SE439698B - DEVICE FOR PRODUCING ELECTROSTATIC IMAGES - Google Patents

Description

7811082-2 eel possibly with erasure of a residual electrostatic image, if any, after the transfer.

A system operating according to the thinking outlined above is described in U.S. Pat. Nos. 3,937,571 and 3,907,560. In this case, the latent electrostatic image is produced on an image drum by means of an ion modulation screen which allows the ions to pass through. a pattern corresponding to the original image, whereby they are forwarded to the image drum. However, it is awkward to use such a screen, and in this approach the time for making a first copy becomes too long. Systems that use charge transfer between two insulating sheets have been analyzed, and photocopying technology refers to electrostatic image transfer. Such a process is described on page 432 of the "Xerography and Related Process", edited by John H. Desrauer and Harold E. Clark, The Focal Press, London and New York, 1965. Electrostatic image transfer relies on the degradation of an air gap in the area between the two insulating means, whereby a charge transfer is obtained from one means to the other by an ionization of the intermediate air. The special problem associated with charge transfer when two insulating sheets with an applied external voltage are brought closer together is that the charge is transferred in the form of a breakdown. This type of charge transfer usually causes the transferred image to become spotty.

There are a lot of other image transfer systems, which, however, suffer from inconveniences of various kinds.

The present invention has for its object to achieve compatibility in the construction of a device for printing resp. for photocopying, the purpose of which is to provide high speed printing and photocopying with excellent image quality. The system used according to the invention to achieve the above is simple, compact and inexpensive. The photocopying system requires fewer processing steps than previously known systems, and the paper path is extremely short and simple. The system includes both photocopying and electrostatic printing or reproduction as well as various parts intended for use in 7811082-2 S in connection with such photocopying and printing resp. reproduction.

A ion generator can be used to pre-charge a photoconductor or to form a latent electrostatic image. Furthermore, a photoconductive three-layer means can be used in the photocopier, whereby an impregnated anodised aluminum dielectric can receive a latent electrostatic image. The photocopier and the electrostatic pressure device give rise to a latent electrostatic image of a dielectric member in different ways, but then they can use identical methods to tone the latent electrostatic image and to effect subsequent processing. In the photocopier, an electrostatic image is formed on a photoreceiving means by means of conventional optical means, and said image is transmitted to a dielectric means. In the electrostatic printing device or the reproduction device, a latent electrostatic image can preferably be produced on a dielectric member by means of an ion generator.

In fact, the invention relates to a device for producing electrostatic images, which device is characterized in that it comprises a first solid dielectric means, a control electrode on one side of said first solid dielectric means with an air area at a connection point between the control electrode and the first solid dielectric means. , and a drive electrode on the opposite side of the first solid dielectric member. A time varying potential is applied between said electrodes to generate an electrical discharge in said air area.

Further included is a source of a first DC voltage between said gate and a further means, an apertured shield electrode, a second solid dielectric means which isolates said shield electrode from the gate and the first solid dielectric means, and a source of a second DC voltage. between said shield electrode and said further means.

The device for producing electrostatic images forms a latent electrostatic image on said further means.

In the device according to the invention, an electrostatic image can advantageously be produced on a dielectric image means by a preferred form of a ion generator. This ion generator enables the application of a potential between two electrodes which are separated by a solid dielectric means so that the breaking of an electric air gap is effected in adjacent field areas. Ions which are thereby generated can be extracted or extracted from the charge and supplied to another means which may be a current conducting support means with a dielectric coating.

In a particular design of said ion generator, the charge initiating potential consists of a high-frequency alternating current, the extraction being carried out by means of a direct voltage. According to another aspect, the extracted or extracted ions can be used directly or applied to a granular mass which moves under the influence of an electric field. Charged particles in said mass can be used to produce an electrostatic pattern using e.g. of a discharge electrode with a gap whose pattern corresponds to the configuration of a character or symbol for which a charged image is desired. In another aspect, the electrodes may consist of multiple electrodes that form intersection points in a matrix array. Ions are extracted from anode openings at selected matrix crossing points by simultaneously arranging both an electrical discharge at the selected openings and an outer ion extraction field.

The extracted ions can form a latent electrostatic image which is later toned and melted. The image can be produced on the dielectric layer and transferred to plain paper. Alternatively, charged granular material can be deposited on plain paper to obtain a visible image or collected on a current-conducting surface. In another design of the ion generator, a solid dielectric member is used which separates two electrodes, at least one of which has an edge on the surface of the dielectric member. When a voltage is applied between the electrodes, e.g. an alternating voltage within the frequency range from about 60 Hz to about Ä MHz, an electric discharge occurs between one electrode and the dielectric surface.

The electrodes, which may be the same or different, may be designed in a variety of different ways, e.g. in the form of a woven metal mesh with open meshes.

The ion generator can be provided with a third electrode which receives. control the discharge of the ions generated in the manner described above. A high frequency alternating voltage is applied between the first electrode, the drive electrode, and the second electrode, the control electrode. The third electrode, the shield electrode, is separated from the control electrode by a second dielectric layer. Ions generated by the decomposition in the air gap can be extracted by the action of the shield electrode and supplied to another organ. In the embodiment with three electrodes, the shield electrode prevents an undesired image erasure when a previously formed latent electrostatic image is present under the ion generator and no extraction voltage is applied to the control electrode. In the three-electrode embodiment, an electrostatic lensing action is obtained through the shield electrode which can be used to regulate the size and shape of electrostatic images produced by means of the ion generator according to the invention.

In both the fundamental embodiments, the latent electrostatic image is toned on the dielectric image means so as to obtain a visible equivalent. The tinted image is then transferred to a reception medium. It is possible to make cleaning of the surface of the dielectric image device resp. discharging any remaining image on it.

In the fundamental embodiments, the dielectric imaging means may include a surface layer consisting of impregnated anodized alumina. Such a member is formed by first dewatering an anodized aluminum member, whereupon surface openings of the dewatered member are impregnated so as to obtain improved resistivity and improved dielectric properties. In this case, the surface openings of the dielectric member can be constituted by pores of the type present in oxide coatings generated by oxidation of the current-conducting member. Furthermore, the dewatering can take place by heating the dielectric member in a vacuum or in a drying box with a relative humidity of less than 10%. Heating usually takes place at a temperature in a range from about 60 ° C to about 180 ° C, with the preferred temperature being about 100 ° C. The time during which heating should preferably take place is about 8 hours.

The dielectric member can be impregnated with an organic resin selected from a group consisting of resins which can be cured by ultraviolet radiation, polyamide resins, ultraviolet activated resins and thermally cured epoxy resins. Furthermore, the dielectric member may be a current conducting substrate or substrate which is located below a dielectric layer and which has substantially moisture-free pores. These pores are sealed in their moisture-free state with the help of a resin material so that improved dielectric properties and resistivity properties are obtained.

In the present case, a residue of atmospheric moisture will inevitably be obtained in the pores, but the pores are sealed in their substantially moisture-free state so that the unfavorable inconveniences with trapped pore moisture are avoided.

In a particular version of both the fundamental embodiments, the tinted visible image on the dielectric imaging drum can be transferred to a receiving medium with simultaneous pressure fixing. Pressure is applied when a receiving path or sheet runs between the dielectric imaging drum and a support roller at a point of contact between these two members.

Two metal scrapers may be located next to the dielectric imaging drum and the support roller to clean the surface of the drum and roller after image transfer. If any residual image happens to be on the dielectric image drum, it can be erased by means of electrodes on either side of the dielectric layer, between which electrodes high-frequency alternating current discharges are formed. Discharge can also be achieved by means of a grounded conductor or semiconductor which is kept in intimate contact with the surface of the dielectric layer. The grounded conductor may be a heavily loaded metal scraping knife, and the grounded semiconductor may be a semiconductor roller.

