the invention will now be described in detail with reference to specific preferred embodiments thereof , it being understood that these examples are intended to be illustrative only . the invention is not intended to be limited to the materials , conditions , or process parameters recited herein . all parts and percentages are by weight unless otherwise indicated . representative dielectric imaging layer materials and process conditions for forming the layers to produce continuous films without pin holes for electroceptors are described in examples i to xix . a binks spray booth model bf - 4 was used in conjunction with a binks model 21 automatic spray gun and a type 42753 reciprocator to apply coating compositions to a cylindrical mandrel in the following examples . this equipment is available from binks company , franklin park , ill . the model 21 gun was equipped with various fluid nozzles and air atomization nozzles . the coating composition to be sprayed was placed in a pressure pot and about 10 psi air pressure was applied to the pot to force the coating composition through a hose to the spray gun . the spray gun was operated in an automatic mode in conjunction with the motion of the reciprocator . the electrically conductive drum substrate to be sprayed was mounted on a turntable in the booth and rotated at a predetermined rate . the drum for examples i to xvii were of aluminum having a length of about 24 . 5 cm , an outside diameter of about 84 mm and a thickness of about 4 mm . the spray gun traversed the length of the drum and spraying occurred from top to bottom in a vertical direction . the spray cycle was repeated to obtain the desired thickness . a primer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the primer coating on a plurality of aluminum drums were as follows : ______________________________________materials : 0 . 1 percent volume solids solution made from 1 . 0 gms polyester resin ( dupont 49 , 000 , available from e . i . dupont de nemours & amp ; co .) solvent : 522 gms methylene chloride and 600 gms 1 , 1 , 2 trichloroethanetemperature : 21 ° c . ( 70 ° f .) relative humidity : 48 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 4fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 0gun model : 21______________________________________ after drying at room temperature ( 22 ° c .) for about 2 hours , the deposited primer coating had a thickness of about 1 micrometer and a dielectric constant of about 3 . 28 ( 10 6 cps or hz ). the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate resin ( makrolon ) 5705 , available from basf corporation ) solvent : 1100 gms 1 , 1 , 2 trichloroethanetemperature : 21 ° c . ( 70 ° f .) relative humidity : 42 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 45fluid nozzle : 63cair nozzle : 63peneedle setting : 1 . 2gun model : 21______________________________________ each spray pass deposited on the average about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness variations . drying was effected by oven heating under the following conditions which were determined to be sufficient for defect free coatings , but not optimized for efficient drying or for minimum manufacturing costs : after drying , the deposited dielectric imaging layer coating had a thickness of about 126 micrometers ( 5 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polysulfone ( p - 3500 , available from union carbide corporation ) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 21 ° c . ( 70 ° f .) relative humidity : 48 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 45fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 25gun model : 21______________________________________ each spray pass deposited on the average about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 127 micrometers ( 5 mils ), a dielectric constant of about 3 . 1 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 5 . 6 percent by volume solids solution made from 56 gms polysulfone ( p - 3500 , available from union carbide corporation ) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 23 ° c . ( 74 ° f .) relative humidity : 42 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 9 for 1 milfluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 25gun model : 21______________________________________ each spray pass deposited on the average about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 25 micrometers ( 1 mil ), a dielectric constant of about 3 . 1 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be continuous and free of pin holes , but coating thickness varied by about 10 percent . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i ( except for rotation speed being twice as fast ) were as follows : ______________________________________materials : 5 . 