EP1058165A1 - A direct electrostatic printing device wherein charged toner particles are brought proximate to a printhead structure using an electrostatic powder spray gun - Google Patents
A direct electrostatic printing device wherein charged toner particles are brought proximate to a printhead structure using an electrostatic powder spray gun Download PDFInfo
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- EP1058165A1 EP1058165A1 EP99201790A EP99201790A EP1058165A1 EP 1058165 A1 EP1058165 A1 EP 1058165A1 EP 99201790 A EP99201790 A EP 99201790A EP 99201790 A EP99201790 A EP 99201790A EP 1058165 A1 EP1058165 A1 EP 1058165A1
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- European Patent Office
- Prior art keywords
- toner particles
- printhead structure
- spray gun
- printing device
- charged toner
- 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.)
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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
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- 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 recording method and an apparatus for use in the process of Direct Electrostatic Printing (DEP), in which an image is created upon a receiving substrate by creating a flow of toner particles from a toner bearing surface to the image receiving substrate and image-wise modulating the flow of toner particles by means of an electronically addressable printhead structure.
- DEP Direct Electrostatic Printing
- toner particles are deposited directly in an image-wise way on a receiving substrate, the latter not bearing any image-wise latent electrostatic image.
- 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 electric 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 support for a toner receiving substrate 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 substrate, interposed in the modulated particle stream.
- the receiving substrate is transported in a direction perpendicular to the printhead structure, to provide a line-by-line scan printing.
- the shield electrode may face the toner delivery means and the control electrodes may face the receiving substrate.
- a DC-field is applied between the printhead structure and a single back electrode on the receiving substrate. This propulsion field is responsible for the attraction of toner to the receiving substrate that is placed between the printhead structure and the back electrode.
- printhead structures with multiple rows of printing apertures are used.
- Such printhead structures have be disclosed in e.g. US-A-4 860 036 a printhead structure has been described consisting of at least 3 (preferentially 4 or more) rows of apertures which makes it possible to print images with a smooth page-wide density scale without white banding.
- the main drawback of this kind of printhead structure deals with the toner particle application module, which has to be able to provide charged toner particles in the vicinity of all printing apertures with a nearly equal flux.
- the problem of equal toner flux has been addressed in several ways (see e.g. US-A-5 040 004, US-A-5 214 451, US-A-5 136 311, EP-A-731 394 ).
- the printing speed achievable with DEP devices does not only depends on the possibility of using a printhead structure with multiple rows of printing apertures, nor does the printing quality only depend on providing charged toner particles in the vicinity of all printing apertures with a nearly equal flux, but both printing speed and printing quality depend also on the amount of charged toner particles that is presented per unity of time in the vicinity of the printing apertures.
- EP-A-740 224 it has been disclosed that the relative speed of rotation of the CTC (charged toner conveyor),of the magnetic brush bringing charged toner particles on the surface of the CTC and the image receiving substrate must be related to each other for bringing enough toner particles in the vicinity of the printing apertures. Also in this disclosure it has been disclosed to use a CTC with a radius that is adapted to the extension of the rows of printing apertures in the printing direction. In US-A-5 738 009 and the European equivalent EP-A-736 822 it is disclosed that when extracting the toner particles directly from a magnetic brush, without using a CTC, the speed of rotation of the magnetic brush has to be high.
- DEP Direct Electrostatic Printing
- DEP Direct Electrostatic Printing
- the object of the invention is realised by providing a direct electrostatic printing device for printing images onto a receiving substrate, comprising
- Fig. 1 shows schematically a first possible implementation of the direct spray embodiment of this invention, wherein the toner particles for image formation are directly extracted from a stream of toner particles ejected by an electrostatic spray gun.
- Fig. 2 shows schematically a second possible implementation of the direct spray embodiment of this invention.
- Fig. 3 shows schematically a third possible implementation of the direct spray embodiment of this invention.
- Fig. 4 shows schematically a fourth possible implementation of the direct spray embodiment of this invention.
- Fig. 5 shows schematically a fifth possible implementation of the direct spray embodiment of this invention.
- Fig. 6 shows schematically a possible implementation of the spray/CTC embodiment of this invention, wherein a layer of charged toner particles is applied to a conveyor for charged toner particles by means of an electrostatic spray gun.
- This spray gun can be used either to present a stream of charged toner particles directly in the vicinity of the printing apertures or to load, per unit of time, a large amount of charged toner particles on charged toner conveyer (CTC) from where a dense stream of toner particles is presented to the printing apertures.
- CTC charged toner conveyer
- the invention comprises two embodiments, a first one wherein in a DEP device a stream of charged toner particles is presented to the printing apertures direct from an electrostatic spray gun (the direct spray embodiment) and a second one wherein in a DEP device a layer of charged toner particles is applied to a CTC by an electrostatic powder spray gun (the CTC-spray embodiment).
- Electrostatic powder spray guns are well known in the art of finishing materials by coating the materials with a dry powder instead of by a solvent based paint.
- Electrostatic powder spray guns - herein after indicated a "spray gun” for short - are commercially available and have been disclosed in, e.g., US-A-5 622 313, US-A-5 776 249, US-A-4 653 696, US-A-4 802 625 and US-A-5 482 214.
- a spray gun can easily be adapted to give a flat spray, therefore an even amount of particles over a large area can be provided.
- a flat spray can be quite fast moving, this presents a disadvantage when a flat spray is used for coating materials since the oncoming particles have a relatively high speed and can easily dislodge the previously deposited particles.
- this disadvantage turns into an advantage, since the possibility of dislodging previously deposited particles helps to keep the printhead structure clean both at the surface of the printhead, facing the spray gun, and in the printing apertures due to the impact of the particles on the printhead.
- the toner particles are charged in the spray gun in two ways : either the gun has a high voltage charging electrode which produces a corona to charge the powder, or the gun has means to charge the powder by friction, i.e., triboelectrically. Both types of spray gun are useful in a DEP device of this invention.
- a spray gun as toner source has further the advantage that it is easy to construct a DEP device, either of the direct spray type or the CTC-spray type, wherein only right sign toner particles arrive in the vicinity of the printing apertures and wherein the wrong sign toner particles and/or the non-charged toner particles are taken out of the flow of toner particles.
