US3918966A - Liquid development of an electrical image in which a pulsating field is employed - Google Patents

Abstract

A method of developing an electrical image or transferring an unfixed image in which the image is during development or during transfer subjected to a pulsating field with a fast attack and slower decay to repeatedly break the bonds tending to hold the developed image to a surface. A directional image field is used to control final settlement of the developer particles.

Description

United States Patent Metcalfe et al.

The Commonwealth of Australia care of The Secretary, Department of Supply. Parkes, Canberra. Australia Filed: Sept. 26, 1973 Appl. No: 401,106

Assignee:

Foreign Application Priority Data Sept. 28. 1972 Australia 629/72 US. Cl. 96/1 LY; 96/1.4; 427/17 Int. Cl.'- G03C 13/10; 603G 17/00 Field of Search 96/1 R. 1 SD. 1 LY. 1 PE.

References Cited UNITED STATES PATENTS 3/1959 W'alkup 96/1 C 1/1963 Mott 96/1 C 11/1966 Lehmann ..96/1SD X 7/1967 Gund1ach.... 96/1 SD X 9/1969 Waly 96/1.3

1 1 Nov. 11, 1975 3.486.922 12/1969 Cassiers et a1 427/15 3.515.548 6/1970 Lange 16/1 R 3.560.203 2/1971 Honjo et a1 96/1 LY 3.576.623 4/1971 Snelling 96/1 LY 3.657.091 4/1972 Forest 96/1 PE X 3.759.222 9/1973 Maksymiak et a1 96/1 SD X 3.784.397 1/1974 52110 et al. 96/1 LY X 3.804.510 4/1974 Sato et a1. 96/1 LY X 3.811.764 5/1974 Forest 96/1 PE X FOREIGN PATENTS OR APPLICATIONS 796.679 10/1968 Canada 96/1 LY 267.341 5/1964 Australia 96/1 LY 281.765 4/1966 Australia 96/1 LY 1.214.155 12/1970 United Kingdom 96/1 LY 1.165.038 9/1969 United Kingdom 427/15 2.112.015 10/1971 German 96/1 LY 7.005.615 10/1970 Netherlands 96/1 LY 7.005.938 10/1970 Netherlands 96/1 LY Primary E.\'amt'net'Charles L. Bowers. .lr.

Assistant Examiner-John R. Miller Attorney. Agent, or Ft'rntHaseltine. Lake 8.: Waters 1571 ABSTRACT A method of developing an electrical image or transferring an unfixed image in which the image is during development or during transfer subjected to a pulsating field with a fast attack and slower decay to repeat edly break the bonds tending to hold the developed image to a surface. A directional image field is used to control final settlement of the developer particles.

9 Claims, 2 Drawing Figures U.S. Patent Nov. 11, 1975 GE N m w W @FJ W m A 1 n F u m Q .L m .i l. 1.. a

LIQUID DEVELOPMENT OF AN ELECTRICAL IMAGE IN WHICH A PULSATING FIELD IS EMPLOYED This invention relates to methods of and means for developing and transferring images otherwise developed. The invention is usable with electrical images produced in any way but particularly to what are known as chargeless" processes.

BACKGROUND OF INVENTION According to the normal methods of developing images, such as latent electrostatic images produced by applying a developer to a photoconductive membrane on which an image has been formed by charging and light bleeding, certain difficulties have occurred during the application of a developer, either in the form of a dry powder carried on granules or the like, or a toning medium suspended in an insulating liquid.

Among these problems are the contamination of the background areas where deposition should not take place, and also the attainment of the required densities and correct shade values in, for instance, continuous tone methods, and such effects as edge intensification adds to the problem of development, particularly with what are known as dry developers. When it is desired to transfer an image from an area where it was developed, which is usually achieved while the image is still in an unfixed or a wet condition, complete transfer of the image is usually not achieved, and also during the transfer there is a tendency to lose definition in the image, and to overcome this it has been proposed to pass a field, including an alternating biased field, through the image in a direction such that the developed image is forced away from the photoconductive membrane on which it was made and on to the sheet on which the image is subsequently fixed, either by a heat fusion or by evaporation of the carrier liquid or by other means. The art is taught, for instance, in (1.8. Pat. No. 3,464,8l8 The art of using alternating current with a bias for development is taught in US. Pat, Nos. 3,657,091 and 3,811,764.