6 percent volume solids solution made from 56 gms polycarbonate - polyester resin blend ( lexan 4501 , available from general electric co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 16 ° c . ( 60 ° f .) relative humidity : & lt ; 58 percentdrum rotation speed : 300 rpmgun to drum distance : 23 cm ( 9 in ) number of passes : 16fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 2gun model : 21______________________________________ each spray pass deposited on the average about 4 . 7 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : the dried layer had a thickness of about 75 micrometers , a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be smooth , continuous and free of pin holes , but coating thickness varied by about 10 percent . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 35 gms polycarbonate resin ( makrolon 5705 , available from basf corporation ) solvent : 1100 gms 1 , 1 , 2 trichloroethanetemperature : 23 ° c . ( 74 ° f .) relative humidity : 65 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 33fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 5gun model : 21______________________________________ each spray pass deposited on the average about 2 . 3 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 76 micrometers ( 3 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . a series of dielectric imaging layer coatings were prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layers on a primer coated aluminum drum ( prepared as described in example i ) were as follows : ______________________________________materials : 224 gms polycarbonate ( lexan 145 , available from general electric co .) solvent : 4400 gms 1 , 1 , 2 trichloroethanetemperature : 21 ° c . ( 70 ° f .) relative humidity : & lt ; 58 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 6gun model : 21______________________________________ dry film thicknesscoating no . number of spray passes mils ( μm ) ______________________________________vii - a 5 0 . 5 ( 12 . 7 ) vii - b 10 1 ( 25 . 0 ) vii - c 20 2 ( 51 . 8 ) vii - d 41 4 ( 102 . 6 ) vii - e 51 5 ( 127 ) vii - f 61 6 ( 152 ) vii - g 81 8 ( 203 ) ______________________________________ each spray pass deposited on the average about 2 . 5 μm of dry polymer coating . the drum was rotated about 1 minute between spray passes to allow excess solvent to evaporate for those coatings of up to about 4 mils thick and for about 2 minutes between spray passes for the thicker layers thereby preventing coating sag and orange peel defects which in turn cause uneven coatings . drying was effected by oven heating using the conditions discussed in example ii . after drying , the deposited dielectric imaging layer coatings had a thickness as described in the table above , a dielectric constant of about 2 . 93 ( 10 6 cps or hz ) and a surface and bulk resistivity of greater than about 10 10 ohm cm . the coatings were carefully examined and found to be uniform , continuous and free of pin holes except for coatings vii a , b and c in which coating thickness varied from about 15 percent for vii a to about 10 percent for vii b and c . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate coester ( lexan 3250 , available from general electric co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 45 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 29fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 6gun model : 21______________________________________ each spray pass deposited on the average about 2 . 6 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 76 micrometers ( 3 mils ), a dielectric constant of about 3 . 1 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coatings were carefully examined and found to be uniform , continuous , free of pin holes , but coating thickness varied about 10 percent . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 147 gms polycarbonate coester ( lexan 4701 , available from general electric co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 45 percentdrum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 42fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 6gun model : 21______________________________________ each spray pass deposited on the average about 3 . 3 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 138 micrometers ( 5 . 5 mils ), a dielectric constant of about 3 . 1 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coatings were carefully examined and found to be uniform , continuous , free of pin holes and bubble defects . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate resin ( xp 73010 . 00 , available from dow chemical co .) solvent : 1100 gms 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 45 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 36fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 3gun model : 21______________________________________ each spray pass deposited on the average about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 100 micrometers ( 4 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate resin ( lexan 145 , available from general electric co .) solvent : 522 gms . methylene chloride 600 gms . 