high dielectric material surface similar to those discussed above relative to the previous figures. As a particular sector rolls out of contact with the suspension maintained on the injecting electrode 10 it also rolls out of electrical contact with the connector member 58 and into contact with connector member 54. The sector thereby acquires the same electrical potential as the injecting electrode and there is no field between that sector and the injecting electrode. Therefore, there can be no corona arcing or air ionization between those sectors in contact with the connector members 54 and injecting electrode. The connectors 54 may be electrically contacted to provide a limited negative potential and act in a manner similar to the connector mechanism 40 of FIG. 1.

A suitable drive means such as motor M-3 is provided on the blocking electrode 18 to cause it to roll across the injecting electrode in no slip contact therewith. Imaging occurs in the same manner as discussed above for the embodiment shown in the preceding figures.

FIGS. 4 and 5 illustrate a preferred embodiment of an electrode for use in an imaging system as described in the previous illustrative figures. The electrode 18 has a dielectric coated surface 70 made of a material having the required properties as stated above in relation to the previous figures. Coated, vacuum-deposited, or painted on the surface 72 (opposite surface 70) of the blocking material are conductive strips 74. These strips can be aluminum, copper or any other conductive material capable of being applied to the surface of the blocking material. The bond with the blocking material should be high enough to prevent deterioration during the operation of the electrode in the imaging system described in relation to the other figures.

An electrical connector roll 76 rides along the inner surface 72 of the blocking material 78 such that it contacts one or more of the strips of conductive material coated on the surface 72. The roll 76 is bearing mounted for rotation at a fixed axial position along the inside circumference of the strip coated blocking surface. An inner support member 80 gives form to the electrode and may be made out of any material such as a hard rubber or metal or the like.

Passing through the central axis of the cylinder thus formed is a shaft 82 which is connected to any suitable drive means for moving the blocking electrode over the injecting electrode with which it will come in contact during imaging. The connector roll 76 rides at the lowermost portion of the roll for contacting only those strips of conductive backing material which are confined to an area that will contact the imaging suspension and prevent corona arcing during imaging.

FIG. 5 shows a front view partly sectional of the electrode illustrated in FIG. 4. A conductive strip 83 is shown being contacted by the connector roller 76. The connector roller is electrically connected to a DC source 84 which supplies negative potential to the connector roller and to the strips that it electrically contacts. The blocking material 78 surrounds the roller and extends, along with the conductive strips, beyond the support member 80 of the electrode 18. This enables the connector roller 76 to ride along the inner circumference of the blocking surface for creating an electric field between the lowermost strips and the injecting electrode in close proximity thereto.

The strips 74 extend across the entire contact length of the blocking electrode with the imaging electrode 10 so that the connector rollers 76 need contact only a small portion of the strip to form a field across the entire length of the electrode. The strips 74 should be placed as near as practicable to each other just as the pins in FIGS. 1 and 2 in order to provide the best field affects for imaging.

A substitute for the coated or painted conductive strips in this embodiment could be the use of conductive wires or rods embedded into the roller support member 80 and contacted on the side of the support member rather then the back of the blocking material which in this case would be wrapped around the support member and wire conductors.

While this invention has been described with reference to the structures disclosed herein and while certain theories have been expressed to explain the experimentally obtainable results obtained, it is not confined to the details set forth; and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is:

1. In an apparatus for imaging electrophoretic suspensions having a first electrode adapted to support an image formed from the suspension,

a second electrode having a blocking surface for contacting the suspension on the first electrode such that the suspension is maintained therebetween in a contact zone,

means to couple at least one of said electrodes to an electrical supply source, and

means to expose the suspension between the electrodes to activating electromagnetic radiation, the improvements including,

means to electrically isolate a portion of the second electrode in the contact zone, and

means to electrically connect to said means to couple to apply an electrical field between said electrodes whereby the portion of said second electrode in the contact zone has a field with respect to the first electrode.

2. The apparatus of claim 1 wherein said second electrode blocking surface is an endless member.

3. The apparatus of claim 1 wherein said means to electrically connect includes first contact means for applying an electrical potential from said means to couple on a first portion of the second electrode within the contact zone and second contact means to provide a lesser potential on a second portion of said second electrode.

4. The apparatus of claim 1 wherein said means to apply an electrical field includes a plurality of conductive pins.

5. The apparatus of claim 1 wherein said means to apply an electrical field includes conductive segments.

6. The apparatus of claim 5 wherein said conductive segments include strips on the side of the blocking surface opposite the side adapted to contact the suspension, said strips extending parallel to the electrode interface and across the length of the contact zone between the electrodes.

7. The apparatus of claim 5 wherein said conductive segments include sectors contacting the blocking surface on the side opposite the electrode interface, and extending across the length of the contact zone between the electrodes.

8. The apparatus of claim 5 wherein said segments are spaced to provide half-tone image patterning during imaging of the suspension.

9. A blocking electrode for an electrophoretic suspension imaging system including a blocking surface,

means to support said surface,

conducting means between said means to support and said surface,

means to electrically isolate a portion of said conducting means,

means to electrically contact said conducting means whereby the conducting means contacted are connectable to an electrical potential supply source.

10. The apparatus of claim 9 wherein said conducting means includes a plurality of conductive segments and said means to isolate includes electrical insulating means positioned such that each of the plurality of conductive segments are electrically separated from other of the plurality by the insulating means.

11. The apparatus of claim 9 wherein said conducting means includes pins extending into the blocking surface.

12. The apparatus of claim 9 wherein said conducting means includes conductive sectors abutting said blocking surface between said surface and said support means.

13. The apparatus of claim 9 wherein said conducting means includes conductive strips extending parallel to each other.

14. The apparatus of claim 9 wherein said conducting means includes a semi-conductor.

15. The apparatus of claim 9 wherein said blocking material surface is formed as an endless member.

16. The apparatus of claim 15 wherein said means to electrically contact includes a liquid conductor floatable on the conducting means and connectors attached to said liquid conductor.

Claims

1. In an apparatus for imaging electrophoretic suspensions having a first electrode adapted to support an image formed from the suspension, a second electrode having a blocking surface for contacting the suspension on the first electrode such that the suspension is maintained therebetween in a contact zone, means to couple at least one of said electrodes to an electrical supply source, and means to expose the suspension between the electrodes to activating electromagnetic radiation, the improvements including, means to electrically isolate a portion of the second electrode in the contact zone, and means to electrically connect to said means to couple to apply an electrical field between said electrodes whereby the portion of said second electrode in the contact zone has a field with respect to the first electrode.

9. A blocking electrode for an electrophoretic suspension imaging system including a blocking surface, means to support said surface, conducting means between said means to support and said surface, means to electrically isolate a portion of said conducting means, means to electrically contact said conducting means whereby the conducting means contacted are connectable to an electrical potential supply source.