CA1107343A - Ac corona to remove background from the transfer member of a thermomagnetic copier - Google Patents

Abstract

ABSTRACT
A process for reproducing graphic information wherein a magnetic image is formed in a premagnetized layer of acicular chromium dioxide by heating the chromium dioxide selectively to above its Curie point. Ferromagnetic toner particles are then applied uniformly to the chromium dioxide layer, so as to adhere only in the magnetized areas. The toner particles are electrostatically transferred to a substrate and fused into position. Alternating current coronas or other static neutralizing devices are used to neutralize unwanted charges on toner particles which would otherwise cause fuzzy images and unwanted background markings on the final copies.

Description

73~a3 Background o~ the InYention Field~o~ t.he InventIon; The pre.sent i~Vention relates to a pro.cess for dr~ printing o~ information. The process involves forming a magnetic image on a mas.ter ~ollowed by decorating th.e magnetic image wlth ferromagnetic toner particles which are the~ electrostatically transferred to a dielectrlc subst:rate and ~ixed in place.
Descrip~ion of the Prior Art: Both Xerography and magnetography are known. Xerography lnvol.ves: forming an electrostatic charge on a photoconductive material such as selenium, imagewise exposing the photoconductive material to light whereby the exposed areas lose their charge; and applying a pigmented, ~inely divided, electrically charged powder whlch is attracted to and held on the electrostatic image. The charged toner image-is then transferred to copy paper either with an opposite electrostatic charge or by .
means of pressure.

In magnetography a magnetic image is ~ormed, and : ferromagnetic particles applied thereto which adhere to the magnetized areas o~ the image. The particles are then :: :
~: transferred to copy paper either by pre~sure or magnetically.
The pressure technique causes objectionab:le wear to the imaging member and can also cause~bulldup of a ~llm on the imaging member which causes smudglng. ~
In magnet.l.c tran.sfer it has been ~ound difficult o e~.ect~t:ran~er of toner wlthout. erasing the:latent magneti~c~mage on the imaglng member~
ummary of the In~entlQ~
The~p~esent in~enti.:on relate:s to ~ormin~ a latent 3a ~ ~magnetlc~image,.decorating the ~latent ma&net:ic image with ~3 an uncharged ferromagnetic toner, and then transferring the toner to a substrate electrosta~ically whereby the problems of pressure or magnetic transfer are o~ercome and using static neutralizing devices such 3.S alternating current coronas ~o neu~raliæe electrostatic charges on those toner partlcles which would otherwise cause ~uzzy images on the ~lnal cople~ and unwanted background markings.
By uncharged toner we mean toner which has not purposely been charged by means such as corona or tribo-electric means but which may contain small triboelectric charges o~ either polarity.
Descr ~ oo ~r ~be Drawin~
Figure 1 i5 a schematic side view of a printer used to perform the proces~ of the pre~ent invention.
Figure 2 is a side view of a printer equipped ;~ with a magnetic printing head used to perform the proce~s of the present invention.
Figure 3 is a diagram of the exposure of the magnetic master by radiant energy.
20 ~ Figure 4 is a dla~ram o~ the latent magnetic image.
Fi~ure 5 i~ a diagram o~ the oned ma~etic ; image superposed ad~acent the copy paper.
~; Flgure 6-is a dlagram o~ the copy paper decorated with the transfer image.
Figure 7 is a dlagram o~ the ~inal copy decorated with~the ~used image.
Figure 3-7 show the stepwlse ~ormation o~ the latent magnetic image, the decoration thereof with toner, 3 the trans~er o~he toner to~the copy paper, and the ~usion 3~1L3 of the toner to the copy paper.
Figure 8a is a schematic view of the developed surface of drum 15 o~ Figure 1 showing the result af practicing magnetographic copying without the electro-static neutralizers of the instant invention.
Figure 8b is a ~chematic view simllar to Figure 8a showing the use of the alternating current coronas of the i~vention.
An aluminized polyester ~ilm having a layer of spatially periodic magnetized chromium dioxide par ticles in a binder adhered to the sur~ace thereof which is to be used as a copying device is exposed to uni~orm illumination as shown in Figure 3. As can be seen ~rom Figure 3 the printin~ on the translucent document prevents the illumination from reaching the ma~netized . chromium dioxide particles, thus, leav~ng them : magnetized in the areas under the printing~. On the other hand, those areas of the document being copied , .
which contain no printing do not prevent the illumlnation from reaching the magnetized chromium dioxide particles, thus heating them to above their Curle point of about 116C, thu~ demagnetizin~ them. In this way the latent ::magnetic;image shown in Fi~gure 4 is prepared. Ferro-magnetlc toner particles are applied to the la~ent magnetic~ image to ~orm a developed magnetic image and copy paper is: brought~into superp~osition therewith as shown in Figure 5. A corona discharge device then electrostatically :eharges the~ back o~t~e paper. An electrostatic force suf~icient:~to o.Vercome ~he magnetic attractio~ bet.ween the ~;3~ ~ previously uncharged:toner partlcle~an~ne latent magnetic -.