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 47 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 50fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 6gun model : 21______________________________________ each spray pass deposited on the average about 2 . 3 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 125 micrometers ( 5 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate co ester ( xp73036 . 00 , available from dow chemical co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloromethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 60 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 36fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 5gun model : 21______________________________________ each spray pass deposited about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 100 micrometers ( 4 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polyetherimide resin ( ultem 1000 , available from general electric co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 47 percentdrum rotation speed : 185 rpm ± 10 percent [ tc - 200 ] gun to drum distance : 23 cm ( 9 in ) number of passes : 39fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 5gun model : 21______________________________________ each spray pass deposited about 2 . 6 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 102 micrometers ( 4 mils ), a dielectric constant of about 3 . 1 and a resistivity of about 10 10 ohm - cm . the dried coating was carefully examined and found to be uniform , continuous and free of pin holes . a dielectric imaging layer was prepared by dissolving a film forming polymer and a primer adhesive together in a blend comprising 56 gms polycarbonate coester ( lexan 4701 , available from general electric co .) and 2 gms of polyester resin ( dupont 49 , 000 , available from e . i . dupont de nemours & amp ; co .) in a solvent blend of 522 gms methylene chloride and 1 , 1 , 2 - trichloroethane . the polymer blend solution was coated using the spray and drying conditions of example viii on a non - primed aluminum drum which was previously vapor degreased . after drying , the deposited dielectric imaging layer coating had a thickness of about 125 micrometers ( 5 mils ), a dielectric constant of about 3 . 1 and a surface resistivity of greater than 10 10 ohm - cm . the dried coating was carefully examined and found to be firmly adhering to the aluminum substrate , uniform , continuous and free of pin holes . a dielectric imaging layer was prepared by mixing 3 volumes of imron 500s clear enamel with 1 volume of imron 192s activator polyurethane composition and the viscosity adjusted with 8485s solvent to a dupont viscosity cup of 18 - 22 seconds . the imron enamel , activator and diluent were obtained from e . i . dupont de nemours & amp ; co . the polyurethane was applied to a vapor degreased aluminum roll by spray coating and then air dried for 8 hours at 60 ° c . followed by heating for 2 hours at 100 ° c . to achieve a dry coating thickness of 200 micrometers ( 8 mils ). the dielectric imaging layer was continuous , free of pinholes , had a dielectric constant of about 4 , and exhibited a surface resistivity of greater than 10 10 ohm - cm . the coating firmly adhered to the substrate and had a uniform thickness of ± 2 . 5 % end to end and ± 5 % around the roll . when the roll was corona charged to about 1500 volts with a negative potential , the voltage variation on the coating around the drum was & lt ; 50 v . a dielectric imaging layer was prepared as described in example xiv except that 56 gms of a copolyester polymer ( petg 6763 , available from eastman chemical products , inc . a subsidiary of eastman kodak co .) composed of copoly ( 1 , 4 - cyclohexylendimethylene / ethylene ) terephthalate ) was used in place of the lexan 4701 . after drying , the deposited dielectric imaging layer had a thickness of about 150 micrometers ( 6 mils ), a dielectric constant of about 3 . 5 and a surface resistivity of greater than 10 10 ohm - cm . the dried coating was uniform in thickness and free of pinholes . a dielectric imaging layer was prepared by dissolving lexan 3250 polycarbonate polymer in a solvent blend of methylene chloride and 1 , 1 , 2 - trichloroethane as described in example viii in which 60 weight percent of batio 3 ( available from ferro corporation ), based on the weight of the polymer , was dispersed by roll milling with glass beads to obtain a uniform dispersion . the composition was diluted with additional solvent to obtain a spray coatable consistency . the composition was applied to a primer coated aluminum drum ( prepared as described in example 1 ) and dried for 24 hours at 60 ° c ., 90 ° c . for 24 hours , and 120 ° c . for 3 hours . the deposited dielectric imaging layer coating had a thickness of about 288 micrometers ( 11 . 5 mils ), a dielectric constant of about 6 . 8 and a surface resistivity of greater than 10 10 ohm - cm . the layer was white , continuous , uniform and free of pinholes . nickel drums having a length of about 245 mm , an outside diameter of about 84 mm and a thickness of about 0 . 