- the receiving substrate is coupled to a DC-voltage source by bringing a back electrode kept at a DC-voltage near or in contact with the receiving substrate. It is also possible to operate a DEP device according to this invention when the receiving substrate is coupled to a DC-voltage source by first applying at least one conductive layer on a substrate, and by connecting the conductive layer to a voltage source. Thus in this case the DEP device operates without back electrode. Such a device has been described in EP-A-823 676. Also when using a DEP device according to this invention for printing PCB's (printed circuit boards) the DEP device can be operated without back electrode by coupling the conductive layer of the PCB-precursor to a voltage source. Such a method has been described in European Application 98201302 filed on April 22, 1998.
- a DEP device wherein a spray gun forms directly a stream of charged toner particles near the printing apertures.
- This embodiment can be implemented in various ways.
- the spray gun is mounted so that it directs a stream of toner particles in a direction essentially perpendicular to the plane of the printing apertures and its powder outlets are arranged so that the toner particles are directed from the spray gun direct towards the printing apertures, i.e. the imaginary line drawn from the outlets of the spray gun parallel trough the particle stream, does cross the printhead structure and under a basically right angle.
- a housing (101) with walls has a printhead structure (102) in one of the walls.
- printing apertures (103), coupled to control electrodes (104) are present.
- a spray gun (105) is mounted on a pivot (105a), with the powder outlets projecting a mixture of negatively charged toner particles (106a), i.e., for sake of the example, "right sign” toner, together with some non-charged toner particles (106b) and some positively charged toner particles (106c), i.e. "wrong sign” toner, directly to the printing apertures.
- an electrode (107) is provided that is kept at a DC voltage with a negative polarity, for attracting wrong sign toners (106c), i.e. positively charged toner particles.
- the housing is kept at a DC voltage (DC1).
- a back electrode (108) is placed so as to define a gap, d, between the printhead structure and the back electrode.
- An image receiving member (109) is passed through said gap in the direction of arrow A.
- the back electrode is kept at a second DC voltage (DC2) different from DC1 so a to create an electric potential difference (an electric field) between said housing and said back electrode.
- DC2 DC voltage
- the negatively charged toner particles (106a) are attracted towards the back electrode and by image wise modulating the voltage applied to the control electrodes (104) by a voltage source (DC3) coupled to said control electrodes the toner particles pass the printing apertures image-wise and form a toner image on the image receiving member.
- the toner particles that were positively charged (106c), i.e. the wrong sign toner particles, are attracted by the electrode (107) and also collected in the housing. Also the right sign toner that was not used for image formation is collected in the housing.
- a means for moving toner particles (110) moves the toner from the housing again towards a container (not shown) and from there the toner is circulated back to the spray gun.
- the kinetic energy given to the stream of charged toner particles by the spray gun has to be accurately controlled for avoiding that toner particles pass through printing apertures simply by virtue of the high kinetic energy, although the control electrode around the printing apertures is kept at an electric potential prohibiting the passage of charged toner particles. Also non charged toner particles are projected directly in the direction of the printing apertures and risk to pass the printing apertures in a random way.
- the spray gun is arranged so that the imaginary line drawn from the outlets of the spray gun parallel to the particles stream, does not cross the printhead structure or when it crosses the printhead it does not so under a right angle.
- a housing (101) with walls comprising a printhead structure (102), with printing apertures (103) and control electrodes (104) arranged in one of said walls and electrically isolated from said wall.
- a spray gun (105) is arranged in a wall of said housing so that a particle stream containing a mixture of negatively charged toner particles (106a), i.e., for sake of the example, "right sign" toner, together with some non-charged toner particles (106b) and some positively charged toner particles (106c), i.e.
- "wrong sign" toner is ejected in a direction essentially parallel to the wall containing the printhead structure.
- the spray gun is movably mounted in said wall around a pivot (105a) so that it is possible, during a cleaning step, the direct the toner particles towards the printhead structure where, by the impact of the toner particles the printhead structure is cleaned.
- an electrode (107) is provided that is kept at a DC voltage (DC4) with a polarity equal to said first polarity.
- the housing is kept at a DC voltage (DC1).
- DC1 DC voltage
- a back electrode (108) is placed so as to define a gap, d, between the printhead structure and the back electrode.
- An image receiving member (109) is passed through said gap in the direction of arrow A.
- the back electrode is kept at a second DC voltage (DC2) different from DC1 so a to create an electric potential difference (an electric field) between said housing and said back electrode.
- DC2 DC voltage
- This stream comes into the electric field created by the electric potential difference
- the negatively charged toner particles (106a) are attracted towards the back electrode by the electric potential difference
- the toner particles that were not charged (106b) in the spray gun are not attracted towards the back electrode and are collected in the housing.
- the toner particles that were positively charged (106c), i.e. the wrong sign toner particles, are attracted by the electrode (107) and also collected in the housing. Also the right sign toner that was not used for image formation is collected in the housing.
- a means for moving toner particles (110) moves the toner from the housing again towards a container (not shown) and from there the toner is circulated back to the spray gun.
- a DC-voltage source DC1
- a further implementation of the direct spay embodiment of this invention wherein the imaginary line drawn from the outlets of the spray gun parallel to the particles stream, does not cross the printhead structure, is schematically shown in figure 3.
- a housing (101) with walls is provided comprising a printhead structure (102), with printing apertures (103) and control electrodes (104) arranged in one of said walls and electrically isolated from said wall.
- a spray gun (105) is arranged in a wall of said housing so that a particle stream containing a mixture of negatively charged toner particles (106a), i.e., for sake of the example, "right sign" toner, together with some non-charged toner particles (106b) and some positively charged toner particles (106c), i.e.
- "wrong sign" toner is ejected in a direction basically perpendicular to the printhead structure (102) but the imaginary line from the outlets of the spray gun does not cross the printhead structure.
- the stream of ejected toner particles bounces on an element (112) arranged for bending the stream of toner particles in a direction essentially parallel to the printhead structure.
- this implementation works as the implementation shown in figure 2, but it has the advantage that the construction of the housing incorporating the spray gun and the printing apertures can be made more compact.
- Said bouncing element (112) preferably is made of a plastic material with sufficient elasticity so that charged polymeric particles are repelled without losing kinetic energy after collision upon said bouncing element.
