JPH0262862B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to electrostatic printing, and in particular to electrostatic imaging methods and apparatus used in electrostatic printing that provide excellent image quality. [Prior Art] As a method for directly forming a latent image (hereinafter referred to as an electrostatic image) due to electrostatic charges on a dielectric recording medium using ions, for example, a multi-needle electrode recording head is used to connect the needles and the dielectric recording medium. Some use the discharge, or the destruction of the air, that occurs in the small air between the surface and the surface. In the case of void destruction, in order to apply an appropriate level of potential and maintain the electrostatic image perfectly, the spacing between the voids should be 0.0002 to 0.0008 inches (approximately 0.005 to 0.002 mm).
need to be maintained. Even with this method, the electrostatic image is not uniform and the sharpness (contrast) and resolution are not sufficient. In addition, regarding the use of corona discharge, there is a current limit in ordinary corona discharge from a thin wire or point source, and the maximum discharge current density obtained so far is
It is ^about 10μA/cm2. This greatly limits printing speed. Furthermore, corona wires are thin and break easily, and because their operating potential is high, they collect dust and become dirty, requiring cleaning and replacement quite frequently. Due to these problems, it has not been put into practical use. [Object of the Invention] An object of the present invention is to provide an electrostatic image forming method and apparatus that enable electrostatic printing with excellent image quality. [Structure and operation of the invention] In order to achieve the above object, the electrostatic image forming method of the present invention applies an alternating potential between an excitation electrode and a control electrode separated by a dielectric member, and An ion-generating electric discharge is generated in the air region formed by the joint between the end face of the solid dielectric member and the solid dielectric member, and a direct current voltage Vc is generated between the control electrode and the counter electrode arranged on the back side of the dielectric recording member. Ions are extracted from the discharge by applying a DC voltage between the screen electrode and the counter electrode, which are placed between the control electrode and the dielectric recording surface.
The method is characterized in that the extraction of the ions is controlled by applying Vs to form an electrostatic image on the dielectric recording medium. Further, in the electrostatic image forming apparatus of the present invention, a plurality of excitation electrodes are arranged in parallel on the surface of the first solid dielectric member, and a plurality of control electrodes are arranged on the opposite surface of the first solid dielectric member, intersecting with the excitation electrodes. The control electrode and the excitation electrode are arranged in parallel in the direction in which the control electrode intersects with the excitation electrode, and a hole is provided at each intersection of the control electrode and the excitation electrode. An electrostatic image forming device is an electrostatic image forming device in which a dielectric recording material on a counter electrode is arranged between the screen electrodes and supported so that each hole of the screen electrode is placed opposite to each hole of the control electrode. in the hole of the control electrode, which is arranged opposite to the plurality of excitation electrodes, and which is arranged at the intersection with the selected excitation electrode by selectively applying an alternating potential between the counter electrode and the plurality of excitation electrodes. ion-generating electric discharge is generated, and by selectively applying a DC voltage Vc between the plurality of control electrodes and the counter electrode, and applying a DC voltage Vs between the screen electrode and the counter electrode. ions are extracted from the electrical discharge generated in the hole of the selected control electrode provided at the intersection with the selected excitation electrode, and controlled to form an electrostatic image on the dielectric recording medium. This is a characteristic feature. In the present invention, an electrostatic image is formed on a dielectric recording medium by a preferred form of ion generator.
