CA1108686A - High speed imaging of electrophotographic film by fine beam scanning - Google Patents

Abstract

ABSTRACT
An electrophotographic member is charged and imaged continuously, progressively using a laser beam modulated with intelligence from digital data in a store preferably using apparatus which mounts the member on the one hand, and a charging device and a beam directing arrangement On the other hand so that there is rotary and axial movement of the member relative to the said device and arrangement or visa-versa.
Toning and/or fixing and/or transfer apparatus can be provided in association with the aforesaid apparatus, or separate therefrom.
Preferably imaging is performed using radiant energy, converting a master image into digital data or information, storing the same and thereafter using the stored data to image the electrophotographic member. The data used can be data generated on real time, computer generated or received from a terminal input.

Description

1~@i8686 The field of the invention is the high speed imaging of electrophotographic members b~ a synthesizing process using data which has been acquired by scanning a master image~ The electrophotographic member is charged. Thereafter, the reproduced latent image is built through a form of scanning technique in which a master image is reproduced using the same scanning pattern. An original can be reformed and a different image with the same content produced, as for example in the case of text. The latent image is achieved through the use of radiant energy beams of very fine diameter. The latent image is developed by toning and fixing, or by toning, transfer and fixing.

The disclosure herein is directed to manufacture of printing plates, but the invention is not so limited~ The invention has particular advantage in the production of printing plates because of the requirement for printing that there be dots or other geometric shapes formed on the plate which will hold or repel ink as in the technique which is familiarly known as ben day screen printing. The production of a visible image through the use of dots or the like which are so fine that they cannot be resolved by the naked eye is advantageous for fields other than printing because the data representing an image can be conveniently stored compactly and called up at will.
It is believed that the invention arises from an unobvious combination and is unique in its ability to apply

- 2 -~1~8686 information onto an electrophotographic member at extremely high speed and with a resolutlon that is many orders better than ink jet printing, for example. Electrostatic media comprising amorphous selenium members and zinc-oxide-resin paper cannot be imaged at high speeds of the order of micro-seconds at low energy and thus have not been available or considered useful for this purpose by those skilled in the art. In contrast, the electrophotographic member provided herein can be imaged in several nanoseconds and with high resolution.
- The use of high energy beams of light, as for example, laser beams, have been minimized ~in attempting to image electrophotographic members generally because of, (a) the slow speed of conventional electrophotographic members, (b) the inability to prevent light scatter and the low resolution, and (c) the inability of known media to discharge completely coupled with the need for extremely high energy beams to achieve a degree of discharge which can approach absence of charge needed for clean imaging.
Electrophotographic media such as zinc-oxide-resin coated paper and the amorphous selenium drum cannot achieve high speed imaging, crisp images, high resolution and complete discharge. In order to image such media, the laser beam used would have to have high energy so t~hat the beam would be likely to burn the material. It is not known that any success has been achieved with these two media. Even if complete success were attained,a transparent electrophotographic r 1~3i36~

member that is flexible, archival in quality, robust and tough in construction and capable of being used directly as a printing plate would not be provided.
The invention herein takes advantage of the high quantum gain, particularly in the visible spectrum that is characteristic of the particular electrophotographic member.
With the electrophotographic member used herein the absorption of a single photon will cause the discharge of approximately more than one electron at the blue end of the spectrum and almost one electron in the green-yellow center so that the energy required of a laser beam which is writing ; on a charged surface is extremely low. The said electro-photographic member is characterized also by a response to - . - . . .. . , ~ .
charge "fast" enough to charge or discharge in nanoseconds.
For example, if a large area of an electro-, photographic member is required to be imaged, as in the manufacture of newspaper printing plates, the difference between about two or three minutes and an hour at low energy which would be required to image other media is material and significant.
If the imaging produces a reslution equivalent to only a few lines per millimeter as compared to form 8 to 16 lines per millimeter, the use of laser techniques with electrophotography is not justified.
; 25 In the case of the invention, a cylinder, say 100 centimeters in circumference, of the electrophotographic material such as zinc oxide or selenium would require too much time and the best resolution which could be achieved 11086~36 ¦ would be much less than satisfactory.
The ability of conventional media to respond to laser beams or fine pencils of light, requires energies of the order of milliwatts and even watts in some cases, placing important and stringent qualifications on the type of laser that can be used. Zinc oxide paper, for example, being formed of finely ground particles of zinc oxide in a matrix of organic resin, requires as much energy to -~
image as required for many photographic films, and does not produce a transparent member as can be achieved with photographic film.
- It is known to image photographic film with laser beams, but thickness of the emulsion in photographic film, of the order of fifty times the thickness of the thin coating of the film of the invention is such that the laser beam scatters internally to prevent the achievement of fine resolution.
Although photoyraphic film is processed chemically and a good deal of its sensitivity is represented by the manner in which it is processed, its original speed is related to grain size. The faster the film, the larger the grain size. Using photographic film, a compromise must be made between the speed of writing the information onto the film and the eventual size of grain. Laser beams are capable of being modulated by acousto-optical devices at very high speeds. FOr example, laser beams can be turned on and off in 20 nanoseconds. No known commercial 11~861~6 photogxaphic film is capable of being imaged at this speed with high resolution especially where a low energy beam (microwatts) is used.
Another aspect of the imaging of photographic film is concerned with resolution, especially where the tones of an image are dependent upon the fidelity of dots and their placement. The particles of silver which are precipitated in the processing of silver halide film grow in a more or less haphazard manner so that the uniform morphology of dots, for example, projected onto the film is not preserved.
This affects the crispness and the resolution of images.
The successful application of high speed imaging techniques using electrophotographic media requires preservation o~ the latent image obtained until development by toning, for example. In the intervening time the charge gradient of the latent image is capable of being dissipated due to migration of charge, as in the case of selenium and zinc oxide. Selenium owes its use~ulness to a very high surface resistivity in darkness, but this is not different from its resistivity transversely so that as soon as an image is formed the charge slowly migrates. It also has a tendency to concentrate the toner where the charge gradient is the greatest, that is at places where high and low charge exist side by side. Thus, images have a tendency to have their borders darker than other locations and have the centers of dark areas light instead of solid.

