EP0719648B1 - Appareil d'impression électrostatique directe comprenant une structure de tête d'impression avec un flux de courant inférieur ou égal à 50 microA entre les électrodes de commande et d'écran - Google Patents

Appareil d'impression électrostatique directe comprenant une structure de tête d'impression avec un flux de courant inférieur ou égal à 50 microA entre les électrodes de commande et d'écran Download PDF

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Publication number
EP0719648B1
EP0719648B1 EP19950203348 EP95203348A EP0719648B1 EP 0719648 B1 EP0719648 B1 EP 0719648B1 EP 19950203348 EP19950203348 EP 19950203348 EP 95203348 A EP95203348 A EP 95203348A EP 0719648 B1 EP0719648 B1 EP 0719648B1
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EP
European Patent Office
Prior art keywords
electrode
printing
insulating material
diameter
printing apertures
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Expired - Lifetime
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EP19950203348
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German (de)
English (en)
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EP0719648A1 (fr
Inventor
Jacques C/O Agfa-Gevaert N.V. Die 3800 Leonard
Guido c/o Agfa-Gevaert N.V. DIE 3800 Desie
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Agfa Gevaert NV
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Agfa Gevaert NV
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/385—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material
    • B41J2/41—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing
    • B41J2/415—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit
    • B41J2/4155—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit for direct electrostatic printing [DEP]