The ion generator applies a potential between two electrodes separated by a solid dielectric member to cause electrical void collapse in fringing field regions. The ions thus produced are then extracted from the discharge and applied to further components. This further member can be an electrically conductive support with a dielectric coating. According to one aspect of the ion generator, the firing potential is a high frequency AC voltage and extraction is accomplished using a DC voltage. According to another aspect, the extracted ions are used directly or are subjected to a particulate material that is moved under the action of an electric field. Such charged particles can be used, for example, to form an electrostatic pattern using a discharge electrode having a gap in which the charged image is patterned according to the shape of a desired character or symbol. According to yet another aspect of the preferred ion generator, there may be multiple electrodes forming the intersections of a matrix array. Ions are extracted from the electrode holes at selected matrix intersection points by simultaneously applying an electrical discharge at the selected holes and an external ion extraction electric field. The extracted ions can be used to form an electrostatic latent image that is later toned and fused. The image can be formed on the dielectric layer and transferred to plain paper. Alternatively, the charged particulate material can be deposited on plain paper or collected on a conductive surface to form the image. In yet another aspect of the preferred ion generator, for example, the device is formed by a solid dielectric member separating two electrodes, and at least one of the two electrodes is formed on the surface of the dielectric recording medium. Has an edge. Applying a voltage, eg, an alternating voltage in the frequency range of about 60 Hertz to about 4 Megahertz, between the electrodes causes an electrical discharge to occur between one of the electrodes and the dielectric surface. In the present invention, a third electrode is used to control the ion discharge generated as described above. A high frequency AC potential is applied between a first excitation electrode (driver electrode) and a second control electrode. A third screen electrode is separated from the control electrode by a second layer of dielectric. The ions produced by the air destruction can be extracted under the influence of a screen electrode and applied to further components. According to one aspect of the three-electrode ion generator embodiment, the screen electrode is configured such that a previously formed electrostatic latent image is present below the ion generator;
and prevents unwanted image erasure if no extraction voltage is applied to the control electrode. According to a further aspect of the three-electrode embodiment, the screen electrode provides an electrostatic lensing action that can be used to control the size and shape of the electrostatic image formed by the ion generator of the present invention. give. The present invention uses a three-electrode type recording head as described above, but prior to explaining the same, an example using a two-electrode type recording head, which was previously studied by the present inventor, will be explained. A Examination example using a two-electrode mode FIG. 4 shows a dielectric 101 and each conductive electrode 102-1 and 1
The ion generator 100 that causes air destruction during 02-2 is shown. Sky = 104-a and 10
An electrical discharge occurs when the edge electric fields Ea and Eb at 4-b are larger than the breakdown electric field of the air, resulting in a breakdown region 10 adjacent to the electrode end.
Charging of the dielectric 101 occurs at 1-a and 101-b. Upon reversal of the alternating potential of power supply 103, there is a reversal of charge in breakdown regions 101-a and 101-b. Thus, the generator 100 of FIG. 4 causes two void breakdowns per cycle of applied alternating potential from power supply 103, thus producing an ion supply of alternating polarity. The extraction of ions resulting from generator 100 of FIG. 4 is illustrated by generator-extractor 110 of FIG. The generator 110A is a conductive electrode 11
2-1 and 112-2. To prevent air breakdown near electrode 112-1, electrode 112-1 is wrapped or surrounded by insulating material 113. An alternating potential is applied to the conductive electrodes 112-1 and 112- by the power source 114A.
Pour between 2. Additionally, the second electrode 112-2 covers region 1 of the dielectric 111 to provide an ion source.
It has a hole 112-h in which the desired void breakage occurs with respect to 11-r. Ions formed in holes 112-h are transferred between electrode 112-2 of generator 110A and grounded auxiliary electrode 112-3 of extractor 110B by a DC potential applied by power source 114-B. can be extracted in the direction of arrow A by applying an external electric field to . The exemplary insulating surface charged by the ion source in FIG.
-d conductive base 115-
A dielectric (electrophotographic) paper 115 made of p. When switch 116 is moved to position X and grounded as shown, electrode 112-2 is also at ground potential and ion generator 110A and dielectric paper 115
There is no external field in the region between. However, when switching switch 116 to position Y,
The potential of power source 114B is applied to electrode 112-2. This is ion generator 110A and dielectric paper 1
An electric field is generated between the back surfaces of 15. Ions extracted from the void-destruction region are transferred to the dielectric layer 115-d.
electrify the surface of the Many materials can be used for dielectric layer 111. Possible choices include aluminum oxide, glass enamel, ceramics, plastic film and mica. Aluminum oxide,
Glass enamels and ceramics present difficulties in manufacturing sufficiently thin layers (ie, about 1 mil) to avoid unreasonable demands on the driving potential source 114A. Plastic films containing polyimides, such as Kapton®, and nylon, are prone to deterioration as a result of exposure to chemical byproducts of the void destruction process in holes 112-h, particularly ozone and nitric acid. . Mica does not have these drawbacks and is therefore the preferred material for dielectric 111.