The invention is described in detail in the following with reference to the accompanying drawings, in which Fig. 1 shows a schematic view of the whole electrophotographic device in accordance with a preferred version of the first fundamental embodiment, Fig. 2 is a sectional partial view of the vicinity between a photoconductive means and a dielectric imaging drum, Fig. 3 is a schematic view of a photoconductive means in the form of a band and a dielectric imaging drum in accordance with an alternative version of the first fundamental embodiment, Fig. N is a perspective sectioned Fig. 5 is a sectional perspective view of a charge transfer means utilizing a photoreceiving device, Fig. 6 is a schematic view of an electrostatic transfer printing device, Fig. 7 is a partial sectioned view. view of a charge erasing unit for an electrostatic pressure device or reproduction device resp. photocopier, Fig. 8 is a partial sectional view of a charge erasing unit for an electrostatic printing device or reproducing device or photocopier according to an alternative embodiment, Fig. 9 is a schematic sectional view of an ion generator, Fig. 10 is a schematic Fig. sectional view of an ion generator and an extractor, Fig. 11 is a plan view of an ion generator intended for use in electrostatic printing, Fig. 12 is a plan view of a matrix generator for an electrostatic dot matrix printing apparatus, Fig. 13 is a partial perspective view of a physical model of an ion generator, Fig. 1N is a schematic view of an exemplary copier utilizing the ion generator of Fig. 13, Fig. 15 is a sectional view of an alternative ion source, Fig. 16 is a sectional view of an aerosol charging system for dot matrix printing at a high speed by means of the ion generator, Fig. 17 is a sectional view of a line scanning printing system using the specified ion generation method, Fig. 18 is a sectional view of an electrostatic precipitator used in connection with said ion generation method, Fig. 19 is a graph showing the relationship between electrode voltage and paper voltage in said ion generation method. Fig. 20 is a perspective view of a toned electrographic image of a dielectric member with a current conductor such as a backstory, which image is produced by the matrix generator of Fig. 12; Fig. 21 is a schematic sectional view of a ion generator according to a alternative embodiment, Fig. 22 is a schematic sectional view of an ion generator and extraction device in the embodiment of Fig. 21, and Fig. 23 is a circuit diagram of an alternative circuit that may be used in the ion generator and extraction device of Fig. 22.

The present invention will be described in connection with an electrophotographic device with double transmission in the following section I and in the form of a printing device or reproduction with electrostatic transmission in section III. In these two cases, a latent electrostatic image is obtained on a dielectric image roller in different ways. Sections II, IV and V will be devoted to special components which can be used in the electrophotographic device and in the printing device as well as in other contexts. Section II describes a three-layer photoreceptor which can be advantageously used to form a latent electrostatic image for transfer to another dielectric member. The ion generator and the extraction device according to section IV can be used for electrostatic charging resp. discharge, dust separation, separation and coating. The impregnated anodised aluminum members according to section V are used in contexts where smooth surfaces with good electrical properties are needed. 7811082-2 “i I Double transfer electrophotography Figs. 1-3 show an electrophotographic device 10 with double transfer comprising three cylinders and different treatment stations.

The upper cylinder is a photoconductive member 11 which includes a photoconductive coating 13 disposed on a current conducting substrate or substrate 17, a semiconductor substrate 15 being disposed between these two layers. The said cylinder will be described in detail in Section II below. Suitable materials which can be used in the photoconductive surface layer 13 include cadmium sulfide powder finely divided in a resin binder (Cds of photoconductive quality are used, usually doped with such activating substances as copper and chlorine), cadmium sulfoselenide powder finely divided in a resin binder of the formula CdSxSey, where x + y = 1), or the equimolar complex of polyvinylcarbazole and trinitrofluorenone.

The photoconductor is electrostatically charged at the station 19 and then exposed at the station 21 so as to obtain a latent electrostatic image on the surface of the photoconductor. The photoconductor can be charged by means of a conventional corona beam device or alternatively by using the method of ion generation which will be described in section IVA below (Fig. 1H). The optical image that provides the latent image on the photoconductor can be formed by any optical scanning method among several commonly known ones. This latent image is transferred to a dielectric cylinder 25 formed by a dielectric layer 27 mounted on a metal cylinder 29.

The latent electrostatic image of the dielectric cylinder 25 is toned and transmitted by pressure to a receptor 35 or receiver which is a medium fed between the dielectric cylinder 25 and a transfer roller 37. Means may be provided for removing excess tones from the cylinder 25. and the roller 37 and for erasing any electrostatic image remaining on the cylinder 25 after the transfer (these means are indicated at H3, H5 and H7). A device for toning and for the subsequent steps is shown generally ID at 30 in Fig. 1 and will be described in detail in Section IIIB below. The method by which a latent electrostatic image is transmitted from the photoconductor 11 to the dielectric cylinder 25 is based on charge transfer as a result of air gap degradation. The process when the photoconductive surface 13 is uniformly charged and exposed results in a charge density distribution corresponding to the exposed image as well as a variable potential pattern nos the photoconductive surface 15 with respect to the grounded current conducting substrate 17.

With regard to Fig. 2, it should be mentioned that the charged portion of the photoconductor 11 is rotated to a position where it is very close (less than 0.05 mm) to the dielectric surface 2 ". An outer potential 53 is applied between the electrodes in the current-conducting substrates. 17 and 29 of the two drums, a typical initial charge of about 1000 volts being applied to the photoconductive layer lj, whereupon an additional 400 volts of the externally applied potential 33 is applied. The total charge corresponding to 100 volts is reduced by about 800 volts. during the exposure process.

For the charge transfer to work, there must be sufficient electrical voltage in the air gap for the air to be ionized. The required potential depends on the thickness and dielectric constants of the insulating materials, as well as on the size of the air gap. (Compare Dessauer and Clark, "Kerography and Related Process", The Focal Press, London and New York, 1965, page Ä27.) The electrical stress will vary depending on the local charge density, but if the voltage is sufficient for air gap degradation to obtained, this will result in a charge transfer from the photoconductive surface 13 to a dielectric surface 27 in a pattern which forms an image of the latent image.

This means that a certain threshold potential must be generated across the air gap. Substantially half the charge will be transmitted, leaving a potential of about 600 volts kowmer to go to a dielectric surface 27. the required threshold potential can be obtained as a result of the uniform charging and exposure of the photoconductive surface 13, or else a external potential 7811082-2 II added potential is also exploited. Uild quality is increased as a rule ¿by using nn an external potential.

It is important that the integrity of the latent electrostatic image is maintained in the presence of flare transmission, which occurs under certain conditions when charge transfer occurs when the two insulating surfaces are close to each other. How has it been found that this effect is significantly reduced by adding a semiconductor layer 15 between the photoconductive surface layer 15 and the current-conducting substrate 1? in comparison with the case where the usual two-layer photoconductor is used. Although the phenomenon by which the needle conductor layer eliminates the breakdown is not fully understood, it is considered that the time constant introduced by the semiconductor layer has the effect of smoothing or reducing the very rapid behavior that otherwise occurs in the case of breakdown. Suitable layer properties and materials are mentioned in Section II below.

By utilizing this preferred design of the photoconductive member II, it is possible to avoid blurring the details of the transmitted image. A typical range of air gap distances for charge transfer in the manner described is between about 12 microns and about 38 microns.

By using the above-mentioned method for charge transfer, some of the problems that arise as a result of undesirable discharge properties of the photoconductive means are reduced. If an external bias potential is used to achieve a threshold potential, a higher voltage is obtained on the dielectric drum than would be the case with a single transmission system which relies on the contrast potential of the photoconductor surface. This in turn results in greater contrast between the light and dark areas of the toned, visible image.

In order to obtain copy-to-copy uniformity, especially in the case of certain photoconductors which exhibit fatigue, it is advantageous to discharge the latent residual image remaining on the photoconductor after the latent image has been transferred to the dielectric surface 27. This erasing can be conveniently performed by means of a lamp 23 which provides sufficient light for the photoconductor to be discharged below a required level. The erasing lamp 23 can be either of the fluorescent type or of the incandescent type.

In a particular working example of an electrophotographic system, the device in question was designed in the manner schematically shown in Fig. 1. The cylindrical current-conducting core 29 of the dielectric cylinder 25 was made of aluminum designated 7075-T6 which had been machined to a diameter of 7.5 cm. The length of this cylindrical core, excluding its machined bearings, was 22.5 cm. The layers were dewormed, and the aluminum was anodized using the Sanford process (cf. S. Hernick and R. Pinner, "The Surface Treatment and Finishing of Aluminum and its Alloys", Robert Draper Ltd., Uze edition, 1971/72, volume 2, p. 567). The finished alumina layer had a thickness of 60 .mu.m. The current-conducting core 29 was then heated in a vacuum oven at a temperature of 150 ° C for 12 hours and then allowed to cool to 50 ° C.

After the core had been removed from the furnace, it was applied to a low viscosity epoxy substance (resin R9-2039 from Hysol Company - 100 parts by weight; harder no. H2-3MON - 11 parts by weight) by brush coating. The epoxy substance was allowed to impregnate the pores and the excess on the surface was then wiped off. The epoxy substance was cured at 78 ° C for 18 hours in a vacuum oven, thereby forming the dielectric surface layer 27. The surface layer 27 of the dielectric cylinder 25 was then finalized to a size of between 12.5-1o'6 and 22, s-1o'5 cm by means of silicon carbide sieve paper designated 600.

The pressing roller 37 consisted of a solid machined core Ä1 with a diameter of 5 cm, on which a polysulfone sleeve 39 with an outer diameter of 6.25 cm was applied during press fitting.