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lmage ls generated causing the toner particles to tran~fer to the copy p~per and be adher~d ther~to with surprisingly hi~h efficiency as shown in Figure 6~ This electrostatic transfer has no effect on the latent magnetic lmage which ~y be reu~ed many times. Refer~nce i5 made to co-pending applicatlon Ser~ NoO 767~ 511~ filed February 14, 1977. The trans~erre!d toaer particle~ ~re th~n fu~ed to the copy paper as shown in Flgure 7 by heat~
The toner partlcles pre~erably are magnetlc pigment~ encapsulated in a ~ultable thermoplas-tLc binder.
Gener~l~y the toner p~rticles have an average ~ize ranging from 10 to 30 microns with a preferred average size ra~glng from 15 to 20 mlcr~ns. Spherical parkicle~ 3uch as prepared by spray drying are pre~erred bec~u~ of thoir superlor flow properties which can be enhanced by ~; th~ addition of minute amounts of a ~low additi~re such as fumed silica. A further dcscription of the preparat~on o~ toner particles may be f~un~ ~ U.S, Patent 3,6273682.
20 N~en u8~1g the appara~u~ disclo~ed herein the ~oner p~rkicles u~ed hereln should have a lo~ eleckrical conductivity so that they will tran~fer readilyA I:e the particle~ have hlgh conduct~vity, they will be pa~sed bac~ and forth bet~een the drum and the paper causing a dii:euse image and low trans~'er efficiency. Gerlerally the toner powder electrical conductllfit~ i9 below 1 x 1O~13 mho/cm.
Referr:lng to Figure lg the docu~ent which is to ~-be copied i8 placed o~ shel~ 11 ar~d urged against gate 12"
The copier i~ then activated to llft gate 12 and lower 3O feed roll 13 into cont~ct with the docume3~t. Feed roll ~ 5-. ', " .

13 ~eeds the document into the nip between endles~ belt 14 and drum 15. Endless be.lt 14 is made o~ a transparent ~ilm such as poly(ethylene terephthalate) about 2-7 mils (0.05-0.18 mm) in thickness. Rollers 16, 17 and 18 serve to drive and guide endless belt 14. The surface of drum 15 is pre~erably a poly(ethylene te:rephthalate) film about 5 mils (0.13 ~n) in thickness. The convex surface of this ~ilm is coated with a conductive layer such as by being aluminized with a layer of aluminum to a surface resistivity ~ 10 o~ 1 to 1,000 ohms. The aluminum layer preferably is : grounded. The conductive support may also be a plastic such as polyoxymethylene sleeve coated or ~ormulated with aluminum, nickel, copper or other conductlve material.
The support may also be the conductive metal itself.
The surface of the aluminum is coated with a layer of ferromagnetic material such as acicular chromium dioxide in an alkyd or other suitable binder. Generally, the acicular chromium dioxide layer is ~rom 0.001 to 0.Q12 mm ~: : in thickness and contains from 40 to 85 welght percent ~ ~ 20 .acicular chromium dioxide and from 15 to 60 weight percent alkyd.or other suitable`resin hinder. Suitable acicular ~: chromium dioxide can be prepared in accordance with the teachings oP U.S. Patent~2,956,955, issued October 18, 19609 to Paul~Arthur, Jr. However, the preferred acicular chromium dioxide particles are produced by techniques dis~
closed in U.5. Paten~ 2,923,683 and 3,:512,930..
Drum }5 rotate.s: in a counterclockwise dlrection.
he ferroma~net.ic. coating on khe drum is:~magnetized b~ :