- said bouncing element (112) also is provided with a surface coating that helps in tribocharging the impacting toner particles. For that reason the tribological properties of said coating is chosen on the basis of their tribo-position in the tribological range of materials, suitable for the tribobehaviour of the polymeric particles used. Excellent materials useful for coating said bouncing element can be found in the literature with regard to surface coatings used in coating carrier particles for two-component electrophotographic developing systems.
- the rubbery material of said bouncing element (112) can also be made partially conductive (e.g.
- FIG. 10 An other implementation of the direct spay embodiment of this invention, wherein the imaginary line drawn from the outlets of the spray gun parallel to the particles stream, does not cross the printhead structure, is schematically shown in figure 4.
- a housing (101) with walls is provided comprising a printhead structure (102), with printing apertures (103) and control electrodes (104) arranged in one of said walls and electrically isolated from said wall.
- a spray gun (105) is arranged in a wall of said housing so that a particle stream containing a mixture of negatively charged toner particles (106a), i.e., for sake of the example, "right sign" toner, together with some non-charged toner particles (106b) and some positively charged toner particles (106c), i.e.
- "wrong sign" toner is ejected under a given angle (a) to the printhead structure (102) so the imaginary line from the outlets of the spray gun forms an angle a with the printhead structure and does not cross the printhead structure.
- the stream of toner particles may reach the wall of the housing wherein the printhead structure is present simply by the kinetic energy given to the particles, but not at the location of the printhead structure.
- the direct spray embodiment of this invention can also be implemented using more than one spray gun.
- FIG 5 an implementation with two spray guns is shown.
- a housing (101) with walls is provided comprising a printhead structure (102), with printing apertures (103) and control electrodes (104) arranged in one of said walls and electrically isolated from said wall.
- a spray gun (105) is arranged in a wall of said housing so that a particle stream containing a mixture of negatively charged toner particles (106a), i.e., for sake of the example, "right sign" toner, together with some non-charged toner particles (106b) and some positively charged toner particles (106c), i.e.
- "wrong sign" toner is ejected in a direction essentially parallel to the wall containing the printhead structure.
- the spray guns are movably mounted in said wall around a pivot (105a) so that it is possible, during a cleaning step, the direct the toner particles towards the printhead structure where, by the impact of the toner particles the printhead structure is cleaned.
- two electrodes (107) are provided that are kept at a DC voltage (DC4) with a polarity equal to said first polarity for taking the wrong sign toner (106c) out of the flow. Also the non charged toner particles are, at least partially, collected on these electrodes (107).
- Electrodes are rotatably arranged so that they turn in opposite directions and a nip is formed between the two rotating electrodes.
- the means (110) for moving the non used toner particles can then create a vacuum in the nip so that the wrong sign toners together with the non-charged toner is easily removed from the electrodes.
- two rotating electrodes (111) coupled to a voltage source DC5 with polarity opposite to the polarity of the charge on the toner particles, are placed near the printhead structure for aiding the deflection of the "right charge" toner particles, 106a, from the streams of toner particles towards the printhead structure.
- this implementation operates as the implementation shown in figure 2.
- said rotating electrodes (111) can for a nip from which the excessive right-sign toner particles can be removed and recuperated.
- DEP device wherein the charged toner particles are brought near to a printhead structure on a surface of a conveyer for charged toner particles (a Charged Toner Conveyer or CTC) are well known in art.
- CTC Charged Toner Conveyer
- the charged toner particles can be applied on the surface of the CTC, - which is kept at a DC voltage different from the DC voltage coupled to the receiving substrate, - by a magnetic brush.
- a housing (101) with walls has a conveyer for charged toner particles, i.e. a CTC (117) in one of the walls, the CTC is movably mounted so as to turn in the direction of arrow B.
- the CTC is coupled to a DC-voltage source (DC1) and to an AC-voltage source (AC1).
- DC1 DC-voltage source
- AC1 AC-voltage source
- Said CTC-roller is preferably a metallic roller, e.g. a roller of aluminium with a surface coating.
- Said surface coating can have properties tuned for optimal tribologic and electric characteristics, e.g. it can comprise carbon black and tribo-particles in a polymeric rubbery matrix.
- a spray gun (105) is mounted, with the powder outlets (105b) projecting, for sake of the example, negatively charged toner particles (106) to the CTC.
- a corona (113) is provided for further equalising the charge distribution of the toner particles on the CTC.
- An electrode (115) is installed for attracting the "wrong sign" toner that would have reached the CTC, despite of the presence in the housing of an electrode (107) that is kept at a DC voltage with a negative polarity, for attracting wrong sign toners (106c), i.e. positively charged toner particles, the non-charged toner particles are projected in the housing.
- a back electrode (108) kept at a second DC voltage (DC2) different from DC1 so a to create an electric potential difference (an electric field) between said CTC and said back electrode.
- a second DC voltage
- the printhead structure is arranged in such a way as to define a gap, d, between the printhead structure and the back electrode.
- An image receiving substrate is moved through said gap, d, in the direction of arrow A.
- a voltage source DC3 coupled to said control electrodes the toner particles pass the printing apertures image-wise and form a toner image on the image receiving member.
- the toner particles that were positively charged (106c), i.e. the wrong sign toner particles, are attracted by the electrode (107) and collected in the housing. Also the right sign toner that was not used for image formation is collected in the housing.
- a corona downstream from the printhead structure a corona (114) is placed and kept at a DC voltage suited to detach the toner particles, that were not used in the process from the CTC.
- a cleaning member (116) is placed further away from the corona (114) so as to further clean the surface of the CTC.
- the spray gun brings charged toner particles (106a) always to a clean CTC surface so that this surface provides always fresh toner particles to the surface of the CTC. This ensures that the charge distribution of the toner particles on the CTC is kept constant during printing, which results in increased reproducibility of the printing result over the time.
- All toner particles (non-charged particles, "wrong sign” toner and “right sign” that was removed from the CTC) that were collected in the housing are moved by a means for moving toner particles (110) again towards a container (not shown), wherein the particles can be charged again and from there the toner is circulated back to the spray gun.
- the spray guns used in this invention can be guns charging the particles with a high voltage charging electrode as well as spray guns charging the particles triboelectrically, .