1~3~3686 Mention made above with respect to total discharge is related to the need for clean backgrounds in the development of images that are composed of dots or other geometric shapes. If there is incomplete discharge as is the case of selenium members, upon toning, the smaller toner particles tend to gather in the areas which are supposed to be colorless and destroy the fidelity of the resulting image. As stated, the electrophotographic media should completely discharge so that the background has no vestigial or remaining charge to attract toner.
This is an essential criterion for a printing plate.
One of its important attributes of the ;~ electrophotographic member utilized herein is the ability to be discharged incrementally so as to achieve varying degrees of surface charge whose potential was proportional to the degree of darkness of the original or master image which was being reproduced. It was recognized that an important factor in achieving an eventual image was the control of toning time to achieve the proper grey scale and hence processing was considered a critical factor.
Applicant has discovered that grey scale can be achieved by the number of dots and for high ~uality, ;
their placement in a given incremental area with respect to other areas. Each dot is saturated, that is, as black as possible so that processing is not critical. All that is required is to match the toner to the minimum voltage which is achieved during the laser writing. The time required for writing a comple'e image need only be limited by the voltage chosen as the minimum, this being the darX decay voltage.
Accordingly, there are only two types of incremental areas in the latent image, namely those comprising dots whose voltages are above the minimum voltage established for toning and those areas which have no surface potential at all.
The dots thus are all saturated and when toned will have an absolute toned value relative to the surroundings which would normally be dead white (in the case of black and white toning). It has been found that the subject electrophotographic member is ideal for this type of imaging since it is capable of being absolutely toned at very low voltages, say of the order of ten volts and less, while also being capable of total discharge in areas alongside of the toned increments. It should be understood and appreciated that the subject electrophotographic member originally was not intended to be used in ~his manner.
Accordingly, the invention provides a method of imaging through the use of electrostatic techniques which comprises scanning in accordance with a predetermined scanning pattern, a master image with a reading beam of ; energy that can be modulated by variations of the reflectivity or absorptivity which constitute the master image, coverting the modulations into a stream of r ; 25 electric signals related to said variations, converting the stream of electrical signals into radiant energy in fine beam form, said radiant energy beam bein~ modulated in a predetermined relation to the modulations oE the ~(3~36~6 reading beam, thereafter directing the fine beam in darkness to write the signals onto a charged area of an electrophotographic member having a charge-accepting thin film, transparent, microcrystalline, electrically and opticalLy anistropic, high quantum gain, wholly inorganic photoconductive coating, in a scanning pattern which is related to the master image to produce a latent image of the content of the master image on the coating, and thereafter developing the latent image.
Further, ~he invention provides apparatus for practicing the aforesaid method, said apparatus including a source of data that is in binary form representative of information capable of being developed into a master image, a radiant energy device having a fine beam of discrete bursts of energy derived from the source and capable of producing the master image if used to write the fine beam upon a suitable responsi~e medium, an electrophotographic member including a photoconductive coating capable of ; accepting and discharging a charge at hish speed, means -^`?
for charging the coating of the member in darkness to a surface potential capable of being fully discharged by said fine beam, means capable of receiving said fine beam, means :~ for directing said fine beam onto said coating in darkness, means mounting the electrophotographic member in darkness and means for effecting relative movement between the mounting means and the directing means so as to cause any said beam received to engage against and scan the coating _ g _ .
for producing a latent image of said master image if the coating has previously been charged, and means for developing any latent image formed.
The preferred embodiment of this invention will now be described, by way of example, with reference to the drawing accompanying this specification in which:
Figure 1 is a perspective vie~, more or less diagrammatic in nature, illustrating some of the apparatus for practicing the invention;
Figure 2 is a fragmentary sectional view through a member of electrophotographic film for use with the invention;
Figure 3 is a block diagram of the apparatus of the invention and including a diagrammatic representation of the writing structure.
Figure 4 is a block diagram showing the functions contemplated through the u~e of the invention to produce images.
Figure 5 is a perspective view, more or less ` 20 diagrammatic in nature, illustrating another form of the invention.
Figure 6 is a fragmentary sectional view through the wall of a cylinder of metal having a sputtered photoconductive coating bonded to its outer surface.
As stated, the invention will be described in connection with the re~uirements for making a printing plate, but it is not so limited. The invention revolves li~86~6 around the discovery that a particular electrophotographic member is ideally suited for use with the modulated fine beam of radiant energy when applied in a manner not originally intended.
The requirements for imaging in accordance w~h -the invention to achieve the results of high resolution, extended grey scale and the other benefits which are discussed herein are first, that the surface potential o~
the electrophotographic film being imaged is required to èxceed a certain voltage, say of the order of 6 to 10 volts: second, that the energy of the fine beam of radiant energy doing the writing muet be sufficient to discharge the illuminated charged surace of the electrophotographic film to zero without damaging the film and leaving the non-illuminated parts fully charged;
and third, that the toner and the toning process must tone the charged areas absolutely, that is in saturation.
~; For comment on the above three points, which are -not the exhaustive requirements, it should be pointed out that conventionally the surface potential of all commercial electrophotographic members other than the one which is utilized herein, when fully charged, is in the vicinity of 600 volts, consequently requiring extremely high radiant energy to discharge the same. At that it is impossible fully to discharge the same. In the case of laser beams, the laser is required to have extremely high energy to produce a fine beam capable of ef~ecting the ~ !~
11 . ~