The current-conducting substrate 17 on the photoconductive member 11 consisted of an aluminum sleeve made of aluminum tubes designated 6061, its wall thickness being 0.3 cm and its outer diameter amounting to 5 cm.

The exterior was machined and aluminum anodized (again in this case using the Sanford process) to a thickness of 50 .mu.m.

In order to obtain the intended level of conductivity of the oxide layer, nickel sulphide was deposited in the oxide pores by dipping the oxidized sleeve in a solution of nickel acetate (50 5 / l, pñ = 6) for three minutes. To prepare the semiconductor layer 15, the sleeve was then immediately immersed in concentrated sodium sulfide for two minutes, after which it was rinsed in distilled water. This process was unforced three times. The impregnated anodized layer was then sealed in water (9290, pH = 5.6) for ten minutes. The semiconductor substrate 1a was provided with a photoconductor 13 comprising a binder layer by spraying and consisting of photoconductor grade cadmium sulfoselenide powder rolled together with a thermosetting acrylic resin from DeSoto Chemical Company, diluted with methyl ethyl ketone suitable for spraying. The coating thickness in the dry state was 40 .mu.m, and the cadmium pigment concentration in the resin binder was 18% by volume. The resin was crosslinked by heating at 180 ° C for three hours.

The dielectric cylinder 25 was driven via gears from an AC motor so that it had a surface speed of 20 cm / s. The pressing roller 30 was stored in pivotable and spring-loaded side racks so that it could be pressed against the dielectric cylinder 25 at a pressure of 60 kg per linear contact centimeter.

0.5 cm wide strips of tape were placed around the periphery of the photoconductor sleeve 11 at each end so that the photoconductor was kept at a small distance from the oxide surface of the dielectric cylinder. The photoconductor sleeve was stored freely in layers and driven by friction of the tape resting on the oxide surface.

The photoconductor charging crown 19, the one-component toner 51 for the latent image and the optical exposure system 21 were all substantially equal to the corresponding components used in the copier No. 444 of oevclop KG Dr. Eisbein & Co., (Stuttgart).

Flexible stainless steel scrapers Ä) and 45 were used to keep both the oxide cylinder 25 and the polysulfone pressing roller 57 clean. In the embodiment shown in Fig. 7 where the device 93 for erasing the electrostatic image is shown, the latent residual image was erased by means of an alternating current corona 97 in combination with a screen or a mesh 95 with a mesh size of 99 mesh and with an open area of RE Å, this screen being held at ground potential and pressed to light contact with the oxide surface 27. The 78.21082-2 H tungsten corona wire 97 having a diameter of 76.2 .mu.m was located at a distance of 0.47 cm from the screen or the net. This corona wire was supplied with an AC potential of 60 Hz and a peak value of 9 kV.

In the one in Pig. 2 shows the embodiment of the photoconductor and the dielectric cylinder had a direct voltage 33 applied to a bias voltage on the photoconductor sleeve 11 so as to obtain a potential of -H00 volts relative to the core 29 of the dielectric cylinder, which was maintained at ground potential. The photoconductive surface 13 was charged to the potential of -1000 volts relative to its substrate 17. An optical exposure of 25 lux seconds was used to discharge the photoconductor in areas of bright light. In uncharged portions, a latent image of -400 volts was transferred to the oxide dielectric 27. This image was tinted and then transferred to plain paper 35 which was fed into the pressing nip at the intended time from a sheet feeder.

Copies were obtained at a rate of 30 per minute, the images obtained having a pure background resp. good density in the black portions and a resolution better than twelve line pairs per millimeter. No car heating other than that which occurred during the pressure transfer was required.

In another embodiment of the dual transfer copier, the photoconductive sleeve 11 is replaced with a photoconductor II 'in the form of a flexible band, as shown in Fig. 3. The photoconductor III is made of a photoconductive layer L of polyvinylcarbazole and trinitrofluorenone read in tetrahydrafuran and applied to a scattering conductive gagyer base li '(base pager with the designation LEB No. 45 from West Virginia Pulp and Paper) to a dry thickness equal to 30 .mu.m. The photoconductive strip III' is supported by two current conducting rollers 177. 'a and l7'b, respectively, which were driven by the dielectric cylinder 25 via friction.The lower roller l7'b êålê fi es f5TSPännïnß9 fi ~ 4UU V01t- The photoconductor 13' was charged to 1009 volts by means of the double corona device l9 'shown in Fig. 3. the electrostatic image was generated by a flash exposure 21 ', and the whole image was thus obtained without the aid of scanning optics 7811082-2 IS' The remainder of this device was identical to the device in the previous example. The sample, apart from the dielectric cylinder 25, which was made of a non-magnetic stainless steel coated with a 15 .mu.m thick layer of high density alumina. This coating was applied using a plasma spray method from Union Carbide Corp. (Linde Division).

After the oxide surface had been sprayed on, it was ground and polished to the finished size 25-10 "cm. Also in this case, high quality copies were obtained, even with operating speeds as high as 75 cm / s.

II The Three-Layer Photoreceptor The introduction of a semiconductor substrate between the photoelectric surface layer and the current-conducting core of a photoreceptor device entails considerable advantages when this method is used in the production of charge transfer images. For example, the photoreceptor embodiments shown in Figs. Ä and 5 are included in the embodiment shown in Figs. 5 shows the electrophotographic device with double transmission.

In the embodiment shown in Fig. 4, the photoreceptor device 50 consists of a drum 60 with a photoconductive layer 61 placed on top of a semiconductor layer 65 on a current-conducting substrate 65.

In the conventional transfer method, the electric field associated with the discharges of the electrostatic image produced on the drum 60 results in the image deteriorating during the transfer process. The effect of this image degradation is mitigated in accordance with the present invention by enclosing the semiconductor 65 between the current conducting substrate 65 and the photoconductor 61.

Other types of photoreceptor devices in accordance with the invention can be made, for example in the embodiment shown in Fig. 5 with a flexible band 60 ', where a photoconductive layer 61' is located on a semiconductor layer 65 ', which in turn is applied to a current conducting substrate 65 '. In order to obtain the desired conductive substrate 65 ', a conductive coating may be applied to a plastic film, or else the substrate or substrate may be a thin metal foil consisting of e.g. of nickel. . The current-carrying substrate 65 of the drum 60 shown in Fig. 4 is, as an example, made of aluminum, but an arbitrary combination of materials which gives the desired conductivity can also be used.

It has been found empirically that the semiconductor layers 63 and 63 'can preferably have a thickness in the range from about 25 μm to about 19 mm. The resistivity of the semiconductor layer must be such that charge is passed through the layer in a reasonable time. The resistivity can thus advantageously amount to less than 1012 ohm-centimeters. On the other hand, the resistivity must be large enough to obtain a suitable time constant for smoothing the charge transfer, with a concomitant reduction in the deterioration of the transfer image obtained so far.

The lower resistivity level of the semiconductor layers 63 and 65 'depends on the thickness of the superimposed photoconductive layer and the operating speed. It has been found that a resistivity of more than 105 ohm centimeters is generally suitable.

The semiconductor layer can be realized in a variety of different ways. It may consist of a semiconductor plastic material or a semiconductor elastomeric material. As a suitable current-conducting agent, carbon black can be used, while a suitable matrix on which said carbon black can be applied may consist of an epoxy species.

The semiconductor layer can thus be produced by atomizing carbon black in a resin matrix and thereby achieving a resistivity in the above-mentioned range. In a similar way, a large number of rubbers can be used in combination with carbon black or carbon black so that the desired resistivity is obtained.

The photoconductor can be of the type commonly used in electrostatic imaging. Among materials which have been found to work satisfactorily with the semiconductor layer 65 or 65 'are polyvinylcarbazole in complexes with trinitrofluoronone, cadmium sulphide which is finely divided into various binders including epoxy materials, silicones and thermoplastics, selenium and selenium alloys, including amorphous selenium, and zinc oxide with fatigue.

In the case of photoconductors for binder layers, the semiconductor layer can also be made of the same material as the photoconductor but with a higher concentration of photosensitive elements. Thus, a photoconductive layer of cadmium sulfide in an epoxy substance and having a concentration of 18% acts as an insulator in the dark, while the same layer with a 30% cadmium sulfide concentration behaves as a semiconductor in the dark.

The three-layer photoreceptor described above can be advantageously used anywhere where one wishes to transfer a latent electrostatic charge image to any other dielectric member, for example an intermediate dielectric layer which is later toned, and the image produced by toning is transferred to a copy on plain paper. or a dielectric sheet that is self-toned to obtain an image.

III Electrostatic transfer printing Electrostatic transfer printing takes place in such a way that a latent electrostatic image is produced on a dielectric surface (eg an image roller) and this image is then further processed.

