CA1170117A - Electrostatic printing and copying - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Electrostatic printing is disclosed in which an electrostatic latent image is formed on an imaging roller, toned, and transferred by pressure to plain paper. Toner transfer efficiency is improved by providing a skew between the dielectric imaging roller and a pressure roller. The latent image is formed by an ion generator consisting of two electrodes separated by a mica dielectric. The ion generator is fabricated by laminating a metal roll to mica using pressure sensitive adhesive, and etching the roll to form electrodes.
An alternative ion generator consists of a dielectric-coated wire and a series of transverse conductors. A preferred method of fabricating the dielectric roller involves anodizing an aluminum cylinder, and impregnating the surface pores with a metallic salt of a fatty acid while maintaining the pores in a substantially moisture-free state.
In photocopying, an electrostatic latent image is optically created on a precharged photoconductor and transferred to a dielectric member where it is developed with toner particles and the toner image is transferred to plain paper.
The apparatus for either printing or photocopying may be employed for duplex imaging with simultaneous pressure transfer and fusing of the toned images.

Description

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BACKGROUND OF TH NVENTION
This lnvention relates to electrostatic prlntlng and photocopying, partlcularly at hlgh speeds.
Electrostatlc prlnters and photocopiers share a number of common feàtures as a rule, although they carry out different processeR. Electrostatlc printers and photocoplers which are capable of producing an image on plain paper may generally be contrasted ln terms of the method and apparatus used to create a latent electrostatlc--image on an lntermedlate member.
Copiers generally do so by uniformly charglng a photoconductor electrostatlcally ln the dark, and optlcally exposlng the charged photoconductor to an image corresponding to the lmage to be reproduced. Electrostatlc prlnters use non-optical means to create a latent electrostatlc lmage on a dielectrlc surface, in respon~e to a ~lgnal indlcatlve o~ an lmage to be created.
In theory, a~ter creatlon o~ the electrostatic latent lmage, the same apparatus could be used to carry out the common steps of tonlng the lmage, transferrlng lt to plain paper, and preparlng the member bearing the electrostatic latent lmage for a sub~equent cycle, usually by erasure of a resldual latent electroAtatlc image. It would, in ~act~ be desirab;le to standardl~e the apparatus to per~orm these ~unctlons.
One commonly employed prlnciple for generating lons is the corona dlscharge from a small diameter wlre or a point source.

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Illustratlve U.S. Patent Nos. are P. Lee 3) 358,289; Lee F.
Frank 3,611,414; A.E. Jvlrblls 3,623,123; P.J. McGlll 3,715,762; H. Bresnik 3,165,027i and R.A. Fotland 3,961,564.
Corona dlscharge~ are used almost excluslvely ln electrostatlc coplers to charge photoconductors prlor to exposure, as well as for discharglng. These applicatlons requlre large area blanket charging/dlscharglng, as opposed to ~ormation o~ discrete electrostatic lmages. Unfortunately, standard corona ,, dlscharges provide limited currents. The maxlumum dlscharge current density hereto~ore obtained ha~ been on the order o~ 10 mlcroamperes per square centimeter. Thls can impose a severe printlng speed llmitation. In addltion, coronas can create slgnlficant maintenance problemsO Corona wire~ are small and fragile and easily broken~ Because of their hlgh operating potentlals they collect dirt and dust and must be frequently cleaned or replaced.
Corona dlscharge devlces whlch en~oy certaln advantages over standard corona apparatus are dlsclosed ln Sarld et al., U.S. Patent No. 4,057,723; Wheeler et al. 4,068,284; and Sarld 4,1109614. These patents dlsclose various corona char~lng devlces characterlzed by a conductlve wire coated with a relatlvely thlck dlelectric material9 ln contact with or closely ~paced ~rom a ~urther conductlve member. A supply of posltive and negative lons i~ generated ln the air space surrounding the coated wlre9 and ions of a particular polarity .

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are extracted by a dlrect current potentlal applled between the ~urther conductive member and a counterelectrode. Such devlces overcome many of the above-mentloned disadvantages of prlor art corona charging and dlscharging devices but are unsuitable rOr electrostatic lmaging. Thls limitatlon is lnherent ln the feature of large area charglng, which does not permlt formatlon of dlscrete, well-defined electrostatic imagesO This prior art corona device requlres relatlvely hlgh extraction potentials due to greater separat-lon from the dielectrlc receptor.
Various toner lmage transfer methods are known in the prlor art. The transfer may be accomplished electrostatically, by means of a charge of opposlte polarlty to the charge on the toner partlcles, the former charge being used to draw the toner partlcle~ o~f the dlelectric member and onto the image receptor. Patents lllustrative of this transfer method include U.S~ Patent NosO 2,944,147; 3,023,731; and 3,715,762.
Alternatlvely, the lmage receptor medlum may be passed between the toner-bearing dielectrlc member and a transfer member, and the toner lmage trans~erred by means of pressure at the polnt of contact. Patents illu trative of thls method lnclude U.S~
Patent Nos. 3,701,966; 3,907,560; and 3,937,5710 Usually, the toner lmage ls fused to the ima~e receptor subsequently to transfer o~ the lmage, at a further process station.
Po~t~u3ing may be accompllshed by pressure, as in U.S. Patent No. 3,874,894, or by exposure of the toner partlcles to heat, as ln U.S. Patent No. 3,023,731, and ReO No. 28,6930 ~' ~ 17011 ~

It ls possible, however, to accompllsh trans~er and fuslng of the lmage simultaneously, as shown ~or example ln the patents clted above as illustratlve of pressure transrer. Thls may be accomplished by a heated roller, as in Re. No. 28,693, or slmply by means of high pressure between the i~age-bearing dielectrlc me~ber and a trans~er member, between whlch the image receptor passes.
A problem whlch ls typlcally encountered in transferrlng a toner image solely ~~y means Or pressure 18 the exlstence of a residual toner image on the dlelectrlc member after image transrer, due to lnefflclencle~ ln toner transfer. The resldual toner partlcles requlre scraper blades or other removal means, and accumulate over tlme at the varlous process station~ associated wlth the dlelectrlc member~ lncludlng the apparatus ~or ~ormlng the latent electrostatlc lmage. These toner accumulatlons decrease the rellabllity of the apparatus, necessltating servlce at lntervals. Furthermore, inef~lclencie~ ln toner transfer may lead to mottling o~ the images formed on the lmage receptor sheets. These problems have not been overcome in the prior art through the use of extremely hlgh pre~sures at the trans~er nip.
A phenomenon which ls commonly ob~erved when ~ub~ecting rollers to hlgh pressures 1~ that o~ "bowing" o~ the rollers.
This phenomenon occurs when the rollers are sub~ected to a high compressive rorce at the ends, thereby imparting a camber to ~ 7' '' ~ ' ' ' ' ' ' ~011'~
each roller. The efrect ls to have hlgh pressure at the ends of the rollers but lower pressure at the center. It is known ln the prior art to alleviate thl~ problem when encountered ln pressure fusing apparatus by skewlng the pressure rollers, i.e.
by ad~usting the mounting of the rollers to create an oblique orlentatlon of the roller axes. Representatlve United States patents lnclude U.S. Patent Nos. 3,990,391; 4, lsa ~104;
4,192,229; and 4,200,389. Thls technique has the dlsadvantage of causlng "walklng"-of a receptor sheet fed between the rolls.
In additlon, thls apparatus commonly encounters the problem Or wrlnkling of the receptor sheets.
Hardcoat anodizat~on of aluminum and alumlnum alloys is an electrolytlc proce~s which is used to produce thick oxide coatlng~ with 3ubstan~ial hardness. Such coatings are to be dlstlngulshed from natural fllms of oxide whlch are normally present on alumlnum surfaces and froM thln, electrolytically ; ~ormed barrter coatings.
The anodizatlon Or aluminum to ~orm thick dlelectric coatings takes place ln an electrolytlc bath contalnlng an oxlde, such as sulfuric or oxallc acid, ln whlch aluminum oxide ls slightly soluble. The production technique~, pr~pertles, and applications of these aluminum oxide coatlngs are described ln detall ln The Surface Treatment and Finlshln~ o~ Alumlnum by S. Wernlck and R. Pinner, fourth edition, 1972, published by ~obert Draper Ltd., Paddington, England (chapter IX page 563). Such coatings are extremely hard and ~`

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mechanically superior to uncoated aluminumO However~ the coatlngs contaln pores ln the ~orm of ~lne tubes wlth a poroslty on the order of 101 to 10l2 pores per ~quare inch. Typlcal porosltles range from 10 to 30 percent by volume. These pores e~tend thr-ough the coating to a very thin barrler layer o~ alumlnum oxlde~ typlcally 300 to 800 Ang~troms.
U.S. Patent No. 3,664,300 dlscloses a process ~or surface treatment o~ xerographlc lmaglng cyllnders wherein the surface ls coated with zlnc stearate to provlde enhanced surface lubrlcatlon and improved electrostatlc toner transfer. Thls treatment technique does not, however, result ln a permanent dlelectrlc surface of requisite hardness and smoothne~s for pressure transPer and fusing Or a toner lmage.
For lmpro~ed mechanlcal propertles a~ well as to pre~ent stainlng, lt is customary practlce to seal the pores. One standard sealing technique involves partlally hydrating the oxlde through lmmerslon ln bolllng water, usually containlng certain nickel ~alts, whlch ~orm an expanded boehmlte structure at the mouth~ of the pores~ Oxlde seallng in this manner wlll not support an electrostatic charge due to the lonic conductivlty of molsture trapped in the pores.
It ls o~ten deslrable in electrostatic prlnting and copying to creat~ an lmage on both sldes of a sheet o~ paper or other receptor. In electrophotography, the most accurate .

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reproductlon of a two-slded origlnal document would requlre thls ~aculty. In electrographlc printing, duplex imaglng affords signlficant savlngs in paper costs and permlts a greater flexlbllity ln printing formats.
A crlterlon whlch should be consldered in modlfylng an exlstlng slngle-sided printlng or copying system to permlt duplex lmaglng ls the extent to whlch the system ~ust be modi~ied or supplemented. It ls advantageous to employ a system which is struc'~urally compatlble with two-sided image productlon requlring only mlnor changes.
Another factor of some importance ls the speed and efflciency wlth which the system transfers the two images. In particular, it is deslrable that such a system allow the slmultaneous ~using o~ the two images onto a receptor medium.
The lnventlon provldes compatlbility of design ~or electrostatlc printing and photocopylng apparatus. It also provides high speed printlng and photocopying with excellent image quality.
The lnventlon ~urther provides a plain paper photocopying 3ystem whlch 1~ simple, compact9 and low in cost~ The photocopying s~tem requlres ~ewer proce~ing steps, than those o~ conventlonal copylng ~ystemsg with an extremely short and simple paper path.
The lnventlon 1 further able to reduce crltlcal mechanlcal tolerances in providing a latent electrostatic image .~

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ln an electro~tatlc prlnter. It thus reduces the malntenance problems assoclated wlth the formatlon of such an lmage~ and lt can facilitate the generation of ions, partlcularly at high current densltles, for use ln electrostatlc printlng and photcopylng, as well as other appllcatlons.
A partlcular fabricatlon technique is glven for lon generators characterized by a lamlnate of mica and foll electrodes. This deslgn is durable, resisting delamlnation due to molsture and erosfon due to ozone, nltrlc-acld and other envlronmental substances. Such a laminate is physically stable over a wide range of temperatures, and can carry hlgh peak voltage RF slgnals over a long servlce llfe.
The inventlon also provldes an alternatlve ion generator deslgn based upon a corona electrode, whlch achleves high current denslties wlth an easily controllable source of ion~0 This apparatus does not require the crltlcal periodlc maintalnance normally characteristic of such corona devlces, and avolds the obJectlonable operatlonal characterlstics Or corona wires.
The lnventlon provldes electrostatic imaglng apparatus ~or pressure transfer of a toner lmage ~rom a dlelectrlc surface to plain paper and the like. Such apparatus e~fects simultaneous fusing Or the toner lmage, and ls characterized by a hlgh efflciency of toner trans~er.
A preferred embodiment of the inventio~ lncorporates an lmpregnated aluminum layer for the dlelectrlc member. This .

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dlelectrlc surface possesses smoothness and hardness propertles whlch racilltate toner transfer, while possesslng suf~lclent reslstivlty to obtain a latent electrostatlc lmage untll tonlng. The dielectrlc surface created by thl~ pre~erred method maintains the above propertles at elevated humldities.
The apparatus of the lnventlon may be employed in duplex lmaging onto plain paper and the like. This duplex lmaging en~oys the advantage of the avoldance o~ offset images and other problems often associated wlth duplex lmaglng. It also achleves a simultaneous transrer and ~using o~ two lmages onto a receptor medlum.
SUMMARY OF THE INVENTION
m e lnve'ntlon encompas~es both electrophotography and electro~tatlc prlnting~ as well as preferred components to be employed ln these processes. The lnventlon also ~ncompas~e~
two alternatlve ion generator deslgns, the flrst o~ whlch may be used to precharge a photoconductor or to form a latent electrostatlc lmage, as well as other applicatlons. The ~econd lon generator i~ speci~lcally adapted to the formatlon Or an electro~tatlc lmage.
A first aspect of the inventlon relates to the structure of,the lon generators, whlch are characterlzed by the use o~ a glow discharge to generate a pool of po~itlve and negative ions, which may be extracted for appllcation ts a further member. In the fir3t lon generatorJ a varylng potential is applled between two electrodes separated by a solld dlelectrlc 1 :~7V I l '~

member to cause an electrical air gap breakdown adJacent the Junctlon o~ the edge sur~ace o~ at least one of the electrodes and the solld dielectrlc member. In the second lon generator, a varylng potentlal ls applled between an elongate conductor having a dlelectrlc sheath and a transverse conductlve member in order to generate lons at a crossover polnt of these structures. Both lon generator embodlments may be characterized as lncludlng a control electrode and a drlver electrode; an extraction potential applied to the former electrode ls used to extract lons from the glow dlscharge created by the varyin~ potential.
Another aspect of the lnventlon i~ seen ln the shared processlng stages in the electrostatic copler and prlnter apparatus Or the lnventlon. After an electrostatlc latent lmage has been ~ormed on a dlelectric cyllnder, the image is toned and pres~ure tran~erred to plaln paper or any ~ultable lmage receptor. Pre~erablyg thls trans~er is achieved by lnsertlng the lmage receptor between the dlelectrlc cylinder and a transPer roller und~r high pres~ure. Advantageously, thls pres~ure trans~er 18 e~ected with slmultaneou~ fuslng of the toner lmage. Provlslon may be made ~or cleanlng the surface o~ the dlelectric cylinder and transfer roll, and ~or dlscharglng any resldual electrostatlc image on the dielectrlc surface.
In a preferred embodlment o~ the invention, the pres~ure transfer of the toner lmage e~fected by dielectrlc and transfer ., I .