Definitions

  • This invention relates to an apparatus used in the process of electrostatic printing and more particularly in Direct Electrostatic Printing (DEP).
  • DEP Direct Electrostatic Printing
  • electrostatic printing is performed directly from a toner delivery means on a receiving member substrate by means of an electronically addressable printhead structure.
  • the toner or developing material is deposited directly in an imagewise way on a receiving substrate, the latter not bearing any imagewise latent electrostatic image.
  • the substrate can be an intermediate endless flexible belt (e.g. aluminium, polyimide etc.).
  • the imagewise deposited toner must be transferred onto another final substrate.
  • the toner is deposited directly on the final receiving substrate, thus offering a possibility to create directly the image on the final receiving substrate, e.g. plain paper, transparency, etc.
  • This deposition step is followed by a final fusing step.
  • the method makes the method different from classical electrography, in which a latent electrostatic image on a charge retentive surface is developed by a suitable material to make the latent image visible. Further on, either the powder image is fused directly to said charge retentive surface, which then results in a direct electrographic print, or the powder image is subsequently transferred to the final substrate and then fused to that medium. The latter process results in an indirect electrographic print.
  • the final substrate may be a transparent medium, opaque polymeric film, paper, etc.
  • DEP is also markedly different from electrophotography in which an additional step and additional member is introduced to create the latent electrostatic image. More specifically, a photoconductor is used and a charging/exposure cycle is necessary.
  • a DEP device is disclosed in e.g. US-P-3,689,935.
  • This document discloses an electrostatic line printer having a multi-layered particle modulator or printhead structure comprising :
  • Selected potentials are applied to each of the control electrodes while a fixed potential is applied to the shield electrode.
  • An overall applied propulsion field between a toner delivery means and a receiving member support projects charged toner particles through a row of apertures of the printhead structure.
  • the intensity of the particle stream is modulated according to the pattern of potentials applied to the control electrodes.
  • the modulated stream of charged particles impinges upon a receiving member substrate, interposed in the modulated particle stream.
  • the receiving member substrate is transported in a direction orthogonal to the printhead structure, to provide a line-by-line scan printing.
  • the shield electrode may face the toner delivery means and the control electrode may face the receiving member substrate.
  • a DC field is applied between the printhead structure and a single back electrode on the receiving member support. This propulsion field is responsible for the attraction of toner to the receiving member substrate that is placed between the printhead structure and the back electrode.
  • a DEP device is well suited to print half-tone images.
  • the densities variations present in a half-tone image can be obtained by modulation of the voltage applied to the individual control electrodes.
  • large printing apertures are used for obtaining a high degree of density resolution (i.e. for producing an image comprising a high amount of differentiated density levels).
  • Providing printing apertures in a DEP printhead structure comprising two electrodes (control electrode and shield electrode) separated by an insulating plastic material, to yield a printhead capable of producing images with high resolution and also with uniform density pattern is not an obvious process.
  • All printing apertures in the printhead structure must have exactly the predetermined diameter, the electrodes must stay in place and have a well defined and constant shape, and the walls of the printing apertures through the insulating plastic must be smooth to avoid clogging of the printing apertures.
  • each aperture must be individually addressable such as to be able to yield any density between zero and maximum density.
  • every printing aperture has to be addressable to the same extent in order to yield smooth density pattern.
  • DEP Direct Electrostatic Printing
  • said printhead structure comprises a control electrode and a shield electrode separated by an insulating (plastic) material and printing apertures made through both said electrodes and said insulating material wherein said printing apertures are not easily clogged by toner particles and are individually addressable in a stable an reproducible way.
  • a DEP device that comprises a back electrode (105), a printhead structure (106) comprising individual control electrodes (106a) in combination with printing apertures (107) and a shield electrode (106b), both electrodes separated by an insulating material and a toner delivery means (101) presenting a cloud (104) of dry toner particles in the vicinity of said printing apertures (107), characterised in that said apertures (107) are such that, when applying a potential difference of 200 V between said shield electrode and each individual control electrode, a current of at most 50 ⁇ A flows from said each individual control electrode to said shield electrode.
  • said current between said each individual control electrode to said shield electrode is at most 10 ⁇ A, most preferably at most 3 ⁇ A.
  • said insulating material is at most 100 ⁇ m thick, more preferably at most 75 ⁇ m.
  • said insulating material is a plastic material, e.g. polyimide, polyester, polycarbonate, etc.
  • Fig. 1 is a schematic illustration of a possible embodiment of a DEP device according to the present invention.
  • said insulating material is at most 100 ⁇ m, more preferably at most 75 ⁇ m thick.
  • DEP it is important that every single printing aperture is addressable in such a way that the amount of toner particles passing through said single printing aperture is a smooth function of the voltage applied between the control electrode surrounding said aperture and the shield electrode.