In the case of chargeless processes, that is a process in which a surface simply receives patterned rays which then leave a differential effect or differential dielectric constant on the surface capable of being developed, a further problem exists in that the magnitude of the differential variation is relatively low compared to what ,can be achieved by charging and then light bleeding, and this lower image value has resulted in the problem that only very fine developers could be used because coarser developers would not move effectively, or be retained, on the weaker latent images which thus result. Even with fine developers there has been the problem that densities are relatively low and therefore heavy deposits of developer cannot be achieved, and one of the principle objects of the present invention is to provide a method of and means for developing improved images, particularly, though not exclusively, images on what are known as the chargeless system.

It can be mentioned at this stage that the chargeless system was developed largely to overcome artifacts which are caused through uneven charging according to the methods used at present. and many forms of charging have been devised to try and overcome this irregularity in the charge on the photoconductor which then, of course, is reproduced in the developed image.

Such a chargeless process was disclosed in Australian Patent No. 243,184 in the name of The Commonwealth of Australia the basic application having been lodged on the 5th Mar. 1959.

It follows also that chargeless images require advanced techniques to transfer them, because of the lower image density which has in the past been obtainable, but this is also true of normally produced images including dry developed images, and the present invention is directed to providing a better form of transfer for any of the known systems.

SUMMARY OF INVENTXON We have discovered that much more effective development of images can be obtained by any of the known systems, including the chargeless system, if during development, and also during transfer if this is required, a pulsating field with fast attack and slower decay is applied to the area where the development is taking place, or while the transfer is being effected.

The pulsating field is preferably such that a saw-tooth wave is produced which has a sharp leading edge and a trailing decay portion, so that each impulse reaches a maximum when first initiated and then dies away to the next impulse, the frequency depending on the developer and the conditions and results required. The frequency may be in the order of 50 cycles to many thousands of cycles, although when the developer is applied by roller or the like it is preferred to have a high frequency, preferably in excess of a few thousand cycles, as otherwise it is found that the traversing of the developer roller across the surface, which roller is energised to apply the impulses, will result in transverse markings varying in intensity between pulses.

The concept of the invention is that because of Van der Waals forces which exist on the developer particles as they are deposited on the surface, the pulsating field causes the particles hold to be broken so that they do not simply deposit on the surface and remain there, but are in a state of agitation so that an image is repeatedly built up and at least partly destroyed, the interesting phenomenon being that during this action the developer particles are kept in motion at the interface of the surface being developed and, therefore, are able to deposit very much more heavily than would otherwise be possible. It is assumed that this is because the particles already deposited do not necessarily shield the area, but rather as all particles are oscillating there can be an extensive build up at even a low charge area as this area is not effectively covered until such time as development is completed, which occurs after a required time when the pulsating field is removed. At this stage the particles settle down and remaining in position. The same theory applies when the developer particles are to be transferred from the membrane on which they have been deposited because here again the sharp pulsations ensure that the hold of the particles on the surface is broken by the pulsation, and therefore the Van der Waals forces are countered by this action, and it is assumed that this is the reason why a better transfer of the particles is then possible because during transfer their effective attraction to the surface on which they are first deposited is lessened and, because of the agitated conditions under which they are transferred, the particle can be packed much more effectively on the receiving sheet. Extensive tests have shown that even with chargeless development of images, high densities can be obtained, not only by using ultra-fine developer particles but we have found that when the pulsating field is present, also relatively coarse developers, with extensive depth of cover of developed areas, can be achieved.

The theory which we believe to be applicable is that under normal developing conditions, particularly where the field strength of the latent image is relatively low, particles deposit under this field and then shield the area and prevent further developer particles moving to the latent image, but when the pulsating current is applied. the Van der Waals forces which tend to hold the particles in place and together are broken, and the particles thus can be packed in a more consolidated form and to a greater depth.