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rollers may be enhanced by providing a skew between the dlelectrlc and transfer rollers. In the nip between the rollers, the ratlo o~ the dielectric surface speed to the lma~e receptor speed is advantageously in the range oP about 1.01 to 1.1, most advantageously between 1.02 and 1.04. Best results are achleved where the dielectric surface has a smoothness in excess Or 20 microinch rms, and a hlgh modulus of elasticity.
The trans~er roller ls preferably coated with a stress-absorbing plastlcs materlal~ The roller materlals are advantageously chosen so that the lmage receptor wll~ have a tendency to adhere to the surface of the trans~er roller ln pre~erence to that o~ the dlelectrlc roller. The apparatus provldes e~ectlve toner trans~er and ~uqlng wlthout wrlnkllng o~ the receptor medlum.
In the preferred verslon Or the ~lrst lon generatorj thi~
device comprises a plurallty of foll electrodes bonded to opposlte faces of a mlca dlelectrlc sheet. The invention provldes a preferred method for fabrlcatlng lamlnatlons of mlca and conductlve materlal~, whlch technlque may be advantageously employed to produce such an lon generator. Suoh lamlnatlons lnclude a sheet of mlca, one or more metalllc sheets, and bondlng layers Or pres~ure sensltive adheeiveO ~he conductive layer or layers may be selectively removed as by etching to create a deslred electrode pattern.
Another aspect o~ the invention relates to a pre~erred method o~ ~abrlcatlng a dielectrlc member havlng a smooth3 hard , , j ~70117 surface with a reslstlvlty ln excess of 1012 ohm-centlmeters;
such a technlque may be employed to advantage in produclng a suitable dlelectrlc cyllnder. This method provldes ~or the preliminary dehydratlon o~ an anodlc alumlnum member followed by lmpregnation o~ surface pores of the dehydrated member wlth a metallic salt of a fatty acld. After completion of the lmpregnating stage, any excess impregnant ls removed ~rom the member's sur~ace. In the preferred version of this technlque, the surface is then~pollshed to a better than 20 mlcrolnch flnish. The lmpregnant materlal conslsts essentially o~ a Group II metal with a fatty acid contalning between 8 and 32 carbon atoms, ~aturated or unsaturated.

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BRIEF DESCRIPTION OF THE DRAWINGS
Ihe above and additional aspects of the lnvention are illustrated with re~erence to the detailed descrlption whlch follows, taken in con~unction wlth the drawlngs ln whlch:
FIGURE 1 ls a sectional schematic vlew o~
electrophotographlc apparatus ln accordance with a pre~erred embodiment o~ the lnvention;
FIGURE 2 is a partlal sectlonal schematlc vlew of the nlp area Or the upper rollers o~ Figure l;
FIGURE ~ ls a sectlonal schematlc vlew o~
electrophotograhlc apparatus ln accordance with an alternatlve embodlment of the inventlon;
FIGURE 4 13 a sectlonal schematlc vlew o~ electrostatlc prlntlng apparatus in accordance with a pre~erred embodiment Or the inventlon;
FIGURE 5 is a partlal sectlonal schematic vlew of an lllustrative charge neutrallzing devlce for the dielectric roller o~ Flgure 4;
FIBURE 6 ls an elevation vlew o~ a pre~erred mountlng arrangement ~or electrostatlc prlnting apparatus o~ the type lllustrated ln Figure 4;
FIGURE 7 is a schematlc vlew of the rollers of Flgure 7 as seen rrom above;

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FIGURE 8 ls a geometrlc repre3entatlon Or the contact area of the rollers o~ Figure 6;
FIGURE 9 is a plot of resldual toner as a ~unction of end to end skew ~or ~he apparatus of Example IV 3;
FIGURE 10 ls a sectional vlew of lon generatlng apparatus ln accordance with the pre~erred embodiment;
FIGURE 11 ls a sectional view of the lon generatlng apparatus o~ Flgure 10, further ~jhowlng lon extractlon apparatus and an lon~receptor member;
FIGURE 12 ls a plan view o~ dot matrlx printlng apparatus o~ the type lllustrated in Flgure 11;
FIGURE 13 ls a ~chematlc sectlonal vlew of a mlca ~oll lamlnate ln accordance wlth the lnvenkion;
FIGURE 14 ls a partlal perspective vlew o~ an electrostatlc imaging devlce in accordance with an alternatlve embodlment of the lnvention;
FIGURE 15 ls a ~chematic sectlonal view o~ the apparatu~
of Flgure 14, further includlng ion extraction apparatus and an lon receptor member;
FIGURE 16 is a cutaway perspective vlew Or an alterna~ive ver310n o~ the lmaging apparatus of Figure 14;
FIGURE 17 18 a cutaway perspective vlew of a ~urther alternative verslon o~ the electrostatic imaglng appara~u~ o~
Flgure 14;
FIaURE 18 ls a plan vlew o~ matrix lmaging apparatus o~
the type shown ln Flgure 14;

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FIGURE 19 i~ a sectional schematlc vlew o~ a three electrode embodlment of the lmaging device of Flgure 16;
FIGURE 20 is a perspective vlew Or an electrostatlc imaglng devlce ln accordance wlth yet another embodlment of the lnvention;
FIGURE 21 is a plan vlew Or a serlal prlnter incorporatlng an electrostatlc lmaging devlce o~ the type illustrated in Flgure 15;
FIGURES 22-27 are--~equential schematic views of electrostatic lmaglng apparatus of the type lllustrated in Figure 4~ adapted to duplex lmaglng in accordance wlth the inventlon;
FIGURES 28-32 are partlal perspectlve vlews of electrostat~c lmaglng apparatus of the type illustrated in Flgure 4, showlng an electrostatlc latent image and a resulting toner lmage ror varlous stages of the duplex trans~er process in accordance wlth the inventlon;

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DETAILED DESCRIPTION
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I. Introductlon Two maln embodlments of the lnventlon are described, namely the double trans~er electrophotographlc apparatu3 which ls the sub~ect o~ Section II, and the electrostatlc transfer prlnter whlch ls the sub~ect of Section III. The~e two embodiments dlffer ln the means by whlch a latent electrostatic image is created on a dlelectrlc imaging roller; thereafter, identlcal apparatus may be employed.
The skewed roller apparatus of Section IV is proritably employed to provlde enhanced toner transfer and ~uslng ln either of the main embodiments. The ion generator and extractor of Sectlon V may be used in either of the maln embodlments. Section VI dlscloses an alternatlve lon generator and extractor whlch may be incorporated in the printing apparatus of Sectlon III. The impregnated anodlzed aluminum members of Sectlon VII are ~ultable ~or applications requirlng good dlelectrlc propertles and a hard, smooth surface. These are qualities whlch are preferred in the imaglng roller o~ both baslc embodlmentsO The apparatus of elther main embodiment may be modifled to provide duplex lmaglng capabillty, as disclosed ln Section VIII.
II. Double ~ransrer Electrophotographic- System Flgures 1 to 3 show double transfer electropho~ographlc apparatus 10 comprised Or three cyllnders, and varlous process statlons~ -.:

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The upper cyllnder ls a photoconductive member 11~ whlch includes a photoconductor coatlng 13 supported on a conducting substrate 17 9 wlth an lntervenlng semlconductlng substrate 15.
Advantageous materlals ~or the photoconductor ~urrace layer 13 include cadmium sulphlde powder dispersed ln a resin binder (photoconductlve grade CdS is employed, typically doped wlth actlvating substances ~uch as copper and chlorine), cadmlum sulphoselenide powder dlspersed ln a resin binder (de~lned by the ~ormula CdSxSey~- ~fiere x+y-l), or organlc photoconductors such as the equimolar complex of polyvinyl carbazole and trinitrofluorenone.
The photoconductor i~ electrostatlcally charged at charging statlon 19 and then exposed at exposing station 21 to.
form on the sur~ace of the photoconductor an electrostatic latent image o~ an origlnal. The photoconductor may be charged employing a conventlonal corona wire assembly, or alternatlvely it may be charged using the lon generat1ng scheme described in subsectlon V below (Flgure 14). The optlcal lmage which provldes the latent lmage on the photoconductor may be generated by any o~ several well known opt~cal scannlng schemes. Thls latent lmage is trans~erred to a dlelectric cyllnder 25 ~ormed by a dielectrlc layer 27 coated on a metal substrate 29~ The latent electrostatic lmage on the dielectric cylinder 25 ls toned and trans~erred by pressure to a receptor medlum 35 whlch ls fed between the dlelectrlc cyllnder 25 and a trans~er roller 37O There are means 43, 45, 47 to remove ,:~`''', , .. _ ... .. . .. .. _ _ . _ _ . _ ,, , , . . ~ .

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resldual toner from cyllnder 25 and roller 37 and to erase any electrostatic image remalning on cylinder 25 a~ter transfer.
Apparatus ~or effectlng tonlng and subsequent steps, shown generally at 30 ln Figure 1, is discussed in detall ln subsection IIIB below~
The method by which a latent electrostatlc image is transferred from the photoconductive cylinder 11 to the dielectric cylinder 25 employs a charge transfer by air gap breakdown. The proce~s o~ uni~ormly charglng and exposing the surface o~ the photoconductor coating 13 results ln a charge den~ity distribution corresponding to the exposed image, and a variable potentlal pattern o~ the surface o~ the photoconductor coatlng 13 wlth re pect to the grounded conductive substrate 17. Wlth re~erence to Flgure 2, the charged area o~ the photoconductor 11 ls rotated to a positlon of close proximity (less than 0.05 mm) to the dlelectric surface, An e~ternal potential 33 is applled between electrodes ln the conductive substrate of the photoconductlve cyllnder 11 and the metal substrate 29 o~ the dielectrlc cylinder 25J wlth a typlcal . lnltial charge of about 1,000 volts on photoconductive layer 13, to whlch an additlonal 400 volt~ are added by t~e externally applied potentlal 33. The aggregate charge of 1,400 volts ls decreased by about 800 volts during the e~po~ing process.
It i~ posslble to malntain the photoreceptor 11 ln dlrect contact with the dlelectric roller 25, an arrangement which 1 170~ 1 ~

provldes the advantase Or slmplicity ln mountlng and drivlng the cyllnders~ An effective TESI proces~ may be achleved under these condltion~, but thls wlll result ln toner transfer to the upper cyllnder and therefore wlll requlre addltional cleaning apparatus.
The charge transrer process requires that a sufficient electrical stress be present in the alr gap to cause ionizatlon of the alr. The requlred potential depends on the thlckness and dlelectric constants of the insulating materlals, as well as the wldth of the alr gap (see Dessauer and Clark, Xerograph~ and Related Processes, the Focal Press, London and New York, 1965, at 427?. Electrlcal stress wlll vary according to the local charge density, but lf sufflclent to cause an air gap breakdown it wlll result in a tran~fer o~ charge ~rom photoconductor surface 13 to dlelectric surface 27, in a pattern duplicating the latent lmage. Thls mean that a certaln threshold potential must be generated across the air gap. Roughly half the charge will be transferred~ leaving a potentlal of around 500 volts on the dlelectrlc surface 27.
The nece~sary threshold potential may exlst aq a result o~
the unl~orm charging and exposure of the photoconductor sur~ace or an e~ternally applied potential may be employed ln addltlon.
Image quallty 1~ generally enhanced through the use Or an external potentlal.
It is lmportant to maintain the lntegrity of the latent electrostatic image, in the ~ace o~ disruptlve charge transfer, ~s 11~01.1~
which occurs under certain conditlon~ when charge transrer is effected on the approach of the two lnsulating sur~aces~ It has been ob~erved that the addltion of a semlconductlng layer 15 between the photoconductive surface layer 13 and the 5 conductlve substrate 17 considerably reduces this effect as compared wlth using the usual two-layer photoconductor.
Although the phenomenon by whlch the semlconducting layer ellmlnates the dlsruptlve breakdown ls not completely understood, lt is b~ ~ ved that the tlme constant introduced by thls semiconducting layer has the e~ect o~ smoothlng or reducing the preclpitous behavlor otherwise assoclated wlth dlsruptive breakdown. The employment of this pre~erred constructlon o~ the photoconductor member 11 avoids a mottllng and blurrlng Or detall ln the transferred lmage. A typical range o~ alr gap di3tances ~or charge trans~er using thls conflguratlon would be on the order of 0.0125 ko 0.0375 mm.
The use Or this method o~ charge tran~er allevlates some of the problems resultlng from undeslrable dl~charge characterlstics o~ the photoconductlve member. The employment 2Q of an external potential in achleving a threshold potential~
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leave~ a higher voltage on the dielectrlc cyllnder than would be the case of a slngle ~ransrer system relylng on the contra~t potentlal Or the photoconduc$or ~ur~ace. Thls, ln turn~, results ln a ~reater contra~t between the light and dark portlons of the tonad, vlslble lmage.
In order to provide unlrormlty from copy to copy, partlcularly wlth certaln photoconductor~ which exhibit ~7 ., . .; . , .