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11~8~86 maximum discharge. In the case of the electrophotographic member used herein, when fully charged, the potential of the surface is of the order of 30 volts, yet the electric field is at least one order greater than the field say of the ordinary salenium drum. when charged, the dark decay commences, and after some period of time in the herein electrophotographic film falls to as low as 6 to 10 volts and still provide sufficient voltage to enable saturation toning. The selenium photoconductors and zinc oxide papers never discharge to the value of 10 volts, always having a residual "noise" voltage which is of the ord~r of 40 or so volts.
With respect to the energy of the beam, since very low energies, of the order of microwatts, are sufficient to discharge electrophotographic members herein utilized, small, economical lasers can be used and are easily modulated by acoustical-optical de~ices.
The type of beams needed to discharge other photoconductive materials or to image silver halide film would burn holes in said electrophotographic member.
With respect to toning, the toner is required only to saturate the dots and hence there is no criticality in toni~g. Time of toning is not related to the grey scale produced.
The electrophotographic member utilized herein is anisotropic optically in that there is no scatter of light when the laser beam strikes the coating, the incident ~f~ 6 beam penetrating and discharging in a depth less than half a micron. The crystalline structure has internal reflection and does not scatter normally in incident light. The latent image is formed at or on the surface, and subsequent toning responds only to the sharpness of the surface latent image. -With respect to resolution, mention made of 8 to `
16 lines per millimeter is a matter of practicality for the manufacture of a printing plate in a short time.
The only limitation to the resolution capability of the -electrophotographic member use'd herein is the size of the incident radiant energy beam and the size of the smallest information center in the film. With respect to the former, it is feasible to produce beams of light with lasers and the like that are of the same order as the crystallite size. With toner particles smaller than this , size, which is of the order of 700 Angstroms, the theoretical resolution obtainable is over 10,000 lines ,, , per millimeter.
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The electrophotographic film utilized herein is shown in section in Figure 2, the same comprising a - material which is produced by radio frequency sputtering processes under carefully controlled conditions. The ~, .
- material 10 is based upon a substrate 12 comprising a 25 synthetic resin sheet material of a polyester type such as manufactured by E.I. DuPont De Nemours (U.S.A.), Celanese Corporation (U.S.A.) or Kalle A.G. (Germany) as a very stable, transparent, tough, flexible film extruded in ; ~ :