So far as the direction of the pulsating field is concerned in relation to the developer particles, we have found that this can vary according to conditions, and in the case of transfer is preferably in the direction which tends to move the particles on to the receiving surface and away from the surface on which the image was formed, but it will be realised that because of the pulsations and the somewhat slower decay, the first action will probably be to break the Van de Waals forces, but as the pulse decays the particles can move back again but with a somewhat lesser intensity effect because of the decaying field, and this type of wave, therefore, would seem to produce a movement in one direction although during the movement the particles may be pulsating quite extensively. The effect has been found to be quite different to that which exists where a constant field is used to try and move particles from one surface on to another.

in the case of development, the field is preferably again in the same direction so that during the pulsations the Van de Waals forces on the particles as they near the surface and before they reach a balance are repeatedly repulsed so that, while they are drawn by the field to settle in a particular position of the image, their movement is of a pulsating nature so that they cannot immediately attach but are kept in an agitated state adjacent to an area where they will finally be allowed to deposit when the pulsating field is removed or countered.

While we do not wish to be bound to the basic theory set out above, it should be remembered that according to the Van de Waals force theory, electrons in a cloud of negative electricity in a molecule are in rapid motion, and the charge distribution may therefore be thought of as fluctuating in time.

The hold actually occurs at any instant in that the dipole in one molecule will cause an electric field to act on a neighbouring molecule and this will disturb the motion of the electrons in the second molecule, and it is the interaction of the two dipole movements which result in the holding force which tend to keep the molecules of the developer locked to the surface on which such a developer has been deposited, and to each other and while the electron cloud keeps the molecules from actually contacting the surfaces, an equilibrium exists which it is the purpose of the present invention to upset by means of the pulsating current applied to the developer particles at the site where they are deposited.

The Van de Waals force, of course, varies with particle size but can be many times the force of gravity, but nevertheless the introduction of the pulsating current, which can be applied by a roller or an electrode through the membrane on which development is being effected causes the better development or transfer to be effected, an electrode on the back of this membrane, completing the circuit, or the field may be applied to a conductive layer on the membrane on which the photoconductor is supported, a second electrode of course being then used on the developer side somewhat remotely from the area of deposition. The method of applying the field is not important so long as it is present at the interface being developed or from which the developer is being transferred.

The pulsating field can be biased to be above or below earth potential to impress a constant field on it acting in one direction, and it will be realised that this allows an undirectional biasing effect to be obtained as well as the superimposed pulsating direct current.

In order however that the invention may be more fully appreciated an embodiment of mechanism for carrying out the invention which was developed during research is now to be described but it is to be clear that the invention need not necessarily be limited to this.

In the FIG. 1 embodiment a variable frequency power supply 1 is connected to the primary of a transformer 2 by means of a wave shaping triac 3 operating under control of an i.c. phase control unit 4 to produce at the secondary S of the transformer unit 2 pulses which are then rectified by the diode 6 and filtered if necessary by the filter circuit 7, the resulting pulsating current being then applied through the centre tap of the resistor 8 to a developer roller 9 which has the sheet 10 containing the latent image passed between it and a pressure roller 11 which as shown is connected to earth. The potential can be regulated by adjusting the potentiometer 12.

A filter 13 prevents radiation from the triac 3.

14 indicates in dotted lines a receiving sheet when the device is used for transfer purposes in which case the roller 9 is merely a pressure roller to apply the bias as the sheet 10 will have been previously developed and the developed sheet is then pressed against the sheet 14 to transfer the image from the sheet 10 to the sheet 14.

The FIG. 1a diagrams 15, 16 and 17 show the form of output which can be achieved, the positive pulses being of course shaped by the phase control 4 in known manner to cut required parts of each cycle to give the necessary type of agitation to the particles. The pulses can have a positive or negative characteristic by appropriately positioning the rectifying diodes 6 so that direc tional effects can be obtained.

As an analogy in the present case attention could be drawn to the bias used during tape recording where the bias made possible highly effective recording which would not be obtainable without a bias, the theory of operation in that case being that the oscillation keeps the magnetic orientation in a mobile state to thereby allow a relatively small signal to give the correct orientation to the particles.

In the case of the present invention of course the analogy is not identical but the general principle of having the developer particles in a state of agitation when they are subject to the image field appears to have advantages as significant as was the advantage of using bias in magnetic tape recording, and the results obtained by this method were by no means obvious because in the one case a magnetic orientation was involved whereas in the present case a physical displacing action of particles is necessary.