7 ~ 7 fatl6~e, lt ls advantageous to dlscharge the resldual latent lmage remalnlng on the photoconductor a~ter the latent image has been transferred to the dlelectrlc surface 27. Thls erasure may be convenlently carrled out by an erase lamp 23 whlch provldes suf~lcient lllumination to dlscharge ~he photoconductor below a requlred level. The erase llght 23 may be elther fluorescent or incandescent.
Example~
In a speciflc operative example of an electrophotographlc system o~ the construction descrlbedJ the cylindrlcal conducting core 29 of the dielectrlc cylinder 25 was machlned rrom 7075-T6 alumlnum to a dlameter o~ 76 mm~ The length of thls cylindrical core, e~cluding machlned ~ournals, was 230 mm.
: me Journals were masked, and the aluminum anodi ed by use of the Sanrord process (see S. Wernick and R. Pinner, The urfaoe Treatment and ~inlshln~`of Aluminum and its Allo~s, Robért Draper Ltdo~ 4th Edltion 1971/72, Vol. 2, Page 567). The ~lnished aluminum o~lde layer was 60 micrometres ( m) in thickness. The c~linder 25 wa~ then placed ln a vacuum oven at ;
~- 20 30 lnches mercur~. Arter half an hour, the oven temperature was set at 150Co me cyllnder was maintalned at this . . .
temperature and pres~ure for ~our hours. The heated cyllnder wa~ bru h-coated ~lth melted zlnc stearate and returned to the vacuum oven ~or a few minutes a~ 150C, 30 lnches mercury.
The cylinder was removed rrom the oven and allowed to cool.

1~7~

27 of the dlelectrlc cylinc~er 25 wa3 then ~inlshed to 0~125 to 0.25~ m rms using 60o grit silicon carbide paper.
The pressure roller 37 conslsted of a solid machlned 50 mm diameter core 41 over whlch was press fitted a 50 mm inner diameter, 62.5 mm outer dlameter polysulphone sleeve 39.
The conducting substrate 17 of the photoconductor member 11, comprlsing an alumlnum sleeve, was ~abrlcated o~ 6061 alumlnum tublng wlth a 3 mm wall and a 50 mm outer dlameter.
The outer sur~ace was-nrachlned and the alumlnum anodized (again, uslng the San~ord process) to a thlckness o~ 50 m. In order to provlde the proper level of oxlde layer conductlvity, nlckel sulphlde was preclpltated ln the oxide pores by dipping the anodlzed sleeve in a solution of nickel acetate (50 g/l, pH
of 6) for 3 mlnutes. To ~orm the semlconduc~lng layer 15, the sleeve was then lmmediately i~mersed into concentrated sodium sulphlde for 2 mlnutes and then rinsed in dlstilled water.
Thls procedure was repeated three times. The impregnated anodlc layer was then sealed ln water (92 Celcius, pH o~
5.6) for ten minutes. The semlconducting substrate 15 was spray coated with a blnder layer, the photoconductor coating 13 conslstlng of photoconductor ~rade cadmlum sulphoselenlde powder mllled wlth a h~atset DeSoto Chemical Co. acrylic resin, dlluted with methyl ethyl ketone to a vlsco~lty sultable ~or spraying. me dry coatlng thlcknes was 40 m9 and the cadmlum plgment concentratlon in the resln binder was 18% by volume.
me resin was crosslinked by ~lrlng at 180C ~or three hours.

. ., 1 1 7~

The dlelectrlc cyllnder 25 was gear drlven from an AC
motor to provlde a surface speed of twenty cms per second. The pressure roller 37 was mounted Oll plvoted and sprlng-loaded side frames, causlng lt to press agalnst the dielectr1c cylinder 25 with a pressure of 55 kg per linear cm of contactO
The side frames were machlned to provide a 1.10 end-to-end skew between rollers 25 and 37.
Strlps of tape 0.025 mm thick and 3 mm wide were placed around the clrcumference of the photoconductor sleeve 11 at each end ln order to space the photoconductor at a s~all lnterval from the oxide surface of the dielectric cyllnder 25 The photoconductor sleeve was freely mounted ln bearin~s and friction driven by the tape which rested on the oxide sur~ace.
The photoconductor charging corona station 19~ single component latent lmage toning apparatus 31, and optical exposing station 21 were essentially identical to those employed in the Develop KG Dr. Eisbein & Co. (Stuttgart) No.
444 copier.
The toner removal means 43 and 45 comprised ~le~ible stalnless steel scraper blades and were employed to maintaln cleanllness of both the oxide cylinder 25 and the polysulphone pressure roll 37. The resldual latent image was era~ed uslng a semiconductlng rubber roller ln contact with the dielectric surface 27 (see Flg. 5).
With reference to the photoconductor-dielectrlc cylinder embodiment of Figure 2, a DC power supply 33 was employed to .~

., :

1 1 7 ~
blas the photoconductor sleeve ll to a potential o~ mlnus 400 voits relative to the dielectrlc cylinder core 29, which was malntained at ground potential. The photoconductor surface 13 ~as charged to a potential of minus 1,000 volts relative to lts substrate 17. An optical exposure of 25 lux-seconds was employed ln dlscharging the photoconductor ln highlight areas.
In undischarged areas, a latent image of mlnus 400 volts was trans~erred to the oxlde dlelectric 27. This image was toned, and then transferred to a plain paper receptor medium 35 which was inJected lnto the pressure nip at the appropriate time from a sheet feeder.
Coples were obtalned at a rate of 30 per mlnute, havlng clean background, dense black images, and a resolution ln excess of twelve llne pairs per millimetre. No lmage fuslng, other than that occurrlng durlng pressure transfer, was requlred.
Example II-2 In another embodlment of the double transfer copier, the photoconductor sleeve 11 was replaced wlth a flexlble belt photoconductor 11', as shown ln Flgure 3. The photoconductor 11' was comprised o~ a photoconductor layer 13' whlch was formed from a one to one molar solution o~ polyvinyl carbazole and trlnltrofluorenone dissolved ln tetrahydra~uran, and coated onto a conducting paper base 15' (West Vlrglnla Pulp and Paper 45 No. LTB base paper) to a dry thlckness o~ 30 m. The photoconductor rollers 17'a and 17'b were friction driven from 1170~

the dlelectrlc cylinder 25. The lower roller 17'b was blased to mlnus 400 volts. The photoconductor was charged to 1J0OO
volts with the double corona assembly 19' shown ln Flgure 3.
m e electrostatic latent image was generated by a rlash exposure 21' so that the entlre lmage frame was generated wlthout the use of scannlng optlcs.
The rest of the system was identlcal to the prevlous example wlth the exceptlon of the dielectrlc cyllnder 25, whlch was fabrlcated from non-magnetlc stalnless steel coated wlth a m layer of hlgh denslty alumlnum oxide~ The coatlng was applled uslng a Union Carblde Corp. (Linde Division) plasma spray technlque. After spraying, the oxlde surface was ground and polished to a 0025 m rms flnish. Again, hlgh quality coples were obtained, even at operatlng speeds as hlgh as 75 cms per second.

III. Electrostatic Transfer Printing The electrostatlc transfer printing apparatus to be described includes apparatus for forming a latent electrostatlc lmage on a dlelectric surface (e~g. an imaglng roller) and means for accomplishing subsequent process steps.
A. Latent Electrostatlc Image Formatlon Apparatu~ ~or generatlng charged partlcles and for extractlng them to be applled to a further surface is disclosed in detail in section V below. Any of the embodlments of such apparatus which are sultable for formlng a latent electrostatic lmage on a dlelectrlc surface may be employed ln the electrostatlc prlntlng apparatus dlscussed ln this sectlon; for example, see the embodlments of Flgures 11, 12, and 13 and partlcularly the preferred matrlx prlntlng apparatus of Figure ~011'~

13, which may be employed for multiplex prlntlng.
Alternatlvely, the prlnting apparatus may lncorporate any embodlment of the electrostatic lmaging device discussed ln section VI below.
All of the above charging devlces are characterized by the productlon of a "glow discharge," a silent dlscharge formed ln alr between two conductors separated by a solid dlelectric.
Such discharges have the advantaKe of being self-quenchlng, whereby the charging of the solld dlelectric to a threshold value wlll result in an electrical discharge between the solld dlelectric and the control electrode. By appllcatlon of a time-varying potentlal, glow dlscharges are generated to provide a pool of lons of both polarltles.
It ls useful to characterize all of the charglng device lS embodlments ln terms Or a "control electrode" and a "driver electrode." The control electrode is maintained at a glven DC
potentlal in relation to ground, whlle the drlver electrode is energized around this value using a tlme-varying potential such as a high voltage AC or DC pulse source. In the apparatus of sectlon V, the apertured conductor comprlses the control electrode; ln the illustrated embodlments of section VI, the coated conductor or wire constltutes the drlver electrode. In an alternative drlving scheme for the latter devlce, the coated conductor may be employed as the control electrode.

~i 1 ~ 70 1 ~ ~

B. Subsequent Processlng ldentical apparatus may be employed for both electrophotography and prlntlng to carry out process steps subsequent to the creatlon on the dielectric cyllnder of a latent electrostatic lmage (compare Flgures 1 and 4). The apparatus of Figure 4 will be consldered ~or illustrative purposes.
In Figure 4, the dielectric layer 75 of the dielectric cyllnder 73 should have sufficiently hlgh resistance to support a latent electrostatlc image during the perlod between formation o~ the latent image and toning, or, in the case o~
electrophotographic apparatus, between lmage trans~er and toning. Consequently, the reslstivity of the layer 75 must be ln excess o~ 1012 ohm centlmeters. The pre~erred thlckness f the lnsulatlng layer 75 is between 0.025 and 0.075 mm. In addltlon, the surface of the layer 75 should be hlghly reslstant to abrasion and relatively smooth, with a flnlsh that is preferably better than 0.25~ m rms, ln order to provide for complete transfer o~ toner to the receptor sheet 81. The smoothness of dlelectric ~ur~ace 75 contrlbutes to the efflclency of toner transfer to the receptor sheet 81 by enhanclng the release properties of this surface. The dlelectric layer 75 addltionally has a high modulus of elasticity, typlcally on the order of 107 PSI, so that it is not distorted slgnlficantly by high pressures in the transfer nip.

. ~ .

:

I 1'~01 1 ~

A number of organlc and lnorganlc clielectric rnaterials are sultable ~or the layer 750 Glass enamel, ~or exampie, may be deposited and fused to the surface of a steel or aluminum cylinder. Flame or plasma sprayed hlgh density alumlnum oxide may also be employed in place of glass enamel. Plastics materlals, such as polyamides, polyimides and other tough thermoplastic or thermosetting resins, are also suitable.
A preferred dielectric coating is anodized aluminum oxide impregnated with a metal salt of a fatty acid, as described in section VII, infraO
The latent electrostatic image on dielectric surface 75 ls transformed to a vislble image at toning station 79. While any conventional electrostatic toner may be used, the preferred toner is of the slngle component conductlng magnetic type descrlbed by J.C. Wilson, U.S. Patent No. 2,846,333, issued August 5, 1958. This toner has the advantage o~ simplicity and cleanliness.
The toned image ls transferred and ~used onto a receptive sheet 81 by hlgh pressure applied between rollers 73 and 83.
It has been observed that providing a non-parallel orlentation, or skew, between the rollers o~ Figure 4 has a number of advantages in the transfer/fuslng process. An image receptor 81 such as plaln paper has a tendency to adhere to the compllant surface of the pressure roller 83 in preference to the smooth, hard surface of the dielectric roller 73. Where rollers 73 and 83 are skewed~ this tendency has been observed ;~``' 1 1 70 1 :1 ~

to result in a "slip" between the image receptor 81 and the dielectric surface 75. The most notable advantage is a surprlsing improvement in the efficiency of toner transfer from dielectrlc sur~aGe 75 to image receptor 81. This efriciency may be expressed ln percentage terms as the ratio of the welght of toner transferred to that present; on the dielectric roller before transfer. Apparatus o~ this nature ls disclosed in section IV.
The bottom roller 83 consists of a metallic core 87 which may have an outer covering of engineering plastics 85. The surface material 85 or roller 83 typlcally has a modulus of elastlclty on the order of 200,000-450,000 PSI. The image receptor 81 will tend to adhere to the sur~ace 85 in preference to the dlelectrlc layer 75 because of the relatively hlgh smoothness and modulus of elastlcity of the latter surface. In the embodiment of sectlon IV, one function of thls surface 85 is to bond image receptor 81 when the latter is sub~ected to a slip between the roller sur~aces. Another function of the plastlcs coatlng 85 ls to absorb any high stresses introduced into the nlp ln the case o~ a paper ~am or wrinkle. By absorblng stress ln the plastlcs layer 85~ the dielectric coated roller 73 wlll not be damaged during accidental paper wrinkles or ~amsO Coating 85 is typlcally a nylon or polyester sleeve havlng a wall thickne~s ln the range f 3 to 12D5 mm.

, 11~.01:1 ~

The pressure required for good fuslng to plain paper is governed by such factors as, for example, roller diameter, the toner employed, and the presence of any coatlng on the surrace of the paper. It has been dlscovered, in addltion, that the skewlng o~ rollers 73 and 83 will decrease the trans~er pressure requlrements. See section IV, below. Typical pressures run from 18 to 125 kg per llnear cm of contact.
Scraper blades 89 and 91 may be provlded ln order to remove any resldual paper dust, toner accidentally lmpacted on the roll, and alrborne dust and dirt from the dlelectrlc pressure cyllnder and the back-up pressure roller. Slnce substantlally all of the toned lmage ls transferred to the receptor sheet 81, the scraper blades are not essentlal, but they are deslrable ln promotlng reliable operatlon over an extended perlod. The quantlty of resldual toner ls markedly reduced in the embodiments Or section IV, infra.
The small resldual electrostatic latent lmage remainlng on the dielectric surface 75 after transfer of the toned lmage may be neutralized at the latent image dlscharge station 93. The action of tonlng and trans~errlng a toned latent lmage to a plain paper sheet reduces the magnitude o~ the electrostatic lmage, typically ~rom several hundred volts to several tens of volts. In some cases where the tonlng threshold is too low, the presence of a residual latent lmage will result in ghost images on the copy sheet, whlch are ellminated by the discharge station 93.

. ~

- .

~:i7Vll'~

At very high ~urface velocitles of dielectric coatlng 75, the remaining charge can agaln result in ghost lmages. In thls case~ multiple discharge statlons will ~urther reduce the residual charge to a level below the toning threshold. Erasure of any latent electrostatic lmage can be accompllshed by uslng a high frequency AC potentlal between electrodes separated by a dielectrlc, as described ln sectlon V below.
The latent resldual electrostatlc lmage may also be erased by contact dlscharglng. The sur~ace of the dielectrlc must be malntalned ln lntimate contact with a grounded conductor or grounded semiconductor in order e~fectively to remove any resldual charge from the surface of the dielectric layer 75, for example, by a heavily loaded metal scraper blade. The charge may also be removed by a semiconductlng roller whlch ls pressed into lntlmate contact with the dlelectrlc ~urface.
Flgure 5 shows a partial sectlonal view of a semiconductor roller 93 ln rolllng contact with dielectric surface 75.
Roller 98 advantageously has an elastomer outer surface.