premagnetlzer l~,. which.rec.ords a per~odic pat.kern. A
: 30 number of~.te.chniques are known for doing t~his magne~.i.c ;:

~ 73~3 structuring. We find 3~0 to 1000 magnetic reversals per inch (12 to 40 per mm) on the magnetizable sur~ace to be a working range and prefer about 400~600 magnetic reversals per inch (15 to 24 per mm).
Alternatively, a film ~3tructured by groo~es contalning acicular chromium dioxide can be used for the sur~ace of drum 15 in which case a slmple DC magnet can be used as premagnetizer 19. Generally from 200 to ~00 grooves per inch (7.5 to 12 per mm) across the drum will be used giving 400 to 600 magnetic reversals per inch (15-24 per mm).
The magnetized drum sur~ace in contact with the document is then moved past an exposure sta~lon indicated generally at 20. The exposure station consists o~ lamp 21 and reflector 22. A sultable lamp 21 is a xenon fla h, which has a color temperature equlvalent to 6000C. The ; surface of drum 15 is exposed stepwise until the entire document has been recorded as a latent magnetic image on the surface Or drum 15. The chromium dioxide as used herein has a Curie temperature o~ about 116C. The marking .
~ 20 of tAe document being copied, pencil llnes, printing or ;~ the like, shade the areas of the chromium dioxide over which such marklng~ are ~ltuated during e~poBure thereby preventlng these area reaching the Curie point. ~hus, a~ter exposure, :: :
the sur~ace of i;he drum will ha~e magnetlzed areas o~chromlum dloxide corresponding to the marked areas of the translucent document being copied.
After exposure, the document being copied is ~: ~ : : . .
dropped into tray 23. ~ ~