  • the toner density upon the receiving paper under each printing aperture has in its ideal way a Gaussian distribution which is completely identical for every individual aperture. It is moreover important, since it is necessary to be able to print with a DEP device - when several printing apertures cooperate - patches of even density, that the amount of toner particles passing through every printing aperture follows the same smooth function of the voltage applied between the control electrode surrounding said aperture and the shield electrode. When this it not so, the electronic control system of the DEP device has to become complicated since it has to accommodate for the different functions of amount of toner particles versus applied voltage, associated with different printing apertures.
  • insulated has, in this context, not to mean that, at the working potential difference (mostly between 200 and 300 V), absolutely no current should flow through the printing apertures from the control electrode (surrounding said printing aperture) to the shield electrode. It was found that in order to operate a DEP device in a stable and reproducible way during an acceptable period of time, a current of at most 50 ⁇ A flowing through the printing apertures from the control electrode (surrounding said printing aperture) to the shield electrode, when applying a potential difference of 200 V between said control and shield electrode, could be tolerated.
  • the electrodes are preferably made of metal, most preferably of copper or aluminium.
  • a current larger than 50 ⁇ A is allowed to flow through the printing apertures from the control electrode (surrounding said printing aperture) to the shield electrode, local heating of the printhead structure around the printing aperture is taking place.
  • This local heating can result in changing adhesive behaviour to the passing toner particles which can lead to further melting, carbonization and a further increase in current flow which again can even cause melting of the metal electrodes, the molten metal then can flow trough the printing aperture, making contact between control and shield electrode.
  • This filamentary contact even more current can flow through the aperture and more heating takes place, that can - in the extreme - result in burning of the insulating material between both electrode and in total unemployability of the printing aperture.
  • printhead structures with small (diameter smaller than 200 ⁇ m, preferably smaller than 100 ⁇ m) printing apertures can be made with various fabrication methods known in the art, as long as the resulting printing aperture is such that, when applying a potential difference of 200 V between said control and shield electrode, a current of at most 50 ⁇ A flows through said printing aperture.
  • Plasma etching is normally carried out by means of a gas or a gas mixture, which is transformed into plasma by high-frequency energy.
  • a gas or a gas mixture which is transformed into plasma by high-frequency energy.
  • the reactive particles of the plasma can be ions or free radicals which do react very efficiently with organic substrate materials such as e.g. polyimide and acrylic adhesives, which will completely dissolve.
  • organic substrate materials such as e.g. polyimide and acrylic adhesives
  • a preferred method for making a printhead structure (106) comprising individual control electrodes (106a) in combination with printing apertures (107) and a shield electrode (106b), both electrodes separated by an insulating material is characterised by the steps of :
  • the method for producing printhead structures according to the present invention comprises the steps of
  • the method for making a printhead structure according to the present invention comprises the step of laser burning it is preferred that a hole having a diameter of at most 60 % of said whole diameter of said printing apertures is made by laser burning.
  • a hole having a diameter of at most 60 % of said whole diameter of said printing apertures is made by laser burning.
  • several holes having a diameter of at most 35 % of said whole diameter of said printing apertures are made by laser burning in the surface of said insulating material determined by said whole diameter.
  • a non limitative example of a device for implementing a DEP method using toner particles according to the present invention comprises (fig 1):
  • a DEP method using two electrodes (106a and 106b) on printhead 106 is shown, it is possible to implement a DEP method using devices with different constructions of the printhead (106). It is, e.g. possible to implement a DEP method with a device having a printhead comprising only one electrode structure as well as with a device having a printhead comprising more than two electrode structures.
  • the printing apertures in these printhead structures can have a constant diameter, or can have a broader entrance or exit diameter.
  • the back electrode (105) of this DEP device can also be made to cooperate with the printhead structure, said back electrode being constructed from different styli or wires that are galvanically insulated and connected to a voltage source as disclosed in e.g. US-P 4,568,955 and US-P 4,733,256.
  • the back electrode, cooperating with the printhead structure can also comprise one or more flexible PCB's (Printed Circuit Board).
  • said toner delivery means 101 creates a layer of multi-component developer on a magnetic brush assembly 103, and the toner cloud 104 is directly extracted from said magnetic brush assembly 103.
  • the toner is first applied to a conveyer belt and transported on this belt in the vicinity of the printing apertures.
  • a device according to the present invention is also operative with a mono-component developer or toner, which is transported in the vicinity of the printing apertures (107), via a conveyer for charged toner.
  • a conveyer can be a moving belt or a fixed belt. The latter comprises an electrode structure generating a corresponding electrostatic travelling wave pattern for moving the toner particles.
  • the magnetic brush assembly (103) preferentially used in a DEP device according to an embodiment of the present invention can be either of the type with stationary core and rotating sleeve or of the type with rotating core and rotating or stationary sleeve.
  • carrier particles such as described in the EP-A 675 417, filed on April 14th 1994, and titled “a method and device for direct electrostatic printing (DEP)" can be used in a preferred embodiment of the present invention.