EXAMPLE III-l In a specific operatlve example of an electrographic printer ln accordance wlth the lnventlon, the cylindrical conducting core 5 o~ the dielectrlc cylinder l was machlned from 7075-T6 alumlnum to a 3 lnch diameter. The length o~ the cylindrlcal core, excluding machined Journals, was 9 lnchesO
The ~ournals were masked and the aluminum anodized by use of 1 :1 701 1 ~

the Sanford Process (see S. Wernlck and R. Plnner, The_Surface Treatment and Flnlshin~ of Aluml_um and Its Alloys, Robert Draper Ltd. ~ourth edltion, 1971/72 volume 2, page 567). The finished alumlnum oxlde layer was 60 microns in thickness. The conductlng core 5 was then heated in a vacuum oven, 30 lnches mercury, to a temperature of 150~C which temperature was achieved in 40 mlnutes. The cyllnder was malntained at thls temperature and pressure for four hours prior to lmpregnatlon.
A beaker of zinc stearate was preheated to melt the compound. The heated cyllnder was removed ~rom the aven and coated with the melted zlnc stearate using a paint brush. The cylinder was then placed in the vacuum oven for a few mlnutes at 150C, 30 inches mercury, thereby formlng dlelectrlc surface layer 3. The cylinder was removed from the oven and allowed to cool. A~ter coollng, the member was pollshed wlth successlvely finer SlC abraslve papers and oil. Flnally, the member was lapped to a 4,5 microlnch flnish.
The pressure roller 11 consisted of a solid machlned two lnch dlameter alumlnum core 12 over which was press flt a two lnch inner diameter, 2.5 lnch outer dlameter polysulfone sleeve 13. The dielectrlc roller 1 was gear driven from an AC motor to provide a surface speed of 12 inches per second. The transfer roller ll was rotatably mounted in sprlng-loaded side frames, causlng lt to press agalnst the dlelectrlc cylinder wlth a pressure of 300 pounds per llnear lnch of contact. The side frames were machlned to provide a skew Or 1.1 between rollers 1 and 11.

k1 11701~

A charglng device of the type described in U.S. Patent No.
4,160,257 was manufactured as follows. A 1 mil stainless steel foil was lamlnated on both sides of` a 1 mil sheet Or Muscovite mlca. The bonding material and technique is detalled ln Example V-1J lnfra. The stalnless foll was coated with resist and photoetched with a pattern similar to that shown in Figure 22, with holes or apertures ln the ~lngers approximately .oo6 inch in diameter. The complete print head consisted of an array o~ 16 drive llnés and 96 control electrodes which ~ormed a total of 1536 crossover locatlons capable o~ placing 1536 latent image dots across a 7.68 inch length o~ the dielectric cylinderO Corresponding to each crossover location was a ~oo6 inch dlameter etched hole in the screen electrode. Bias potentials of the various electrodes were as ~ollows (wlth the cylinder's conducting core maintained at ground potential):

screen potential -600 volts control electrode potentlal -300 volts (during the applicatlon of a -300 volts print pulse, thls voltage becomes -600 volts) driver electrode blas -600 volts The DC extraction voltage was supplied by a pulse generator, wlth a print pulse duratlon of 10 mlcroseconds.

' , ' 01 1 ~

Charglng occured only when there was slmultaneously a pulse of negative 300 volts to the ringers 44~ and an alternating potentlal of 2 kilovolts peak to peak at, a ~requency of 1 Mhz supplled between the fingers 44 and selector bars 43. The prlnt head was maintalned at a spaclng of 8 mlls from dlelectrlc cyllnder 3.
Under these condltions lt was found that a 300 volt latent electrostatlc lmage was produced on the dlelectrlc cyllnder in the form of discrete dots. The image was toned using single component tonlng apparatus essentlally identical to that employed ln the Develop KG Dr. Elsbeln and Company (Stuttegart) NoO 444 copler. me toner employed was ~ 1186 (a trade mark of Phillip A. Hunt Ch ~ cal Cbrporation of N~w Jersey, U.S.A.).
The prlnting apparatus 70 included user actuatable sheet-feedlng apparatus (not shown) for ~eedlng individual sheets 81of paper between cyllnders 73 and 83~ The paper ~eed, tonlng apparatus, and cyllnder rotatlon were drlven ~rom a unitary drive assembly (not shown). Paper ~eed was synchronized with the rotatlon of dlelectric cyllnder 73 to ensure proper placement of the toned image.
Digital control electronlcs and a digital matrix character generator~ deslgned according to principles well known to those skilled in the art, were employed ln order to ~orm dot matrix characters. Each character had a matrix size o~ 32 by 24 polnts. A shaft encoder mounted on the shaft of the dlelectric cyllnder was employed to generate approprlate timlng pulses for the dlgltal electronics~

.

01~

Flexlble steel scraper blades 89 and 91 were employed to malntain cleanllness of dielectr:Lc cyllnder 73 and transfer cyllnder 83. Wlth reference to the electrostatlc lmage erasing embodlment shown at 98 ln Figure 5 the resldual latent lmage was erased using a semiconductlng rubber roller ln contact wlth the dlelectric sur~ace 75.

IV. Toner Transfer Apparatus Wlth Skewed Rollers Figure 6 shows'~'in a plan vlew illustratlve transfer prlnting apparatus 70 of the type shown schematically in Figure 4, including details of a preferred mountlng arrangement.
Side frames 59 and 6~ house bearing retainers 57 and 67, whlch are fltted to rollers 73 and 83 ln order to allow the rotatlon of the rollers whlle constraining thelr horlzontal and vertlcal movement. Substantially ldentical side ~rames and bearing retalners are located at the other end of rollers 73 and 83.
Bearlng retainers 57 and 67, which advantageously are of the type known as "sel~-allgnlng", fit withln lips 51 and 61 on ~he respectlve side frames~ and agalnst shoulder~ (not shown) on the respectlve rollers. The side frames are mounted on one slde to superstructure 55, and are mounted on the other end ln sprlng-loaded Journals 58 in order to provide a prescrlbed upward pressure against roller 73, Roller 73 i8 drlven at a d~slred ro~ational veloclty by means not shown3 whlle roller 83 ls frlctlonally driven due to the contact o~ the rollers at the nlpO

i' '~1 11~011~

The mountlng illustrated in Figure 9 ls machined ln order to provide a speclfled "skew", or deviatlon of the axls o~
rollers 73 and 83 from a parallel orientatlon. Rollers 73 and 83 may be ad~ustable around a plvot point at one end, by varying the angular relatlonship (ln the vertical plane) of the rollers at the other end. Alternatively, the rollers may plvot around a central polnt o~ contact, by ad~usting the offset of one of the rolls about the axls of the other, thls adJustment being equal at both ~ends. Thls latter, "end-to-end" skew will be assumed hereinafter for illustrative purposes.
The mountlng arrangement shown in Figure 6 may be easily adapted to electrophotographic apparatus of the type shown ln Flgure 1. In a further embodiment, the dielectric lmaging roller (upper roller) may comprise a photoconductive surface layer over a conducting substrate. With reference to the sectlonal view o~ Figure 4, the imaglng apparatus 71 may be replaced with any sultable apparatus known in the art for depositlng a unlform charge on surface 75, and ~or exposing the surface to a pattern o~ light and shadow whereby the charge is selectlvely dlsslpated to ~orm a latent electrostati:c lmage.
As in the dielectrlc embodlment~ photoconductlve sur~ace 75 ls advantageously smooth and abrasion reslstant, wlth a hlgh modulus o~ elastlcity. See Example IV-4.
As shown in Figure 6, axle 50A is dlsposed ln ~nd-to-end skew, whlch may be measured as an o~f~et L ln the plane o~ slde ~rame 59~ A more signi~lcant measure of skew, however, is the l ;l ~V l l ~

angle between the proJected axes of rollers 73 and 83 as measured in the horlzontal plane, or plane of paper feed. An illustratlve value o~ skew to effect the ob~ects of the inventlon ls 0.10 lnch, measured at the center of roller bearlngs 57 and 67, whlch are separated by a dlstance of 10.375 lnch for 9 lnch long rollersO Thls represents an angle of roughly 1.1.
Flgure 7 schematlcally lllustrates skewed rollers 73 (with axls B-B) and--83 (with axis C-C) as seen rrom above.
Roller 83 is skewed at the bearlng mounts by horlzontal offset L from the vertlcally proJected axis B'-B' of roller 73. Thls corresponds to an angle ~ between axes B-B and C-C. Axls B-B ls perpendicular to the directlon A of paper feed.
Figure 8 ls a geometrlc representation of the surface of contact of the rollers at the nip, showlng the dlrectlon of paper feed before and after engagement by the rolleræ. A~ a sheet of paper 81 travelling ln dlrection A enter~ the nlp, lt is sub~ected to dlvergent forces ln direction D (perpendlcular to the pro~ected axls B"-B" of roller 3) and E (perpendlcular to the pro~ected axls C'-C' of roller 21)o Because of the relatlvely hlgh smoothness and modulus of elasticlty of the surface 75 Or roller 73, the paper will tend to adhere to the lower roll, and there~ore to travel in dlrectlon E. Thls results in a sur~ace speed dl~erential or "~lip" between the surfaces of paper and roller.
Due to the compresslon of the lower roller 83 at the nlp, paper 81 will contact both roller surfaces over a finlte ~' 1~01~'~

distance M in dlrection D. The ~ldth of the contact area, M, can be calculated using a formula found ln Formulas For Stress and Straln (4th editlon) by Ronald J. Roark, publlshed by McGraw-Hlll Book Company. The formula for the case Or two cyllnders ln contact under pressure with parallel axes can be found on page 320 of the Roark Text, table XIV~ sectlon 5. The transaxlal wldth in inches of the contact area of the two cylinders ls given by:

where:
P represents the cylinder loadlng in pounds per llnear lnch;
Dl and D2 represent the diameters of the cyllnders ln lnches;
Vl and V2 represent Poisson's ratlo ln compresslon for the materlals of the cylinders; and El and E2 represent the modulus of elasticlty ln compression for the materials of the cyllnders, in pounds per square lnch. Wlth reference to the resultant triangle ln Figure 8, the surface of receptor 81 will undergo a;
proportional slde travel N with respect to the surface of roller 73, the factor of proportionality being the sur~ace speed dlfferentlal.
The skewing of rollers 73 and 83 in the above descrlbed manner results ln a surprislng lmprovement in the efficiency of toner transfer from dielectric surface 73 to image receptor 81.

,~

li701~

This efflclency may be expressed in percentage terms as the ratlo o~ the weight of toner transferred to that present on the dielectrlc roller before transfer. This bears a complementary relationship to the welght of resldual toner on the dlelectrlc roller after transfer. ~he lncrease ln transfer efflciency, which is the most notable advantage of the lnvention, mlnlmlzes the service problems attributable to the accumulation of residual toner at the process statlons associated with the image roller 73, including scraper blades 89 and 91~ erase head 93, and image generator 71. Thls e~fect depends on the choice of surface materlal 75 and toner.
It is another surprlslng advantage o~ thls technique that thls enhanced toner trans~er ls achleved wlthout wrinkling of the receptor medlum 81J These advantages accrued even in the case of nonflbrous substrates 81~ such as-Exam~le IV-l Apparatus of the type illustrated ln Flgures 4 and 9 lncorporated a 9 lnch long, 4 lnch outer diameter roller 73 havlng a dlelectric surface 75 of anodlcally formed porous alumlnum oxlde, which had been dehydrated and lmpregnated with zlnc stearate ~see section VII) and then sur~ace pollshed~ The dielectrlc surface o~ roller 73 was polished to obtaln a finish of better than 10 microlnch rms.
The pressure cylinder 83 included a 9 lnch long steel mandrel with an outer diameter of 3.125 inches over which was 1~7Vll~

pressed a 0 375 lnch thlck sleeve of polyvlnylchlorlde. ~he roller~ were pressed together at 350 pounds o~ pres~ure per llnear inch of nlp~
A latent electrostatic lmage was formed on the dlelectric surrace of roller 73 by means of an lon generator of the type disclosed in sectlon V. The varlous voltages to the ion generator 71 were maintained at constant values. ~he tests were conducted under the same amblent condltlons throughout.
m e toner employed was ~ 1186 (a trade mark o~ the Phillip A.
Hunt Ch ~ cal Corporation). The slngle component latent image tonlng apparatus was essentially identlcal to that employed ln the Develop KG Dr. Elsbeln & Co., ~Stuttgart) No. 444 copler.
The toner was transferred onto Flnch white bond paper9 #60 vellum of Finch, Pruyn and Co. m is paper was fed lnto the nip between the dlelectrlc and pressure rollers at a constant speed throughout the tests.
Uslng the above speclflcatlons, the apparatus was operated at 0 skew, .55 skew, and 1.1 skew, where the skew was measured as a OolO inch o~set at the bearing retainers o~ the 9 inch long pressure roll. The results shown in Table IV-A
were obtalned by collecting the residual toner and comparing its welght to the known welght o~ toner before transfer. No after trans~er printlng was present on the upper cyllnder durlng the tests wlth 0.55 and 1.1 skew. However, trans~er was so poor durlng the test wlthout skew that prlnting was plalnly vlsible on the upper cyllnder after transfer.

TA
.. . _ . . . ... _ . . . _ _ . _ .

PERCENTAGE OF
END-TO-END SKEWTONER NOT_TRANSFERRED
none 12.60 ~55o .10 1 .1 ~10 Example IV-2 The apparatus of Example IV-l was employed with DESOTO toner 2949-5 (a trade mark of DeSoto Inc., of Illinois, U.S.A.). The toner was transferred onto coated OCR IMAGETROL~
paper (a trade mark of S.D. Warren). The rollers were pressed together without skew at 420 pounds per linear inch, resulting in a transfer efficiency of 92.6 percent, measured by comparing the weight of toner before image transfer to the weight of residual toner. The rollers were then pressed together at 1.1 skew, with a pressure of 200 pounds per linear inch, and all other parameters unchanged, resulting in a transfer efficiency of 99.95 percent.