2 mm were coated with a polyvinyl fluoride polymer ( tedlar , available from e . i . du pont de nemours & amp ; co .) dispersion . the coating dispersion were applied to the drums using a doctor metering process which was capable of forming a coating having a thickness ( after drying ) up to about 500 micrometers by adjusting a gap between a doctor blade and an adjacent drum wall . the rheology of the coating dispersion was controlled by adjusting the resin solids , milling process conditions , and additives such as described in u . s . pat . no . 4 , 698 , 382 ( dupont ) and in a paper entitled &# 34 ; poly ( vinyl fluoride ) properties and coating technology &# 34 ; by j . j . dietrick , t . e . hedge , and m . e . kiecsma , presented at the 8th annual symposium on new coatings and new coatings raw materials , sponsored by the north dakota state university polymer and coatings department , may 30 , 1966 , so that sagging , orange peel and other coating thickness variations were minimized . the coatings were coalesced at 200 ° c . for 10 minutes and then dried for 20 minutes at 200 ° c . coatings were produced with thickness from about 100 micrometers ( 4 mils ) up to about 500 micrometers ( 20 mils ), in increments of 50 micrometers ( 2 mils ), a dielectric constant of about 7 . 9 ( depending on the coating additives employed ), and a surface resistivity of greater than 10 10 ohm - cm . the coatings were continuous , uniform and free of pinholes . coating thicknesses from end to end were ± 2 . 5 percent and ± 5 percent around the drums . generally , those drum coatings having a thickness of from 225 micrometers ( 9 mils ) and a dielectric constant of 7 up to coatings having a thickness of 450 micrometers ( 18 mils ) and a dielectric constant of 9 were found to produce good test prints when employed in the device described in example xx below . a dielectric imaging layer coating solution was prepared by dissolving a film forming polymer in a solvent . the specific conditions for applying the imaging layer coating on a primer coated aluminum drum prepared as described in example i were as follows : ______________________________________materials : 56 gms polycarbonate coester ( xp73038 . 00 , available from dow chemical co .) solvent : 522 gms methylene chloride 600 gms 1 , 1 , 2 trichloroethanetemperature : 20 ° c . ( 68 ° f .) relative humidity : 60 % drum rotation speed : 185 rpm ± 10 percentgun to drum distance : 23 cm ( 9 in ) number of passes : 27fluid nozzle : 63bair nozzle : 63peneedle setting : 1 . 5gun model : 21______________________________________ each spray pass deposited about 2 . 8 μm of dry polymer coating . the drum was rotated about 1 minute in between spray passes to allow excess solvent to evaporate thereby preventing coating sag and orange peel defects which , in turn cause coating thickness non - uniformities . drying was effected by oven heating under the following conditions : after drying , the deposited dielectric imaging layer coating had a thickness of about 76 micrometers ( 3 mils ), a dielectric constant of about 2 . 93 ( 10 6 cps or hz ), and a surface and bulk resistivity of greater than about 10 10 ohm - cm . the electrographic drums of examples ii through xix were substituted for the xerographic drum in a modified xerox 2830 xerographic copier which utilizes biased magnetic brush development . the xerox 2830 xerographic copier , prior to modification , comprised an electrophotographic drum around the periphery of which are mounted a charging station to deposit a uniform electrostatic charge , an exposure station , a magnetic brush development station , a paper sheet feeding station , an electrostatic toner image transfer station , a toner image fusing station , and a blade cleaning station . the xerox 2830 xerographic copier was modified to substitute a fluid jet assisted ion projection head similar to the head illustrated in fig2 for the exposure station of the copier . the magnetic brush developer employed comprised toner particles having an average particle size of about 12 micrometers and comprising a styrene copolymer pigmented with about 10 percent carbon black and carrier particles having an average size between about 50 and about 100 micrometers comprising uncoated , insulating ferrite particles . the magnetic brush developer also contained minor amounts of an external additive comprising zinc stearate and colloidal silica particles . the adjustable biasing power supply connected to the magnetic brush developing station allowed testing of the samples under various image development conditions of from 0 to 40 % of the latent image potential . by introducing this reverse bias , of the same polarity as the ions forming the latent image , and applying the bias between the conductive layer of the electrographic drums and the development roll , non - uniformities in the non - image areas of the latent image can be kept more free of unwanted