A. Production of a Latent Electrostatic Image An apparatus for generating charged particles and for extracting or extracting them so that they can be applied to another surface is described in detail in Section IV below. Any of the embodiments of a device suitable for producing a latent electrostatic image on a dielectric surface can be used in the current electrostatic printing device. Compare, for example, the embodiments of Figs. 11, 12, 13 and 15, preferably the matrix printing embodiment of Fig. 12, which can be used in multiplex printing. The embodiment with sections three electrodes described in sections IV-B below means that further control is obtained in terms of image size and image shape, and undesirable erasures of the image can be avoided during matrix printing.

B. Subsequent treatment Identical apparatus can be used to perform processing operations after a latent electrostatic image has been produced (eg by means of the electrographic device according to section V), which apparatus is common both in the case of photography and printing. Compare Figs. 1 and 6.

According to Fig. 6, the dielectric layer 75 of the dielectric cylinder 73 should have sufficient resistance to be provided with a latent electrostatic image during the period between the production of the latent image and the toning or, in the case of electrophotographic apparatus, between image transmission. and toning. Consequently, the resistivity of the layer 75 must be greater than 1012 ohm centimeters. The insulating layer 75 should preferably have a thickness of between 0.025 mm and 0.075 mm. In addition, the surface of the layer 75 should be highly resistant to abrasion and relatively smooth, and its surface treatment should be better than 25-106 cm in order to obtain complete transfer of toner to the receiving sheet 81. In addition, the dielectric layer 75 must have a large modulus of elasticity so that it is not distorted to any great extent by high pressures in the transfer nip.

A number of organic and inorganic dielectric materials can be used for the layer 75. For example, glass enamel can be deposited and fused to the surface of a steel or aluminum cylinder. High density alumina and applied by flame or plasma spraying can also be used instead of glass enamel. Plastic materials such as polyamides, polyimides and other tough thermoplastic or thermosetting resins are also suitable. However, the preferred dielectric coating is impregnated anodized alumina in the manner described in Section V below.

The latent electrostatic image on the dielectric surface 75 is converted into a visible image at the toning station 79.

Although any conventional electrostatic toner can be used, the current conductive magnetic component type toner described in U.S. Pat. No. 2,846,333 is preferred. This toner has the advantage of being simple and clean to operate with.

The tinted image is transferred and fused to a receiving sheet S1 by applying a high pressure between the rollers 73 and 85. The lower roller 83 consists of a metal core 87 which may be provided with an outer casing 85 of plastic. The pressure required for good attachment to ordinary paper is determined by such factors as, for example, the roll diameter, the toner used and the presence of a possible coating on the surface of the paper. Typical pressures range from 11 kg to 126 kg per linear contact 7811'Û32 „2 'H' centimeters. The purpose of the plastic coating 85 is to absorb any high stresses which are introduced into the nip if the paper gets stuck or wrinkled. By absorbing stresses in the plastic layer 85, the roller 73 coated with a dielectric will not be damaged if paper is accidentally stuck. The coating 85 can usually be a nylon sleeve or polyester sleeve with a thickness of between about 3 mm and about 12.5 mm. This coating does not need to be used, for example, if you are in the process of providing a highly controlled web with pressure and where this web is such that it is not likely that paper will get stuck resp. wrinkled.

Scrapers 89 and 91 may be present, and their task is to remove any remaining paper dust, tones that accidentally strike the rollers, and dust carried in the air resp. dirt from the dielectric pressing cylinder and the assisted pressing roller. Since virtually the entire tinted image is transferred to the receiving sheet 81, the scrapers are not absolutely necessary, but it is desirable that they be included so that long-term operation is reliable.

The small latent electrostatic residual image remaining on the dielectric surface 75 after the tinted image has been transmitted can be neutralized at the latent image discharge station 95. By toning and transferring a tinted latent image to a plain sheet of paper, the voltage of the electrostatic image decreases, usually from several hundred volts to several tens of volts. In some cases it will happen that if the tinting threshold value is too low, the presence of a latent residual image will result in ghost images on the copied sheet, which images are, however, eliminated by the discharge station 95. This will be an erasure performed. by means of the arrangement according to Fig. 7. According to Fig. 7, the dielectric cylinder 73 provided with a dielectric coating 75 is kept in contact with or at a small distance from a screen or a net 95 with open meshes, said screen being kept at a general seen the same potential as the current-conducting cylinder 77. The shield is mounted on a holder 99, and an AC corona wire 97 is placed behind the shield or net at a distance usually between 6 mm and 12.5 mm. 7811982-2 940 A large alternating voltage with a frequency of e.g. 60 Hz is applied to the wire 97. The screen 95 forms a reference ground plane near the dielectric surface, and the AC corona wire 27 supplies both positive and negative ions. Any local field at the screen 95 resulting from a latent electrostatic image on the dielectric surface 75 attracts ions generated by the corona wire 97 against the dielectric layer, thereby neutralizing the bulk of any remaining charge.

With very high surface velocities of the dielectric coating 75, the remaining charge can again result in ghost images.

In this case, the residual charge can be reduced to a level below the fade threshold by arranging several discharge stations.

Alternatively, any present latent electrostatic image may be erased by means of a high frequency AC discharge between electrodes separated by a dielectric as will be described in Section IV below.

The latent electrostatic residual image can also be erased by contact discharge. The surface of the dielectric must be kept in close contact with a grounded conductor or grounded semiconductor in order for any remaining residual charge to be effectively removed from the surface of the dielectric layer 75, e.g. using a hard pressed metal scraper. The charge can also be removed by using a semiconductor roller which is pressed to a good abutment against the dielectric surface. Fig. 8 shows a sectional partial view of a semiconductor roller 98 which is in roll contact with the dielectric surface 75. The roller 98 may advantageously have an outer side consisting of an elastomer.

IV Ion generation and extraction The ion generator and the extractor are in principle provided with two electrodes which are separated by a solid dielectric member (section A), but there may be advantages in adding a third electrode (section B).

A. Embodiments with two electrodes Fig. 9 shows a ion generator 100 which gives rise to air gap degradation between a dielectric 101 and each of its current-conducting electrodes 102-1 and 102-2 when using an alternating voltage source 103. When adjacent electric fields EÅ resp. EB 7811082-2 a1 In the air gaps 104-a and IOH-b exceeding the near-field of the air, an electric discharge will be obtained, which causes the dielectric 101 to be charged in the portions 101-a and 101-b adjacent the electrode edges. When the alternating voltage of the voltage source 103 is reversed, the charge will be reversed in the decomposition portions 101 ~ a and 101-b. The generator 100 shown in Fig. 9 will thus give rise to an air gap breakdown twice per period of the applied alternating voltage from the source 103, whereby ions of varying polarity are thus obtained.

The extraction or extraction of ions obtained in connection with the generator 100 in Fig. 9 is illustrated by the generator extractor 110 in Fig. 10. Generator 110A includes a dielectric III between the current conducting electrodes 112-1 and 112-2. In order to prevent air gap degradation near the electrode 112-1, this electrode is encapsulated in or surrounded by an insulating material 111 fi. Alternating voltage is applied between the current-conducting electrodes 112-1 and 112-2 by an alternating voltage source 114A. In addition, the second electrode 111-2 is provided with a hole 112-h at the location where the desired air gap degradation occurs relative to a portion III-r of the dielectric III to provide an ion source.

The ions formed in the gap 112-h can be extracted by a direct voltage originating from a voltage source read so as to obtain an external electric field between the electrode 112-2 and a grounded auxiliary electrode 112-3. An exemplary insulating surface to be charged by the ion source in Fig. 10 consists of a dielectric (electrographic) paper 115 with a current-conducting base 115-p coated with a thin dielectric layer 115-d.

When a switch 116 is set to the position X and thereby grounded in the manner shown, the electrode 112-2 will also be at ground potential, with no external field present in the area between the ion generator 110A and the dielectric paper 115. When however, switch 116 is switched to position Y, the potential of the voltage source 11hß will be applied to electrode 112-2. In this way, an electric field is created between the ion reservoir 111-Ä and the backing of the dielectric paper 115. The ions extracted from the air gap degradation region then charge the dielectric layer surface. 7811082-2 then: A number of different materials can be used to serve as the dielectric layer III. Possible such materials include alumina, glass enamel types, ceramic materials, plastic films and mica. Alumina, glass enamel types and ceramic materials present difficulties in producing a sufficiently thin layer (approx. 25 .mu.m) so that the requirements for the voltage source serving as a drive source do not become too great. Plastic films, including polyimides such as Kapton (registered trademark) and nylon, show a tendency to change as a result of being exposed to chemical by-products in the air gap decomposition process in the 112-h opening (especially ozone and sales c). ~ acid). Mica does not have these disadvantages, and it therefore constitutes the material preferred for the dielectric III. It is best to use potassium mica, H2 Enl; (SiO¿) 3.