Muscovitemica,
H ₂ KAl ₃ (SiO ₄ ) ₃ is particularly preferred. The generator-extractor 110 of FIG. 5 is readily used, for example, to form characters on dielectric paper in high speed electrophotographic printing. Examples of sources for electrophotographic printing of text are shown in FIGS. 6 and 7. In FIG. 6, the character generator 120 is replaced with an electrode 122-1 made of an etched conductive sheet.
and a pair of opposing electrodes 122-2, 122-3, and 122-4.
1. Etched or masked electrode 122-
1 is illustrated with etched letters A, B and C. The edge electric field at the edge of the etched character is caused by
When produced by an alternating potential applied between 2-1 and a counter electrode, it provides a dense source of ions.
Thus, if one wishes to generate ions for printing a selected character, e.g. the letter B, a high frequency alternating voltage power supply (not shown) is required.
is applied between etched electrode 122-1 and its associated counter electrode 122-3. This provides a dense supply of ions in the area of dielectric 121 at the edge of the etched letter B in mask 122-1. The ions are then extracted and transferred to a suitable dielectric surface, such as dielectric paper 115 of FIG. An electrophotographic latent image B is formed on the dielectric surface 115. The matrix ion generator 130 of FIG. 7 can be used to form dot matrix characters on dielectric paper. Generator 13
0, finger electrodes 132-1 to 132-4 as control electrodes each having a set of holes are arranged on one side, and selector bars 133-1 to 133- as a set of excitation electrodes are arranged on the other side.
The separation selector utilizes a dielectric sheet 131 arranged with 4 finger electrodes 13
2 for each different hole 135. When an alternating potential is applied between the selector bar 133 and the ground, ions are generated in the hole where the selector bar and the finger electrode intersect.
Ions can be extracted from the pores if the selector bar is energized with a high voltage alternating potential and its finger electrodes are heated with a direct current potential applied between the finger electrode and the counter electrode on the surface of the dielectric to be charged. For example, selector bar 133-3
Printing is performed at the position corresponding to the hole 135 ₂₃ by applying a high frequency potential between the finger electrode 132 - 2 and ground and simultaneously applying a direct current potential between the finger electrode 132 - 2 and the opposing electrode of the dielectric recording member. The unselected fingers and the counter electrode of the dielectric member are maintained at ground potential. This method creates a dot matrix column (array)
By multiplexing the voltage generators, the number of required voltage drivers is significantly reduced. for example,
If one desired to print a dot matrix array across an 8" wide area with a dot matrix resolution of 200 dots per inch, 1600 generators would be required if no multiplexing was used. For example, by using the row of Figure 7 with 20 alternating frequency generation selectors,
Only 80 finger electrodes are required, reducing the total number of generators from 1600 to 100. To prevent air breakdown from the finger electrode to the dielectric sheet 131 in areas not associated with the holes 135, it is desirable to coat the ends of the finger electrode with an insulating material. Unnecessary air breakage around the finger electrodes can be eliminated by potting these electrodes. In manufacturing and operating matrix ion generators of this type, it is desirable to maintain substantially uniform levels of ion flux generated at the various matrix intersection points. Dielectric sheet 1
Since a lower ion flow occurs in the holes 135 where 31 corresponds to the thicker part, the dielectric sheet 1
A change in the thickness of 31 causes a commensurate change in ion outflow power. It is a particularly advantageous property of mica that it has a natural tendency to exfoliate along a plane of very uniform thickness, making it particularly suitable for the matrix ion generator illustrated in FIG. becomes. In this respect, the uniformity of the thickness of the dielectric sheet 131 is much more important than the actual value of its thickness. The geometry of module 140 shown in FIG. 8 can be used to form rectangular areas of charge. Charged electrodes 142-1 and 142-2 are connected to electrode 1 by dielectric member 141.
42-3, and place the electrode 142-3 in an insulating material 145. Electrodes 142-1 and 14
The region between 2-2 provides a slot in which a dry discharge is formed when a high frequency alternating potential is applied between electrodes 142-1 and 142-2 and electrode 142-3. The charged array of FIG. 8 can be used in plain paper copiers to replace the corona commonly found in such copiers. FIG. 9 illustrates a plain paper copying machine 150 that uses a charge train of the type shown in FIG. Charging element 152- having the shape shown in FIG.