- a spray gun equipped for charging the particles with a high voltage charging electrode e.g. a GEMA MPS-1L gun (trade name of Ransburg-Gema SA, St- Gall, Switserland), said high voltage charging electrode is set to a value yielding charged toner particles with sufficient but not to high charge over mass ratio.
- a GEMA MPS-1L gun trade name of Ransburg-Gema SA, St- Gall, Switserland
- a direct electrostatic printing device wherein the means for providing a stream of charged toner particles proximate to a printhead structure comprises an electrostatic powder spray gun, can be used with any printhead structure known in the art, it can be used e.g. with a printhead structure as described in US-A-5 889 540, US-A-5 714 992, EP-A-812 696, EP-A-895 867, European Application 99200479 filed on February 18, 1999, European Application 99200478 filed on February 18, 1999 and European Application 99200480 filed on February 18, 1999. It can also be used with a printhead structure in mesh form as described in US-A-5 036 341.
- a DEP-device according to this invention wherein the means for providing a stream of charged toner particles proximate to a printhead structure comprises an electrostatic powder spray gun, can be used in large format printers as described in e.g. EP-A-849 645, EP-A-849 087 and European Application 98203008 filed on September 8, 1998.
- a DEP device according to this invention implemented in the CTC/spray embodiment can incorporate a CTC wherein the dimensions are adapted to the extension of the array of printing apertures in the printhead structure as described in, e.g., EP-A-740 224.
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Abstract
A direct electrostatic printing device is described wherein the means
for providing a stream of charged toner particles (106) proximate to a
printhead structure (102) comprises an electrostatic powder spray gun
(105).
Two embodiments are disclosed, one wherein the flow of toner
particles towards the image receiving member (109) is directly generated
from the spray gun and one wherein the spray gun is used to apply a
layer of charged toner particles on a conveyor for charged toner
particles.
Description
This invention relates to a recording method and an apparatus
for use in the process of Direct Electrostatic Printing (DEP), in
which an image is created upon a receiving substrate by creating a
flow of toner particles from a toner bearing surface to the image
receiving substrate and image-wise modulating the flow of toner
particles by means of an electronically addressable printhead
structure.
In DEP (Direct Electrostatic Printing) toner particles are
deposited directly in an image-wise way on a receiving substrate,
the latter not bearing any image-wise latent electrostatic image.
This 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,
or from electrophotography in which an additional step and
additional member is introduced to create the latent electrostatic
image (photoconductor and charging/exposure cycle).
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 :
- a layer of insulating material, called isolation layer ;
- a shield electrode consisting of a continuous layer of conductive material on one side of the isolation layer ;
- a plurality of control electrodes formed by a segmented layer of conductive material on the other side of the isolation layer ; and
- at least one row of apertures.
Each control electrode is formed around one aperture and is
isolated from each other control electrode.
Selected electric 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 support for a toner receiving substrate
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 substrate, interposed in the modulated
particle stream. The receiving substrate is transported in a
direction perpendicular to the printhead structure, to provide a
line-by-line scan printing. The shield electrode may face the toner
delivery means and the control electrodes may face the receiving
substrate. A DC-field is applied between the printhead structure and
a single back electrode on the receiving substrate. This propulsion
field is responsible for the attraction of toner to the receiving
substrate that is placed between the printhead structure and the
back electrode.
In DEP devices intended for high speed printing, printhead
structures with multiple rows of printing apertures are used. Such
printhead structures have be disclosed in e.g. US-A-4 860 036 a
printhead structure has been described consisting of at least 3
(preferentially 4 or more) rows of apertures which makes it possible
to print images with a smooth page-wide density scale without white
banding. The main drawback of this kind of printhead structure
deals with the toner particle application module, which has to be
able to provide charged toner particles in the vicinity of all
printing apertures with a nearly equal flux. The problem of equal
toner flux has been addressed in several ways (see e.g.
US-A-5 040 004, US-A-5 214 451, US-A-5 136 311, EP-A-731 394).
The printing speed achievable with DEP devices does not only
depends on the possibility of using a printhead structure with
multiple rows of printing apertures, nor does the printing quality
only depend on providing charged toner particles in the vicinity of
all printing apertures with a nearly equal flux, but both printing
speed and printing quality depend also on the amount of charged
toner particles that is presented per unity of time in the vicinity
of the printing apertures.
In EP-A-740 224 it has been disclosed that the relative speed of
rotation of the CTC (charged toner conveyor),of the magnetic brush
bringing charged toner particles on the surface of the CTC and the
image receiving substrate must be related to each other for bringing
enough toner particles in the vicinity of the printing apertures.
Also in this disclosure it has been disclosed to use a CTC with a
radius that is adapted to the extension of the rows of printing
apertures in the printing direction. In US-A-5 738 009 and the
European equivalent EP-A-736 822 it is disclosed that when
extracting the toner particles directly from a magnetic brush,
without using a CTC, the speed of rotation of the magnetic brush has
to be high.
The disclosures above do solve the problems above but when very
high printing speed is necessary, the speed of rotation the CTC and
the magnetic brush have to be extremely high which entail problems
of mechanical wear of the bearings of the CTC and the magnetic
brush.
It has been proposed in EP-A-763 785 to use instead of a CTC a
fluidized bed of charged toner particles in the vicinity of printing
apertures, this approach was very useful when printhead structures
with large extension in the printing direction were used (i.e.
printhead structures with multiple rows of printing apertures).
This approach minimised the moving parts in the device (no rotating
CTC and/or rotating magnetic brush) but it proved very difficult to
have enough toner particles presented per unity of time in the
vicinity of the printing apertures.
There is thus a need for a DEP device wherein it is possible to
provide in a simple and reliable way a large amount of toner
particles in the vicinity of the printing apertures for printhead
structures having multiple rows of printing apertures.
It is an object of the invention to provide a device for Direct
Electrostatic Printing (DEP) for high speed printing with few moving
parts and with a printhead structure with multiple rows of printing
apertures wherein charged toner particles are provided in the
vicinity of all printing apertures with a nearly equal flux.
It is an other object of the invention to provide a device for
Direct Electrostatic Printing (DEP) for high speed printing wherein
clogging of the printing apertures is minimised.