Example IV~3 The apparatus of Example IV-l was employed with the following modifications. The pressure cylinder 83 comprised a 9 inch long steel mandrel with a 1.945 inch outer diameter, over which was pressed a 9 inch long Celcon sleeve with a 3.50 ' 41 :, . ~.. , . ~ .

~, ~

. - . :

- .

~l~Vll~

lnch outer diameter. (Celcon ls a trademark of C~lanese Chemical Co, for thermoplastic llnear acetal resin~). The two rollers were pressed together at 200 pounds o~ nip pre~sure per llnear lnch Or nlp~
The toner employed was COATES RP0357 (a trade mark of the coates sros. and co. Ltd. of Pennsylvania, U.S.A.). The toner was transferred onto Finch white bond paper #60 vellum.
Uslng the above speci~ications, the apparatus was operated with end-to-end skew, varled over a range of angles from 0.0 to 1.1. The appara~u~ was operated u~ing a constant welght of toner prlor to transfer, and the residual toner present on dielectrlc roller 73 was collected and welghed. The results are shown ln Table IV-B, and are graphed in Figure 9. In the case of the test using no skew~ the residual toner was visible as prlntlng remaining on the upper ro'ler.
These tests showed a dramatic improvement ln the efficlency of toner trans~er when the skew was lncreased from 0.0 to .42; thls resulted ln a decrease ln the weight o~
resldual toner by a factor of 53~ Increases ln skew from .42 to o85 and ~rom ~55 to 1~1 further reduced the welght of resldual toner by factors o~ somewhat better than 2O

,.,,~

... .. . ..
', .

~011~

~~ TABLE IV-B _ _ TOrlER TRANSFER EFFIC~ENCY, EXAMPLE IV-3 Oo 6.034 .42 0.114 55 0.066 85 0.050 97 - ~ 0.036 1.1 0.031 ~ _._ . .. _. _ . , _ . _ Example IV-4 The apparatus of Example IV-4 was employed wlth the modlficatlon that the imaging roller 73 comprised a photoconductive roller. An alumlnum sleeve was rabrlcated o~
6061 alumlnum tublng wlth a 1/8" wall and 4" out~r diameterO

The sleeve was spray ~oated with a binder layer photoconductor consisting o~ photoconductor grade SYLVANIA
PC-100 (a trade mark of GTE Products Corporation of ConnPcticut, U.S~A.) cadmium sulfide pigment of Sylvania Comp. Electronics Corp., dispersed in a melamine-acrylic resin, diluted with methyl ethyl k~tone to viscosity suitable for spraying. The resin was cros~linked by firing at 600 for three hours.

A photoconductor char~;ing corona and op~ical e~po31ng system were essentially ldentical to those employed ln the Develop KG Dr. Eisbeln & CoO (Stuttgart) No. 444 Copier, The toner transrer efficiency underwent lmprovements comparable to L those of Example ~V-l ~or increasing skew angles of O.O
0.55, and 1.1~

~ ~.

.
.

1~70117 V. Ion Generation and Extraction Flgure 10 deplcts an lon generator 100, which produces an alr gap breakdown between a dielectric 101 and respectlve conductlng electrodes 102-1 and 102-2 uslng a source 103 of time-varying potential, illustratively a perlodlcally alternating potential. When electric frlnging flelds EA and EB in the air gap 104-a and 104-b exceed the breakdown field of alr, an electric discharge occurs which results ln the charglng o~ the dleréctrlc 101 in reglons 101-a and 101-b ad~acent the electrode edges. Upon reversal of the alternatlng potential of the source 103, there ls a charge reversal ln the breakdown reglons 101-a and 101-bo The generator 100 of Figure 19 therefore produces an air gap breakdown ~w~ce per cycle o~
applled alternatlng potential ~rom the source 103 and thus generates an alternatlng polarity supply of lons.
The extraction of ions produced by the generator 100 o~
Figure 10 is illustrated by the generator-extractor 110 of Figure 11. The generator llOA lncludes a dielectric ll between conductlng electrodes 112-1 and 112-2. In order to prevent air gap breakdown near electrode 112-1, the electrode 112-1 iB
encapsulated or surrounded by an insulatlng materiai 113.
Alternating potentlal is applied between the conduotlng electrodes 112-1 and 112-2 by a source 114A. The second electrode 112-2 has a hole 112-h where the desired air gap breakdown occurs relatlve to a region lll-r of the dlelectric 111 to provlde a source of ions.

.,, ~:

,. , , : ~

~17V11'7 The ions formed ln the gap 112-h may be extracted by a dlrect current potential applled from a source 114 ~ to provlde an external electric fleld between the electrode 112-2 and a grounded auxiliary electrode 112-3. An lllustrative insulating surface to be charged by the ion source ln Flgure 20 ls an electrographic paper 115 conslsting of a conductlng base 115-p coated with a thin dlelectrlc layer 115-d.
When a switch 116 is swltched to posltion X and 18 grounded as shown, thé electrode 112-2 ls also at ground potentlal and no external field ls present in the region between the ion generator llOA and the dlelectrlc paper 115.
However, when the switch 116 is swltched to position Y, the potential of the source 114B ls applled to the electrode 112-

2. This provldes an electrlc field between the lon reservolr 111-4 and the backlng o~ dlelectrlc paper 115. The lons extracted rrom the alr gap breakdown reglon then charge the surface of the dielectrlc layer 115-d.
A number of materials may be used for the dlelectric layer 111. Posslble cholces lnclude aluminum o~lde, glass enamels, ceramics, plastics fllms, and mlca. Aluminum oxide~ glass enamels and ceramics pre~ent difflculties in ~abrlc~tlng a sufficiently thin layer (l.e. around 0.025 mm) to avold undue demands on the drlving potentlal source 114A. Pla~tlcs fllms 3 lncluding polylmides such as that known by the Trade Mark Kapton, and Nylon~ tend to degrade as a result of exposure to chemical byproducts of the alr gap breakdown process in ~5 .~

. .... ... ... , , _ , :3 1 7 1~

aperture 112-h (notably ozone and nltrlc acid). Mlca avold~
these drawbacks, and is therefore the preferred material ~or dielectrlc 111. Especlally preferred ls Muscovlte mica, H2KAl3 (S104)3 ~e generator and lon extractor 110 of Flgure ll ls readily employed, for example, ln the formatlon of characters on dlelectrlc paper ln high speed electrographlc printlng.
Devices embodying thls prlnciple may be used ~or charging and discharglng a photoconductor as in the apparatus o~ sectlon II;
suitable embodiments are disclosed in U.S. Patent No.
4,155,093. To employ ion extractlon in the formatlon of dot matrix characters on dielectric paper, the matrix lon generator 130 of Figure 12 may be employed. The generator 130 makes use of a dlelectrlc sheet 131 wlth a set of apertured alr gap breakdown electrodes 132-1 to 132-4 on one side and a set o~
selector bars 133-1 to 133-4 on the other side, with a separate selector 133 being provlded for each different aperture 135 in each different finger electrode 132.
When an alternating potential is applied between any selector bar 133 and ground~ ions are generated ln apertures at the intersections of that selector bar and the flnger electrodes. Ions can only be extracted from an aperture when both lts selector bar 1s energized with a hlgh voltage alternating potential and lts finger electrode is energized with a direct current potentlal applied between the ~inger electrode and the counterelectrode of the dlelectric surface to ~, ~' 11'7011~

be charged. Matrlx locatlon 13523, ~or example, is prlnted by simultaneously applylng a hlgh ~requency potentlal between selector bar 133-3 and ground and a direct current potentlal between ~inger electrode 132-2 and a dlelectrlc receptor member's counterelectrode. Unselected flngers as well as the dielectrlc member's counterelectrode are malntained at ground potential.
By multlplexlng a dot matrix array ln thls manner, the number of required voitage drlvers ls slgni~lcantly reducedO
If for example, lt is deslred to prlnt a dot matrix array across an area 200 mm wlde at a dot matrix resolution of 80 dots per cm, 1600 separate drlvers wouid be requlred i~
multiplexlng were not employed. By utllizing the array of Flgure 12 wlth, for example~ alternatlng frequency driven flngers, only 80 finger electrodes would be requlred and the total number o~ drlvers is reduced from 1600 to 100.
In order to prevent alr gap breakdown ~rom electrodes 132 to the dlelectrlc member 131 in regions not assoclated wlth apertures 135, lk ls desirable to coat the edges of electrodes 132 wlth an insulatlng materlal. Unnecessary air gap breakdown around electrodes 132 may be ellmlnated by potting these electrodes.
In constructlng and operating a matrix lon generator of thls construction, lt ls desirable that the ion currents generated at various matrlx crossover points be maintained at a substantially uniform level. Thickness variatlons ln the , ~

, ~ ~ . ,, . .... . . ,, . . . , . -- -dlelectrlc layer 131 will result in commensurate varlatlons ln the ion current output, in that a lower lon current will be produced at an aperture 135 at which the dielectric 131 ls thicker. It ls a particuarly advantageous property Or mlca that lt has a natural tendency to cleave along planes of extremely unlform thlckness, maklng lt especially sultable for the matrix ion generator illustrated in Flgure 12. In this regard, the unlformlty of thlckness of layer 131 ls much more important than the actual value of that thlckness.
Ion generators of the type lllustrated in Figures 11 and 12 may be fabrlcated uslng a layer o~ mica lamlnated to thin sheet~ o~ metalllc foil, by etching the foll to create an array of electrodes on each side o~ the mlca. Electrodes 102-1 and 102-2 (Fig. 11) are formed by lamlnatlng a thin sheet o~
conductlve ~oil to each ~ace o~ the mica sheet 101. Wlth re~erence to the sectlonal view of Flgure 25, a mlca sheet 171 o~ unl~orm thickness 19 bonded to two layers of ~oil 174 and 175. The bondlng ls achleved uslng thln layers of pressure sensltive adhesive 172 and 173.
2V m e preferred dlelectric materlal 18 Muscovlte mlc~, H2KA13(S104~3. It ls deslrable to have a sheet o~
uniform thlckness in the range from about 2 ~ - 75 ~ , most pre~erably 10 ~ - 15~ . m e thlnner mlca sheets are generally harder to handle and more expenslve, while the thicker mlca requlres higher ~F voltages between electrodes 102-1 and 102-2 (see Figure ll)o The mlca should be ~ree o~ cracks, fractures, and similar de~ects.

`:

~7011~

The ~oil layers 174 and 175 advantageously comprise a metal whlch may be easily etched ln a pattern of electrodes 132, 133. Illustratlve materlals include nlckel, copper, tantalum, and tltanlum; the pre~erred material, however, ls stalnless steel~ A foll having a thlckness from about 6 ~ - 50 is deslrable, wlth the preferred thlckness belng around 25 ~ .
A wide variety of pressure sensitive adheslves are suitable for layers 172 and 173. A number of characteristlcs should be consldered in chooslng an approprlate pressure sensitlve adheslve, The adheslve should be thermoplastlc, and be reslstant to molsture and chemicalsO It should be able to withstand the hlgh temperatures resultlng from high voltage alternatlng potentials, on the order of kllovolts. The adheslve should be ~ultable ~or bondlng of metal to mlca.
Illustrative adhesive formulatlons which satlsfy the above criteria lnclude solutions of organopolysiloxane resins, as well as pressure sensitive adhesives.
me mlca is coated with a pressure sensltlve adhe~ive formulatlon uslng any well known technique whlch permlt~
preclse control o~er the coating thickness. ~he adheslve layers desirably ha~e a thlckness ln the range 0.5 ~ - 5 ~ , most preferably ln the range 0.6 ~ - 2.5~ . m e thlckne~s may be determlned after laminatlon by ~ubtractlng the known thlckness of the mica and foll sheets from the total thlckness of the laminate. The adhesive may be applied manually, as by brush coatlng, spraylng, and dipping. The preferred method of 1 :~ 7 ~

coating ls that of dlpping the mica lnto a bath Or pressure sensltive adheslve, followed by wlthdrawal of the mlca at a callbrated ~peed. Generally, a faster speed of wlthdrawal result~ ln a thlcker pressure sensitlve adheslve coatlng on each side of the mlca sheet 171.
In the preferred embodlment of the invention, the pressure sensltive adheslve is applied to the mlca in solution. The resln may be diluted to a deslred viscoslty uslng a varlety of solvents, well known to those skllled ln the art. In general, higher viscosity formulatlons will result in a thlcker layer of pres~ure sensltive adhesive ~or a given method of appllcation.
Advantageously, the pressure sensitlve adheslve formulation ha~
a viscosity ln the ran~e from about 10 cps. - 100 cps. The mixture advantageously is filtered prior to coating onto the mlca sheet 1710 The coatlng o~ mica sheet 171 preferably lnvolves dipplng the sheet lnto the pressure sensitive adheslve bath to completely cover both sldes; lt is not necessary, however, to coat the edges of the mlca sheet in the pre~erred embodlment, whlch calls for a separate protective medium for the edges of the lamlnatlon. In lleu o~ or in additlon to a protective coatlng around the edges of the mica sheet 171, a protectlve layer Or tape may be applled to the edges o~ the mlca-foll lamlnatlon. The tape provldes protectlon agalnst mlgratlon o~
molsture between layer~ of the mica~ Alternatlvely, the tape may be removed after processlng of the mica, during which it ' 117011~

provldes a protective layer, as ~urther dlscussed herein.
Preferably, the tape ls coated on one face wlth pressure sensitive adheslve whlch may be the same type as used to bond the mica-foll layer~.
In the case of certaln pressure sensltlve adheslves, the adheslve coatlng ls cured in order to cross-link the formulatlon and thereby enhance 'Lts adhesive character. Thls may be done using any suitable technique for the given adheslve ~ormulatlon, such as heat or radiatlon curlngO
The ~oll sheets 174 and 175 are cut to de~ired dlmenslons, and cleaned prlor to applicatlon to the mlca sheet 171. Each sheet ls placed in reglstratlon wlth one face o~ the mica sheet, and then bonded to the mlca by applying pressure evenly over the ~oll layers.
A~ter laminatlon of the ~oll layers 174 and 175 to mica sheet 171, the foil is selectively removed to create a desired pattern, as for example the pattern o~ electrodes 132 and 133 shown ln Flgure 12. In the pre~erred embodlment, the deslred pattern is created by a photoetchlng process. This involves coatlng the ~oll wlth a photoreslstant materlal; covering the coated foll wlth a photomask to create the deslred patterns;
exposing the masked laminate to ultravlolet radiation; and etchlng the lrradiated foll in order to remove those portions which have been rendered soluble during the preceding steps.
The pre~erred verslons of this process uses a positlve photoresist9 which ls characterized in that those areas whlch 1~7011~

are exposed to ultraviolet radiatlon wlll be rendered soluble and later dlssolved.
In the case of solvent based photoreslst, there ls a tendency Or the solvent to leach out the pressure ~ensltlve adheslve around the edges of the laminatlon. In addltlon, the photoresist will not coat well due to edge e~fects, creatlng a danger of etch-through~ For these reasons, lt ls advlsable to tape the edges to provide a protectlve layer durlng these processlng steps; the tape may be removed after etching.
Alternatlvely, one may employ a dry film photoreslst, which wlll adequately protect the edges of the lamlnatlon lf applied ln a thlckness of around 35 ~ .
In accordance with a partlcular embodlment, a heat slnk may be appended to the mlca-foil laminate. The heat slnk is applied to the lamlnation ~ace containing selector bars 133 ln order to absorb heat resultlng from high voltage alternatlng potentlal~. A variety o~ materials are suitable as well known ln the art; in the case o~ electrically conductlve materials, an lnsulatlng layer must be lncluded to isolate the heat slnk ~rom selector bars 133.
In the examples which ~ollow, all proportions given are by weight unless otherwise noted.