various thicknesses. The preferred substrate is of the order of a fraction of a millimeter in thickness. A thin film layer of ohmic material 14 is sputter deposited onto the surface of the substrate 12, the ohmic layer comprising preferably an alloy of indium oxide and tin oxide in the ratio of about nine to one. The thickness i9 between about 100 AngstrOms and 500 Angstrams to be conductive and yet quite transparent. A bonding layer 16 of a few Angstroms of cadmium sulfide can ke sputtered onto the substrate before laying down the ohmic layer 14. The upper coating 18 is the photoconductive material, being sputtered also and having a thickness of the order of 3000 Angstroms. Other thicknesses are usable, but generally they are substantially less than a micron.
It is practical to sputter the coating 18 dlrectly onto a sheet of metal for imaging conditions that do not j require transparency of the substrate, thereby eliminating '~ the need ~or a separate substrate 12. In Figure 6 such an electrophotographic member 10' is illustrated comprising the same type of coating 18 deposited on a sheet member 14' that serves as ohmic layer and substrate at the same time.
The sheet metal member 14' can be foil or rolled sheet from several microns to a millimeter thick and be fabricated from aluminum, nickel, stainless steel or alloys of these or other metals. The problem of grounding the middle ohmic layer 14 of the member 10 is eliminated since it is a simple matter to contact layer 14'. Furthermore, the heat resistant properties of metal are very much better .: . : . . .:

i86 than polyester so that sputtering heat, imaging heat and fixing heat post no problems.
The invention herein encompasses a system wherein the member 10' is a seamless, continuous cylinder to be mounted on a mandrel for imaging and supported in a printing press for printing as will be explained in connection with Figure 5.
The preferred material for the photoconductive coating is pure cadmium sulfide, which may be selectively doped with copper or carbon or the like to improve the response at the red end of the spectrum. The-coating `~
is formed of hexagonal crystallites of cadmium sulfide having very uniform morphology, vertically oriented and displaying single crystal characteristics in testing with electronic beams. There is a very thin barrier layer on the surface which has a surface resistivity of the order l7 to 1o20 ohms per square whether in light or darkness and whether charged or discharged. In the bulk and transversely, the coating exhibits electrical anisotrophy, the resistivity in darkness when charged being of the order of 10 5 ohm centimeters and in light being substantially less in the ratio of about 10 . The coating is extremely smooth on its surface and preserves the morphology of toner which is applied and fixed or transferred. It is abrasion-resistant and highly flexible. The entire member 10 itself isless than a millimeter thick, and can be passed around rollers easily without the likelihood of being scratched in passing ~86~6 through machinery. The member 10' is capable of being made with a total thickness of less than a millimeter and hence also can be very flexible.
The crystalline structure has no internal scattering and hence does not diffuse light which is directed into it normally during writing as happens in the case of all other known electrophotographic members having thicknesses which are very much greater or, as in the case of photographic films, emulsions which diffuse light.
The electrophotographic member 10 or 10' has a quantum gain which ~s very'high~ resulting in'the production of at least one electron for each absorbed - -' photon thereby providing a very substantial gain mechanism.
'' 15 The member can be charged or discharged at speeds of the order of nanoseconds. conventional electrophotographic ` members cannot be charged and discharged at speeds of this degree, and still retain the charge if not illuminated for periods of time of the order of minutes to a degree which still provides sufficient potential for saturation toning.
The high surface resistivity means that there is no loss of charge gradient through migration or edge effect when the surface is toned~ Each of the crystallite tips acts as an independent field domain, and since the -crystallites are about 700 Angstroms in diameter, thelimit of resolution depends only upon the size of particles in the toner.

~ 16 -Z36~1~

In Figure 3 there is illustrated a system for imaging by means of a radiant energy beam, which is in this instance a laser beam. The block 20 is representativa of a device which can scan a master image such as a document, photograph, paste-up or the like. This device can be mechanical and/or electrical. The information which is acquired by the scanning, which could be, for example, a i I light beam of very fine diameter, is transmitted to a device which converts the variations of beam intensity into electrical analog signals. For example, the device -could comprise a photoresponsive device such as a -photoelectric cell or a photomultiplier~ The block 22 represents th~e device. The resulting output from the device 22 is a stream of electric signals at 24 which are analog in nature, that is, their amplitude and/or intensity has a relationship with the reflectivity and absorptivity of the master image. If the master image is printed matter, the variegations are produced by different intensities and absence of printing ink. If the master image is a film, the scanning can be done by passing a beam through the film. If the master image is a document there can be typing, writing, etc. on the document. The master can be an electronic image scanned by an electron beam.
The analog signals at 24 now are converted into analog bits which are the equivalent of the analog signals ._, , .