The~imagewlse magnetlzed drum 15 is rotated past 30 ~ a~toner decorator. The toner deoorator comprises a trough , 24 fitted with rapidly rotating roll 25 and bar 26. Static eliminator 62' removes any charges on toner particles that emerge from the toner decorator. A vacuum knife 31 is used to remove whatever toner par-ticles may have adventitiously become attached to the demagnetized areas of the chromium dioxide on the surface of drum 15.
The paper 32 on which the copy is to be mad,e is fed from roll 33 around idler rolls 34, 35, 36 to feed rolls 37 and 38. Backing roll 39 cooperates with roll 40 equipped with cutting edges 41. Rolls 39 and 40 are activated by means not shown to cut the paper 32 to the same length as the length of the document being copied. The paper is then ~ed by feed rolls 42 and 43 into physical contact with the surface of drum 15. The paper 32 in contact w~th the surface of drum 15 is fed past corona discharge device 44O Corona discharge device 44 preferably is of the type known as a COROTRON* which comprises a corona wire spaced about 11/16" (17.5 mm~ from the paper and a metal shield around about 75 percent of the corona wire leaving an opening of about 90 around the corona ' ~' wire exposed ~acing the paper 32. The metal shi~eld is insulated from the corona wire. The metal shieId is main-tained at ground potential, Generally the corona wire wi~l be from 0.Q25 to Q,25 mm. in diameter ~nd will be maintained at from 3Q00 to lQ000 volts. The corona wire may ~e at either a negative or a positive'potential with negat~ve potential being preferxed. The COROTRON 44 electrostatica,lly char~es the ~ck siae Q~ paper 32~ This lightly pins the paper to the drum, and upon separation of the paper from the drum has caused image-wise transfer of toner p~rticles 3Q * denotes trade mark ~'~,1' ~73~3 to paper 32. At the region in which paper 32 separates from the surface of dru~ 15 uncler the action of endless vacuum belt 50, the toner particles remain held in image-wise fashion to paper 32. We have observed that COROTRON 44 should be disposel~ over the arc of intimate contact for best results. If COROTRON 44 is not so located or if there are forces present preventing the paper 32 from forming an arc of intimate contact, the resul-tant image becomes fuzzy.
There is only a light amount of pressure between paper 32 and the surface of drum 15 (i.e., merely enough to hold them adjacent each other). The pressure between paper 32 and drum 15 is essentially entirely generated by the electrostatic attraction generated by corona discharge device or COROTRON
44. Nevertheless transfer efficiency is surprisingly high and approaches 100~ for toners with nontacky surface charac-teristics and low conductivity. The paper 32 is then removed from the surface of drum 15 by the action of the vacuum belt 50 in conjunction with the action of puffer 45 that forces the leading edge onto the sur~ace o~ endless vacuum belt 50 ~: 20 driven by rollers 51 and 52. Endless vacuum belt 50 trans- :
ports paper 32 past infrared lamps 53, 54, 55 which heat the thermoplastic resin encapsulating the ferroma~netic material in the toner particles causing them to melt and fuse to the -~ paper 32, The decorated paper 32 is then fed into hopper 56.
When multiple copies o:E the same document are to be made, a control;means, not shown, is so actuated that drum 15 is continuously rotated without activating demaynetiæer 60, vacUum box 61, magnetizer 19 or lamp 21 because ~he electrostatic trans~er of the toner particles does not affect the magnetic state in the chromiu.m dioxlde layer on ~;
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the surface of drum 15. Many copies can be printed from a single exposure at speeds of up t:o 300 feet/minute. Over 10,000 copies fro~l a single image have been demonstrated.
Toner particles which clo not transfer may themselves become electrostatically charged in the transfer zone adjacent to the COROTRON 44. These charges do not bleed to ground because of the nature of the toner. Subsequently, these particles will pick up other particles electrostatically in decorator 24 and ultimately transfer these to produce unwanted markings. To prevent this, a static eliminator 62 is used.
In accordance with the present invention this is an alternating current discharge bar, but may be any static neutralizing device known such as nuclear bars. It has been found that a 60 Hz, 700~ volt Simco unit is satisfactory for this purpose.
A percentage o~ toner particles that do not transfer are in image areas. Particles in image areas still charged upon passing image decorator 24, pick up toner particles electrostatically which are so tightly held that vacuum knife 31 cannot remove them causing the image to '7bloom" or grow larger with a fuzzy outline upon repeated copying. Static eliminator 62 completely prevents this unwanted phenomenon.
There are also some toner particles sparsely distributed over nonimage areas which do not transfer to the paper and which become electrostatically charged in the transfer zone. They also attract toner electrostatically in the decorator 24 which cannot be subsequently removed entirely by the vacuum kni~e 31 resultin~ in unwanted background on the final copies Static eliminator 62 also prevents this unwanted phenomenon.