, -117011~

EXAMPLE V-l , 220 parts Methylphenyl polysiloxane resln solution 1 part 2,4 Dlchlorobenzoyl peroxlde 1 part Dlbutyl phthalat;e A pressure-sensltlve adheslve composltion as set forth in the above table was formulated, t;hen diluted to 90 cps. wlth butyl acetate. The resulting llquid was filtered under a pressure o~ approxlmately 30 PSI, and poured into a graduate, The ~ollowlng step3 were carrled out ln a dust-rree envlronment. A sheet of mlca havlng a thlckness ln the range 20-25 microns was cleaned using lint-free tissues and methyl ethyl ketone (MEK)o After drying, the mica sheet was suspended from a dipplng ~ixture and lowered lnto the pressure-sensitlve adheslve formulatlon until all but two milllmeters was submersed. The mica was then withdrawn ~rom the adhesive bath at a speed of 2 cm/mlnute, providing a layer o~ adhesive approximately 3 mlcrons in thlckness. The coated mlca was stored in a dust-free jar and placed in a 150C. oven for flve minutes in order to cure the pressure-sensltlve adheslve.
Two sheets o~ stainless steel 25 microns thlck were cut to the desired dimenslons and cleaned uslng MEK and lint-~ree tlssue~. One of the sheets was placed in a reglstration fixture, followed by the coated mica and the second ~oll sheet.
Bondlng was e~fected by appllcatlon of llght ~inger pressure from the middle out to the edges, followed by moderate pressure ~

.

11~01~

using a rubber roller. Any adhesive remainir~g on expose~ mica surfaces was removed using MEK and lint-free tissues. The edges of the lamination were then covered with a .6 mm wide KAPTON Tape (a trade mark of E . I . DuPont de Nemours and c~., of Delaware u. S.A. ) coated with the above pressure sensitive adhesive formulation.
The foil layers were respectively etched in the patterns of electrodes 132 and 133 (Figure 22) using a positive photoresist-.

An lon generator was ~abricated ln accordance wlth Example V-l, modl~led as follows: The pressure sensitive adheslve was formulated ~rom an acryllc copolymer of vinyl acetate. me adheslve was dlluted to 50 cps. uslng but~l acetate.

,~- EXAMPLE V-3 An lon generator was fabrlcated ln accordance wlth Example V-I, and placed ln a mountlng ~lxture wlth the selector bars 23 upwardO A capacitor glass mounting block o~ dimenslons compatible with the mlca was prepared ~or mounting ~y application o~ a layer o~ sllicon adheslve resln in accordance wlth the table o~ Example V l, followed by smoothlng of the adhesive u~lng a metering blade. The mountlng block was clamped ln registration wlth the lamlnate, and any excess adheslve at the edges was removed u~ing cotton ~wabs. The completed structure was set aslde ~or 24 hours to allow the adhesive to set.

, :
.

1 170 1~ ~

VI. Electrostatlc Imaging Device Uslng Dlelectrlc-Coated Wlre Figure 14 shows ln perspective a basic embodlment of an electrostatic lmaglng devlce whlch may be utlllzed, ~or example, ln the prlntlng apparatus o~ Fi~ure 4. Prlnt devlce 180 lncludes a series o~ parallel conductlve strips 184, 186, 188, etc. lamlnated to an insulating support 181. One or more dlelectric coated wlres 193 are transversely oriented to the conductlve strlp electrodes. The wire electrodes are mounted ln contact with or at a rnlnute distance above (l.e. ~ess than 2 mlls~ the strlp electrodes. Wlre electrode 193 conslsts of a conductlve wire 197 (which may conslst o~ any suitable metal) encased ln a thlck dlelectrlc materlal 195. In the preferred embodlment, the dlelectrlc 195 comprises a fused glass layer, which ls ~abrlcated ln order to mlnlmlze volds. Other dielectrlc materials may be used in the place o~ glas~, such as slntered ceramlc coatings. Organic lnsulatlng materlals are generally unsultable for thls application~ as mo~t such materials tend to degrade with tlme due to oxldlæing products ~ormed ln atmospherlc electrlcal dlscharge~ Although a dielectric-coated cylindrical wire ls lllustrated in the preferred embodlment, the electrode 193 is more generally defined as an elon~ate conductor of indeterminate cross-sectlon, wlth a dlelectrlc sheath~
Crossover points 185~ 187, 189J etc. are found at the lntersectlon of coated wlre electrodes 193 and the respectlve :, .
.

1 1 70 1 1 ~
strlp electrodes 184, 186, 188, etc. An electrlcal discharge 1~ formed at a glven cro~sover point as a result of a hlgh voltage varyln~ potentlal supplled by a generator 192 between wire 197 and the correspondlng strip electrode. Crossover region3 185, 187, 189~ etc. are preferably posltloned between 5 and 20 mllsO ~rom dielectric receptor 200 (see Flg. 15).
The currents obtalnable ~rom an lon generator of the type lllustrated ln Flgure 14 may be readily determlned by mounting a current senslng pr~obe at a small distance above one o~ the crossover locatlons 185, 187, 189, etc. Current measurements were taken uslng an illustratlve AC excltatlon potential of 2000 volt~ peak to peak at a frequency o~ 1 MHz., pulse wldth of 25 microseconds, and repetition perlod of 500 mlcroseconds~
A DC extraction potential o~ 200 volts was applied between the strip electrode and a current senslng probe spaced 8 mlls above the dlelectric coated wire 193. Currents ln the range ~rom about .03 to .08 microamperes were measured at AC excltatlon potentlals above the alr gap breakdown value, which for this geometry was approximately 1400 volts peak to peak. At excltation voltages above the breakdown value, the extractlon current varled llnearly wl~h excltation voltage. The extractlon current varled llnearly with extractlon voltage, as well. For probe-wire spaclngs ln the range 4-20 mlls, the extractlon current was lnversely proportlonal to the gap width.
Under 4 mils, the current rose more rapldly. With the above excitatlon parameters, the lmaging device was found to produce ~ .

~ ~7() ~ 1 ~

latent electrostatic dot images in perlods as short as 10 mlcroseconds.
In the ~ectlonal vlew o~ Fi~ure 15, ions are extracted from an ion generator o~ the type shown in Flgure 14 to ~orm an electroYtatic latent image on dlelectrlc receptor 200. A high voltage alternatlng potential 192 between elongate conductor 197 and transverse electrode 184 results ln the generation of a pool of posltlve and negative ions as shown at 194. These lons are extracted to form an electrostatic lmage on dielectric surface 200 by means of a DC extraction voltage 198 between transverse electrode 194 and the backing electrode 205 of dlelectrlc receptor 200. Because of the geometry o~ the lon pool 194, the e~tracted lons tend to form an electrostatlc lmage on surface 200 ln the Yhape of a dot.
A ~urther imaglng devlce embodlment is lllustrated in Figure 16 showlng a prlnt head 210 slmllar to that lllustrated in Figure 14, but modifled as ~ollows. me dielectrlc coated p wire 213 i~ not located above the strlp electrodes, but lnstead ls embedded in a channel 219 in lnsulating support 211. The gèometry of thls arrangement may be varied ln the separation (lf any) of dlelectric coated wire 213 from the side wall~ 212a and 212b of channel 219; and ln the protruslon (if any) of wire electrode 213 ~rom channel 219.
Figure 17 ls a perspectlve vlew o~ lon generator 220 o~
the same type as that illustrated ln Flgure 16 wlth the ~ ~ 70 l ~ ~

modlflcation that the strlp electrodes 224, 226, and 228 are replaced by an array of wlres. In this embodiment wlres having small diameters are most effective and best results are obtalned with wlres having a diameter between 1 and 4 mlls.
The air breakdown in any of the above embodlments occurs ln a region continguous to the Junctlon of the dlelectric sheath and transverse conductor (see Flg. 15). It is therefore easier to extract ions from the print heads of Flgs. 14 and 17 than from that Or F18. 14 in that this reglon ls moré
accessible ln the former embodlments. The ion pool may extend as far as 4 mlls ~rom the area of contact, and therefore may completely surround the dielectric sheath where the latter has a low dlameter.
In the pre~erred embodlment~ the tran~verse conductors contact the dlelectric sheath. A~ the qeparatlon of these members has a crltical effect on lon current output, they are placed in contact ln order to malntain conslstent outputs among varlous crossover points. Thls also has the benefit of minlmizlng drlvlng voltage requlrsments. It is feaslble, however to separate these structures by as mucH a~ 1~2 mll~
It ls useful to characterize all of the above embodlments ln terms of a "control electrode" and a "driver electrode".
The electrode excited wlth the varylng potentlal ls termed the driver electrode, while the electrode supplled wlth an ion extraction potential ls termed the control electrode. The energlzlng potentlal ls generlcally descrlbed herein as ., ,,;`, ' .

. :
' ' 1 1 7 0 1 ~ ~

"varylng," referring to a time-varylng potential whlch provides air breakdown in opposite dlrectlons, and hence lons Or both polaritles. Thls ls advantageously a perlodically varyln~
potentlal with a frequency ln the range 60 Hz. - 4 MHz. In any of the lllustrated, pre~erred embodiments, the coated conductor or wire constltutes the drlver electrode, and the transverse conductor comprlses the control electrode. Alternatively, the coated conductor could be employed as the control electrode, Figures 14, 16l and 17 lllustrate various embodlments involving llnear arrays of crossover points or print locations.
Any of these may be extended to a multiplexlble two-dlmensional matrix by addlng additlonal dielectric-coated conductors. Wlth re~erence to the plan view o~ Flgure 18> a two-dlmensional matrlx print head is shown utill~lng the basic structure shown ln Flgure 14, with a multlplicity o~
dlelectric-coated conductors. A matrix prlnt head 230 ls shown having a parallel array o~ dlelectrlc-coated wlres 231A, 231B, 231C etc. mounted above a crossing array of ~lnger electrodes 232A, 232B, 232C, etc. A pool of ions is formed at a given crossover locatlon 233X y when a varying excltatlon potential is applied between coated wlre 231X and finger elec$rode 232Y.
- Ions are extracted from thls crossover location to ~orm an electrostatlc dot lmage by means o~ an e~traction potential between finger electrode 232Y and a ~urther electrode (see Flgure 15).

1 1 ~01 ~ ~

In any Or the two-dimensional matrlx print heads, there ls a danger of accldentally erasing all or part of a prevlously rormed electrostatic dot image, This occurs in the ion generator illustrated in Figure 18 when a crossover location 233 is placed over a prevlously deposlted dot lmage, and a hlgh voltage varylng potential ls supplled to the correspondlng coated w~re electrode 231. If in such a case no extraction voltage pulse ls supplled between the correspondng finger electrode 232 and ground, the previously established dot lmage will be totally or partlally erased. In any o~ the embodiments of Flgures 14-17, this phenomenon may be avolded by the lnclusion Or an additlonal, apertured "screen" electrode, located between the control electrode and the dielectrlc receptor ~urface 200. The screen electrode acts to electrically isolate the potential on the dielectric receptor 200, and may be addltlonally employed to provide an electrostatic lenslng actlon.
Figure 19 shows in sectlon an lon generator 240 of the above-descrlbed type. The structure o~ Figure 16 ls supplemented with a screen electrode 255, which is lsolated from control electrode 244 by a dlelectric spacer 252. The dlelectric spacer 252 de~ines an alr space 253 which is substantlally larger than the crossover reglon 245 of electrodes 242 and 244. This is necessary to avoid wall charging ef~ects. The screen electrode 255 contains an aperture 257 which is at least partlally positloned under the crossover reglon 245.