1 to charge the copying machine drum 151. If the drum is selenium or a selenium alloy and it is desired to charge the surface to a positive potential of, for example, 600 volts, then the slotted electrode is held at 600 volts. After charging,
Drum 151 is discharged by an optical image provided by a scanner at station 153. The resulting electrostatic latent image is toned at station 156, and the toner is transferred onto a plain paper sheet 158 using a transfer ion generator 152-2 according to FIG. 8, with the slotted electrode again held at a positive potential. transcribed. The residual electrostatic latent image and uncharged toner on the surface of the drum can be electrically discharged by using a discharge unit 152-3 according to FIG. Here, the slotted electrode is maintained at ground potential and the residual charge and toner on the surface of the drum causes ions to be extracted from the void breaks in the slot, thus effectively discharging the surface. A cleaning brush 154 is used to remove any residual toner remaining on the surface and then prepare the drum for recharging. Also shown in FIG. 9 is a dot matrix charging head 155 which may be arranged according to FIG. This allows plain paper copiers to be used as printing machines. In that case drum 151
is discharged at station 153 and recharged by dot matrix printing head 155, allowing reproduction apparatus 150 to function as both a copier and a printer. Additionally, reproduction device 150 can function as a copier and a printer simultaneously if overlays are desired. Thus,
The ion generator and extractor according to FIG. 5 serve as image forming means and residual discharge means in a printing press.
It can also be used as a preliminary charging means and a discharging means in an electrophotographic apparatus. FIG. 10 illustrates an apparatus for application to a multiplexed dot matrix charging head 171 of the type shown in FIG. 7 in a system 170 for high speed printing of dot matrices on plain paper. The charging head 171 is connected to the slot 176.
An aerosol consisting of a dye dissolved in a suitable solvent is charged, carried by a low velocity air stream introduced through the intervening space 175. The ezolol particles are charged by the ion generation system and enter the electric field region formed by the DC potential applied between electrodes 173 and 174. The electric field directs the charged aerosol particles onto a plain paper system 172 that moves through the device at a speed approximately equal to the speed of the aerosol. FIG. 11 shows a mechanical line scan printing device 1.
80 is illustrated. The slotted electrode 1 is used together with a dielectric film 185 and a fast moving conductive bead 187 to form a moving void breakdown region.
86 is used. Bead 187 mounted on wire 188 is driven through a pulley by a high speed motor (not shown).
A high frequency alternating current source 183 provides the potential necessary to create a void within the slot of the electrode 186. Dielectric paper 181 is charged by the charging potential supplied by amplifier 184 . The output of amplifier 184 is connected between conductive dielectric paper support 182 and slotted electrode 186. Line scanning is accomplished by mechanical movement of bead 187 and selected areas are printed by applying a potential between support 182 and slotted electrode 186. As before, the electrostatic latent image formed can be toned and fused by any conventional method. The amount of ions extracted from the charge is determined by amplifier 1
Depending on the extraction potential provided by 84, a continuous toned image can be formed in the manner described above. Generally speaking, the relationship between the electrode voltage and the voltage on the ion-receiving surface, e.g. paper, is as follows for charging systems of the type shown in FIGS.
Typically, it will be as shown in FIG. The electrode voltage is a DC voltage applied between the perforated electrode and the opposing electrode on the surface of the conductor to be charged. Paper voltage is the electrostatic latent image potential of a charged dielectric member, such as dielectric (electrophotographic) paper. The foregoing discussion describes the general principles and features of the two-electrode embodiment; the examples discussed below merely illustrate its specific application. Study Example 1 Laminate 1 mil stainless steel foil to both sides of 1 mil Muscovite mica. Stainless steel foil is coated with resist, and the diameter of approx.