The object of the invention is realised by providing a direct
electrostatic printing device for printing images onto a receiving
substrate, comprising
- a means for providing a stream of charged toner particles proximate to a printhead structure,
- means for coupling the receiving substrate to an electric potential so as to create an electric field for attracting said toner particles, as a toner flow, from said stream to the receiving substrate,
- said printhead structure having a first side and a second side located so as to have said first side facing said stream of toner particles and said second side facing the receiving substrate, said printhead structure having an array of printing apertures extending there through from said first side to said second side, said printing apertures being coupled to control electrodes for electrically modulating said toner flow in accordance with image data to cause said toner particles to be deposited onto the receiving substrate to form an image,
Fig. 1 shows schematically a first possible implementation of
the direct spray embodiment of this invention, wherein the toner
particles for image formation are directly extracted from a stream
of toner particles ejected by an electrostatic spray gun.
Fig. 2 shows schematically a second possible implementation of
the direct spray embodiment of this invention.
Fig. 3 shows schematically a third possible implementation of
the direct spray embodiment of this invention.
Fig. 4 shows schematically a fourth possible implementation of
the direct spray embodiment of this invention.
Fig. 5 shows schematically a fifth possible implementation of
the direct spray embodiment of this invention.
Fig. 6 shows schematically a possible implementation of the
spray/CTC embodiment of this invention, wherein a layer of charged
toner particles is applied to a conveyor for charged toner particles
by means of an electrostatic spray gun.
It was now found that the problems associated with high speed
direct electrostatic printing could largely be overcome when the
device incorporates an electrostatic powder spray gun. This spray
gun can be used either to present a stream of charged toner
particles directly in the vicinity of the printing apertures or to
load, per unit of time, a large amount of charged toner particles on
charged toner conveyer (CTC) from where a dense stream of toner
particles is presented to the printing apertures. Thus the
invention comprises two embodiments, a first one wherein in a DEP
device a stream of charged toner particles is presented to the
printing apertures direct from an electrostatic spray gun (the
direct spray embodiment) and a second one wherein in a DEP device a
layer of charged toner particles is applied to a CTC by an
electrostatic powder spray gun (the CTC-spray embodiment).
Electrostatic powder spray guns are well known in the art of
finishing materials by coating the materials with a dry powder
instead of by a solvent based paint.
Electrostatic powder spray guns - herein after indicated a
"spray gun" for short - are commercially available and have been
disclosed in, e.g., US-A-5 622 313, US-A-5 776 249, US-A-4 653 696,
US-A-4 802 625 and US-A-5 482 214.
A spray gun can easily be adapted to give a flat spray,
therefore an even amount of particles over a large area can be
provided. A flat spray can be quite fast moving, this presents a
disadvantage when a flat spray is used for coating materials since
the oncoming particles have a relatively high speed and can easily
dislodge the previously deposited particles. When used in a DEP
device, this disadvantage turns into an advantage, since the
possibility of dislodging previously deposited particles helps to
keep the printhead structure clean both at the surface of the
printhead, facing the spray gun, and in the printing apertures due
to the impact of the particles on the printhead.
The toner particles are charged in the spray gun in two ways :
either the gun has a high voltage charging electrode which produces
a corona to charge the powder, or the gun has means to charge the
powder by friction, i.e., triboelectrically. Both types of spray
gun are useful in a DEP device of this invention.
The use of a spray gun as toner source has further the advantage
that it is easy to construct a DEP device, either of the direct
spray type or the CTC-spray type, wherein only right sign toner
particles arrive in the vicinity of the printing apertures and
wherein the wrong sign toner particles and/or the non-charged toner
particles are taken out of the flow of toner particles.
Although the invention is explained herein below using
negatively charged toner particles, it is clear that the invention
also works with positively charged toner particles by a simple
adaptation of the polarity of the electric potentials.
In the embodiments, described below, the receiving substrate is
coupled to a DC-voltage source by bringing a back electrode kept at
a DC-voltage near or in contact with the receiving substrate. It is
also possible to operate a DEP device according to this invention
when the receiving substrate is coupled to a DC-voltage source by
first applying at least one conductive layer on a substrate, and by
connecting the conductive layer to a voltage source. Thus in this
case the DEP device operates without back electrode. Such a device
has been described in EP-A-823 676. Also when using a DEP device
according to this invention for printing PCB's (printed circuit
boards) the DEP device can be operated without back electrode by
coupling the conductive layer of the PCB-precursor to a voltage
source. Such a method has been described in European Application
98201302 filed on April 22, 1998.
In the direct spray embodiment of the invention a DEP device is
provided wherein a spray gun forms directly a stream of charged
toner particles near the printing apertures.
This embodiment can be implemented in various ways.
In a first implementation, the spray gun is mounted so that it
directs a stream of toner particles in a direction essentially
perpendicular to the plane of the printing apertures and its powder
outlets are arranged so that the toner particles are directed from
the spray gun direct towards the printing apertures, i.e. the
imaginary line drawn from the outlets of the spray gun parallel
trough the particle stream, does cross the printhead structure and
under a basically right angle. In figure 1, this is schematically
shown. A housing (101) with walls has a printhead structure (102)
in one of the walls. In the printhead structure, printing apertures
(103), coupled to control electrodes (104) are present. In a wall
of the housing (101) opposite to the wall containing the printhead
structure, a spray gun (105) is mounted on a pivot (105a), with the
powder outlets projecting a mixture of negatively charged toner
particles (106a), i.e., for sake of the example, "right sign" toner,
together with some non-charged toner particles (106b) and some
positively charged toner particles (106c), i.e. "wrong sign" toner,
directly to the printing apertures. In the housing an electrode
(107) is provided that is kept at a DC voltage with a negative
polarity, for attracting wrong sign toners (106c), i.e. positively
charged toner particles. The housing is kept at a DC voltage (DC1).