toner particles . referring to the fluid jet assisted ion projection head illustrated in fig2 for the type of head substituted for the exposure system , the upper casting 51 was cast of stainless steel . the conductive plate 58 , insulating layer 60 , and thin film element layer 63 were supported on a planar substrate 64 having a thickness of about 1 , 016 micrometers . a pair of extensions on each side of planar substrate 64 form wiping shoes which rode upon the outboard edges of the dielectric image layer 66 spaced the ion projection head 50 about 760 micrometers from the imaging surface of dielectric image layer 66 . the exit channel 68 included an cavity exit region 70 about 250 micrometers ( 10 mils ) long and an ion modulation region 71 about 508 micrometers ( 20 mils ) long . a planar substrate 64 was employed comprising a large area marking chip comprising a glass plate upon which was integrally fabricated thin film modulating electrodes , conductive traces and transistors . the width across the cavity 54 was about 3175 micrometers ( 125 mils ) and corona wire 56 was spaced about 635 micrometers ( 25 mils ) from the cavity wall 62 nearest the cavity exit . a high potential source 72 of about + 3 , 600 volts was applied to corona wire 56 through a one megohm resistance element 74 and a reference potential 76 + 1 , 200 volts applied to cavity walls 62 . the individually switchable thin film element layer 63 ( an array of 300 control electrodes per inch not shown ) were each connected through standard multiplex circuitry ( represented by two position switch 80 ) to a low voltage source 78 of + 1 , 220 volts or + 1 , 230 volts , 10 to 20 volts above the reference potential . each electrode controlled a narrow &# 34 ; beam &# 34 ; of ions in the curtain - like air stream that exited from ion modulation region 71 . the conductive electrodes were about 89 micrometers ( 3 . 5 mils ) wide each separated from the next by 38 micrometers ( 1 . 5 mils ). the distance between the thin film element layer 63 and cavity wall 62 at the closet point was about 75 micrometers ( 3 mils ). laminar flow conditions prevailed at air velocities of about 1 . 2 cubic feet per minute . the metal drum of each of the tested samples were electrically grounded . in operation , the imaging surface on the dielectric imaging layer on each electrographic drum was uniformly charged to about - 1500 volts at the charging station , imagewise discharged to - 750 volts with the ion stream exiting from the fluid jet assisted ion projection head to form an electrostatic latent image having a difference in potential between background areas and the image areas of about 150 volts , and developed with toner particles deposited from the two - component magnetic brush developer applied at the magnetic brush development station . the dielectric imaging layers of examples ii , iii , vii d , vii e , vii f , ix , x , xi , xii , xiii , xiv , xv , xvi , xvii , and xviii all repeatedly produced print images having about 1 . 2 density units , resolution up to 300 lines or spots per inch , no discernable image spread or blooming and clean background in tests of several hundred print cycles . the dielectric image layers of examples iv , v , vi , vii a , vii b , vii c , viii , and xix produced print densities of less than about 0 . 6 , but image resolution was good and print background was low . dielectric imaging layer vii g produced the highest image density at about 1 . 3 , but the images were broader or had bloomed to dimensions greater than that of the original input . the developer housing of the modified xerox 2830 machine was purged of the two component developer material and loaded with a developer consisting of single component toner particles . the toner particles comprised a styrene copolymer pigmented with carbon black and magnetite and had an average particle size of about 12 micrometers . the developer housing was spaced about 10 mils ( 254 micrometers ) from the dielectric imaging surface . an electrostatic latent image was formed on the dielectric imaging layer of example xv as described above and developed with the single component developer . the images produced had a density of about 1 . 0 , resolution of 300 spots per inch , clean background and no discernable image blooming . polyimide film ( kapton , available from e . i . du pont de nemours & amp ; co .) having a length of about 990 mm a width of about 305 mm and a thickness of about 75 micrometers was coated on both sides with a coating of fluorocarbon resin ( teflon fep , available from e . i . du pont de nemours & amp ; co .) having a thickness about 25 micrometers on each surface to yield a composite sheet having a thickness of about 125 micrometers . this composite sheet was spray coated on one of the fluorocarbon resin surfaces with a carbon black pigment dispersion in an olefinic binder ( le 12644 , available from red spot paint and varnish co . inc .). the resulting conductive carbon black coating was about 10 micrometers thick after drying . since the dielectric constants of the kapton film and fep fluoropolymer were 3 . 