Photoetch in a pattern similar to that shown in Figure 7 with holes or holes in the 0.015 cm fingers. This provides a charging head that can be used to generate a dot matrix character electrostatic latent image on dielectric paper according to FIG. Charging occurs only when there is simultaneously a negative potential of 400 volts on the finger containing the hole and an alternating current potential of 2 kilovolts peaking at a frequency of 500 kilohertz applied between the finger and the counter electrode. A distance of 0.020 cm is maintained between the print head assembly and the dielectric surface of the electrophotographic sheet. The duration of the printing pulse is 20 microseconds. It is found that under these conditions an electrostatic latent image of approximately 300 volts is produced on the dielectric sheet. This image is then toned and fused to provide a dense dot matrix character image. The on-current extracted from the charging head, collected by electrodes spaced 0.020 cm from the charging head, is found to be 1 milliampere per square centimeter. The charging head has a lifespan of approximately 2000 hours. Study Example 2 Study Example 1 is repeated using a polyimide derivative instead of muscovite mica. As mentioned above, 1
Mil stainless steel foil is laminated to 1 mil thick Kapton polyimiso film. The same results as in Study Example 1 are obtained at an applied high frequency potential of 1.5 kilovolt peak. The charging head provides a lifespan of approximately 50 hours. Study Example 3 An electrostatic charging head of the type shown in Figure 6 was laminated on both sides of a 1 mil polyimide sheet.
Processed using mill stainless steel foil. To print fully formed characters on dielectric surfaces,
Letters 1/10" tall are etched into the foil on one side of the sheet while fingers covering each letter are etched into the other side of the foil as shown in FIG.
A 1-2 mil thick bridge is left unetched to establish conductivity within the normally isolated areas of the letters. The character stroke width is etched to 6 mils. Printing is accomplished by applying the potential of Example 2 with a pulse width of 40 microseconds. The toned image has sharp edges and high optical density. The character width of this statue is
It is 0.030cm. Study Example 4 A continuous toned image is obtained by extracting a large number of ions from the charging head per unit time in proportion to the applied ion extraction potential. This is illustrated in Figure 12, where the apparent surface potential on the dielectric surface is plotted as a function of the potential difference between the ion generating electrode and the dielectric counter electrode. The distance between the ion generating electrode and the dielectric surface was 0.015 cm, and the charging time was 50 microseconds. B Three-electrode embodiment Next, problems in forming an electrostatic latent image in a two-electrode embodiment as described above will be explained, followed by a description of forming an electrostatic latent image in a three-electrode embodiment according to a preferred embodiment of the present invention. Matrix image generating member 1 shown in FIG.
30 can be incorporated into an electrostatic printing device.
However, as seen with respect to Figure 9,
Ion generator-extractor 110 shown in FIG.
can be used to form electrostatic images on dielectric surfaces and to discharge such images. Thus, with further reference to FIG. 5, when switch 116 is closed in Y, electrode 112-2 is held at a positive potential V ₁ and a positive electrostatic latent image of smaller magnitude V ₂ is placed on surface 115-d. It is formed. However, when switch 116 is in position X, the previously formed electrostatic latent image is
, then generator 110A behaves as a cancellation unit. This phenomenon will be further explained with reference to FIG. 13 in connection with the dot matrix printing embodiment of FIG. At time t ₁ ,
Predetermined holes 135 ₂₃ on the matrix ion generator 130 (FIG. 7) are connected to the finger electrodes 132 -
2, while a high frequency potential is applied to selector bar 132-3. This causes the formation of an electrostatic dot image of negative polarity occupying regions 203 and 204 on dielectric surface 201 with bucking electrode 202. At a later time t ₂ , hole 135 ₂₃ forms areas 204 and 2
05, the selector bar 133-3 is further energized, but charging is not desired, so the negative pulse is applied to the finger electrode 1.
32-2 is not applied. However, the presence of a negative electrostatic image in region 204 indicates that hole 135 ₂₃
attracts positive ions from the area, erasing the image previously formed in this area. Adding a third electrode to the two electrode structures described above alleviates this problem and provides additional benefits in terms of controlling the size and shape of the electrostatic image formed by this type of ion generator. It was discovered that the present invention can be achieved. An ion generator 210, which is an example of a three-electrode ion generator according to the present invention, is shown in cross-section in FIG. The ion generator 210 has excitation electrodes 211 separated by a solid dielectric layer 213.
and a control electrode 215. AC potential source 212
is used to provide a void break in hole 214. A third screen electrode 219 is separated from the control electrode by a second dielectric layer 217. The terminology adopted for the three electrodes draws similarities to vacuum management theory. The terms "excitation" electrode and "control" electrode can effectively be extended to equivalent electrodes in two basic electrode embodiments. The second dielectric layer 217 has holes 216 which are advantageously substantially larger than the holes 214 of the control electrode.
