EP0836124A1 - Verfahren für direktes elektrostatisches Drucken mit Extraktion von Ionerteilchen aus einem Zweikomponentenentwickler mit einem leitendem Träger - Google Patents

Verfahren für direktes elektrostatisches Drucken mit Extraktion von Ionerteilchen aus einem Zweikomponentenentwickler mit einem leitendem Träger Download PDF

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Publication number
EP0836124A1
EP0836124A1 EP97202621A EP97202621A EP0836124A1 EP 0836124 A1 EP0836124 A1 EP 0836124A1 EP 97202621 A EP97202621 A EP 97202621A EP 97202621 A EP97202621 A EP 97202621A EP 0836124 A1 EP0836124 A1 EP 0836124A1
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EP
European Patent Office
Prior art keywords
toner particles
particles
toner
carrier particles
printing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97202621A
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English (en)
French (fr)
Inventor
Guido Desie
Raf Voets
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Agfa Gevaert NV
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Agfa Gevaert NV
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Publication date
Application filed by Agfa Gevaert NV filed Critical Agfa Gevaert NV
Priority to EP97202621A priority Critical patent/EP0836124A1/de
Publication of EP0836124A1 publication Critical patent/EP0836124A1/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/22—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20
    • G03G15/34—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the powder image is formed directly on the recording material, e.g. by using a liquid toner
    • G03G15/344—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the powder image is formed directly on the recording material, e.g. by using a liquid toner by selectively transferring the powder to the recording medium, e.g. by using a LED array
    • G03G15/346—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 in which the powder image is formed directly on the recording material, e.g. by using a liquid toner by selectively transferring the powder to the recording medium, e.g. by using a LED array by modulating the powder through holes or a slit
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G9/00—Developers
    • G03G9/08—Developers with toner particles
    • G03G9/10—Developers with toner particles characterised by carrier particles
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2217/00—Details of electrographic processes using patterns other than charge patterns
    • G03G2217/0008—Process where toner image is produced by controlling which part of the toner should move to the image- carrying member
    • G03G2217/0025—Process where toner image is produced by controlling which part of the toner should move to the image- carrying member where the toner starts moving from behind the electrode array, e.g. a mask of holes