1 0 - , The actlon of decorator 24 causes a number o~ toner particles to become tribo-charged by contacts with each other and the various surf'aces. Such electro-statically charged particles become bound to the surf'ace of drum 15 by so-called "mirror'! lmages~ The nature of' the toner does not hence allow the charæe to b.leed off to the grounded surface as do any tribo~charge dlrectly on the surface o~ drum 15. I~ permit.te~ to remaln on the sur~ace o~ drum 15 these particles, randomly distributed, would a~ect the cle~nliness o~ the background of' the final ttranS~erred) image on the copy paper. Vacuum knife 31 lq highly e~fecti~e in removing the~e particles but some of these particles, pro-bably more highly chaxged or physically maller than others, are sufficiently held to the surface:of drum 15 to not be ~ removed by vacuum knife 31. A second static eliminator 62' i5 provided a~t~er image decorator 24 and before-vacuum kni~e 31 to remove the electrostatic charge on such par~icles thu~
enhancing the action o~ vacuum knife 31. Static eliminator 62-is required for repetl~ive, stable reproduc~ion o~ the ` 20:~ latent magnetlc image. Elimlnator 62' 1s required to produce background area~o~ ~uperior cleanliness. In com-blnation, the~two elimi~ator cooperate to~produce ma~neto- :
graphic.~copies~o~ superior quality and~permlt copying~in high multiples f'rom~a slngle latent ma~netic lmage.
hen i.t :is desired to prepare copies ~rom a di~ersnt document~ demagnetizer:~ 6o, which conveniently can be a~DC:
magnetlc~ head:~ln the case o~continuously coated:~ilm, ~ :
is~aotlvated~:and the~c~hromium dloxlde is~unlformly magnetlsed.
Whatever toner~partioles~may be remaining on~ the:;prevlQ~usly magnetized:area~: of chromium dioxide, are removed by ~acuum ,~3 ~J'~'L~

box 61 whlch preferably acts in conjunction with brushes.
The chromium dioxide is then magnetized by magnetizer 19 to provide a periodic magnetic struc~ure and the process described above repeated.
It is to be understood that substrates other than paper, such as cloth and dielectric ~ilms, can be used.
Flgure 2 shows an alternate form o~ printer using a magnetic printing head such as have been re~iewed by W. H. Meikle~ohn in A.I,P. C~n~erence, Proc. (Pt. 2) 10, tl973) pages 1102 to 1114. In the example o~ Figure 2 magnetic printlng head 71 is used to form the latent image on the magnetic sur~ace of drum 72 whlch has the same structure as drum 15 described abo~e. Magnetic printing head 71 is a multltrack printing head such a~
have been developed ~or fixed heads for track discs. Pre-ferably track density ~ill about about 200 magnets per inch (8 per mm~ which ls adequate to print wlth good resolution.
Generally the multitrack write head will be activated by head drivers wh~ch can be activated by a read-only memory , character generator. The~read~only memory character generator can respond to an in~ormation stora~e device such as a magnet~c tape which~may be part o~ the printer or remote there~rom. Alternatively,~ a Xeyboard can activate the multltrack write-head, Nherein magnetio~structurlng is accomplished with the magnetic write head. Drum 72 rotates in a countercloc}~ise directlon carrying the 1 kent image past statlc elimlnator 107.~ Electrostatic charges carried on~any partlcles on the su~faee o~ drum~72 are neutralized ~
by~ eliminator 107. Such~¢harged~particles can be adventitiously 30~ adhered partlcle~ or particles in an~image area that~did~ ~