has. This is the wall charging effect.
effects). Screen electrode 219 is at least partially in hole 214
including a hole 218 located below. In an electrophotographic matrix printing machine, for example, the excitation and control electrodes can be the selector bar and finger electrodes of FIG. 7, respectively, and the screen electrode is an additional finger electrode with holes that match the pattern of the excitation electrodes. Or it can consist of a continuous perforated metal plate or other member whose openings are adjacent to all the printing holes. The latter aspect of the screen electrode is
For example, it can take the form of an open mesh screen. The application of the above ion generator in electrophotographic matrix printing is illustrated in FIG. In this case, it should be noted in advance that, in order to explain the effect of screen electrodes in matrix printing, FIG. This is for explaining the effects in a state where the potential Vc is applied and a state where it is not applied, and switching of the alternating current potential to the selector bar is omitted. The selective application of alternating current potentials to the selector bars has already been done in the matrix printing machine shown in FIG. Second
The figure shows an auxiliary electrode 22 as a grounded counter electrode.
Conductive base 223 whose back side is supported by 5
and a dielectric layer 221. The ion generator 210 of FIG. 1 is shown used with dielectric paper 220. When the switch 222 closes at position Y, the alternating current potential across the dielectric layer 213, the negative potential Vc on the control electrode 215 and the screen electrode 2
A negative potential Vs on 19 is present at the same time. Hole 21
The negative ions of 4 are subjected to an accelerating electric field that causes them to form an electrostatic latent image on the dielectric layer 221, as in the two-electrode embodiment.
The presence of a negative potential Vs on the screen electrode 219, which is chosen such that Vs is smaller than Vc in absolute value, means a negative potential Vi (less than Vc in absolute value)
does not interfere with the formation of an image that would have a Switch 222 at X and partially hole 2
Due to the electrostatic image formed before the negative potential Vi below 14, partial erasure of the image would occur in the absence of screen electrode 219. The screen potential Vs is chosen such that Vs is greater in absolute value than Vi, so that the screen electrode 21
9 prevents the passage of positive ions from the holes 214 to the dielectric layer 221. See Example 1. Placing the screen electrode 219 in the two-electrode embodiment of the ion generator described above provides advantages beyond preventing image discharge under the conditions described above.
Screen electrodes can be used alone or in conjunction with control electrodes to control matrix imaging. When Vs=0, no latent image is generated due to the above discharge phenomenon. Thus, three-level matrix image control is possible in an electrophotographic matrix printer according to a preferred embodiment of the invention. Screen electrode 219 provides unexpected control over image size. When using a screen electrode over the finger electrode in the dot matrix printing machine shown in FIG. 7 in accordance with a preferred embodiment of the invention, image size is controlled by varying the size of the apertures 218 in the screen electrode. obtain. See Example 2. Furthermore, all variables other than the screen power supply 226 are made constant,
Using such a geometry, it has been found that larger screen potentials produce smaller dot diameters. See Example 3. This technique can be used to create elaborate and structured images. The correct selection of Vs and Vc allows the ion generator 210 to maintain a constant dot image diameter.
and the distance between the dielectric surfaces 221 can be increased. This is achieved by increasing the absolute value of Vs while keeping the potential difference between Vs and Vc constant. See Example 4. Imaging can be controlled by using a screen electrode having an overhanging edge overlying the ion-generating edge of the control electrode in a matrix electrophotographic printer. See Example 5. The screen electrode holes 218 can take the shape of a fully formed character, for example, no larger than the corresponding round or square control electrode holes 214. The electronic wiring diagram used to control the electrophotographic printer of FIG. 2 allows the system to be biased as shown in the circuit diagram of FIG. 231 is a pulse generator.