It will of course be quite obvious to anyone versed in the art that where there is relative movement between a developer roller and a membrane containing a latent electrostatic image being developed, or two membranes when transfer is being effected, the frequency must be such that the characteristic of the applied pulcming 4 sating current is not reflected in the deposition of the Jordosol 2232/50 developer, and obviously also relative motion is not 5 shriilalkydfesln 400 grams (Jordon Chemicals) necessary because the invention can be applied to zinc oxide other forms of development using a biasing plate adja- (colloidal g 1200 slams (Durham) cent to the area where development is taking place so Bromoscresol Green 0.5% by wt. in methyl alcohol that the invention applies to any form of development to milliliters of t f r I Bromophenol Blue 0.5% by wt. in methyl alcohol 10 milliliters The following examples are given to indicate types of Sodium Fluomcein 1% by M in "mm alcohol developer and field strength. l0 milliliters Erythrosin B. 1% by wt. in methyl alcohol 10 milliliters EXAMPLES OF COATINGS Cobalt Naphthenate Electrophotographic coatings may be produced as Zinc Napthenate Solvent 6% solution 0.1 grams 3% solution 1.0 grams followsi (Esso) Also! 95/[30 2.000 milliliters Coating Mowiml polyvinyhbmym (860m 70 grams 0 These materials are ball milled together to fonn an (Hoechst) V electrophotographic composltion.

Zinc oxide colloidal grade 350 grams (Durham Chemicals) Coating 5 The Mowital was taken up in 500 mls. acetone and 50 ax:523 (Myviny' 100 grams mls. methyl ethyl ketone, and ball milled with the zinc zi oxide special 1 grade I000 grams oxide. Durham) This coating can be applied to either film, metal backing or paper.

The Mowital was taken up in 800 millilitres of methyl ethyl ketone and 200 millilitres of methyl alcohol, and

Coming 2 ball milled with the zinc oxide which was previously lsojordosol 4501/60 short oil alkyd resin 430 grams dyed with the following! (Jordan Chemicals) 2' 'd ll d l ti Tgm zff o a an e) .58 arms Sodium Fluorescein l.0% solution in methanol Rose Bengal (sensitiser dye) 0.2 grams l0 mlllll tels Toluol i200 millilite rythr sm 3 L0) solutlon in methanol 5 milliliters Rose Bengal LO'k solution in methanol 2 milliliters Bromocresol Green 0.5% solution in methanol 40 5 milliliters Bromopllenol Blue 0.5% solution in methanol 5 milliliters These materials were ball milled together to form a coating composition.

Cobalt and zinc naphthenate driers were added (0.5% and 0.5% by wt. of solid resin).

This coating composition was let down with 500 millilitres of methyl ethyl ketone solvent and 500 millilitres of perchlorethylene to form the final coating composition.

Coating 3 45 Styrene-butadine copolymer Esso polymer 200 "i' EXAMPLES OF DEVELOPMENT Zinc oxide 500 grams Lead naphthenate 6% solution in mineral spirits l.0 gram Cobalt naphthenate 6% solution in mineral spirits Developer 1 Developer 100 grams Kohinoor Carbon Black Zirconium octoate 6% solution tn mineral spmts 300 "um sunflower ed on (Manna) l '9" 500 grams a.r.v. oil (Visoostatic) (British Petroleum) Cerium octoate 6% solution In mineral spirits 20 mam alkyd resin 0.5 gram Solvent Also! 95/130 900 milliliters Emma Toluol v 65 milliliters Hexyl acetate l0 milliliters 5321.2? :g Dispersed in 1000 mls. lsopar G. With this developer Pentoxone 5 milliliters a pulsating repelling direct current of 200 volts was Disulphine Blue Acridine Orange conductive layer.

l'lb by wt in methyl alcohol 2 milliliters I'll by wt. in methyl alcohol 2 milliliters Erythrosin B l% by wt. in methyl alcohol 2 milliliters r Sodium fluorescein 5 milliliters These materials are ball milled together and dip coated on paper, metal, wood, or film base to form a photo- De Z Copolymeric Blue Developer Hoechst) I00 grams Hostapenn Blue 836 200 grams Styrene butssliene copolymer e.g. "Solprene 1205" (Phillips Imperial Chemical) -continued Developer 2 Copolymeric Blue Developer Developer 7 I grams Vinyl toluene- 40 grams Permanent yellow 00 (Hoechst) acrylate copolymer l0 grams Solprene I205 "Pliolite VTAC (Australian Synthetic Rubber) 7 t VTAC Dispersed in I00 mls. Esso I00 I000 mls. lsnpar E The copolymeric resin were taken up in Solvesso I00 and subsequently milled with the blue pigment and a repelling field similar to that used in the preceding example was used.