.:

0.1 ~ ~

The lon generator 240 may be utllized ~or electrographic matrlx prlntlng onto a dlelectrlc receptor 258, backed by a grounded auxiliary electrode 259. When the swltch ls closed at posltion Y, there ls simultaneously an alternatlng potentlal across dlelectrlc sheath 242, a negatlve potential Vc on control electrode 244, and a negative potential Vs on screen electrode 255. Negati~e lons at crossover reglon 245 are sub~ected to an acceleratlng fleld whlch causes them to form an electrostatic latent Image on dielectric surface 258. The presence of negatlve potential Vs on screen electrode 255, ~hlch ls chosen so that Vs is smaller than Vc in absolute value, does not prevent the formatlon o~ the image, which wlll have a negative potential Vl (smaller than Vc in absolute value).
When the swltch ls at X, and a prevlously created electrostatic image o~ negatlve potential Vi partially under aperture 257, a partlal erasure of the lmage would occur ln the absence o~ screen electrode 255. Screen potential Vs, however, is chosen so that Vs ls greater than Vl ln absolute value, and the presence o~ electrode 255 therefore prevents the passage of positlve ions ~rom aperture 257 to dielectrlc sur~ace 258.
Screen electrode 255 provldes unexpected control over lmage slze, by varying the slze o~ screen apertures 257. Uslng a conflguration such as that shown in Figure 19~ a larger ~ :1 70 1 ~ '~

screen potentlal has been ~ound to produce a smaller dot dlameter. This technlque may be used ~or the formation of fine or bold lmages. It has also been round that proper choices o~
Vs and Vc wlll allow an lncrease ln the dlstance between ion generator 240 and dlelectrlc surface 258 whlle retaining a constant dot lmage dlameter. Thl.9 ls done by increaslng the ab~olute value of Vs whlle keeplng constant the potentlal dif~erence between Vs and Vc.
Image shape may be controlled by using a given screen electrode overlay. Screen apertures 257 may, ~or example, assume the hape of fully ~ormed characters which are no larger than the corresponding crossover reglons 245. Thls technique would advanta~eously utlllze larger crossover regions 245. The lenslng actlon provlded by the apertured screen electrode generally results in improved image de~lnltlon, at the c06t of decreased lon current output.
Figure 20 lllustrates yet another electrostatlc imaging device 260 ~or use in a hlgh speed serlal printer. An lnsulating drum 261 ls caused to ro~ate at a hlgh rate Or ~peed, lllustratlvely around 1200 rpm~ To thls drum i bonded a dlelectric-coated conductor 262 in the form of a helix~ The drum ls disposed over an array o~ parallel control wires which are held rigld under spring tenslon. The dlelectrlc-coated wlre ls malntalned in gentle contact with or closely spaced from the control wlre array. By rotatlng the drum, the helical wlre provldes a seria] scannlng mechanlsm. As the hellx scans ~ X 701 ~ ~

across the wires wlth a high frequency high voltage excltation applled to dielectrlc-coated wlre 262, printing ls effected by applying an extractlon voltage pulse to one o~ the control electrode wires 263.
Figure 21 lllustrates an alternative scheme for provldlng a relative motlon between the prlnt devlce of the lnventlon and a dielectrlc receptor surfaceO A charglng head 270 in accordance wlkh Flgure 18 ls slldably mounted on gulde bars 275. Any suitable means may be provided for reclprocatlng prlnt head 270, such as a cable drive actuaked by a s,tepplng motor. Thls system may be employed to form an electrostatlc image on dielectric paper, a dielectrlc transfer mernber, etc.
The electro~tatic printlng device of the lnvention is further illustrated with reference to the following specific embodimenks.

EXAMPLE'VI-l _ _ An imaglng device o~ the type illustrated in Figure 14 was ~abricated as follows. The insulatlng support 181 comprised a G-10 epoxy fiberglass circuit board. Control electrodes 184, 185, 188, etc. were ~ormed by photoetchin~ a 1 mll stainless steel ~oil whlch had been laminated ko lnsulating substrate 181, provldlng a parallel array o~ 4 mll wide strlps at a separation of 10 mlls. The driver electrode 193 consisted o~ a 5 mil tungsten wlre coated with a 1.5 mil layer of rused glass to form a structure having a total diameter o~ 8 mlls.

'`~r ~p I ~ 7t)1 ~ ~
AC excltation 192 was provlded by a gated Hartley osclllator operatlng at a resonant frequency of l MHz. The applled voltage was ln the range of 2000 volts peak-to-peak with a pulse width of 3 microseconds, and a repetltlon perlod Of S00 mlcroseconds. A 200 volts DC extractlon potential 198 was applied between selected control electrodes and an electrode supportlng a dlelectrlc charge receptor sheet. The ion generating array was positioned 0.01 inches rrOm the dielectric-coated sheet.
0 Thi8 apparatus was employed to form dot matrix characters in latent electrostatic form on dielectric sheet 200. After conventlonal electrostatlc tonlng and fusing, a permanent hlgh quallty image was obtained.

An lon pro~ection print devlce of the type illustrated in Figure 16 was fabricated as follows. A channel 219 of 5 mlls depth and lO mils wldth was milled ln a 0.125 lnch thlck G-10 epoxy flberglas~ circult board. A drlver electrode 213 ldentlcal to that of Example VI-l was lald in the channel.
Photoetched stainless steel foll electrodes 214, 21~, 218, etc.
were lamlnated to clrcult board 211, contactlng dielectric 215, The device exhibited equlvalent performance to the imaging devlce o~ Example VI-l when exclted at the same potential~

The electrostatlc print devlce of Example VI-2 was modifled to provlde imaging apparatus of the type shown in ~l 64 . .

~ ,i ~.. ......

1 1 70 ~ ~ ~

Figure 17. qhe control electrodes comprised a serles of 3 mll dlameter tungsten wlres cemented to support 221. This device achieved approximately double the ion current output as compared with the devices o~ Examples VI-l and VI-2.
In all three examples, the glass coated wire was not firmly bonded in place~ but was allowed to move ~reely along its axls. Thls provided a freedom of motion to allow for thermal expanslon when operating at high driving potentlals.
.

VIIo Fabricatlon Of Dlelectric Members This sectlon describes a serles o~ steps ~or fabricatlng and treating anodlzed alumlnum members which results ln members partlcularly suited to electrostatlc lmaging. The treated member ls adapted to receive an electrostatlc latent image, to carry the lmage with minimal charge decay to a toning statlon, and to impart the toned lmage to a ~urther member preferably by pressure transfer. A number of propertles of particular concern in thls utilization are the hardness and abra~ion re~lstance o~ the oxide surface; the potential acceptance and dlelectrlc ~trength o~ the dlelectrlc layer; the resistivlty o~
the dlelectric layer; and the release properties o~ the sur~ace with respect to electrostatic toner.
Thls method ls advantageously employed ln ~abrlcating the dlelectric cylinders of the apparatus described abave ln sectlons II and III. This method provides a simple and 2~ reliable technlque for ~abrlcatlng alumlnum oxlde layers o~ a ..... . .. ... .. . .... . . . . . . .

~701~ 7 thickness as great as 4 mlls and capable of supportlng several thousand volts. Such cylinders are charactrized by a hard, smooth surface which ls sultably employed ln the slmultaneous pressure transrer and fusing o~ a toner image.
In order to provide a member of sultable conflguratlon, an inltlal ~tep entallq the ~abrlcatlon o~ an aluminum member Or desired form. In the preferred embodiment, the member conslsts of a cyllnder of aluminum or alumlnum alloy, machined to a deslred length and outside diameter. The surface ls smoothed preparatory to the second step of hardcoat anodizatlon.
In the qecond processing stage, the machined aluminum member lq hardcoat anodlzed pre~erably accordlng to the teachings of Wernlck and Plnner; see The Surface Treatment and Flnishln ~ um;and its Alloys by S. Wernlck and R~
Plnner, fourth editlon, 1972, published by Robert Draper Ltd~, Paddington, England~ m e anodlzatlon ls carrled out to a deslred surface thickness, typically one to two mils. Thls results in a relatlvely thlck porous sur~ace layer of alumlnum oxlde characterized by the presence o~ a barrler layer lsolating the porous oxlde ~rom the conductive substrate.
Following anodizatlon, the member's surface is thoroughly rlnsed in de-lonlzed water ln order to remove all anodizing bath and other resldual substances ~rom the sur~ace and the pores. The rln~ed sur~ace may be wlped dry to minlmlze sur~ace molsture.

I l 701 1 7 After anodlzlng the member, and prlor to lmpregnatlng of the pores wlth a sealing materlal, the method of the inventlon requlres a thorough dehydratlon o~ the porous surface layer.
For best results, the dehydratlon is accompllshed immedlately after anodizatlon. If there is a long delay between these two steps, however, it is advlsable to malntaln the member ln a moisture-free environment in order to avold a reaction wlth amblent molsture whlch leads to the formation o~ boehmlte [AlO(OH)2] at pore mouths, effectlvely partlally seallng the porous oxlde so that subsequent lmpregnatlon ls lncomplete and dlelectrlc propertles degraded. Thls partlal seallng can occur at room temperature in normal amblent humldlty ln a period of several days.
Removal of absorbed water from the oxide layer of an anodlzed alumlnum structure may be realized by uslng elther heat, vacuum, or storage o~ the artlcle ln a desicator. The dehydratlon step requires thorough removal of water ~rom the pores. Although all three technlques are efrective, best resultq are reallzed by heating in a vacuum, for example ln a vacuum oven. A prellmlnary step of dehydratlng the member in a vacuum oven ls especlally preferred where the member has been stored in a molst environment for a perlod after anodlzation~
Heatlng of the member ln alr, as compared with vacuum heatlng, - results in only a slightly lower level o~ charge acceptance.
It is pre~erable that any thermal treatment o~ the oxlde prior to impregnation be carried out at a temperature ln the range -.

, ; .

~1701~ ~

from about 80C to about 300C, with the preferred temperature being about 150C. Where precautlons have been taken after anodlzing to minlmlze the retention and accumulatlon of molsture, the dehydratlon step may be accompllshed ln conJunction with the impregnatlon step, as explained below.
After removal of absorbed water from the oxide coatlng lt ls sealed wlth an impregnant materlal. In the present lnvention, the impre~nant material consists essentlally of a compound of a Gr~up II or III metal wlth a long chain fatty acid. It has been dlscovered that a partlcularly advantageous class of materials lncludes the compounds of Group II metals wlth fatty aclds containing between 8 and 32 carbon atoms saturated or unqaturated. The lmpregnant materials may comprlse either a single compound or a mlxture of compounds.
Due to the water repellant nature of these alkallne earth derlvatlves, the product of the lnvention has superior dielectric propertles at high humidltles.
In order to avold lntroduction of molsture into the dehydrated porous surface layer, the member should be malntained ln a substantlally molsture-free state durlng lmpregnatlon~ Thls wlll occur as a natural consequence o~ the preferred method o~ applylng the impregnant materials of the invention. At room temperature these materlals take the form of powders, crystalllne solids, or other solid forms. In the preferred embodiment of the lnventlon, the member is maintalned ~i ~ ~ ~o.~ ~ ~

at an elevated temperature (above the melting polnt of the impregnant material) durlng the lmpregnation step ln order to melt the material or to avoid solldlfying premelted material.
These materlals have suf~iciently low viscoslty after meltlng to readlly lmpregnate the pores o~ the oxlde surface layer. In thls embodlment the period o~ heatlng the member ~rom room temperature to the impregnating temperature may provide the prellmlnary dehydration which ls required to avold trapped molsture ln the pores, o~ten without a prlor separate dehydrating step. Thls preheatlng stage may take minutes or hours depending on the mass and volume o~ the aluminum member.
See Examples VII-l, VII 2. In the alternatlve embodlment o~
the lnventlon dlscussed below, in which the lmpregnant materlals are applied ln solution to the anodlzed member, lt ls advisable to heat the member or take other steps in order to avold relntroduction of moisture during the lmpregnatlon process.
It has generally been found unnecessary to malntaln the heated member ln a vacuum envlronment during lmpregnation, elther to avoid absorptlon o~ molsture or to asslst the lmpregnation of the pores through capillarlty~ In the preferred embodlment, the lmpregnant material may be applled to the oxlde sur~ace under molst ambient condltlons because the heatlng o~ the aluminum member will tend to drlve o~ any absorbed molsture ~rom the oxlde sur~ace. Optlonally, a vacuum may be employecl in order to provlde an extra precaution against reintroductlon of molsture, Special measures may be requlred, ,~ ~

1 1 ~ V .1 1 ~

however, in the alternatlve embodlment ln which the lmpregnant material is di3solved prior to applicatlon to the anodized member~
In the preferred embodiment of the lnventlon, the impregnant material is applied to the sur~ace of the aluminum member a~ter heatlng the member to a temperature above the meltlng polnt of the material. In one version Or this embodlment, the material ls applied to the sur~ace in solld ~orm (as by dusting or blowing it onto the ~urface), whereupon the material will melt~ In an alternatlve version, the materlal ls premelted and applied to the oxlde surface ln llquld ~orm (as by brushlng the materlal onto the member or immerslng the member ln melted material). In either case, the materlal should then be allowed to spread over the oxlde surface layer. mi~ may be done by permittlng a ~low of the melted material, or by manually spreadlng the materlal over the sur~ace uslng a clean lmplement. The member shoùld be malntained at thls elevated temperature ~or a perlod o~ tlme sufflclent to allow the melted materlal to completely impregnate the pores o~ the oxlde surface layer. This perlod will be shorter when uælng a vacuum to assi~t impregnatlon.
In the pre~erred embodlment, i~ the member ls allowed to cool prlor to complete fllling o~ the pores wlth the impregnant material, the materlal wlll tend to solidlfy leavln~
undeslrable air pockets ln the pores. It ls a particularly advantageous aspect of this method that this problem may be ,~, \
~ 1 ~0 1 ~ 7 remedied slmply by reheatlng the aluminum member and allowing a more complete filling o~ the pore~. The member may be reheated for a sub~equent lmpregnation step at any tlme ~ubsequent to the lnltlal lmpregnation, as the impregnant materlal o~ the lnvention ls not permanently cured.
In an alternatlve embodlment of the lnventlon, the lmpregnant materlal is dis~olved prlor to applicatlon oP the oxlde surface layer~ Materlals of` the lnventlon susceptlble to appllcation ln thls manner include the compounds of Group III
metals wlth fatty aclds, as well as the compounds of Group II
metals wlth some of the longer chaln fatty aclds (those havlng around 32 carbon atoms). Solvents whlch are sultable for thls purpose lnclude, for example, benzene, and butyl acetate.
A~ter the material is di3solved, lt may be applied to the member by ~praying or bru~hlng lt onto the oxlde sur~ace layer.
The solutlon ls allowed to penetrate the poresO Any excéss lmpregnant ls removed by wlping the member's sur~aceO In order to avoid relntroduction Or molsture into the dehydrated porous surface layer, the member may be impregnated in a vacuum oven or ln alr at a temperature in the range ~rom about 4oc to 55C. Alternatively, the member may be lmpregnated ln a desicant dry bo~. Advantageously, this method would re~lect that employed in the prior dehydration step.
It ls de~lrable subsequent to preclpltatlon of the impregnant material in the alternative embodlment to heat the member to a temperature above the meltlng polnt o~ the , ................ ,. . :

1 ~70~ 3 ~
material. This fuses the material in the pores, and nlinimizes the occurrence o~ air pockets which are deleterious to dielectric properties. The member may be reheated as in the preferred em~odiment in order to prove a more complete impregnation.
Subsequent to impregnation of the pores, the aluminum is allowed to cool. The member is then treated (as by wiping or scraping) to remove any excess material from the surface leaving only the material in the pores. In order to provide a surface with good release properties for electrostatic toner, a preferred embodiment o the invention includes a final step of polishing the member's surface to a better than 20 microinch finish, and preferably better than a 10 microinch finish.
The advantages of this method will be further apparent from the following non-limiting examples.