The generator and ion extractor 110 shown in Fig. 10 can be used to advantage in producing signs of dielectric paper by electrographic rapid printing. Exemplary starting points for electrographic printing of characters in accordance with the invention are given in Figures 11 and 12.

According to Fig. 11, a character generator 120 is formed by a dielectric member 121 which is sandwiched inserted between an etched current-carrying disk 122-1 and a group of counter electrodes 122-2, 122-3 and 122-4.

The etched electrode or mask electrode 122-1 is, as an example, provided with etched characters A, B and C. The edge fields at the edge of the etched characters constitute an ion source of high density when air gap decomposition in accordance with the invention is obtained by applying an alternating voltage. between the etched electrode 122-1 and the counter electrodes. Thus, when it is desired to generate ions to print a selected character, such as the letter B, a high frequency AC voltage source (not shown) is applied between the etched electrode 122-1 and the cooperating counter electrode 122-3. Thereby, ions are obtained in a quantity with high density in the area around the dielectric 121 at the edges of the etched character B in the mask 122-1. The ions are then extracted or extracted and transferred to a suitable dielectric surface, e.g. the dielectric coated paper 115 of Fig. 10, by applying a DC voltage between the back of the paper and the mask 122-1, thereby obtaining a latent electrographic image B on the dielectric surface of the paper 115.

In order for the invention to be applicable in the production of dot matrix characters on dielectric paper, one must use the matrix generator 130 according to rig. 12. This generator 130 operates on a dielectric sheet or a dielectric disk 131 having a group of perforated air gap decomposition and electrodes 132-1 through. 132-4 on one side and a group of voter rods 133-1 t.o.m. 133-H on the other hand, and an individual selector 133 is assigned to each individual opening 135 in each individual finger electrode 132.

When an alternating voltage is applied between an arbitrary selector rod 133 and earth, ions will be generated in openings at the junctions between the selector rod in question and the finger electrodes.

Ions can not be removed from an aperture except when both its selector rod is activated with a large alternating voltage and its finger electrode is activated with a direct voltage applied between the finger electrode and the counter electrode of the dielectric surface to be charged. For example, the matrix position 13523 is pressed by simultaneously applying a high frequency voltage between the selector rod 133-3 and Earth and a direct voltage between the finger electrode 132-2 and the counter electrode of a dielectric receptor means.

Fingers that are not selected and the counter-electrode of the dielectric member are kept at Earth potential.

By multiplexing a point matrix array in this way, the number of required voltage drivers will be greatly reduced. If one e.g. would like to provide a dot matrix array with pressure on an area with a width of 20.3 cm with a dot matrix resolution of about 79 dots per cm, 1600 individual drive units would be required if multiplexing were not used. By using the grouping according to Fig. 12, it can be achieved that only 80 finger electrodes are needed for 20 alternating frequency driven fingers, whereby the total number of drive units is reduced from 1600 to 100.

In order to prevent air gap degradation from the electrodes 132 to the dielectric member 131 in portions not associated with the openings 135, it is desirable to coat the edges of the electrodes 132 with an insulating material. Unnecessary air gap degradation around the electrodes 132 can be eliminated by 7811082-2 DH that these electrodes are specially treated.

When manufacturing and operating a matrix generator of this type, it is desirable that the ion currents generated at different matrix crossing points should be kept at a substantially uniform level. Tjooklex variations in the dielectric layer 151, on the other hand, result in corresponding variations in the ion output current, whereby a lower ion current is obtained at an opening 155 where the dielectric 131 is thicker. It is a particularly advantageous property of mica that this material has a natural tendency to split along planes of extremely uniform thickness, whereby it becomes particularly well suited for use with the matrix generator illustrated in Fig. 12. In this respect, the fact that the thickness of the layer 151 is constant is of much greater weight than the actual value of said thickness.

The invention can be applied to form a rectangular charging region by means of the geometric design of the module 140 shown in Fig. 15. The charging electrodes 142-1 and 142-2 are separated from the electrode 1 by a dielectric member 141. the electrode 142-5 being embedded in an insulator 145. In the portion between the electrode 142-1 and the electrode 142-2 there is a slot or groove where an air gap discharge is obtained when a high frequency AC voltage is applied between the electrodes 142-1 and 1H2-2. and the electrode 142-5.

The charging array shown in Fig. 15 can be utilized in a plain paper copier to replace the corona members normally found in such a copier.

Fig. 14 illustrates sohematically a copier for plain paper using charging arrays of the type shown in Fig. 15. A copier drum 151 is charged by means of a charging element 152-1 with the design shown in Fig. 1. If the drum consists of selenium or a selenium alloy and you e.g. wishing to charge the surface to a positive potential of 600 volts, the slit electrode 142-1 is kept at 600 volts. After charging, the drum 151 is discharged with an optical image provided by a scanner at the station 155. The resulting latent electrostatic image is toned at the station 156, and the tone is transferred to a sheet 158 consisting of plain paper by means of a transfer ion generator 152-8 according to 7811082-. Fig. 13, wherein the slit electrode is again held at a positive potential. The latent electrostatic residual image in the surface of the drum and any uncharged toner can be electrically discharged by using a discharge unit 152-3, which is also in accordance with Fig. 13. In this case, the slotted electrode is kept at ground potential, whereby a any residual charge on the surface of the drum and toner means that ions are removed from the air gap decomposition in the slot, whereby the surface is thus effectively discharged. A 15k cleaning brush is used to remove residual tones that remain on the surface, after which the drum is ready to be recharged.

Fig. 14 also shows a dot matrix charge head 155 which may be formed in accordance with Fig. 12. In this way, a plain paper copier may be used as a printing device. In that case, the drum 151 is discharged at the station 153, after which it is recharged by the dot matrix printhead 155 so that the machine 150 can serve both as a copier and a printing machine. In addition, the device 150 can operate simultaneously as a copier and a printing device in such cases where overlay is desired. An ion generator and extractor according to Fig. 10 can thus be used as imaging and residual charge means in the printing device according to section III, as well as pre-charging and discharging means in the electrophotographic device 1 section I.

Pig. 15 illustrates an alternative ion generator 160 for use in charging or discharging an insulating surface. In Fig. 15, the slit electrode 1ß2-1, 1H2-2 in Fig. 13 has been replaced by a screen 162-2 or a net with open meshes with longitudinal elements 162-a and transverse members 162-b. The discharge electrodes 162-1 and 162-2 are separated by the dielectric sheet or the dielectric disk 161, and the air gap breaking potential is provided by the AC voltage 163.

Pig. 16 illustrates an apparatus 170 which enables a multiplexed dot matrix charging head 171 of the type shown in Fig. 12 to be used in a high speed dot matrix printing system on plain paper. The charging head 171 charges an aerosol 175, which consists of a dye dissolved in a suitable solvent carried by a low velocity air stream introduced through a slot 176. The aerosol particles are charged by the ion generation system and enter an electric field area established by means of a direct voltage applied between the electrodes 173 and 11a. The resulting field directs the charged aerosol particles toward a sheet of plain paper 172, which sheet moves through the device at approximately the same speed as the speed of the aerosol.

Pig. 17 illustrates mechanical line scan printing in accordance with the invention. A slit electrode 186 is used in conjunction with a dielectric film 185 and a rapidly moving spherical bead 187 to form a movable air gap degradation region. The bead 187 mounted on the wire 188 is driven by pulleys from a rapidly rotating motor (not shown). An AC voltage source 185 for high frequency AC voltage supplies the potential required to break down the air gap in the electrode 186 slot. In this case, a dielectric paper 181 is charged by a charging potential supplied by an amplifier loop, the output of which is connected between the conductive carrier 182 of the dielectric paper and the slotted electrode 186. The line scanning is effected by the mechanical movement of the bead 187. , and selected portions are pressurized by applying a potential between the conductive sheet and the slotted electrode. As in the cases described above, the formed latent electrostatic image can be toned and melted or applied using any conventional methods. Images with continuous tones can be produced in this way, since the number of ions taken out of the charge depends on the extraction potential supplied from the amplifier 18%.

Fig. 18 shows how to use an ion generating system according to the invention as an electrostatic precipitator 190. A tubular electrode 192 is separated from a 19% segmented electrode by a dielectric 191.

An air gap breakdown is obtained in the open portions of the segmented electrode 194 by applying a large alternating voltage by a generator 196. The segmented electrode 194 also receives a bias voltage from a DC voltage source 198. A central ground wire 199 is mounted at the center of the tube 192. Shaft gases ...__.-.- 7811082-2 9.? or other aerosols can be cleaned by electrostatic dust removal as they are passed along the tube. The high density of the ion current from the air gap degradation portions charges solid particles in the aerosol and causes them to be attracted to the central electrode 199.