Outside the housing, opposite to the wall of the housing (101)
containing the printhead structure a back electrode (108) is placed
so as to define a gap, d, between the printhead structure and the
back electrode. An image receiving member (109) is passed through
said gap in the direction of arrow A. The back electrode is kept at
a second DC voltage (DC2) different from DC1 so a to create an
electric potential difference (an electric field) between said
housing and said back electrode. During printing a flow of charged
toner particles with, for the sake of the example, negative polarity
is generated by the spray gun, this stream comes into the electric
field created by the electric potential difference |DC1 - DC2|
wherein this difference is positive. From the stream of charged
toner particles, the negatively charged toner particles (106a) are
attracted towards the back electrode and by image wise modulating
the voltage applied to the control electrodes (104) by a voltage
source (DC3) coupled to said control electrodes the toner particles
pass the printing apertures image-wise and form a toner image on the
image receiving member. The toner particles that were positively
charged (106c), i.e. the wrong sign toner particles, are attracted
by the electrode (107) and also collected in the housing. Also the
right sign toner that was not used for image formation is collected
in the housing. A means for moving toner particles (110) moves the
toner from the housing again towards a container (not shown) and
from there the toner is circulated back to the spray gun.
In this case the kinetic energy given to the stream of charged
toner particles by the spray gun has to be accurately controlled for
avoiding that toner particles pass through printing apertures simply
by virtue of the high kinetic energy, although the control electrode
around the printing apertures is kept at an electric potential
prohibiting the passage of charged toner particles. Also non
charged toner particles are projected directly in the direction of
the printing apertures and risk to pass the printing apertures in a
random way.
It is preferred that the spray gun is arranged so that the
imaginary line drawn from the outlets of the spray gun parallel to
the particles stream, does not cross the printhead structure or when
it crosses the printhead it does not so under a right angle.
It is, in such a construction of a DEP device according to the
direct spray embodiment of this invention, however preferred to
install the spray gun movably so that during operation of the
printing device the stream of toner particles is not projected so as
to physically contact the printhead structure and the printing
apertures but that, during a cleaning cycle, the stream of toner
particles can be directed so that the toner particles reach the
printhead structure and by the impact of them on the printhead
structure clean the printhead by dislodging previously deposited
particles.
An implementation of the direct spay embodiment of this
invention, wherein the imaginary line drawn from the outlets of the
spray gun parallel to the particle stream, does not cross the
printhead structure, is schematically shown in figure 2. A housing
(101) with walls is provided comprising a printhead structure (102),
with printing apertures (103) and control electrodes (104) arranged
in one of said walls and electrically isolated from said wall. A
spray gun (105) is arranged in a wall of said housing so that a
particle stream containing a mixture of negatively charged toner
particles (106a), i.e., for sake of the example, "right sign" toner,
together with some non-charged toner particles (106b) and some
positively charged toner particles (106c), i.e. "wrong sign" toner
is ejected in a direction essentially parallel to the wall
containing the printhead structure. The spray gun is movably
mounted in said wall around a pivot (105a) so that it is possible,
during a cleaning step, the direct the toner particles towards the
printhead structure where, by the impact of the toner particles the
printhead structure is cleaned. In the housing an electrode (107)
is provided that is kept at a DC voltage (DC4) with a polarity equal
to said first polarity. The housing is kept at a DC voltage (DC1).
Outside the housing and opposite to the wall of the housing (101)
containing the printhead structure a back electrode (108) is placed
so as to define a gap, d, between the printhead structure and the
back electrode. An image receiving member (109) is passed through
said gap in the direction of arrow A. The back electrode is kept at
a second DC voltage (DC2) different from DC1 so a to create an
electric potential difference (an electric field) between said
housing and said back electrode. During printing a particle stream
containing a mixture of negatively charged toner particles (106a),
i.e., for sake of the example, "right sign" toner, together with
some non-charged toner particles (106b) and some positively charged
toner particles (106c), i.e. "wrong sign" toner is generated by the
spray gun, this stream comes into the electric field created by the
electric potential difference |DC1 - DC2| wherein this difference is
positive. From the stream of toner particles, the negatively
charged toner particles (106a) are attracted towards the back
electrode by the electric potential difference |DC1 - DC2| and by
image wise modulating the voltage applied to the control electrodes
(104) by a voltage source (DC3) coupled to said control electrodes
the toner particles pass the printing apertures image-wise and form
a toner image on the image receiving member. The toner particles
that were not charged (106b) in the spray gun are not attracted
towards the back electrode and are collected in the housing. The
toner particles that were positively charged (106c), i.e. the wrong
sign toner particles, are attracted by the electrode (107) and also
collected in the housing. Also the right sign toner that was not
used for image formation is collected in the housing. A means for
moving toner particles (110) moves the toner from the housing again
towards a container (not shown) and from there the toner is
circulated back to the spray gun. Instead of having the housing
(101) coupled to a DC-voltage source (DC1) it is possible to use a
housing made from isolating material, and to place electrodes in or
on the housing near the printhead structure where then these
electrodes are coupled to the DC-voltage source (DC1) for creating
together with the DC-voltage on the back electrode an electric field
wherein the charged toner particles are attracted towards the
receiving substrate.
A further implementation of the direct spay embodiment of this
invention, wherein the imaginary line drawn from the outlets of the
spray gun parallel to the particles stream, does not cross the
printhead structure, is schematically shown in figure 3. A housing
(101) with walls is provided comprising a printhead structure (102),
with printing apertures (103) and control electrodes (104) arranged
in one of said walls and electrically isolated from said wall. A
spray gun (105) is arranged in a wall of said housing so that a
particle stream containing a mixture of negatively charged toner
particles (106a), i.e., for sake of the example, "right sign" toner,
together with some non-charged toner particles (106b) and some
positively charged toner particles (106c), i.e. "wrong sign" toner
is ejected in a direction basically perpendicular to the printhead
structure (102) but the imaginary line from the outlets of the spray
gun does not cross the printhead structure. The stream of ejected
toner particles bounces on an element (112) arranged for bending the
stream of toner particles in a direction essentially parallel to the
printhead structure. Basically this implementation works as the
implementation shown in figure 2, but it has the advantage that the
construction of the housing incorporating the spray gun and the
printing apertures can be made more compact. Said bouncing element
(112) preferably is made of a plastic material with sufficient
elasticity so that charged polymeric particles are repelled without
losing kinetic energy after collision upon said bouncing element.