- 17 _ 1~8~6 in an A/D converter 26 of any desired type. A/D converter 26 can be conventional. The resulting data is stored at 28 in a store of a computer. The data can be modified in the computer to provide a program for the writing of the data upon an electrophotographic member,taking into account the number of lines, the length of:the lines, the production of dots, the placement of the dots, their relationship with the surrounding data, and even the size of the dots.
The data storage block 28 represents an important part of the computer which can also include control ~
circuitry as represented by the block 30. This latter block can be an interface device which enables the control of the entire system to be directed from a single location outside the physical computer.
Up to this point, the data in the store 28 has been passing in a stream into the store 28 without regard to the remainder of the system. ~he system can be deenergized after scanning the master image and the information preserved indefinitely as for example on tape or disc or in other storage elements in the store 28 until needed. Facilities for accumulation of multiple sets of data from many different master images before use can be provided or there can be a simultaneous accumulation of a plurality of sets from the same master image such as in the case of color reproduction in which there is a separation of colors through the use of filters and/or by time sharing of the respective colors.

_ 18 -; . - : :
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The block 32 is a laser modulating device of any suitable type, for example, an acousto-optic deflector modulator as manufactured by Isomet corporation (U.S.A.).
The laser itself is represented by the block 34, its beam 36 being directed to the modulating device 32 that is in turn controlled to produce a fine stream of discrete bundles or bursts of photons at 38, reflected by the fixed mirror 40 onto the rotating mirror 42 mounted on the shaft 44. The rotating mirror 42 and shaft 44 are a part of a writing device 46 that carries a rectangular member 48 of the electrophotographic material 10 or 10' described above ~n connection with Figures 2 and 6 in an arcuate trough 50 of metal to which ohmic layer 14 is grounded, , i .
as for example, through clips 52 which hold the member 48 in position. In the case of a member 10' grounding is effected directly to the mandrel.
The member 48 is highly flexible and readily conforms to the interior cylindrical surface of the trough 50, being positioned therein with its photoconductive coating 18 exposed. The shaft 44 is an extension of the shaft 54 which is arranged coaxially with the curuature of the interior of the trough 50. It carries a small wheel 56 that has a plurality of radially extending needles 58 mounted-about its periphery in spaced arrangement. The needles 58 comprise corona generating means operating in conjunction with a corona power supply 60 that is coupled _ 19 --i~8~i~6 to the needles 58 through the connection indicated at 62 in Figure 2 through a slide-ring-wiper device 64 mounted on the shaft 54. The connection extends up the hollow of the shaft 54 as indicated by the broken line 62' in Figure 3 to the wheel 56. The wheel 56 can be made of insulating material, for example, having an annular peripheral metal ring mounting the needles 58 to which the line 62' is , connected.
;~ The shaft 54 is rotated by a suitable drive 66 and at the same time moved axially so that it can write the beam 38 along the entire length of the member 48 in a single pass. The apparatus 46 is set into operation when the wheel 56 and the mirror 42 are located at the extreme left end of the member 48, the wheel 56 being located in a position so that it will start at or beyond the left hand édge of the member 48. As the shaft 54 ~otates, the wheel 56 rotates and the needles 58 spray corona onto the surface of the member 48 charging the same. Simultaneously the shaft 54 is translated axially to the right as viewed , 20 in Figures 1 and 3 rotating the mirror 42 and also translating it. The spacing between the mirror 42 and the wheel 56 is fixed at a distance which is close enough so that there will be a uniform charge available to be written upon and so that the beam 38 is not so close to the wheel 56 as to have the beam and corona overlap. This will normally be determined by the umbra of the corona but can _ 20 -36~6 be a few centimeters. The construction of the corona mechanism will determine this distance.
It can be appreciated that the mirror 42 will reflect the beam 38 throuyh 360 of rotation in a structure of this kind and that if the data rom the store 28 is continuously fed through the control there will be a ; portion lost for each half revolution of the shaft 54.
,~ Accordingly, the control 30 is arranged to discontinue the feeding of data for the portion of rhe revolution during which the mirror 42 reflects the beam 38 away from the member 48. Any suitable sensing device 68 associated with the shaft 54 senses the circumferential disposition of the shaft and hence the position of the mirror 40. This information is pas~ed by way of a line 70 to a synchronizing circuit 72 operating in conjunction with the control structure 30 to delay the passage of data to the J laser modulating device 32 for each portion of the revolution of the sha~t 54 that the mirror 42 is not reflecting the beam 38 directly onto the member 48.
When the entire surface 18 of the member 48 has been imaged in darkness, the apparatus 46 being completely enclosed by a suitable light excluding cabinet indicated symbolically at 74, the member 48 can be toned in place or can be removed and toned in a separate piece of apparatus.
This entire process is indicated in the functional diagram of Figure 4, where the first block 76 indicates the charging of the member 48, the next block 78 indicates the 1~86~6 writing or imaging of the member by the mirror 42, the next block 80 indicates the toning of the member, and the last block 82 indicates the fixing of the member 48. Fixing is done either by heat or chemically, or can be inherent in the type of toner used. With the member 48 in fixed condition, conversion into a printing plate can be effected by suitable treatment to render the toned and untoned portions ink accepting and ink rejecting, respectively.
` Certain types of toned images may not require such treatment.
Alternatively, the member 48 can be used as a transparency after fixing if based upon a transparent substrate as 12. As another aLternative, the member 48 can 'J' . be brought into contact engagement with a receptor such as ' paper, polyester or the like indicated by the block 84, to lS transfer the toned image to the receptor. Thereafter the receptor is fixed as incidated at 86.
An alternative embodiment of the invention which eliminates the need for the rotating mirror 42, the uses of a corona wheel 56, the axial movement of the shaft 54 a~d the need for synchronizing the operati~ of the laser modulator 32 with the productive portion of the mirror rotation, is illustrated in Figure 5.
The device 100 of Figure 5 is intended for imaging a cylinder of electrophotographic film which is indicated at 102. The cylinder 102 formed by joining the ends of a rectangular member of electrophotographic film lO
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i ~86~6 Or 10' or can comprise an integral seamless cylinder of electrophotographic film 10' formed by sputtering the described materials upon a tubular metal member o~ the :: substrate 14' preformed for this purpose.
The device 100 includes a base 104 having end standards 108 mounting.a ~ylindrical mandrel 110 journalled therein and driven by a high speed motor 112.
- A guide or track 114 is mounted parallel with the mandrel110 upon suitable brackets 116 that are mounted on the base 104. The carriage 106 is mounted for sliding movement along the guide 114 having a corona wire 118 stretched between a pair of posts 120 mounted on the carriage 116 and energized from a suitable corona power source through ~ the cable 122. At the end of the carriage 116 opposite : 15 the corona wire 118, there is mounted a reflecting prism 124 which is aligned with and receives the beam 126 of modulated light reflected from the laser device 32,34 by the mirror 128.
The carriage 116 is connected to one reach of a wire loop 130 by a coupling member 132, the wire loop being engaged over an idler roller 134 carried on a bracket 136 mounted to the base 104 and wrapped around a drive wheel 138 adapted to be rotated by a suitable motor 140.
The entire structure is enclosed in a suitablè
enclosure which enables the process of charging, writing and toning to be carried on in darkness~ The same structure used in connection with the system of Figure 3 is useful to read the master image and then write the same image upon - - .