  • Any toner particles, black, coloured or colourless, can be used in a DEP device comprising a printhead structure according to the present invention. It is preferred to use toner particles as disclosed in EP-A-0715218 in combination with a printhead structure according to the present invention.
  • a DEP device making use of the above mentioned marking toner particles can be addressed in a way that enables it to give black and white. It can thus be operated in a "binary way", useful for black and white text and graphics and useful for classical bilevel halftoning to render continuous tone images.
  • a DEP device is especially suited for rendering an image with a plurality of grey levels.
  • Grey level printing can be controlled by either an amplitude modulation of the voltage V3 applied on the control electrode 6a or by a time modulation of V3. By changing the duty cycle of the time modulation at a specific frequency, it is possible to print accurately fine differences in grey levels. It is also possible to control the grey level printing by a combination of an amplitude modulation and a time modulation of the voltage V3, applied on the control electrode.
  • the DEP device The DEP device
  • a printhead structure (106) made from a polyimide film of 50 ⁇ m thickness, double sided coated with a 17.5 ⁇ m thick copper film.
  • the printhead structure (106) had four rows of printing apertures. The further examples differ by the way said printing apertures are made.
  • a common shield electrode (106b) was present on the front side of the printhead structure, facing the toner delivery means.
  • the printing apertures had an aperture diameter of 85 ⁇ m.
  • the width of the copper ring electrodes was 20 ⁇ m.
  • the rows of printing apertures were staggered to obtain an overall resolution of 300 dpi (dots per inch or dots per 25.4 mm).
  • the toner delivery means (101) was a stationary core/rotating sleeve type magnetic brush comprising two mixing rods and one metering roller. One rod was used to transport the developer through the unit, the other one to mix toner with developer.
  • the magnetic brush assembly (103) was constituted of the so called magnetic roller, which in this case contained inside the roller assembly a stationary magnetic core, showing nine magnetic poles of 500 Gauss magnetic field intensity and with an open position to enable used developer to fall off from the magnetic roller.
  • the magnetic roller contained also a sleeve, fitting around said stationary magnetic core, and giving to the magnetic brush assembly an overall diameter of 20 mm.
  • the sleeve was made of stainless steel roughened with a fine grain to assist in transport ( ⁇ 50 ⁇ m).
  • a scraper blade was used to force developer to leave the magnetic roller.
  • a doctoring blade was used to meter a small amount of developer onto the surface of said magnetic brush assembly.
  • the sleeve was rotating at 100 rpm, the internal elements rotating at such a speed as to conform to a good internal transport within the development unit.
  • the magnetic brush assembly (103) was connected to an AC power supply with a square wave oscillating field of 600 V at a frequency of 3.0 kHz with 0 V DC-offset.
  • a macroscopic "soft" ferrite carrier consisting of a MgZn-ferrite with average particle size 50 ⁇ m, a magnetisation at saturation of 29 emu/g was provided with a 1 ⁇ m thick acrylic coating. The material showed virtually no remanence.
  • the toner used for the experiment had the following composition : 97 parts of a co-polyester resin of fumaric acid and propoxylated bisphenol A, having an acid value of 18 and volume resistivity of 5.1 x 10 16 ohm.cm was melt-blended for 30 minutes at 110° C in a laboratory kneader with 3 parts of Cu-phthalocyanine pigment (Colour Index PB 15:3).
  • a resistivity decreasing substance - having the following structural formula : (CH 3 ) 3 N + C 16 H 33 Br - was added in a quantity of 0.5 % with respect to the binder. It was found that - by mixing with 5 % of said ammonium salt - the volume resistivity of the applied binder resin was lowered to 5x10 14 ⁇ .cm. This proves a high resistivity decreasing capacity (reduction factor : 100).
  • the solidified mass was pulverized and milled using an ALPINE Fliessbettarnastrahlmühle type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (tradename).
  • the resulting particle size distribution of the separated toner measured by Coulter Counter model Multisizer (tradename), was found to be 6.3 ⁇ m average by number and 8.2 ⁇ m average by volume.
  • the toner particles were mixed with 0.5 % of hydrophobic colloidal silica particles (BET-value 130 m 2 /g).
  • An electrostatographic developer was prepared by mixing said mixture of toner particles and colloidal silica in a 4 % ratio (w/w) with carrier particles.
  • the tribo-electric charging of the toner-carrier mixture was performed by mixing said mixture in a standard tumbling set-up for 10 min.
  • the distance between the back electrode (105) and the back side of the printhead structure (106) i.e. control electrodes 106a
  • the back electrode (105) was connected to a high voltage power supply of +400 V.
  • To the sleeve of the magnetic brush an AC voltage of 600 V at 3.0 kHz was applied, without DC offset.
  • the etched pattern was used in a process of plasma etching for removing the polyimide at these locations where an aperture has to be created.
  • the rest of the structure is covered with a thin protective mask, that is removed after the etching is completed.
  • the holes were drilled in 10 minutes in an atmosphere of 80 % freon and 20 % oxygen.
  • the pressure of the freon/oxygen atmosphere was 133 Pa (1 Torr).
  • the etching proceeded at an RF-frequency of 13.5 MHz. This gave printhead 1 (PH1).
  • Printheads 2 to 5 (PH2 to PH5), were produced by the combination of laser burning and plasma etching.
  • the laser burning proceeded by an IMPACT (trademark) Laser System (available through LUMONICS Ltd, European Sales Division, Brussels).
  • the apparatus was operated in the contact mask scanning ablation mode.
  • the contact mask was made in the conventional (chemical etching) way from a 25 ⁇ m thick polyimide coated with a 17.5 ⁇ m thick Cu-layer. By the contact mask scanning method a positioning accuracy of a few ⁇ m was attained.
  • the diameter of the resulting holes was widened to the desired value (in this case 85 ⁇ m) by plasma etching as described for the production of printhead 1 (PH1), only the etching times were adapted to the amount of material that had to be removed.