7 and 2 . 1 , respectively , the composite sheet had an effective dielectric constant of about 2 . 7 for the combined layers . the ends of the coated sheet were overlapped and forced together for 20 seconds using a jaw sealer device operating at about 350 ° c . and 20 psi to form an endless belt . the belt was cycled in a test fixture equipped with a belt drive and fitted with a fluid jet assisted ion projection head similar to the head illustrated in fig2 a developer applicator station , paper transport station , image transfer station , toner fusing station and cleaning station . the images produced under the charging conditions described in example xx had a resolution of 300 spots per inch and achieved a print density to about 1 . 1 . dielectric imaging layers were prepared using an electrostatic coating technique . the substrates coated were aluminum drums having a 65 mm diameter , 266 mm length , 2 . 5 mm wall thickness ( nominal ) and surface roughness of about 0 . 4 μm , ( 16μinch ). the substrates were cleaned by ultrasonic immersion cleaning in detergent followed by a freon vapor degrease , and a final isopropanol hand wipe with a lint free cloth . a nordson model # npe cc8 with a nordson model # npe - 2a automatic gun was used to electrostatically apply coating powder to the drums while the drums were rotated at 100 - 150 rpm , ( horizontal ). the electrostatic gun horizontally traversed the drums at 0 . 5 to 1 . 0 inches / sec . nitrogen gas was used for powder delivery and atomization . typical powder delivery settings were : the powder coating materials and conditions for coating and curing were as follows : ______________________________________a ) perfluoroalkoxy teflon ( pfa , available from e . i . dupontde nemours & amp ; co .) dielectric constant 2 . 1 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 70 kvdry thickness 0 . 0035 in ( 88 . 9 μm ), 3 coats / bakesthickness / dielectric constant 42 μmcure temp ./ time 740 ° f . ( 393 ° c . ), 20 minutesb ) co - polymer of ethylene and tetrafluoroethylene ( tefzel , available from e . i . dupont de nemours & amp ; co .) dielectric constant 2 . 6 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 70 kvdry thickness 0 . 0045 in ( 114 . 3 μm ), 4 coats / bakesthickness / dielectric constant 44 μmcure temp ./ time 575 ° f . ( 302 ° c . ), 30 minutesc ) acrylic resin ( pulvalure 154 series , available from gliddencoating and resins ) dielectric constant 3 . 3 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 40 - 50 kvdry thickness 0 . 0055 in ( 139 . 7 μm ), 3 coats / bakesthickness / dielectric constant 42 μmcure temp ./ time 350 ° f . ( 177 ° c . ), 15 minutesd ) clear polyurethane resin ( vedoc , available from ferro corp .) dielectric constant 4 . 0 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 55 - 70 kvdry thickness 0 . 006 in ( 152 . 4 μm ), 3 coats / bakesthickness / dielectric constant 38 μmcure temp ./ time 290 ° f . ( 143 ° c . ), 25 minutese ) crystal clear polyester ( oxyplast , glycidyl polyester , available from fuller o &# 39 ; brien paint co .) dielectric constant 4 . 0 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 70 - 90 kvdry thickness 0 . 006 in ( 152 . 4 μm ), 3 coats / bakesthickness / dielectric constant 38 μmcure temp ./ time 400 ° f . ( 204 ° c . ), 20 minutesf ) clear epoxy ( vedoc ve 101 - a , available from , ferro corp .) dielectric constant 3 . 5 ( 10 . sup . 6 cps or hz ) surface & amp ; bulk resistivity & gt ; 10 . sup . 10 ohm cmgun voltage 55 - 70 kvdry thickness 6 mils ( 152 . 4 μm ), 3 coats / bakesthickness / dielectric constant 44 μmcure temp ./ time 350 ° f . ( 177 ° c . ), 30 minutes______________________________________ the xerox 2830 xerographic copier modified as described in example xx was again modified so that the aluminum drums of example xxii could be substituted in the place of the drums of examples ii to xix . the fluid jet assisted ion projection head had an array of 600 control electrodes per inch . the magnetic brush developer , the cleaning subsystem , paper sheet feeding system , fusing system and charging corotron were repositioned so that the spacing , charging and motion relationships were maintained as in example xx . the dielectric imaging layers all produced excellent prints of about 1 . 1 density units , resolution of 600 lines or spots per inch , sharp well defined character edges and corners , and clean background free of toner deposits . the dielectric imaging layer of xxii a ) was exceptionally easy to clean using a polyurethane wiper blade material . although the invention has been described with reference to specific preferred embodiments , it is not intended to be limited thereto , rather those skilled in the art will recognize that variations and modifications may be made therein which are within the spirit of the invention and within the scope of the claims .