;86 the cylindri~al sleeve 102. In use the wire 118 charges the cylinder 102 a portion at a time and immediately thereafter the beam 126 images the cylinder with the discrete bundles -`~ or bursts of photons designed to apply the dots or other ; 5 regular geometric shapes of charge or absence of charge in forming the latent reproduction of the master image.
The ohmic layer 14 or 14' o the mounted member 102 is grounded.
After imaging, it is convenient to have a movable toning device L42 which can be swung into position on the arms 144 to apply toner to the latent image. As shown here the toner device has a hood 146 with several rollers 148, a plate 150 and a slot 152 all of which are the general ~I type of means that can be used to apply liquid toner, remove the excess, bias the liquid to remove extraneous pa~ticles of toner, apply rinse, etc. No specific structure is intended to be shown for the toning device 142. The remainder of the components of the imaging device 100 of Figure 5 are illustrated more or less diagrammatically.
The parts are required to be constructed to provide for many functions which would be advantageous from an engineering standpoint and to enable convenient use of the invention. For example, the mandrel 110 can be constructed so that it can readily be removed from its journals to enable the sleeve 102 to be mounted thereto and removed therefrom; the guide 114 and its mountings as ~ell as the wire loop 130 should be located so as not to interfere with - ~4 _ ! the attachment and removal of the sleeve 102 and hence can `I be arranged to be swung into and out of position as I mentioned for the toning device 142; controls are required .
for starting up, stopping, and synchronizing the operation S of the motors 112 and 140 to integrate with the operation of the -entire system, etc.
Likewise, considerable electrical connections and cables are not shown in Figure S or in Figure 1.
After toning and fixing, the latter being readily effected by a simple heating operation, the sleeve 102 can be removed from the apparatus 100, treated to render the image ink-receptive and its background ink-repellent. The resulting cylinder is now capable of being installed ip an t ~ offset printing press as a printing cylinder.
Further, instead of charging the photoconductive surface progressively a portion at a time, it is feasible to charge the entire length of a cylinder or half cylinder of the electrophotographic material using a fixed elongate corona wire or other independently mounted corona producing means arranged axially and capable of applying the charge the entire length in one revolution of the support. No axial movement of the corona means would occur.
It would normally be considered impractical to do this because the surface potential along the length of the member 48 or 102 would be uniform when charged but progressively less along the length as the carriage 54 or ,~
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6~Çi .
~^ 166 with the beam directing means only moves along such length. The reason for the decrease is that the dark decay will be greater the longer it takes for the carriage 54 or 116 with beam directing means only to reach any axial position. It would follow from what is known that the latent image would have a variable average surface potential along its length, with a consequent unsatisfactory toned image.
The reason this concept is practical is that the invention enables the toning to be saturated and only depends upon the charged increments exceeding a certain critical voltage. The only requirement for perfect production of a tonable latent image in such example .
! therefore, is that the surface voltage at the end of writing be greater than the critical voltage by a value that provides for a slight additional decrease between the completion of the writing process and the beginning of the toning process. The maximum axial length of any given electrophotographic member can be determined easily by measuring decrease of surface potential in the time required to write along the entire length and adjusting parameters so that the requirement described above is met.
It is preferred to charge and write with the use of moving carriages which have both charging and beam directing devices and arrangements respectively as disclosed herein, so that there is no concern of dark decay decreasing too far for a given length of electrophotographic member.