Definitions

  • This invention relates to a developer and an apparatus for use 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 substrate by means of an electronically addressable printhead structure.
  • the toner or developing material is deposited directly in an image-wise way on a receiving substrate, the latter not bearing any image-wise latent electrostatic image.
  • the substrate is an intermediate endless flexible belt (e.g. aluminium, polyimide etc.)
  • the image-wise deposited toner must be transferred onto another final substrate. If, however, the toner is deposited directly on the final receiving substrate, a possibility is fulfilled 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-A- 3 689 935.
  • This document discloses an electrostatic line printer having a multi-layered particle modulator or printhead structure comprising :
  • Each control electrode is formed around one aperture and is isolated from each other control electrode.
  • 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 (this wording is throughout this document to indicate the means for delivering toner particles) 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.
  • the printhead structure as described in US-A- 3 689 935 suffers from the fact that high speed printing at high printing quality is limited by clogging of some apertures. By implementing a large number of rows of printing apertures, the overall printing speed can, in theory, be enhanced, but in practice it is found that said printing speed is levelled to the amount of toner that can pass through the row of apertures having the smallest flux of toner particles, and banding with a frequency corresponding to the different rows of printing apertures can be easily observed.
  • CA-A-2 135 705 a toner application device similar to a video cassette is used.
  • a flexible band carrying toner particles is moved in a direction orthogonal to the rows of printing apertures, yielding a constant distance, and propulsion field, for every row of printing apertures.
  • the main drawback of this system is the consumption of toner particles from one side of a row of printing apertures to the other side, making it not possible to print with an equal density profile over the complete width of the receiver material.
  • DEP Direct Electrostatic Printing
  • said resistivity is between 10 2 and 10 6 ⁇ .cm.
  • Fig. 1 is a schematic illustration of a possible embodiment of a DEP device according to the present invention.
  • the beneficial effect of using carrier particles with specific volume resistance as defined above can be observed with any magnetic brush, e.g., it is observed when using a magnetic brush with rotating magnetic core and stationary sleeve, a magnetic brush with rotating magnetic core and rotating sleeve, and with a magnetic brush with stationary magnetic core and rotating sleeve.
  • the beneficial effect of using carrier particles with a specific volume electrical resistance between 10 1 ⁇ .cm and 10 9 ⁇ .cm, preferably between 10 2 and 10 6 ⁇ .cm, more preferably between 10 2 and 10 4 ⁇ .cm, is quite pronounced.
  • the mechanism of operation of said invention is as follows : the voltage that is applied to the sleeve of said magnetic brush is partly conducted to the shield electrode structure of said printhead structure if carrier particles are used with a minimal conducting power (specific electrical resistance not too high). Since a fixed magnetic core/rotating sleeve magnetic brush carries developer hairs of differing length to the shield electrode of said printhead structure, the value of said voltage, comprising a DC and/or AC component, is partly extended to said "last" developer particle making contact with said printhead structure.
  • JP-A-08 58142 the use of very conductive carrier particles, e.g., metal powder, metal oxide powder, pure ferrites, etc is disclosed. It was found that the use of such highly conductive carrier particles, having a specific resistivity lower than the lowest value specified in this invention, could occasionally lead to the formation of sparks between the printhead structure and the magnetic brush. It is believed that when an hair of the magnetic brush becomes depleted of insulating toner particles, the conductivity of it is so high as to cause sparking. Therefore it is preferred that the carrier particles according to the present invention are coated with a insulating resin or are composite carriers, comprising magnetic particles in a resinous binder matrix.
  • the conductivity (or resistivity) of such carrier particles can be fine tuned to avoid sparking by adjusting the specific resistivity to a value equal to or higher than 10 1 ⁇ .cm, preferably to a value equal to or higher than 10 2 ⁇ .cm.
  • the specific resistivity can be fine tuned to the toner particles used (e.g. to the insulating resin used in the toner particles), to the desired charge of the toner particles, etc.
  • the carrier particles, described in JP-A-08 58142 exhibit high specific density (> 5 g/cm 3 and even larger than 7 g/cm 3 ).
  • the carrier particles of the present invention show a specific density lower than 5 g/cm 3 .
  • More preferably composite carriers, comprising magnetic particles in a resinous binder matrix are used, in the present invention.