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  • Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)

Claims (11)

  1. Dispositif DEP qui comprend une contre-électrode (105), une structure de tête d'impression (106) comprenant des électrodes de commande individuelles (106a) en combinaison avec des orifices d'impression (107) et une électrode de protection (106b), les deux électrodes étant séparées par une matière isolante, et un moyen de distribution de toner (101) présentant un nuage (104) de particules de toner sec à proximité desdits orifices d'impression (107),
    caractérisé en ce que
    lesdits orifices (107) sont tels que, lorsqu'on applique une différence de potentiel de 200 V entre ladite électrode de protection et chaque électrode de commande individuelle, un courant maximal de 50 µA circule depuis chacune desdites électrodes de commande individuelles jusqu'à ladite électrode de protection.
  2. Dispositif selon la revendication 1, dans lequel un courant maximal de 10 µA circule depuis chacune desdites électrodes de commande individuelles jusqu'à ladite électrode de protection.
  3. Dispositif selon la revendication 1, dans lequel un courant maximal de 3 µA circule depuis chacune desdites électrodes de commande individuelles jusqu'à ladite électrode de protection.
  4. Dispositif selon l'une quelconque des revendications 1 à 3, dans lequel l'épaisseur de ladite matière isolante séparant ladite électrode de protection et lesdites électrodes de commande est inférieure à 100 µm.
  5. Dispositif selon l'une quelconque des revendications 1 à 4, dans lequel le diamètre desdits orifices d'impression (107) est inférieur à 200 µm.
  6. Dispositif selon l'une quelconque des revendications 1 à 4, dans lequel le diamètre desdits orifices d'impression (107) est inférieur à 100 µm.
  7. Dispositif selon l'une quelconque des revendications 1 à 6, dans lequel ladite matière isolante est une matière plastique.
  8. Procédé pour fabriquer une structure de tête d'impression (106) comprenant des électrodes de commande individuelles (106a) en combinaison avec des orifices d'impression (107) et une électrode de protection (106b), les deux électrodes étant séparées par une matière isolante, caractérisé par les étapes consistant à:
    (i) attaquer la matière d'électrode par voie chimique sur le diamètre total des orifices d'impression pour mettre la matière isolante à nu, et
    (ii) soumettre la matière isolante à une attaque au plasma.
  9. Procédé selon la revendication 8, comprenant les étapes consistant à:
    (i) attaquer par voie chimique la matière d'électrode sur le diamètre total des orifices d'impression pour mettre à nu la matière isolante,
    (ii) brûler au laser une partie dudit diamètre desdits orifices d'impression à travers ladite matière isolante, et
    (iii) attaquer au plasma la matière isolante restante jusqu'à ce que l'on atteigne le diamètre total desdits orifices d'impression.
  10. Procédé selon la revendication 9, dans lequel on pratique un trou dont le diamètre maximal représente 60% dudit diamètre total desdits orifices d'impression, par brûlage au laser.
  11. Procédé selon la revendication 9, dans lequel on pratique plusieurs trous dont le diamètre maximal représente 35% dudit diamètre total desdits orifices d'impression, par brûlage au laser, dans la surface de ladite matière isolante déterminée par ledit diamètre total.
EP19950203348 1994-12-27 1995-12-05 Appareil d'impression électrostatique directe comprenant une structure de tête d'impression avec un flux de courant inférieur ou égal à 50 microA entre les électrodes de commande et d'écran Expired - Lifetime EP0719648B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP19950203348 EP0719648B1 (fr) 1994-12-27 1995-12-05 Appareil d'impression électrostatique directe comprenant une structure de tête d'impression avec un flux de courant inférieur ou égal à 50 microA entre les électrodes de commande et d'écran

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
EP94203764 1994-12-27
EP94203764 1994-12-27
EP95200095 1995-01-16
EP95200095 1995-01-16
EP19950203348 EP0719648B1 (fr) 1994-12-27 1995-12-05 Appareil d'impression électrostatique directe comprenant une structure de tête d'impression avec un flux de courant inférieur ou égal à 50 microA entre les électrodes de commande et d'écran

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EP0719648A1 EP0719648A1 (fr) 1996-07-03
EP0719648B1 true EP0719648B1 (fr) 1998-08-12

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Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0795802A1 (fr) * 1996-03-15 1997-09-17 Agfa-Gevaert N.V. Structure d'une tête d'impression fabriquée par revêtement autocatalytique sur un substrat plastique
JP3652493B2 (ja) 1998-02-20 2005-05-25 シャープ株式会社 画像形成装置

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3689935A (en) 1969-10-06 1972-09-05 Electroprint Inc Electrostatic line printer
JPS60135266A (ja) * 1983-12-23 1985-07-18 Nippon Telegr & Teleph Corp <Ntt> イオン流補正方法
US5138348A (en) * 1988-12-23 1992-08-11 Kabushiki Kaisha Toshiba Apparatus for generating ions using low signal voltage and apparatus for ion recording using low signal voltage
US5256246A (en) * 1990-03-05 1993-10-26 Brother Kogyo Kabushiki Kaisha Method for manufacturing aperture electrode for controlling toner supply operation
US5278588A (en) * 1991-05-17 1994-01-11 Delphax Systems Electrographic printing device
US5327169A (en) * 1992-08-05 1994-07-05 Xerox Corporation Masked magnetic brush direct writing for high speed and color printing

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