not transFer. ~uch particles, having passed transfer COROTRON 96, can be highly charged and would pickup oppositely charged toner particles in toner decorator 108 if it were not for the neutralization provided by static eliminator 107.
This can be any o~ the well-known types. Again we prefer a 60 Hz, 7000 volt AC corona discharge for as drum 72 rotates the latent image past toner decorator 108 which comprises a trough 73 fitted with rapidly rotating rolls 7~ and stationary bar 75, the latent image is decorated with toner to produce a developed magnetic image. Static eliminator 107' removes any charges on toner particles that emerge from toner decora-tor 108. Such charges derive from tribo-charging and cause particles to adhere to drum 72. Thus, vacuum knife 81 is able to remove any unwanted toner particle, i.e., not held on an image area.
The paper 82 to which the toner pattern is to be applied is fed from roll 83 around idler rolls 84, 85, and 86 to feed rolls 87 and 88. Backing roll 91 cooperates with roll 92 equipped with cutting edges 93. Rolls 91 and 92 are activated by means not shown to cut the paper 82 to the desired length. The paper is then fed by feed rolls into physical contact with the surface of drum 72. The paper `~ 82 in contact with the surface of drum 72 is fed past corona discharge device or COROTRON 96 which causes the toner particles to be electrostatically transferred to paper 82.
The paper 82 is then removed from the surface of drum 72 by ~ the action of puffer 97 that forces the leading edge onto ,!~ the surface of endless vacuum belt 98 driven by rollers 99 and 100. Endless vacuum belt 98 transports paper 82 past :' . ~ .
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infrared lamps 101, 102 and 103 which heat th~ thermoplastlc resin encapsulating the ~erromagnetlc material in the toner particles causing them to melt and fuse to the paper 82. The decorated paper 82 is then ~ed into tray 104. ~he drum can be continuously rotated to make a plurallty o~ copies.
- When i~ is desired to make a different print, demagnetizer 105 is ac.tuated tQ erc~se the latent magnetic image and vacuum box 106 is used to remove any toner particles re~aining on the old latent magnetic image.

The proces~ can also be operated using either a thermal stylus or a~ electrical stylus to. c.reate the : latent magnetic image, the former by conductive heating and the latter by electrical resistance heating o~ the imaging layer. Either stylus can demagnetize selected areas by heating prevlously magnetized material above the Curie point or it can magnetize selecte~ ~reas thermo-remanently by allowing the heated imaglng material ~o cool through its Curie point in the presence of a ma~netlc : . i -field. A ~ield o~ 20 to 200 Oe adjacent to the stylus : : :
has been~found to be suf~icient for thermoremanent magnetiza tion, while a much stronger ~ield of at least 800 Oe ls necessary to magnetize unheated chromium dioxide su~iciently. .~i ., :~ :
: It is recognlzed, of course, that imaging with electro-magnétlc or~therm~l transducers onto a contlnuous coating wlth lts ~ur:~ace magnetlzed Nith:a DC~magnet will;requlre modulation consist;ent with establishing magnetlc gradients:
for adequate toner attraction in magnetized image areas.
Figure 8a is a;de~eloped~vlew of~the surface of~
.~30:~ drum~15 of Flgure l schematical}y showing employme~t of :
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image decorator 24, vacuum knife 31, and transfer COROTRON
44 without the alternatiny curr~nt coronas (and without functional representations of components not pertinent to explaining the actions of the a-c coronas). At al is shown a sparsely decorated indicia, here for illustrative purposes a letter I, that has not entirely transferred in the transfer zone and has become charged electrostatically.
The sign of the charge is not material. Alongside al is shown an adventitiously adhered particle of toner bl (schematically enlarged) also similarly charged. After the surface of drum 15 passes image decorator 24 at al' is shown the letter I decorated with toner magnetically but also carrying toner adhered electrostatically. At bl' are seen toner particles electrostatically adhered to the adventitiously attached toner particle so forming a cluster.
Moreover, there are some tribo-charged particles randomly adhered to the conductive surface of drum 15, here represented by three such particles cl.
Vacuum knife 31 removes some of the more loosely bound toner particles but some remain at al", bl", and cl'.
Note that the I has started to bloom. After passing the transfer zone adjacent COROTRON 44 most of the toner parti-~ ~ .
cles, wanted and unwanted, have transferred but some remain as shown at al"', bl"l, and cl". The copy made has slightly ~` fuzzy indioia and some dirty background. Note that in the next printing cycle, there are now additional untransferred and charged toner particles at al and bl, which will result ` in even greater blooming of the image and dirtie~r background due to blooming of background particles.~ Furthermore, untransferred~particles at cl become a new nucleation point ~ : :