_ 26 -i ~ ~8686 I ~he use of the phrase "master image" is intended ¦ to signify an actual image, data that is being generated ;j on real time without first actually forming an image, I computer generated data derived from a store or produced :1 5 by artificial methods or the like. No limitation is , intended by use of the convenient phrase "master image".

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Claims (25)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of imaging through the use of electrostatic techniques which comprise:
A. scanning in accordance with a predetermined scanning pattern a master image with a reading beam of energy that can be modulated by variations of the reflectivity or absorptivity which constitute the master image, B. converting the modulations into a stream of electric signals related to said variations, C. converting the stream of electrical signals into radiant energy in fine beam form, said radiant energy beam being modulated in a predetermined relation to the modulations of the reading beam, D. directing the fine beam in darkness to write the signals onto a charged area of an electrophotographic member having a charge-accepting thin film, transparent, microcrystalline, electrically and optically anistropic, high quantum gain, wholly inorganic photoconductive coating in a scanning pattern which is related to the master image to produce a latent image of the content of the master image on the coating, and E. thereafter developing the latent image.

2. The method as defined in claim 1 and the step of storing the electrical signals in a store and converting the stored signals at any time after storage into radiant energy.

3. The method as defined in claim 1 and the steps of converting the modulations of the reading beam first into digital data and then storing same in a store and the fine beam comprises discrete signals representative of said digital data.

4. The method as defined in any one of claims 1, 2 or 3 in which the coating is charged in darkness. ,

5. The method as defined in any one of claims 1, 2 or 3 and the step of effecting the charging progressively over the desired area of the coating a portion at a time and effecting writing of the latent image at the same rate but spaced later in time so that each portion of area charged is immediately thereafter written upon by the fine beam.

6. The method as defined in any one of claims 1, 2 or 3 in which the master image is a visible image and the reading beam is also a radiant energy beam, the modulation of the radiant energy reading beam being produced by the master image being produced by the variations of the reflectivity or absorptivity of the visible image.

7. The method as defined in any one of claims 1, 2 or 3 and the step of effecting the charging progressively over the desired area of the coating a portion at a time and effecting writing of the latent image at the same rate but spaced later in time so that each portion of area charged is immediately thereafter written upon by the fine beam, the fine beam signals being adjusted physically to produce discrete photon bursts of predetermined geometric configuration in a plane normal to the beam, each burst producing a spot of contrasting charge on said coating, the number of spots in any given unit of area being related to the degree of reflectivity or absorptivity of the scanned area of the master image equivalent to said unit area.

8. The method as defined in any one of claims 1, 2 or 3 and the step of effecting the scanning by moving the reading beam and master image relative to one another to cover the master image with a series of parallel read lines along a length of the master image, and duplicating the same relative movement between the fine beam and the electrophotographic coating, to effect the writing.

9. The method as defined in any one of claims 1, 2 or 3 in which the electrophotographic member is formed into a cylindrical formation and a rotary movement of the electrophotographic member and the fine beam relative to one another is effected to write lines equivalent to said parallel read lines onto the photoconductive member.