The magnitude of the control pulse can be varied to produce the desired Vc and Vs by choosing the appropriate bias potential. For example, all of the combinations below are Vs = -700 volts, Vc = -800
Generates a bolt. 1 V bias = -600 volts; △Vs = -100
Volts; △Vc = -200 volts 2 V bias = -500 volts; △Vc = -300
Volts 3 V bias = -400 volts; △Vs = -300
Volts; △Vc=-400 volts 4 V bias=-300 volts; △Vs=-400
Volts; △Vc=-500 volts 5 V bias=-200 volts; △Vs=-500
Bolts; ΔVc = -600 Volts Example The above advantages are further explained with respect to the following non-limiting example: Example 1 Laminating 1 mil stainless steel foil to both sides of a 1 mil muscovite mica sheet. . The foil is coated with resist and photoetched in a pattern similar to that shown in FIG. 7 with holes or holes about 0.015 cm in diameter. thickness
A second mica layer of 0.015 cm is bonded to the foil according to FIG. The finger pattern A screen electrode with 0.0375 cm diameter holes in the same pattern is photoetched from 1 mil stainless steel, and the fingers and screen holes are concentric and bonded to the second mica layer. This structure uses a 1 kilovolt peak AC potential source 212 with Vc = -500 volts, Vs = -400 volts and a frequency of 500 kilohertz to create an electrostatic latent image on dielectric paper as shown in FIG. It has a charging head that is used to give A distance of 0.015 cm is maintained between the print head assembly and dielectric layer 221. Vc takes the form of a printing pulse of 20 microseconds duration. Under these conditions, about −
A latent image in the form of a 300 volt dot is created on the dielectric sheet. This image is then toned and fused to obtain a dense dot matrix character image. The ionic current extracted from the discharge head, collected by an electrode 0.015 cm from the head, is found to be 0.5 milliamps per square centimeter. However, even if screen electrode 219 is omitted, the electrostatic image under the control electrode will be erased unless a printing pulse is applied. Example 2 The electrophotographic printer of Example 1 was tested with various diameters of the screen electrode holes 218 and the size of the resulting electrostatic dot images was measured. The results below are representative.

[Table] In general, the reduction in the pore size of the screen electrode is
It has been found that this results in a corresponding reduction in latent image size without any compromise in image charging. Example 3 The electrophotographic printing machine of Example 1 was tested at various screen potentials Vs, and the dimensions of the resulting electrostatic dots were measured. The results below are representative.

In general, it has been found that increasing the potential on the screen reduces latent image size without making any compromise in image charging. Example 4 The electrophotographic printer of Example 1 was tested using various distances between the print head assembly and dielectric layer 221. By changing the screen potential Vs, Vs and Vc
By keeping the potential difference between
The dimensions of the resulting electrostatic dot images were held constant.
The results below are representative:

[Table] In general, it has been found that by increasing the distance from the print head assembly to the dielectric surface and increasing the screen potential Vs, a constant dot image diameter can be obtained without any compromise in image charging. Served. Example 5 The electrophotographic printer of Example 1 was modified such that the screen had holes 218 in the form of slots instead of holes. The toned electrostatic latent image obtained was oval in shape. Having described various aspects of the invention, it is to be understood that the foregoing detailed description is for illustration only, and that various changes in parts and equivalent substitutions of parts shown and described are within the scope of the claims. It will be understood that what may be done without departing from the spirit and scope of the invention as described. [Effects of the Invention] According to the present invention, the control electrode has an end face disposed opposite to the excitation electrode, and ions are generated in the air region formed by the joint between the end face and the solid dielectric member. By generating electric discharge and extracting and controlling the ions, it is possible to form an electrostatic image on the dielectric recording medium in a shape corresponding to the control depending on the shape of the end face and the screen electrode. Furthermore, the present invention generates an ion-generating electric discharge in the air region formed by the joint between the end face of the control electrode and the solid dielectric member, and extracts the ions onto the dielectric recording medium. The transit time of ions moving within the air region can be made very short. Therefore, the electrostatic image forming method and apparatus according to the present invention can apply a high frequency alternating potential between the excitation electrode and the electrostatic latent image, and can operate at high speed. Furthermore, since the present invention has a screen electrode between the control electrode and the surface of the dielectric recording medium, it has the following two effects. The first is to prevent the formed electrostatic image from being erased. That is, if a screen electrode is not provided, for example, after positive ions generated at the end face of the control electrode are extracted onto the dielectric recording material by voltage Vc to form a positive electrostatic image, this static When a state where no voltage Vc is applied to the control electrode occurs on the electrostatic image, the positive electrostatic image attracts negative ions generated on the control electrode, and this positive electrostatic image is erased. In the present invention, since the electric field between the screen electrode and the counter electrode can be kept constant, it is possible to prevent the electrostatic image from being erased due to fluctuations in the potential of the control electrode on the electrostatic image. Become. The second is to control the formation of an electrostatic image by the electrostatic lens action of the screen electrode.