More preferably said bouncing element (112) also is provided with a
surface coating that helps in tribocharging the impacting toner
particles. For that reason the tribological properties of said
coating is chosen on the basis of their tribo-position in the
tribological range of materials, suitable for the tribobehaviour of
the polymeric particles used. Excellent materials useful for
coating said bouncing element can be found in the literature with
regard to surface coatings used in coating carrier particles for
two-component electrophotographic developing systems. The rubbery
material of said bouncing element (112) can also be made partially
conductive (e.g. by the incorporation of conductive particles such
as carbon black) so that excessive tribocharging of said bouncing
element is prevented by partially grounding said element to a
conductive grounded body, preventing the amount of charged toner
particles in the neighbourhood of said printing apertures to
diminish or fluctuate as a function of printing time.
An other implementation of the direct spay embodiment of this
invention, wherein the imaginary line drawn from the outlets of the
spray gun parallel to the particles stream, does not cross the
printhead structure, is schematically shown in figure 4. A housing
(101) with walls is provided comprising a printhead structure (102),
with printing apertures (103) and control electrodes (104) arranged
in one of said walls and electrically isolated from said wall. A
spray gun (105) is arranged in a wall of said housing so that a
particle stream containing a mixture of negatively charged toner
particles (106a), i.e., for sake of the example, "right sign" toner,
together with some non-charged toner particles (106b) and some
positively charged toner particles (106c), i.e. "wrong sign" toner
is ejected under a given angle (a) to the printhead structure (102)
so the imaginary line from the outlets of the spray gun forms an
angle a with the printhead structure and does not cross the
printhead structure. The stream of toner particles may reach the
wall of the housing wherein the printhead structure is present
simply by the kinetic energy given to the particles, but not at the
location of the printhead structure. In the housing the same
elements as described in figure 2 are present together with an
electrode (111) coupled to a voltage source DC5, with polarity
opposite to the polarity of the charge on the "right sign" toner
particles, that is placed near the printhead structure for aiding
the deflection of the "right charge" toner particles, 106a, from the
stream of toner particles towards the printhead structure.
Basically this implementation works also as the implementation shown
in figure 2, but it has the advantage that the construction of the
housing incorporating the spray gun and the printing apertures can
be made more compact.
The direct spray embodiment of this invention can also be
implemented using more than one spray gun. In figure 5 an
implementation with two spray guns is shown. A housing (101) with
walls is provided comprising a printhead structure (102), with
printing apertures (103) and control electrodes (104) arranged in
one of said walls and electrically isolated from said wall. In two
opposite walls of the housing ,a spray gun (105) is arranged in a
wall of said housing so that a particle stream containing a mixture
of negatively charged toner particles (106a), i.e., for sake of the
example, "right sign" toner, together with some non-charged toner
particles (106b) and some positively charged toner particles (106c),
i.e. "wrong sign" toner is ejected in a direction essentially
parallel to the wall containing the printhead structure. The spray
guns are movably mounted in said wall around a pivot (105a) so that
it is possible, during a cleaning step, the direct the toner
particles towards the printhead structure where, by the impact of
the toner particles the printhead structure is cleaned. In the
housing two electrodes (107) are provided that are kept at a DC
voltage (DC4) with a polarity equal to said first polarity for
taking the wrong sign toner (106c) out of the flow. Also the non
charged toner particles are, at least partially, collected on these
electrodes (107). These electrodes are rotatably arranged so that
they turn in opposite directions and a nip is formed between the two
rotating electrodes. The means (110) for moving the non used toner
particles can then create a vacuum in the nip so that the wrong sign
toners together with the non-charged toner is easily removed from
the electrodes. In the housing also two rotating electrodes (111)
coupled to a voltage source DC5, with polarity opposite to the
polarity of the charge on the toner particles, are placed near the
printhead structure for aiding the deflection of the "right charge"
toner particles, 106a, from the streams of toner particles towards
the printhead structure. Basically this implementation operates as
the implementation shown in figure 2. Here also said rotating
electrodes (111) can for a nip from which the excessive right-sign
toner particles can be removed and recuperated.
DEP device wherein the charged toner particles are brought near
to a printhead structure on a surface of a conveyer for charged
toner particles (a Charged Toner Conveyer or CTC) are well known in
art. E.g. in US-A-4 814 796, US-A-5 337 124, US-A-5 311 266,
US-A-4 491 855, EP-A-740 224 such devices are described. The charged
toner particles can be applied on the surface of the CTC, - which is
kept at a DC voltage different from the DC voltage coupled to the
receiving substrate, - by a magnetic brush. In order to have enough
toner particles on the surface of the CTC in the case of high
printing speed, the speed of rotation the CTC and the magnetic brush
have to be extremely high, which entail problems of mechanical wear
of the bearings of the CTC and the magnetic brush. It was now found
that an electrostatic spray gun could apply a large amount of
charged toner particles to the surface of a CTC in a short time.
This makes it possible to have high printing speed and to use a CTC
with large diameter (low curvature) while not having problems with
toner depletion (i.e. no longer having enough toner particles on the
CTC to print the desired density).
In figure 6 a possible implementation of the spray/CTC
embodiment of this invention is shown. A housing (101) with walls
has a conveyer for charged toner particles, i.e. a CTC (117) in one
of the walls, the CTC is movably mounted so as to turn in the
direction of arrow B. The CTC is coupled to a DC-voltage source
(DC1) and to an AC-voltage source (AC1). The latter voltage source
is optional. Said CTC-roller is preferably a metallic roller, e.g.
a roller of aluminium with a surface coating. Said surface coating
can have properties tuned for optimal tribologic and electric
characteristics, e.g. it can comprise carbon black and tribo-particles
in a polymeric rubbery matrix. In an other wall of the
housing (101), a spray gun (105) is mounted, with the powder outlets
(105b) projecting, for sake of the example, negatively charged toner
particles (106) to the CTC. Near the CTC (117) a corona (113) is
provided for further equalising the charge distribution of the toner
particles on the CTC. An electrode (115) is installed for
attracting the "wrong sign" toner that would have reached the CTC,
despite of the presence in the housing of an electrode (107) that is
kept at a DC voltage with a negative polarity, for attracting wrong
sign toners (106c), i.e. positively charged toner particles, the
non-charged toner particles are projected in the housing. Outside
the housing, opposite to the wall of the housing (101) containing
the CTC (117), a back electrode (108) kept at a second DC voltage
(DC2) different from DC1 so a to create an electric potential
difference (an electric field) between said CTC and said back
electrode. During printing charged toner particles that are present
on the surface of the CTC are attracted in the electric field
created by the electric potential difference |DC1 - DC2| wherein
this difference is positive, forming a stream of toner particles. A
printhead structure (102) having printing apertures (103) coupled to
control electrodes (104) is placed in said stream of toner particles
from the CTC to the back electrode. The printhead structure is
arranged in such a way as to define a gap, d, between the printhead
structure and the back electrode. An image receiving substrate is
moved through said gap, d, in the direction of arrow A. By image
wise modulating the voltage applied to the control electrodes (104)
by a voltage source (DC3) coupled to said control electrodes the
toner particles pass the printing apertures image-wise and form a
toner image on the image receiving member. The toner particles that
were positively charged (106c), i.e. the wrong sign toner particles,
are attracted by the electrode (107) and collected in the housing.