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for unwanted background to~er. Thus, with each successive printlng cycle, copy quality grows progressi~ely poorer.
Now consider Figure 8b showing the use of a-c coronas 62 and 62'. a2 an~ b2 are charged toner, the ~ormer : untrans~erred indicLa, the latter adventitious. After passing a-c corona 62~. a2~ and b2 t remaln but are neutraliæed electrostati.call~, Thus~ the indicla becomes decorated without blooming as at a2l' and ad~ent.itlou~l~ adhered partlc.le b2" does not attract a c].uster o~ to.ner particles.
Howe.ver, t~ibo.-charged particle~ ~ay cling to the surface of drum 15 as at c2.. A~te~ passing a-c. ~oron~ 62', a2"' and b2"' are as before but particles c2~ are neutralized. Thus, on passing vacuum kni~e 31 nearly all toner particles have been removed ~rom demagnetized nonimage areas and only unbloomed decorated indicla a2I remains with the result that the toner image trans~erred to paper ad~acent : aorotron 44 i5 crisp with a clean background... Any untransferred toner as at a2 moreover is within the bounds .~ of the original indicia and subse~uent copies will also be ~ :20 crisp and clean.

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Claims (27)

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

1. A process for repetitive reproduction of graphic information comprising:
(a) transferring toner particles by bringing a substrate capable of maintaining an electrostatic charge into superposed position with an image of uncharged toner particles having an electrical conductivity of less than about 1 x 10-13 mho/cm magnetically adhered to a grounded electrically conductive imaging member having a resistivity of less than about 1 x 10+9 ohm/cm and applying an electric field at this position which electric field is generated by applying an electrostatic charge to the side of the substrate away from the toner particles separating said sub-strate from said imaging member, whereby said toner particles adhere to said substrate upon separation of the substrate from the imaging member;
(b) reapplying toner particles to the imaging member;
(c) repeating step (a);
(d) applying static neutralizing means selected from the class consisting of alternating current coronas and nuclear bars to said imaging member and any toner particles thereon, either between the steps of transferring toner particles to said substrate and reapplying toner particles to the imaging member, or between the steps of reapplying toner to the imaging member and bringing said substrate into superposed position with said imaging member; and (e) removing residual toner from non-magnetized areas of said imaging member between the steps of reapplying toner to said imaging member and transferring toner to said substrate.

2. The process of Claim 1 wherein the static neutralizing means is an alternating current corona.

3. The process of Claim 2 wherein static neutralizing means are used to neutralize any toner particles both between reapplying toner particles to the imaging member and trans-ferring toner particles to the substrate and between trans-ferring toner particles to the substrate and reapplying toner particles to the imaging member.

4. The process of Claim 3 wherein both static neutralizing means are alternating current coronas.

5. The process of Claim 4 wherein the electric field is generated by spraying ions on the non-superposed side of the substrate.

6. The process of Claim 1 wherein the toner particles are fused to the substrate by heat.

7. The process of Claim 1 wherein the static neutralizing means is applied to the imaging member and any toner thereon after toner particles are reapplied to the imaging member but before bringing the imaging member into superposed position with the substrate.

8. The process of Claim 1 wherein the static neutralizing means is applied to the imaging member and any toner particles thereon after transfer of toner to the substrate but before reapplication of toner.

9. The process of Claim 6 wherein the magnetically held image of uncharged toner particles is magnetically held by magnetized acicular chromium dioxide.

10. A process comprising:
(a) spatially periodic magnetizing a layer of acicular chromium dioxide particles in a binder which particles comprise from 40 to 85 weight percent of a layer of from 0.001 to 0.15 mm thick adhered to a grounded electrically conductive layer, bringing said layer of acicular chromium dioxide into super-posed position with a document containing thereon indicia which are to be copied, uniformly illuminating said document whereby radiant energy is transmitted through said document in the areas of said document not covered by indicia whereby the acicular chromium dioxide in the areas where it is illuminated and heated to above its Curie point and demagnetized while the areas of acicular chromium dioxide adjacent the indicia contained on said document are not heated above its Curie point;
(b) applying uncharged toner particles having a conductivity of less than about 1 x 10-13 mho/cm comprising ferromagnetic material and a fixable material uniformly to the chromium dioxide layer whereby said toner particles adhere only to the magnetized areas of the chromium dioxide, maintaining said toner particles in the uncharged condition;
(c) removing toner particles from non-magnetized areas of the chromium dioxide layer;