10. The method as defined in any one of claims 1, 2 or 3 in which the fine beam is a laser.

11. Apparatus for high speed imaging of an electrophotographic material, said apparatus including a source of data that is representative of information capable of being developed into a master image, a rediant energy device having a fine beam of discrete bursts of energy derived from the source and capable of producing the master image if used to write the fine beam upon a suitable responsive medium, an electrophotographic member including a photoconductive coating capable of accepting and discharging a charge at high speed, means for charging the coating of the member in darkness to a surface potential capable of being discharged by said fine beam, means capable of receiving said fine beam, means for directing said fine beam onto said coating in darkness, means mounting the electrophotographic member in darkness, means for effecting relative movement between the mounting means and the directing means so as to cause any said beam received to engage against and scan the coating for producing a latent image of said master image if the coating has previously been charged, and means for developing any latent image formed.

12. The apparatus as defined in claim 11 in which the charging device is arranged to charge a portion of said coating at a time and progressively charge the entire member while the directing device is operating but being located in a position to charge any given portion before it is written upon.

13. The apparatus as defined in claim 11 in which the charging means are arranged to move to charge a portion of the coating at a time and progressively charge the entire coating while the last-mentioned relative movement is taking place but the charging means being located in a position relative to the directing means such that the charging of any given coating portion occurs before said beam will engage said coating portion during its scanning.

14. The apparatus as defined in claim 11 in which said charging means are constructed to charge only a portion of the coating at a time, said directing means comprising a movable carriage having a beam deflector for pointing the writing beam directly to the coating from a point on the carriage, said charging means including a corona producing device mounted on the carriage spaced from said point in a direction which will bring the corona producing device progressively into proximity with each portion of the coating before the writing beam engages the same, but at the same scanning rate.

15. The apparatus as defined in claim 11 in which the charging means are constructed to charge the entire coating progressively but only a portion at a time,a movable carriage having the charging means and directing means both mounted thereon spaced apart and said means for effecting relative movement comprise driving means for moving the mounting means and carriage relative to one another with the carriage disposed in such a manner that any given coating portion will be charged before the beam engages the same.

16. The apparatus as defined in any one of claims 11, 12 or 13 in which said mounting means comprise a support holding said electrophotographic member in a cylindrical configuration and in which means are provided to move the carriage axially along the length of the electrophotographic member while at the same time the carriage and member are moved rotatively one relative to the other.

17. The apparatus as defined in any one of claims 11, 12 or 13 in which said mounting means comprise a support holding said electrophotographic member in a cylindrical configuration, means are provided to move the carriage axially along the length of the electrophotographic member while at the same time the carriage and member are moved rotatively one relative to the other and means are provided to move the carriage on a line outside of the cylinder defined by the electrophtographic member, the coating of the member is on the exterior of the cylindrical configuration and the rotative movement is effected by rotating the mounting means.

18. The apparatus as defined in any one of claims 11, 12 or 13 in which said mounting means comprise a support holding said electrophotographic member in a cylindrical configuration, means are provided to move the carriage axially along the length of the electrophotographic member while at the same time the carriage and member are moved rotatively one relative to the other and means are provided to move the carriage on a line coaxially of the electrophotographic member, the coating is disposed on the inside of the cylindrical configuration and the rotative movement is effected by rotating the carriage on an axis defined by said line.

19. The apparatus as defined in any one of claims 11, 12 or 13 in which the electrophotographic member is a complete cylinder.

20. The apparatus as defined in any one of claims 11, 12 or 13 in which the electrophotographic member is a partial cylinder of generally part circular cross section.

21. The apparatus as defined in any one of claims 11, 12 or 13 in which the directing means comprise an angled mirror mounted on said axis and rotating with said carriage and further including means to discontinue the beam for that part of each revolution that the beam is reflected away from the coating.

22. The apparatus as defined in any one of claims 11, 12 or 13 in which said source includes means for scanning a master image with a reading beam of energy which can be modulated by variations of reflectivity or absorptivity which constitute the master image in accordance with a predetermined scanning pattern, means for covering the modulations into a stream of electric signals, means for converting the stream of electric signals into the said fine writing beam.

23. The apparatus as defined in any one of claims 11, 12 or 13 in which said source includes means for scanning a master image with a reading beam of energy which can be modulated by variations of reflectivity or absorp-tivity which constitute the master image in accordance with a predetermined scanning pattern, means for converting the modulations into a stream of electric signals, a store to enable the storing of said stream of electric signals and means for thereafter converging the stored signals into said writing beam.

24. The apparatus as defined in any one of claims 11, 12 or 13 in which said source includes means for scanning a master image with a reading beam of energy which can be modulated by variations of reflectivity or absorp-tivity which constitute the master image in accordance with a predetermined scanning pattern, means for converting the modulations into a stream of electric signals, a store to enable the storing of said stream of electric signals and means for thereafter converting the stored signals for said writing beam, the said fine beam being a laser beam.

25. The apparatus as defined in claim 11, wherein the source of data is in binary form.