Developer 3 (Copolymeric suspension in lsopar E (Esso). and isoparaffinic hydrocarbon solvent) Isopar E "Solprene I 205 200 mls. 5 grams (solution of I gram of solid in 2 mls.)

"Pliolite VTAC 5 grams (solution of 1 gram of solid in 2 mls.)

0.1 parts by wt.

The developer can be applied by a simple electrode or by a roller.

A pulsating repelling bias at 200 volts was used at 50 cycles per second with the roller moving at 30 centimetres per second. Additional developers are as follows:

Roller pass 250 volts at 100 to I000 cycles at 20 centimeter per second, pulsating repelling D.C.

Developer 5 BIA/8 54 grams Hostlperm Blue B30 (Hoechst) 6i grams Solprene I205 32 grams VTAC. Dispersed in I00 mls. Esso I00 I000 mls. Isopar E Roller pass l0 volts at I0 centimeter per second with a pulse frequency of $0 to 200 cycles per second.

Developer 6 Yellow 40 grams Graphtol yellow 48I3 0 (Sudan) 20 grams Solprene I205 I0 grams VTAC. Dispersed In 100 this. Esso I00 i000 mls. Isopsr 5 Roller pass 500 volts at 20 centimeter per second pulsating repelling D.C. at a cycles per second.

frequency of 50 to 5000 Roller pass I00 volts at I5 centimeter per second A.C. at 50 cycles without directional effect other than the image field.

Developer 8 60 grams Graphtol Red I630 l0 grams Solprene I205 I0 grams VTL Copolymer Dispersed in I00 mls. Esso I00 I000 mls. lsopar E Roller pass 50 volts at 20 centimeter per second pulsating repelling D.C. 50 to 500 cycles.

Developer 9 50 grams Isol Ruby Red grams Brillflst Rose Red 30 20 grams Pale lowering Lithographic Varnish 200 grams Rhodene alkyd resin L42/70 Dispersed in I00 mIs. Esso 100 I000 mls. lsopar E Roller pass 50 volts at 10 centimeter per second pulsating D.C. or A.C. at 50 to 5000 cycles per second.

Developer I0 50 grams Isol Ruby Red 30 grams Brillfut Rose Red I50 grams Alkyd Resin P470 12 grains Beeswax 15 grams Toluene Dispersed in 45 I00 mls. Esso I000 mls. llopar E Roller pass 20 volts at 10 centimeter per second, AC. at I00 cycles per second.

Developer II 100 grams Aluminum bronze metal powder 20 grams Alkyd Resin P470 I5 mls. Toluene Dispersed in $0 mls. Esso I00 I000 mIs. Isopar G RoIIerpass 200 volts at 20 centimeter per second AC. or pulsating D.C. at 50 to 500 cycles per second.

Developer I2 In example 9 the aluminuium bronze metal powder is placed by silver, zinc, aluminium, iron, chromium, copper, tin or other metal powder Roller pass 200 volts at 20 centimeter per second.

A.C. or pulsating D.C. at 50 to I000 cycles per second.

In coating 1 the operating voltage can" be reduced to half that for the lower dielectric constant binder coating of Examples 2 and 3. The reason why alternating current can be used is as said because the coatings are themselves rectifying.

Any of the above examples can be transferred before fixing by applying a directional pulsating voltage of between l and 200 volts at a frequency of to 5000 cycles. I

IDENTIFICATION or TRADE MARKS AND TRADE NAMES BUTON 200, styrene-butadiene copolymer made by Esso.

B.P.V. OlL synthetic automotive lubricating oil containing antioxidant ZDP", dialkyl zinc dithiophosphate in solution, made by British Petroleum Ltd. BRILLFAST ROSE RED 4444, a red phosphotungstomolybolic acid toner.

Coates hydrocarbon dispersible flake black comprises pure carbon black together with ethyl hydroxy cellulose resin.

B580 100 Solvent is a hydrocarbon solvent supplied by Esso Chemicals Australia Limited, having an aromatic content of 98%, flash point of I08F., and distillation range l59-l82C.

ELVACITE RESIN is an acrylic resin manufactured by DuPont, Delaware, U.S.A.