  • Such carrier particles have generally a specific density lower than 5 g/cm 3 and the surface of them is essentially (for more than 80 %) made up by said resinous binder matrix or resinous coating.
  • conductive material particles
  • Said conductive material can be, e.g., carbon black, tin oxide, titanium oxide, silicon carbide, etc.
  • Carrier particles comprising conductive particles at the surface and useful in the present invention have be described in, e.g., US-A-5 346 791 and US-A-5 496 673.
  • the specific volume resistivity can be adjusted to the range according to the present invention by adjusting the thickness of the coating.
  • Organic resins useful in carrier particles according to the present invention can be of any type known in the art and are chosen in combination with the resins used in the toner particles such has to give the toner particles, that come in to tribo-electric contact with said carrier particles, the desired sign and amount of the tribo-electric charge.
  • Suitable resins, for use in carrier particles according to this invention are , e.g., polyester resins, acrylic resins, fluorinated resins, etc.
  • the specific resistivity of the carrier particles is measured as follows (measurement A) :
  • a cylindrical measuring cell made of a cylindrical plastic housing and having a bottom in conductive material (stainless steel) with surface S of 4 cm 2 is packed with carrier particles for an height of 0.4 cm (h).
  • carrier particles for an height of 0.4 cm (h).
  • a plunger made of conductive material (stainless steel) is placed on the carrier particles and loaded with 1 kg weight.
  • An electric circuit is built between the plunger and the bottom of the measuring cell being in contact with the carrier particles.
  • a DC voltage of 100 V is applied over the electric circuit and the current (I) flowing trough the circuit, measured in 10 -3 A. From this measurement the specific resistivity ( ⁇ ) is calculated. When measuring particle with rather low specific resistivity, the DC voltage, is lowered.
  • a non limitative example of a device for implementing a DEP method according to the present invention comprises (fig 1):
  • the back electrode (105) of this DEP device can also be made to co-operate 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-A-4 568 955 and US-A-4 733 256.
  • the back electrode, co-operating with the printhead structure can also comprise one or more flexible PCB's (Printed Circuit Board).
  • the magnetic brush assembly (103) 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.
  • the carrier particles having a specific volume resistance according to the present invention, can be soft magnetic particles as well as hard magnetic particles.
  • Any kind of two-component toner particles, black, coloured or colourless, can be used in a DEP device according to the present invention. It is preferred to use toner particles as disclosed in EP-A 715 218, that is incorporated by reference.
  • a DEP device making use of the above mentioned toner (marking) 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 bi-level 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 106a 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.
  • any thin film material suitable for sensing a distance-dependent electrical field can be used to correct said fluctuation in distance. Therefore the change in electrical field is measured. Since it corresponds to the change in distance, an additional controlling means can take into account this distance fluctuation and correct for it by a voltage or time modulated correction on either the control electrode potential, shield electrode segment potential or applicator segment potential. It is clear for those skilled in the art that any field effect measuring device can also be used in DEP devices that operate with other applicator means as the magnetic brush described in this invention. Other suitable examples are applicator devices with charged toner conveyors, non-magnetic mono-component application devices, magnetic mono-component application devices, polymeric hairs containing brush devices, etc...
  • the DEP device The DEP device
  • a printhead structure (106) was 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.
  • a square shaped control electrode (106a) was arranged around each aperture. Each of said control electrodes was individually addressable from a high voltage power supply.
  • 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 100 ⁇ m.
  • the total width of the square shaped copper control electrodes was 250 ⁇ m, their internal aperture width was also 100 ⁇ m.
  • the width of the aperture in the common shield electrode was 400 ⁇ m.
  • Said printhead structure was fabricated in the following way. First of all the control electrode pattern was etched by conventional copper etching techniques. Then the shield electrode pattern was etched by conventional copper etching techniques. The apertures were made by a step and repeat focused excimer laser making use of the control electrode patterns as focusing aid. After excimer burning the printhead structure was cleaned by a short isotropic plasma etching cleaning. Finally a thin coating of PLASTIK70, commercially available from Griffin Chemie, was applied over the control electrode side of said printhead structure.