As a rule, the relationship between the electrode voltage and the voltage of the ion-receiving surface shown in Fig. 19 prevails, e.g. paper, in the case of charging systems of the type shown in Figs. 10, 11, 12 and 13. The electrode voltage is the DC voltage applied between the half-supplied electrode and the counter-electrode of the dielectric surface that is being charged.

The paper voltage is the latent electrostatic image potential of the charged dielectric means resp. the dielectric (electrographic) paper in the example.

The above examples of use of the ion generation system according to the invention show that this system is applicable in a wide range. As a rule, the corona wires or points in any existing system can be replaced by the device according to the invention. In addition to the applications shown, the method and device according to the invention can be used in many other applications not shown, such as in the case of electrostatic separation resp. electrostatic application of coatings.

Examples The above description has illustrated the general principles and features of the subject matter of the invention. Supplementation shall be made below with particular applications of the invention, it being emphasized, however, that these applications are merely exemplary and do not limit the invention.

Example IV - 1 A stainless steel foil with a thickness of 25, H / um is laminated on both sides of potassium mica with a thickness of 25, h / um.

The stainless steel foil is coated and photoetched with a pattern similar to the pattern shown in Fig. 12, with holes or openings in the fingers having a diameter of approximately 0.15 mm. In this way a charging head is obtained which can be used to generate latent electrostatic dot matrix character images on dielectric paper according to Fig. 10. Charging occurs only when a potential of -H00 volts simultaneously 7811082-2 9.8 lies on the fingers containing the holes and a alternating voltage of 2 kV from peak to peak and the frequency 500 kHz is applied between the finger and the counter electrode. The distance of 0.2 mm is maintained between the print head device and the dielectric surface of the electrographic sheet. The pressure pulse lasts for less than 20 microseconds. It turns out under these conditions that a latent electrostatic image of about 300 volts is generated on the dielectric sheet. This image is later toned and fused to form a dense dot matrix image. The ion current collected by an electrode at a distance of 0.20 mm from the charging head which is taken out from said charging head turns out to be 1 mn / omg. The useful life of the charging head is approximately 2000 hours.

Example Gel IV - 2 Examples IV - 1 are repeated using a polydimelectric instead of potassium mica. As before, a stainless steel foil with a thickness of 25 .mu.m is laminated to a polyimide film by Kapten with a thickness of 25.4 .mu.m. Results that are equivalent to the results according to examples IV - 1 are obtained when a high frequency potential with a peak value of 1.5 kV is applied. The charging head provides a useful life of about 50 hours.

Example IV - 2 An electrostatic charging head of the type shown in Fig. 11 is produced by means of a 25.4 μm thick stainless steel foil laminated on both sides of a 25.4 μm thick polyimide sheet. In order for full-shape characters to be printed on a dielectric surface, 2.54 mm high characters are etched into the foil on one side of the sheet, while fingers covering each character are etched into the other side of the foil, as shown in Fig. 11. In order to establish conductivity in the normally isolated portions of the characters, bridges with a thickness of between 25.4 μm and 50.8 μm are left unetched. The character stroke is etched to the value l52, Ä / um. Printing takes place by applying the potentials according to Example IV - 2 with the pulse width HO microseconds.

Deitonated images have sharp edges and high optical density. The character range in the image is 0.3 mm.

Example IV - 4 The invention is applied to produce continuously toned images by extracting from the charging head a number of ions per unit time in proportion to the applied ion extraction voltage. This is illustrated in Fig. 19 where the apparent surface voltage on a 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 is 0.15 mm, and the charging time is 50 microseconds.

B. Three-Electrode Embodiments The matrix image generator 130 shown in Fig. 12 may advantageously be included in electrostatic printing apparatus of the type described in Section III. However, as mentioned in connection with Fig. 14, a ion generator and extractor 110 of the type shown in Fig. 10 can be used both to create an electrostatic image on a dielectric surface and to remove such an image. Thus, if, still referring to Fig. 10, the switch 116 is set to the position Y, the electrode 112-2 will be held at a positive potential V, a positive latent electrostatic image having a smaller size than V being formed on the surface 115-d. However, if the switch 116 is in the X position and a previously formed latent electrostatic image is located below the aperture 112-h, the generator 110A will act as an erasing unit. This phenomenon is further illustrated in connection with the dot matrix printing embodiment according to rig. 12 at 200 in Fig. 20. At a time t1, a given aperture 13523 in the matrix generator 130 (rig. 12) is activated by a direct current pulse which generates a negative potential on a finger electrode 152-2, while a high frequency potential is applied to the selector rod 155. -3.

This results in an electrostatic, point-based image which is negative in its polarity and which occupies the portions 203 and 204 on the surface 201 of the dielectric with the support electrode 202.

At a later time, the opening 13523 is located over the portions 204 and 205, the selector rod 153-3 still being activated. However, since charging is not desired, no negative pulse will be applied to the finger electrode 132-2. However, the presence of a negative electrostatic image in the 20% portion causes positive ions to be attracted from the aperture 13523, thereby erasing the image previously created in this area.

It has been found that by adding a third electrode to the above-described device with two electrodes, this problem can be reduced, and further advantages are obtained in controlling the size and shape of an electrostatic image which is produced by means of an ion generator of this type. An ion generator 210 designed in this manner with three electrodes is shown in the cross-sectional view of Fig. 21. The ion generator 210 includes a "drive" electrode 211 and a "control electrode 215" which are separated by a nassive dielectric layer 213. A source 212 for alternating voltage has the task of causing air gap degradation in the opening 214. A third electrode or shield electrode 219 is separated from the control electrode by a second dielectric layer 217. The nomenclature used for these three electrodes is to some extent analogous to the electron tube terminology, at least The terms "drive" and "control" electrode can be validly extended to include the corresponding electrodes in the basic two-electrode embodiments. can be significantly larger than the aperture 214 in the gate electrode, which is necessary to prevent wall charging effects. the core electrode 219 contains an opening 218 which is at least partially located below the opening 214. In e.g. an electrographic matrix calculation device, the drive and control electrodes may be the selector rod and finger electrodes of Fig. 12, and the shield electrodes may be either additional finger electrodes with apertures adapted to the pattern of the control electrodes or a continuous, slightly apertured metal plate. bodies, the openings of which are adjacent to all the printing openings. The last embodiment of the shield electrodes can e.g. take the form of a screen or a net with open stitches.

The ion generator described above can be used in electronic matrix printing in the manner shown in Fig. 22.

Fig. 22 shows the ion generator 210 illustrated in Fig. 21 used in conjunction with dielectric paper 220 comprising a current conducting base coated with a dielectric layer 221 and having a grounded auxiliary electrode 225 as a backstory or support. When the switch 220 is in the Y position, an alternating voltage will occur across the dielectric layer 213, a negative voltage VC on the gate electrode 215 and a negative voltage on the shield electrode 219. The negative ions in the opening 214 are exposed. for an accelerating field which causes them to form a latent electrostatic image on the dielectric surface 221, as in the two-electrode embodiment. The nürvaron of negative voltage VS on the shield electrode 219, which voltage is so selected that Vä has an absolute value less than VC, does not prevent the image from being produced, which has a negative voltage VI (whose absolute value is less than VC).

When the switch is in position X and a previously produced electrostatic image with negative voltage VI is located partially below the aperture 21k, the image would be partially erased if the shield electrode 219 were not present. However, the shield voltage VS is so selected that Vš has a larger absolute value than VI, so the presence of the electrode 219 prevents positive ions from passing from the aperture 21H to the dielectric surface 221. Compare, for example, V - 5, by supplying the shield electrode 219 to the ion generator according to the invention, other advantages are achieved in addition to preventing image discharge under the conditions described above. The shield electrode can be used alone or in conjunction with the control electrode to control the production of matrix images. When VS = 0, no latent image is obtained due to the above-mentioned discharge phenomenon. It thus becomes possible to perform three-level matrix image control in an electrographic matrix printer in accordance with the invention.

The shield electrode 219 provides unexpected control of the image size. Using the dot matrix printing configuration shown in Fig. 12 in conjunction with overlying finger screen electrodes in accordance with the invention, the image size can be controlled by varying the size of the screen apertures 218. Compare Examples V-6 below. Furthermore, when such a configuration is utilized, all variables being constant except the screen potential 226, it has been found that a larger screen potential gives rise to a smaller point diameter. Compare Example V - 7.

This method can be used when it comes to producing fine or strong images. It has also been found that appropriate choices of VS and VC mean that an increase can be made in the distance between the ion generator 210 and the dielectric surface 221 while maintaining a constant diameter of the dot image. This is achieved by increasing the absolute value of Vs and at the same time pouring the voltage difference between VS and VC constant. Compare examples v - 8. I.