B880 100 is an aromatic hydrocarbon solvent with 98% aromatics, KB Value 9', final boiling point 182 C. GRAPI-ITOL BLUE BLF, phthalocyanine blue, C.I. pigment blue made by Sandoz.

I-IOSTAPERM BLUE 83G copper phthalocyanine blue, pure beta-form, made by Hoechst C.l. pigment Blue 15, Colour Index No. 74l60. A ISOJORDOSOL 450ll60 short oil alkyd resin made by Jordan Chemicals.

ISOL RUBY RED BKS 7520 (KVK) a lithol ruby red C.I. Pigment Red 57, Agfa, Calcium lake.

ISOPAR G a hydrocarbon liquid solvent with greater than 95% isoparaffinic content, and aromatics and olifins less that l percent, and remainder cycloand normal parat'fins, KB No. 27, final boiling point 177C. ISOPAR E a hydrocarbon liquid solvent with greater than 95% isoparaffinic content, aromatics and olifins less than 1 percent, with remainder cyclo and normal paraffins, KB Value 29, find boiling point I43C. KOI-IINOOR CARBON BLACK supplied by A.C. Hattriclt Ltd. Aust. SUNFLOWER Seed Oll vegetable oil supplied by Meggitts Ltd., Australia.

MOWITAL B601! polyvinyl butyral resin, made by Heechst, Germany; containing polyvinyl seats] 76-?! percent polyvinyl acetate 1 percent and polyvinyl alcohol 10-21 percent.

MICROLITH Pigments comprise a pigment and a resinous carrier. Microlith Black pigment contains pure neutral carbon black together with a toluene soluble carrier resin such as Stabilite Ester l0 of the Hercules Powder Co., U.S.A.

MICROLl'll-I BLUE 46'! comprises a stable phthalocanine blue pigment with a greenish cast to- .gether with Stabilite Ester l0 resin. Colour Index 74l60 MICROLITH GREEN GT comprises a medium shade of phthalocyanine green together with Stabilite Ester l0 resin, the microlith pigments are manufactured by Ciba Co., Switzerland, Colour Index 1245s.

10 PLIOLITE SSD is a styrene/butadiene copolymer. KB value 60, manufactured by Goodyear Corp., U.S.A. PLIOLITE V.T.A.C. is a vinyl tolucne/acrylate copolymer. KB value 36. PERMANENT YELLOW 66 extra, a diazo yellow pigmerit without lake forming groups, G]. pigment yellow 17, colour Index No. 21105. PENTACITE P423 is a modified pentarethyritol ester resin with acid number 20-30. PLIOLITE VT RESIN is a styrene/butadiene type copolymer rubber made by the Goodyear Corp., USA. and prepared by the G.R.S." method in which the butadiene polymerises in the main by a 1,4-addition. Pliolite VT is a vinyl toluenelbutadiene random copolymer rubber, soluble in mineral spirits. PALE LOWERING LITHOGRAPI-IIC VARNlSl-I a polymerized linseed oil varnish made by Meggitts Ltd., Australia, Polylin acid value 40-65 viscosity 7.0-9.5 poises at 25C, from alkali refined linseed oil. RHODENE RESIN L42/70, a safflower oil modified alkyd resin made by Polymer Corporation, Australia, acid value 6-10 with 69-7 1 percent solids, 64% oil length. SOLPRENE i205, styrene-butadiene copolymer Phillips Petroleum Corp., U.S.A., a block copolymer of hutadiene and styrene in the ratio /25 containing 97.5 percent of rubber hydrocarbon, A.S.T.M. No. I205 with majority of styrene molecules added as polystyrene at the end of a long chain of butadiene units. SUPERBECKOSOL 1352/60, a semi-drying safflower oil isophthalic-modified long oil alkyd resin with 59-61% non-volatile matter, acid value 3-6, oil length 60%, viscosity Gardner I-Ioldt Y-Z. VlNYLlTE VYNW, a vinyl chloride-acetate resin, approximate composition vinyl chloride 97%. vinyl acetate 3%, and specific gravity L39.