  • 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 (103a), 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 (103b) 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. And on the other side 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 (mixing rods and metering rod) 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.
  • 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 ⁇ .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.
  • the solidified mass was pulverised and milled using an ALPINE Fliessbettarnastrahlmühle type 100AFG (trade name) and further classified using an ALPINE multiplex zig-zag classifier type 100MZR (trade name).
  • the resulting particle size distribution of the separated toner measured by Coulter Counter model Multisizer (trade name), 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 (wt/wt) 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 +1 500 V.
  • the carrier particles were a magnetite carrier, coated with 2 % by weight with respect to the total weight of the carrier of a silicone-resin coating, said coating comprising for 4 % by weight, with respect to the total coating, of an aminocomponent.
  • the average particle diameter was 67 ⁇ m.
  • the specific volume resistivity of said carrier particles, as measured according to measurement A, was 1.8 10 6 ⁇ .cm.
  • the specific density was 2.75 g/cm 3 .
  • Example 1 was repeated, except for the carrier particles.
  • a macroscopic "soft" ferrite carrier consisting of a MgZn-ferrite with average particle size 88 ⁇ m, coated with 1.6 % by weight, with respect to the total weight of the carrier, of a polystyreneacrylate coating, was used.
  • the specific volume resistivity of said carrier particles, as measured according to measurement A, was 8 10 5 ⁇ .cm.
  • the specific density was 2.87 g/cm 3 .
  • Example 1 was repeated, except for the carrier particles.
  • a commercial silicone coated carrier sold under number PF96-3035 by Powdertech Corp, Valparaiso, In, USA, was used.
  • the average particle diameter was 55 ⁇ m.
  • the specific volume resistivity of said carrier particles, as measured according to measurement A, was 5.5 10 9 ⁇ .cm.
  • the specific density was 2.67 g/cm 3 .
  • Example 1 was repeated, except for the carrier particles.
  • a macroscopic "soft" ferrite carrier consisting of a MgZn-ferrite, coated with 2 % by weight with respect to the total weight of the carrier of a silicone-resin coating, said coating comprising for 4 % by weight, with respect to the total coating, of an aminocomponent.
  • the average particle diameter was 54 ⁇ m.
  • the specific volume resistivity of said carrier particles, as measured according to measurement A, was 1.1 10 14 ⁇ .cm.
  • the specific density was 2.94 g/cm 3 .
  • Example 1 was repeated, except for the carrier particles.
  • a stainless steel carrier, with diameter of about 300 ⁇ m was used. These carrier particles are available under trade name METABRASIVE S70 from Metabrasive Ltd, Capponfield Works, WEST MIDLANDS, UK.
  • the specific resistivity, measured at 10 V DC, was 1.4 10 3 ⁇ .cm and the specific density 7.6 g/cm 3 .
  • the DEP device was adapted to the use of the large carrier particles by setting the distance of the doctor blade to 800 ⁇ m instead of to 400 ⁇ m.
  • Grey scale images with 16 time-modulated levels were printed with different developers as tabulated in table 1.
  • the image homogeneity was visually judged for white-banding artefacts on a scale from 1 to 5, wherein 5 means unacceptable and 1 very good. At the same time the occurrence of carrier loss was also judged.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Developing Agents For Electrophotography (AREA)
EP97202621A 1996-10-10 1997-08-25 Verfahren für direktes elektrostatisches Drucken mit Extraktion von Ionerteilchen aus einem Zweikomponentenentwickler mit einem leitendem Träger Withdrawn EP0836124A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP97202621A EP0836124A1 (de) 1996-10-10 1997-08-25 Verfahren für direktes elektrostatisches Drucken mit Extraktion von Ionerteilchen aus einem Zweikomponentenentwickler mit einem leitendem Träger

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP96202815 1996-10-10
EP96202815 1996-10-10
EP97202621A EP0836124A1 (de) 1996-10-10 1997-08-25 Verfahren für direktes elektrostatisches Drucken mit Extraktion von Ionerteilchen aus einem Zweikomponentenentwickler mit einem leitendem Träger

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4764445A (en) * 1987-06-15 1988-08-16 Eastman Kodak Company Electrographic magnetic carrier particles
US5346791A (en) * 1991-11-29 1994-09-13 Kyocera Corporation Electroconductive magnetic carrier, developer using the same and image formation method
EP0675417A1 (de) * 1994-03-29 1995-10-04 Agfa-Gevaert N.V. Verfahren und Vorrichtung für direktes elektrostatisches Drucken (DEP)

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4764445A (en) * 1987-06-15 1988-08-16 Eastman Kodak Company Electrographic magnetic carrier particles
US5346791A (en) * 1991-11-29 1994-09-13 Kyocera Corporation Electroconductive magnetic carrier, developer using the same and image formation method
EP0675417A1 (de) * 1994-03-29 1995-10-04 Agfa-Gevaert N.V. Verfahren und Vorrichtung für direktes elektrostatisches Drucken (DEP)

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