(d) superposing a dielectric substrate capable of maintaining an electrostatic charge adjacent said acicular chromium dioxide layer;
(e) applying an electric field while said substrate is in superposed position with the acicular chromium dioxide layer which electric field is generated by applying an electrostatic charge to the side of the substrate which is away from the toner particles whereby said toner particles are adhered to said substrate upon separation of said substrate from said layer;
(f) separating said substrate from said imaging member;
(g) reapplying toner to said layer of acicular chromium dioxide;
(h) either between the steps of transferring toner particles to said substrate and reapplying toner particles to the acicular chromium dioxide layer or between the steps of reapplying toner to the imaging member and bringing said substrate into superposed position with the acicular chromium dioxide layer, applying static neutralizing means selected from the class consisting of alternating current coronas and nuclear bars whereby any toner particles on the imaging member bearing an electrostatic charge are neutralized; and (i) repeating steps (b) through (h).

11. The process of Claim 10 wherein the static neutralizing means is an alternating current corona,

12. The process of Claim 10 wherein a static neutralizing means is used to neutralize toner particles both between the steps of transferring toner particles to the substrate and reapplying toner particles to the acicular chromium dioxide layer and between the steps of reapplying toner to the imaging member and bringing said substrate into superposed position with the acicular chromium dioxide layer.

13. The process of Claim 12 wherein both static neutralizing means are alternating current coronas.

14. The process of Claim 13 wherein the electric field is applied by spraying ions on the non-superposed side of said substrate.

15. The process of Claim 14 wherein the substrate is paper.

16. The process of Claim 15 wherein the toner particles are fused to the paper by heat.

17. The process of Claim 16 wherein the toner particles have an electrical conductivity of less than 1 x 10-13 mho/cm.

18. The process of Claim 10 wherein the toner particles have an electrical conductivity of less than 1 x 10-13 mho/cm.

19. An apparatus for applying ferromagnetic toner particles to selected areas of a substrate capable of maintain-ing an electrostatic charge comprising a movable layer of electrically grounded selectively magnetized ferromagnetic particles, drive means to advance said layer, means for applying ferromagnetic toner particles to said layer, means for removing ferromagnetic toner particles from areas of said layer not selectively magnetized, means to bring said substrate into superposed position with said layer, means for applying an electric field while said layer is superposed against said substrate, means for removing said substrate from said layer, and a static neutralizing device adapted to neutralize any charges on any particles left adhering to said layer after said substrate has been removed from superposed position therewith.

20. The apparatus of Claim 19 wherein the static neutralizing device is an alternating current discharge device.

21. The apparatus of Claim 20 wherein a second static neutralizing device adapted to neutralize any charges on the toner particles applied to said layer followed by a vacuum knife is positioned between the means for applying ferromagnetic toner particles to the film and the means for applying the electric field to the substrate.

22. The apparatus of Claim 21 wherein both static neutralizing devices are alternating current discharge devices.

23. The apparatus of Claim 22 wherein the means for applying an electric field to the substrate is a means for applying an electric charge to the side of the substrate away from the toner particles.

24. The apparatus of Claim 23 wherein said means for applying an electrical field comprises means for spraying ions on the non-superposed side of said substrate.

25. The apparatus of Claim 19 wherein magnetic means are provided to selectively magnetize the movable layer of electrically grounded ferromagnetic particles.

26. The apparatus of Claim 19 wherein electrical heating means are provided to selectively thermoremanently magnetize the movable layer of electrically grounded ferromagnetic particles.

27. The apparatus of Claim 19 wherein thermal imaging means are provided to selectively demagnetize previously spatially periodic magnetized areas of the movable layer of electrically grounded ferromagnetic particles.