What is claimed is:

l. The method of developing an electrical image defined by changes of dielectric constant on a photoconductive surface comprising; subjecting the image, in the presence of a liquid developer comprising developer particles suspended in an electrically insulating liquid to a pulsating field having a polarity and intensity to repeatedly break the bonds caused by the Van de Walls forces as the developer particles are drawn to an image area during development, controlling the said pulses to maintain the said developer particles in oscillation during development, but maintaining the electrical image field during development to give a directional component to the particle movement to settle the said particles on the image areas. said pulsating field having a fast strong dislodging force followed by a slower decay whereby the particles after dislodgement have time to resettle under the said electrical image field.

2. The method of claim 1 wherein the pulsating field is produced by phase control cut off of a rectified pulsating current.

3. The method of claim 1 wherein the pulsating field is a direct current field.

4. The method of claim 1 wherein the pulsating field is an alternating current field.

5. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating of polyvinyl-butyral and colloidal grade zinc oxide, the polyvinyl-butyral being taken up with acetone and methylethyleltetone and ball milled with the zinc oxide and applied to a support.

3 ,9l 8,966 l l 12 6. The method as claimed in claim 1 wherein the pho- 8. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating formed of toconductive surface is coated with a coating formed of short oil alkyd resin, colloidal grade zinc oxide, sensishort oil alkyd resin, zinc oxide, coloring material, sotizer die, and toluol, which are ball milled together to dium fluorescein, naphthenate and a solvent, all ball form a coating composition to which a dryer is added. milled together to form an electrophotographic compo- 7. The method as claimed in claim 1 wherein the phosition coated on a support. toconductive surface is coated with a coating formed of 9. The method as claimed in claim 1 wherein the phostyrene-butadine copolymer, zinc oxide, lead naphtoconductive surface is coated with a coating formed of thenate, cobalt naphthenate, zirconium octoate, ce- '0 polyvinyl butyral and zinc oxide which are taken up in riurn octoate, a solvent, toluol, acetate, butanol, penmethylethylketone and methyl alcohol and ball milled toxone, and coloring material, all ball milled together with sodium fluorescein and coloring material to form and coated onto a support to form a photoconductive a coating composition which is deposited on a support. layer. 4- a: w In

Claims (9)

1. THE METHOD OF DEVELOPING AN ELECTRICAL IMAGE DEFINED BY CHANGES OF DIELECTRIC CONSTANT ON A PHOTOCONDUCTIVE SURFACE COMPRISING: SUBJECTING THE IMAGE, IN THE PRESENCE OF A LIQUID DEVELOPER COMPRISING DEVELOPER PARTICLES SUSPENDED IN AN ELECTRICALLY INSULATING LIQUID, TO A PULSATING FIELD HAVING A POLARITY AND INTENSITY TO REPEATEDLY BREAK THE BONDS CAUSED BY THE VAN DE WALLS FORCES AS THE DEVELOPER PARTICLES ARE DRAWN TO AN IMAGE AREA DURING DEVELOPMENT, CONTROLLING THE SAID PULSES TO MAINTAIN THE SAID DEVELOPER PARTICLES IN OSCILLATION DURING DEVELOPMENT, BUT MAINTAINING THE ELECTRICAL IMAGE FIELD

2. The method of claim 1 wherein the pulsating field is produced by phase control cut off of a rectified pulsating current.

3. The method of claim 1 wherein the pulsating field is a direct current field.

4. The method of claim 1 wherein the pulsating Field is an alternating current field.

5. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating of polyvinyl-butyral and colloidal grade zinc oxide, the polyvinyl-butyral being taken up with acetone and methylethyleketone and ball milled with the zinc oxide and applied to a support.

6. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating formed of short oil alkyd resin, colloidal grade zinc oxide, sensitizer die, and toluol, which are ball milled together to form a coating composition to which a dryer is added.

7. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating formed of styrene-butadine copolymer, zinc oxide, lead naphthenate, cobalt naphthenate, zirconium octoate, cerium octoate, a solvent, toluol, acetate, butanol, pentoxone, and coloring material, all ball milled together and coated onto a support to form a photoconductive layer.

8. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating formed of short oil alkyd resin, zinc oxide, coloring material, sodium fluorescein, naphthenate and a solvent, all ball milled together to form an electrophotographic composition coated on a support.

9. The method as claimed in claim 1 wherein the photoconductive surface is coated with a coating formed of polyvinyl butyral and zinc oxide which are taken up in methylethylketone and methyl alcohol and ball milled with sodium fluorescein and coloring material to form a coating composition which is deposited on a support.

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