A series of panels (1.5 inch X 1.5 inch X .067 inch) fabricated of aluminum slloy 7075-T6 were hard-coat anodized in sulphuric acid by the Sanford "Plus" process* to a depth of 1.5 mil. The panels were rinsed with deionized water and wiped free o~ surface moisture. They were then wrapped in moisture absorbant paper an~ stored for about one ~ay.
The anodized panels were unwrapped and heated to a temperature abo~e the melting point of the material to be ~/ 72 ~7011~

appl.ied (see Table VII) and maintained at this temperature for one minute prior to application of the impregnant material.
The material was dusted onto the heated panel where it melted rapidly and was allowed to flow over the oxide surface layer.

s TABLE VII

IMPREGNANT -IMPREGNATING CHARGE ~Volt~ Micron) 10 MATERIAL _ TEMPERATURE(C) ACCEPTANCE __ Barium Stearate 300 22 Zinc Stearate 150 34.5 Magnesium Stearate 150 25 Zinc Octanoate 150 33 Zinc Behamate 150 41.5 Zinc Oleate 150 7 Zinc Octanoate: 300 19 Barium Stearate ~ . _ * Sanford Process Corp: 65 North Avenue, Natick, Masu.

i I

~ ,:

11 7 V 3. ~

The coated member was malntained at the elevated temperature for another minute, and then allowed to cool to room temperature. Thi8 process was repeated wlth a number o~
different lmpregnant materials including in one case a mixture of two dif~erent compounds -- see Table VII.
After cooling, the samples were ground with 240 grit sandpaper and water to a thickness of between 40 and 45 microns. They were then heated on a hot plate at 150C for approximately 30 seconds in order to rapidly evaporate the sur~ace moisture, and then allowed to cool.
The plates were placed over a negative ion discharge and charged to a maxlmum voltage. Thls voltage was measured by a Monroe Electronics electrostatic voltmeter~

A hollow alumlnum cylinder o~ extruded 7075-T651 alloy was machined to an outer diameter of 4 lnches and 9 inch length, with 0.75 inch wall thlcknessO The cyllnder was machlned to a 30 mlcrolnch ~inish, then polished to a 2.25 mlcroinch finlsh.
The cyllnder was hardcoat anodlzed by the San~ord "Plus"
process to a thickness between 42 and 52 microns, t~en rlnsed in deionlzed water and packed ln plastlc bags`.
On the followlng day, the cylinder wa~ unpacked and placed in a vacuum oven at 3Q inches mercury. After half an hour, the oven temperature was set at 150C.~ whlch temperature was achieved ln a further ~orty minutes. The cylinder was . .
..

o.~

malntalned at thls te~nperature and pressure for ~our hours prior to lmpregnatlon.
A beaker of zinc stearate was preheated to melt the compound. The heated cylinder was removed from the oven, and coated with the melted zinc stearate using a palnt brush. The cylinder was then placed back in the vacuum oven for a few minutes at 150C., 30 inches mercury. The cylinder was removed from the oven and allowed to cool.
A~ter cooling, the member was pollshed with successively finer SiC abraslve papers and oll. Flnally, the member was lapped to a 4.~ mlcroinch flnish by appllcatlon of a lapplng compound and oil wlth a cloth lap.
Using the testing method of Example VII-l, the cyllnder's charge acceptance was measured at 980 volts.

VIIIo Duple~ Imaglng Thls section descrlbes a duplex imaglng technique employlng elther the electrophotographic apparatus Or Flgure 1 or the electrostatlc printing apparatus of Fl~ure 4. The apparatus of elther o~ these embodiments may be adapted as dlscussed below to effect simultaneous pressure trans~er and fusing of toner images to opposlte sides of an image receptor medium. Reference should be had to Figure 4 and to the discusslon at sectlon IIIB. In the duple~ imaging method utilizlng this apparatus, receptor sheet 81 is inserted between rollers 73 and 83 only during the second of two toner lmage transfers. An initlal transfer takes place directly from ~lrst .,~

~1~011~

image drum 73 to second lmage drum 83, with no receptor inserted between the two. Such transfer should be substantially complete~ leavlng a toned image on second lmage drum 83 whlch ls the mlrror image of that formed on flrst lmaging drum 73 durlng previous processlng stages.
Second image roller 83 serves a number of functlons ln the duplex imaging process. Initially, it recelves and carries the toned lmage transferred from roller 73. During the second transfer, it should-effect as complete as posslble a transfer of toner to receptor sheet 81. It is therefore desirable that bottom roller 83 have a relatlvely smooth surface, advantageously better than 0.25 microlnch rms. In a preferred embodiment, the second, two-slded transfer to receptor sheet 81 ls accomplished simultaneously with a fuslng of the toned image due to hlgh pressure applied between the two rollers. Such pressure may be provided by pressure drum 83 comprising a metallic core 87 having an outer coating of engineerlng plastic 85.
The pressure requlred for good fuslng to plaln paper ls go~erned by such factors a~, for example, roller dlameter, the toner employed, and the presence of any coating on the surface of the paperO Typlcal pressures run from 18 to 125 kg per llnear cm o~ contact. Roller 83 desirably has a surface 85 of engineering thermoplastic or thermoset materlal, which will absorb any hlgh stresses ln the transfer nlp ln the case of a paper ~am or wrinkle. By absorblng stress in the plastics , 117V~

layer~ the dlelectric coated roller wlll not b~ damaged during accidental paper wrlnkles or Jams. Surface 85 preferably has a relatively low moduluq o~ elasticity as compared wlth dielectrlc 75, ln order to provlcle efflcient toner transfer from roller 73 to roller 83. Illustrative values are a modulus of ela~tlcity on the order of 107 PSI for dielectrlc 75, and approximately 400,000 PSI for layer 85~ Illustratively, surface 85 comprises a nylon or polyester sleeve having a wall thickness in the range 3 to 12.5 mm.
The efflclency of toner transfer from sur~ace 75 to surface 85 depends prlmarily on the relatlve modulus of elastlcity of the two surfaces, as dlscussed above. A second factor to be considered ln chooslng suitable materlals ls the relatlve roughness of the two surfaces. Advantageously, roller 73 has a relatlvely ~mooth surface as compared with roller 83 E~emplary values would be a roughness of around 30 mlcrolnch rms for sur~ace 85, as compared wlth around 10 ~icrolnch rms.
for surface 750 Drums 73 and 83 are advantageously rotated from a common drlve source. First lmage drum 73, for example~ may be dlrectly drlven at a given angular velocity, and second image drum 83 friction drlven by contact with the flrst image roller~
Due to the high pressure wlth whlch the drums are held together, they move at virtually the same llnear sur~ace velocity wlth or without a receptive sheet lnserted between them.

.~j .

1 1 7 O 1 1 ~

The varlous stages of the two-sided imaging process are illustrated ln the schematlc vlews of FIGURES 22 through 27.
In FIGURE 22, a ~lrst latent electrostatic image Ills ~ormed on ~irst lmage drum 73 by image generating station 71. Image Il is toned at toning station 79 (FIGURE 23), and rotated to a positlon of contact wlth second lmage drum 83 to which it is pressure transferred (FIGURE 24). The -first ~mage, now lnverted (-Il), contlnues to rotate on second lmage drum while a second latent electrostatlc lmage I2 ls formed on ~lrst lmage drum 73 (FIGURE 25). Durlng thls period, any resldual electrostatlc lmage on ~lrst image drum 73 may ~e erased at eraslng statlon 93. This second lmage I2 ls toned (FIGURE 26)., and the two toned images are rotated to the nlp, where they are pressure trans~erred to receptlve sheet 81 (FIGURE 27)o If it ls desired to match the posltions of lmages -Il and I2 on receptlve sheet 81, it is necessary to time the formatlon of lmage I2 so that the circumferential dlstance from the nip on roller 73 of leading edge of image I2 equals the clrcum~erentlal distance from the nip on roller 83 of the leadlng edg~ o~ lmage -Il. me tlme lnterval between successlve image formatlons should equal the period of rotatlon of bottom roller 83. Thls is calculable by the ~ormula T = oller 83 Didame~e~
ur ace Spee o o ers ~ .

1 ~ ~0~ 1 ~

In order to counteract the mlrror reversal of ~irst image Il that results ~rom the double trans~er of the lmage, lt ls necessary to provide an inverted latent electrostatlc image at lmage generatlng statlon 71. FIGURE 28 shows the case o~ one-sided printing from the ,top roller 73. In order to transfer arow o~ toned characters onto receptor 81, lmage generating statlon 71 forms an lnverted row o~ latent electrostatic characters along the clrcumference of roller 73. In FIGURE 29, the toned characters'have been tran~ferred to bottom roller 83.
In FIGURE 30, the toned characteræ have been further trans~erred to the bottom side o~ receptlve sheet 81~ As a re~ult of the double trans~er, they are prlnted in an inverted orlentation. Thus, as shown ln FIGURE 31, it is necessary to reverse the orientatlon (l.e. b,ack to normal orlentatlon) of the latent characters on drum 73 for trans~er to the ~econd slde of receptor 81.
Image generating station 71 may comprise a photoconductor member on which a latent electrostatic lmage is formed correspondlng to a scanned optical lmageJ with a trans~er o~
the latent image to lmage roller 20 by TESI (Figure l)O As will be apparent to skilled artlsans, the scannlng optlcs 21 may be slmply modi~led to provlde an lnver~ion o~ alternate images.
In the case o~ electrographlc printlng apparatus, the latent electrostatic lmage on image roller 73 is fo~med by ion generating means ln response to a signal lndlcative of the 1 1 701 1 ~

desired lmage. Image generating statlon 71 may comprlse, ~or example, the lon generator and extractor dlscussed in sectlon V, FIGURE 32 shows ln a plan view a multiplexed ion generator o~
this type. The lon generator 130 includes a serles o~ finger electrodes 132 and a crosslng series of selector bars 133 wlth an lntervenlng dielectrlc layer 131. Ions are generated at apertures 135 ln the finger electrodes at matrlx croæsover polnts. Ions can only be extracted from an aperture 135 when both its selector bar 1~ energized by a--~rlgh voltage alternatlng potentlal supplied by one of gated oscillators 137, and lts finger electrode ls energlzed by a direct current potential supplied by one of pulse generators 136. The tlming Or gated osclllators ls advantageously controlled by a counter 138.
If axls A-A of the print head is orlented along the circumference of upper roller 73, one may lnvert the latent electrostatlc lmage as requlred by the lnventlon by reverslng the order of slgnals to selector bar~ 133 from gated oscillator 137. This may be done by reversing the sequence o~ actuatlng signals from counter 138.

i~ .

, .
.
, ' ' ' ~
~:
.

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for forming a toner image on a receptor sheet, comprising:
an imaging roller;
means for forming a toner image on said imaging roller;
and a transfer roller in rolling contact under pressure with the imaging roller;
wherein said transfer roller and imaging roller are maintained in a non-parallel axial orientation with the receptor sheet fed therebetween to receive the toner image.

2. Apparatus as defined in Claim 1 wherein the receptor sheet adheres to the surface of said transfer roller in preference to the surface of said imaging roller.

3. Apparatus as defined in Claim 1 wherein the imaging roller includes a dielectric surface layer, and the transfer roller includes a surface layer of a material selected from the class consisting of engineering thermoplastic and engineering thermoset materials.

4. Apparatus as defined in Claim 3 wherein the dielectric surface layer of said imaging layer is comprised of porous anodized aluminum impregnated with a metallic salt of a fatty acid.

5. Apparatus as defined in Claim 3 wherein said dielectric surface layer has a smoothness in excess of 20 microinch rms.

6. Apparatus as defined in Claim 1 wherein said imaging roller includes a hard photoconductive surface layer.

7. Apparatus as defined in Claim 2 wherein one of the rollers is frictionally driven by the rotation of the other roller.

8. Apparatus as defined in Claim 2 wherein the toner image is simultaneously fused to the receptor sheet during transfer thereto.

9. A method for forming a toner image on a receptor sheet, which comprises the steps of:
forming a toner image on the surface of an imaging roller, rotating the toner image into an area of contact between the image roller and a transfer roller, said transfer roller having a non-parallel axial orientation with respect to said imaging roller, and feeding the receptor sheet onto the area of contact of said rollers.

10. The method of Claim 9 wherein the toner image is transferred and simultaneously fused to the receptor sheet.

11. A method of producing images on two sides of an image receptor which comprises:
creating a first latent electrostatic image on a dielectric surface of a first image roller;
toning said first latent electrostatic image to form a toned visible counterpart:
transferring the toned first image to a surface of the second image roller in rolling contact with said first image roller, this transfer being accomplished solely by pressure;
creating a second latent electrostatic image on the dielectric surface of the first image roller;
toning said second latent electrostatic image to form a toned visible counterpart;
passing an image receptor between said first image roller and said second image roller; and transferring said toned first image from said second image roller to one side of said image receptor, and simultaneously transferring said toned second image from said first image roller to an opposite side of said image receptor, this step being accomplished solely by pressure with a simultaneous fixing of the toned images to the image receptor.

12. The imaging method of Claim 10 wherein the said first image roller has a hard dielectric surface.

13. The imaging method of Claim 12 wherein said hard dielectric surface has a smoothness better than 15 microinch rms.

14. The imaging method of Claim 12 wherein said hard dielectric surface has a modulus of elasticity on the order of 107 PSI.

15. The imaging method of Claim 11 wherein said second image roller has a surface layer of a material from the class comprising engineering thermoplastic and engineering thermoset materials.

16. The imaging method of Claim 11 wherein the surface of said second image roller has a modulus of elasticity on the order of 400,000 PSI.