The image shape can be regulated by using a given screen electrode overlay in an electrographic matrix printing device. Compare examples V - 9. The screen openings 218 can e.g. be formed as completely shaped characters not larger than the corresponding round or square control openings 214.

The electronic configuration used to control the electrographic printing device of Fig. 22 can be modified to allow biasing of the system, as shown in the wiring diagram of Fig. 23.

Element 231 is a pulse generator. The magnitude of the control pulse can be varied so that the desired values of VC and Vs are obtained by selecting a suitable bias potential. For example, all the following combinations give Vs = -700 volts resp.

V = -800 volts: c l. Vförslh = -6oo. volt; Avs = -loo volt; A vc = -eoo volt _ _. _ _. _ _ '* / ~ 2. vförslm - 500 volt, Avs _ zoo volt, AVC ~ poo volt 3. Vförsp_ = -400 volt; [§'VS = -500 volts; ¿§'VC = -400 volts Il. v .. = -300 volts; Off = -Iloo volts- Off = -5oo volts exp. S '' C 5. vförsß = -eoo volt; Avs = -5oo volts; Ave = -öoo volt.

The above advantages will be further illustrated by reference to the following non-limiting examples.

Example IV - § A stainless steel foil with a thickness of 25.4 .mu.m is laminated on both sides of a sheet or a sheet of potassium mica with a thickness of 25.4 .mu.m. This foil is coated with resist and photo-etched with a pattern similar to the pattern shown in Fig. 12 with holes or openings with a diameter of approximately 0.15 mm. A second mica layer with a thickness of 0.15 mm is joined to the foil according to Fig. 21. A shield electrode with openings with a diameter of 0.375 mm in the same pattern as the openings in the fingers is photoetched from stainless steel with a thickness of 25.4 mm and joined to it the second mica layer in such a way that the finger and cutting openings are concentric. This design gives rise to a charging head which is used to produce a latent electrostatic image on dielectric paper, as illustrated in Fig. 22, where VC = -500 volts, 7811082-2 33 VS = -400 volts, and one has a alternating voltage 212 with a peak value of 1 kV at the Frequency 500 kHz. The distance of 0.15 mm is maintained between the pressure head device and the dielectric surface 221.

VC takes the form of a pressure pulse with a duration of 20 microseconds. Under these conditions, a latent image is formed in the form of a dot of about -300 volts on the dielectric sheet. This image is later toned and fused to obtain a dense dot matrix character image. The ion current taken from the discharge head and collected by an electrode at a distance of 0.15 mm from the head turns out to be 0.5 mA / cm 2. However, when the shield electrode 219 is omitted, any electrostatic image that appears during the control release will be erased when no printing pulse is applied.

Example IV - 6 The electrographic printing apparatus described in Example IV - 5 was examined with a variety of diameters of the screen aperture 218, and the size of the resulting electrostatic dot image was measured. The following results are representative.

Screen aperture diameter (mm) Point image diameter (mm) 0.38 0.38 0.25 0.30 0.20 0.25 It turned out that, as a rule, a reduction in the size of the screen apertures resulted in a corresponding reduction in the size of the latent image without any compromise in image loading.

Example IV - I The electrographic printing apparatus of Example IV - 5 was examined with a plurality of screen potentials, Vs, and the size of the resulting electrostatic point was measured. The following results are representative.

Screen potential (volts) Dot image diameter (mn) -300 0.55 -uoo o, n3 -500 0.30 -600 0.20 It turned out that by increasing the voltage on the screen, the size of the latent image generally decreased without any compromise. miss 1 the image charge. 7811082-2 IW Excmuul IV - 3 the electrographic printing device illustrated in Example IV - 5 was examined using a plurality of distances between the printing head device and the dielectric surface 221. By varying the shield voltage VS and maintaining the voltage difference between VS and VC zonstant, the size of the resulting electrographic punk image could be kept constant. The following results are representative.

Distance (mm) VS (volts) VC (volts) Point image diameter (mm) 0.15 -400 -500 0.38 0.25 -500 -600 0, §8 0.55 -600 -700 0, fi8 It turned out that with increasing distance between the printhead device and the dielectric surface, an increase in the screen voltage VS resulted in a constant point image diameter without any compromise in the image charge.

Example IV - Q The electrographic printing apparatus of Example 1 was modified so that the screen was provided with apertures # 8 in the form of slots 1 instead of in the form of holes. The resulting toned latent electrostatic images had an oval shape.

V. Impregnation of anodized aluminum members As mentioned above, it is preferred to use a dielectric material for the surface 27 of the image roller 25 (in the electrophotographic device of Fig. 1) and for the surface 75 of the image roller 73 (1 the electrostatic printing device of Figs. 6), whereby certain criteria are met.

These criteria include high resistivity, high resistance to abrasion, smooth surface and large modulus of elasticity. The suitable material consists of anodized alumina which is impregnated by the method described below.

Absorbed water can be removed from the oxide layer of an oxidized aluminum member by using either heat, vacuum or storage of the object in a dewaterer. Although all three of these methods are effective, the best results are obtained by heating in vacuo, e.g. in a vacuum oven. Alternatively, the object to be treated can be stored for several hours in a dry box containing a dewaterer. He hereby prefers that any heat treatment of the oxide before the impregnation should be carried out at temperatures below 15000 and preferably not above 10 ° C. At higher temperatures, a certain cracking can occur in the oxide layer due to the greater coefficient of thermal expansion that the aluminum substrate has.

Once absorbed water has been removed from the oxide coating, it can be impregnated with any organic resin.

However, he prefers to work with a completely solid system, as the use of soluble coatings leaves residual solvent in the pores. Therefore, liquid resins which can be crosslinked to form hard, solid coatings are particularly favorable materials. Resins of this kind can be cured either by thermal crosslinking or by radiation crosslinking.

It is also desirable that the resins have low shrinkage true low moisture absorption after curing. In order for the organic resin to have the opportunity to diffuse into the porous organ within a reasonable time, it is advantageous to use liquid crosslinking systems with a viscosity of less than 500 cP.

The methods described above can be used when it comes to treating a solid aluminum cylinder with an impregnated oxide coating for use in the production of electrostatic images. In this case, an electrostatic charge is applied to the insulating surface of the cylinder. This image is then tinted in the manner described in U.S. Patent No. 5,662,595, and the tinted image is transferred to plain paper. Table 2 of the said patent shows that a porous alumina surface which is sealed with Teflon is not satisfactory for electro-. static image production due to the low degradation voltage and the low porisolation resistance as well as the hardness of the coating. A drum coated with an insulating film which can be provided with an electrostatic charge is described in U.S. Pat. No. 3,907,560. The dielectric surface is a barrier layer of alumina film, since it is stated that the porous anodized alumina layer serves as a current conductor and not as a dielectric. Although an oxidized aluminum film in the form of a barrier layer is a good insulator, given that it is not porous, the maximum thickness of barrier layer films is limited to the range between 7811082-2 Sh 0.5 and 1 μm. With this thickness, the maximum stress to which the layer can be subjected will be limited, and the surface will not become hard in the conventional sense, since arbitrary stresses in some positions will be transmitted through the thin film with subsequent deformation of the aluminum substrate.

The limitations of the thin barrier film are overcome according to U.S. Pat. Nos. 3,937,571 and 3,940,270 by the use of a duplex type anodized aluminum coating. This coating is prepared by electrolytically oxidizing an aluminum surface and then continuing the electrolytic oxidation under such conditions that an alumina barrier layer is formed. This not only means that the production of the anodised layer becomes more complicated, but the result is also that the limiting thickness amounts to about 20 μm, and the surface potential to which the oxide layer can be charged amounts to a maximum of 620 volts.

In contrast to the prior art, the present invention provides a simple and reliable method for producing oxide films with thicknesses as high as 100 .mu.m and capable of carrying several thousand volts. The advantages of the invention will become apparent from the following non-limiting examples.

Example of the Prior Art A cylinder made of aluminum alloy 7075-T6 anodized with a hard sulfuric acid coating in accordance with the teachings of Wernick and Pynner. The final thickness of the anodized layer was 60 .mu.m. The anodized cylinder was sprayed with an ultraviolet light curable resin in accordance with the composition 1 according to Table VI - 2 below. This low viscosity liquid appears to impregnate the pores within a period of 1 minute.

After several minutes had elapsed, the surface of the cylinder was dried clean of excess liquid, after which the impregnated cylinder was cured by being exposed to radiation from a medium-pressure mercury vapor lamp. After curing by this irradiation, the cylinder was polished with a sandpaper of the type designation 600 to a surface finish of 25.4-10 "6, removing between about 3 and 4 μm of oxide. A test device was used to generate an electrostatic charge on aluminum oxide. -2 3? - surface of the layer A corona source for ions was charged to the surface, and the surface potential was measured using a feedback electrometer.