For example, when a large potential is applied to the screen electrode, the diameter of the electrostatic image becomes smaller and a sharp image is formed. Furthermore, by changing the size and shape of the holes in the screen, the size and shape of the electrostatic image formed can be changed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an ion generator of an electrostatic imaging apparatus according to a preferred embodiment of the present invention. Figure 2 shows the first
1 is a cross-sectional view of an electrostatic imaging apparatus according to a preferred embodiment of the present invention to which the illustrated example is applied; FIG. FIG. 3 is a circuit diagram showing a modification of the circuit used in the device of FIG. 2. FIG. 4 is a simplified cross-sectional view of an ion generator according to an example of the two-electrode mode studied prior to the present invention. Figure 5 shows
FIG. 2 is a simplified cross-sectional view of an ion generator and an extractor according to a study example. FIG. 6 is a plan view of an ion generator for use in electrostatic printing according to a study example. FIG. 7 is a plan view of a matrix ion generator for an electrostatic dot matrix printing machine according to a study example. FIG. 8 is a partial perspective view showing the physical form of the ion generator according to the study example. FIG. 9 is a simplified diagram showing a copying machine using the ion generator of FIG. 8. FIG. 10 is a sectional view showing an aerosol charging system using the ion generator shown in FIG. 7. FIG. 11 is a cross-sectional view of a line scan printing system using the ion generation method according to the studied example. FIG. 12 is a diagram showing the relationship between electrode voltage and paper voltage in the apparatus shown in FIGS. 5 to 8. FIG. 13 is a perspective view of a dielectric recording medium showing erasing of an electrostatic image produced by the matrix ion generator of FIG. 7; 210...Ion generator, 211...Excitation electrode, 2
12...AC potential source, 213...dielectric layer, 214...
Hole, 215... Control electrode, 216... Hole, 217... Dielectric, 218... Hole, 219... Screen electrode.

Claims (1)

[Claims] 1. An alternating potential is applied between an excitation electrode and a control electrode separated by a solid dielectric member, and the control electrode has an end face disposed opposite to the excitation electrode. , generating an ion-generating electric discharge in an air region formed by the joint between the end face and the solid dielectric member, and generating a direct current between the control electrode and a counter electrode disposed on the back side of the dielectric recording member. extracting ions from said electrical discharge by applying a voltage Vc, and applying a direct current between said counter electrode and a screen electrode having holes disposed between said control electrode and said dielectric recording surface; An electrostatic image forming method comprising controlling the extraction of the ions by applying a voltage Vs to form an electrostatic image on the dielectric recording medium. 2 DC voltage applied to the screen electrode
2. The electrostatic image forming method according to claim 1, wherein Vs is smaller in absolute value than the DC voltage Vc applied to the value control electrode. 3 a first solid dielectric member; a plurality of excitation electrodes arranged in parallel on a surface of the first solid dielectric member; and a surface of the first solid dielectric member opposite to the surface; a plurality of control electrodes arranged above in parallel in a direction intersecting the excitation electrode and each having a hole at the intersection with the excitation electrode; a screen electrode having a plurality of holes; the control electrode and the screen electrode. and a second solid dielectric member disposed between the two so as to be spaced apart from each other, and supporting each hole of the screen electrode so that each hole of the control electrode faces each hole of the control electrode. An image forming device, the device being arranged to face a dielectric recording medium on a counter electrode, and applying an alternating potential between an excitation electrode selected from the plurality of excitation electrodes and the plurality of control electrodes. applying a DC voltage Vc between the control electrode selected from the plurality of control electrodes and the counter electrode; and applying a DC voltage Vs between the screen electrode and the counter electrode. Therefore, ions are extracted and controlled from the electrical discharge generated in the hole provided at the intersection of the selected control electrode with the selected excitation electrode, and an electrostatic image is formed on the dielectric recording medium. An electrostatic image forming apparatus characterized by forming an electrostatic image. 4. Claim 3, wherein the second solid dielectric member has holes corresponding to the holes of the control electrode, and the holes have a larger diameter than the holes of the control electrode. The electrostatic image forming apparatus described in .