At the highest charge levels used, there was a voltage of only a few volts on the surface. This voltage decreased to zero within about 1 second. The dielectric strength of said layer was determined by applying an electrical contact with a radius of curvature of 1.25 cm to the alumina surface and subjecting it to a slight pressure, and the applied voltage between this electrode and the aluminum substrate was increased until large currents were passed through the layer. Using both direct current and alternating current and by determining the degradation potential in a number of places, it was determined that the degradation voltage was in the range 900-1200 volts.

Thus, it turns out that both the charge levels and the dielectric pour strength achieved by this example of the prior art were unsatisfactory.

The following examples illustrate the advantages of the present invention over the prior art in tabular form. 38 7811082-2 w fi AMZ al owdcoxox vase Æs fi Coon al ßmß hwnwu Hm fi ßzwaomuä mpwpx fi xw OZM fi hvxw f m f üwx HH H fl mnæu mm m: w5E55xm> fi Mßëä f p w Q o f roow al oommlošm m .måna uooo al 33 wššbmammø's etc. __ 3 SM: E: sxß> fi fi MSA al p m. oomïoo fl ooomàšw fi ___ .Snus oooo fl 53. æc fi gppwnmmn asèuw ._ 3 cws§Sßxæ> fi sma fifi u æ oom fi lømm oommfoøøm n _83: oog fi 23 æ fi npßwnmmm eøšø __ a: m5es \ uo nøw. m \ amëe fi u m \ oomóou oooWooüä .n .Såna 0003 33 wšsunßnaan a: 5 weàš »N \ nßæs fl v m oouzoox ooom | oowH H Hmuc fi oooma aa fl v wc fi cpvm fl ßmb E5 \ mfi w2 m œ mm 00 H mn 0000. e: om Hmnaéwow m \ mww fl xkoamws fl c oowuoo fi oom fl xooä fi a | uvm >> d fi nßse fi u: N wm fifi> awm = _. c nmäe fl p w oo: H | oom fl ooxmnoomm ~ hmøcß oooo fi H flfi u wc fi zuumsnms = _. M amaa fl v w oomuoøw ooomaoøm fi H hm fl cß oooo fi H flfl u wc fl nnuw fi nmb = _. N malm oow fl looa H cwwcn E: \ ow wnñmwoæ H ux fi xm æmmc fi scmmm ws fi cswmm mwc fi cvpmw pmnmu fi mo lmw fl h flfifl M fl w fififl Iâ fl åmaßw MQÖHUNÅ ... m w fifi 0 w0. uøøu fl omu | v> anømß | wwsHnmcwmnmEH mc fi hmcwmnmëfi mnwm w H> H fi wßßa 7811082-2 31 _. .ooom fl ø fi> m fifi ms ux fl xm m fl gëms som um fi u fl pëøm umnxwxm wuønmø flfl o fi m www nm> m m fifl mn omm | Amo oo fi H flfi p Hawanø awpm »fi wøxm fi> - om <» wav uoom fl HHH »w« p »« n @@: nwëh fl onëßmsonhvmh fl o fl omm Awxhmâ flfl dbv o fi vmmaouo fl m .UGß u mmm UE. o> | Na wn fi n fi ou: am nox fififi m vp fl nwmwc fi cmm fl :: o> «mø ws fl nnoo som H @ u» xH> H nøHum »xH> OH N mc ws fl cvvmmcmëaßm w ns wn fifl vumw fl æëë fl m .H. \ @m = na nmëswv m \ omænooæ ooMH | QoHH w nmøc al øoom f H flfi ß mn f mwum al MMB ES wm wanmwow ma ux al xw mn al ccmmm wswccmmm wcw al ßumm nmhøw f xo Immcwn umwc fi c ønms fi mm MVM fifl WE Jam Wo Wo fi nwmw fi HQ xvuß al MMN uvhnnumz xwmGHnmcmhQEH wz al hmcmhmë fi whmw wm fifi mcmßmm microns al xoonß | E fl HG fi EAH <Hmmëmx al ZHø2HZZHmmmD wa Q al mämkm Awpäowv a | Hb flfi w fi ßæ 7811082-2 Ho wa ^ .®E.G0u fi mo..oGH .mc fi ë fi o ß Gow fi wsmv AH hovßmmaæadx oo fl ^. <2.cou: mo..oCH ~ wQ «E: o ß cøwnoëmv wcmumnsm fl mmt; Hmowooøm m 3 Anfzßsmø fi oïa fi oo Épmäh .E _35 .hemåt mëøäs ïšnàm oo fi fi. W.z.:mw fl o ~ .mnoo æmpwmn mo.> Fl n Howæmv wcævmnñm flfl omm ænom | æmm 4 m. H os ^ .oo: o fi mum Hæco fi pwzv oææmlww hovwmh fl om ußaw fi hsxd M M Hocwumoc fi ëß fi æumë fl n M cocmwwom fl øm S. »ßšää fl w fi o fl uå fi mnlm. H å .. OEM fi š fi äo m o fl awvm fl humëmomcmm ms uß fl mnxm fi w fl oxm fl w fl hv fl maomz A-Wfz .. n-OU m: wwmš fi öuv wfâs “Eg fi šns wn fi c fi m fi pwm ... fi š fifl mu H »mHwvpz fl> Hæ flfi mvß: ha Q flfi vpmwcaëëmw H Qäümd fi BOHAZH Em fl mïm fi ü H dQz%> Z4 MHmBm4mwUZMHZüHMmEH m | H> H fi mnmå 7811082-2 * H In all the examples in Table VI - 1 regarding heating of the aluminum, the irrigation was carried out: below the aluminum was still hot (HOÜC-5500). The samples treated in a vacuum oven were allowed to remain in the vacuum while they cooled to the treatment temperature.

Although no attempt was made to perform impregnation with organic resins, it is obvious that heating in a vacuum oven followed by vacuum impregnation of the anodized coating would result in the excellent electrical properties presented by the above examples where the method of the present invention has applied.

Although different aspects of the invention have been given above, it should be emphasized that the detailed description made above is for the purpose of serving only as an example and that various changes in the parts as well as the exchange of equivalent means with respect to the means described are within the scope of the invention. as defined by the appended claims.

Claims (9)

7811082-2 42 PATENT REQUIREMENTS 1. An apparatus for producing electrostatic images, characterized in that it comprises a first solid dielectric member (21), a gate electrode (215) on one side of said first solid dielectric member having an air gap. region (21R) at a connection point between the control electrode and the first solid dielectric member, a drive electrode (211) on the opposite side of the first solid dielectric member, a time-varying potential (212) being applied between said electrodes to generate an electrical discharge in said air area, a source (22%) for a first direct voltage (VC) between said control electrode (215) and a further means (220), an apertured shield electrode (219), a second solid dielectric means (217) I isolating said shield electrode (219) from the control electrode (215) and the first solid dielectric means (213), and a source (226) for a second 1IKSPä flfl inS (VS) between said shield electrode (219) and said surface further means (220), the device for producing electrostatic images forming a latent electrostatic image on said further means (220). Device according to claim 1, characterized in that said control electrode (215) has an edge surface which forms a connection with the first solid dielectric member (213) adjacent to said air area (2lä). Device according to claim 1, characterized in that said further means (220) comprise a dielectric detection means (221) with a current-conducting back piece (225). Device according to claim 1, characterized in that the control electrode (215), the shield electrode (219) and the second solid dielectric member (217) contain corresponding discharge openings or that said second dielectric layer (217) includes an opening having larger diameter than the corresponding opening (214) in the gate electrode (215). Device according to claim 1, characterized in that said second (226) direct voltage (Vs) has the same polarity as the first (22Ä) direct voltage (vb) and smaller absolute value. Device according to claim 1, characterized in that a plurality of drive and control electrodes (132, 133) form intersection points in a matrix array (130) which is designed so that the control electrodes (132, 133) contain apertures (135) at the matrix electrode junction areas and a plurality of shield electrodes adapted to the control electrodes contain nal (218) corresponding to said apertures (135). Device according to claim 1, characterized in that the shield electrode (219) comprises a half-equipped mask which may have a predetermined character pattern or that the shield electrode (219) consists of a woven metal screen with open meshes. Device according to claim 1, characterized in that; said further means (220) comprises a rotatable imaging drum with a current conducting core (77) and a dielectric surface (75) and further comprises a device (79) for toning said latent electrostatic image together with a rotatable pressing drum (83) in contact with said imaging drum for transmitting the toned image to a receiving medium (81). Device according to claim 8, characterized in that the toned image is simultaneously transferred and fused into the image receiving medium (81) during its travel between the image production drum (73) and the rotatable pressing drum (83).