Also the right sign toner that was not used for image formation is
collected in the housing. Near the CTC, downstream from the
printhead structure a corona (114) is placed and kept at a DC
voltage suited to detach the toner particles, that were not used in
the process from the CTC. A cleaning member (116) is placed further
away from the corona (114) so as to further clean the surface of the
CTC. By doing so the spray gun brings charged toner particles
(106a) always to a clean CTC surface so that this surface provides
always fresh toner particles to the surface of the CTC. This
ensures that the charge distribution of the toner particles on the
CTC is kept constant during printing, which results in increased
reproducibility of the printing result over the time. All toner
particles (non-charged particles, "wrong sign" toner and "right
sign" that was removed from the CTC) that were collected in the
housing are moved by a means for moving toner particles (110) again
towards a container (not shown), wherein the particles can be
charged again and from there the toner is circulated back to the
spray gun.
The spray guns used in this invention can be guns charging the
particles with a high voltage charging electrode as well as spray
guns charging the particles triboelectrically, .
Using a spray gun equipped for charging the particles with a
high voltage charging electrode e.g. a GEMA MPS-1L gun (trade name
of Ransburg-Gema SA, St- Gall, Switserland), said high voltage
charging electrode is set to a value yielding charged toner
particles with sufficient but not to high charge over mass ratio.
By using said gun for charging toner particles commercially
available from Agfa-Gevaert N.V., Mortsel Belgium for use in
CHROMPRESS (trade name Agfa-Gevaert N.V., Mortsel Belgium)and
setting the high voltage charging electrode to a voltage exceeding
20,000 V a q/m-ratio of -30 µC/g and higher was obtained, resulting
in blurry images and high toner sticking upon said CTC-surface. By
lowering the voltage applied to said high voltage charging electrode
to about 5,000 to 10,000 V a q/m-ratio of about -10 to -30 µC/g
could be obtained. For the embodiment 6 in which said charged toner
particles are propelled towards said CTC-roller, it was found that a
charging voltage of about 3,000 to 7,000 V led to the best printing
results. However, it must be clear for those skilled in the art
that for the direct spray embodiment said charging voltage can be
set to a much higher value because toner adhesion is less important
if compared to the spray/CTC-embodiment. In this case the air
pressure has to be fine-tuned so that said highly charged toner
particles are not blown through said printing apertures due to their
acquired kinetic energy. Otherwise, this could only be prevented by
using higher image-wise modulated voltages that would lead to a much
too expensive apparatus. Therefore it is preferred in both
embodiments of this invention to use a spray gun operated at an air
pressure below 10 bar (i.e. below 106 Pa).
A direct electrostatic printing device according to this
invention wherein the means for providing a stream of charged toner
particles proximate to a printhead structure comprises an
electrostatic powder spray gun, can be used with any printhead
structure known in the art, it can be used e.g. with a printhead
structure as described in US-A-5 889 540, US-A-5 714 992,
EP-A-812 696, EP-A-895 867, European Application 99200479 filed on
February 18, 1999, European Application 99200478 filed on February
18, 1999 and European Application 99200480 filed on February 18,
1999. It can also be used with a printhead structure in mesh form
as described in US-A-5 036 341.
A DEP-device according to this invention wherein the means for
providing a stream of charged toner particles proximate to a
printhead structure comprises an electrostatic powder spray gun, can
be used in large format printers as described in e.g. EP-A-849 645,
EP-A-849 087 and European Application 98203008 filed on September 8,
1998.
A DEP device according to this invention implemented in the
CTC/spray embodiment can incorporate a CTC wherein the dimensions
are adapted to the extension of the array of printing apertures in
the printhead structure as described in, e.g., EP-A-740 224.
Claims (13)
- A direct electrostatic printing device for printing images onto a receiving substrate, comprisinga means for providing a stream of charged toner particles proximate to a printhead structure,means for coupling the receiving substrate to an electric potential so as to create an electric field for attracting said toner particles, as a toner flow, from said stream to the receiving substrate,said printhead structure having a first side and a second side located so as to have said first side facing said stream of toner particles and said second side facing the receiving substrate, said printhead structure having an array of printing apertures extending there through from said first side to said second side, said printing apertures being coupled to control electrodes for electrically modulating said toner flow in accordance with image data to cause said toner particles to be deposited onto the receiving substrate to form an image,
said means for providing a stream of charged toner particles proximate to said printhead structure comprises an electrostatic powder spray gun. - A direct electrostatic printing device according to claim 1, wherein said stream of charged toner particles is directly provided proximate to said printhead structure by said spray gun.
- A direct electrostatic printing device according to claim 2, wherein said spray gun provides said stream of toner particles in a direction essentially parallel to said printing apertures in said printhead structure.
- A direct electrostatic printing device according to claim 2, wherein said spray gun provides said stream of toner particles in a direction essentially perpendicular to said printhead structure on a bouncing element arranged for bending said stream of toner particles in a direction essentially parallel to the printhead structure.
- A direct electrostatic printing device according to any of claims 1 to 4, wherein proximate to said printhead structure an electrode is present for attracting right-sign-toner particles towards said printhead structure.
- A direct electrostatic printing device according to any of claims 1 to 5, wherein an electrode is present for attracting wrong-sign-toner particles and preventing said wrong-sign-toner particles of coming proximate to said printhead structure.
- A direct electrostatic printing device according to any of claims 1 to 6, wherein at least two spray guns are used.
- A direct electrostatic printing device according to any of claims 4 to 7, wherein said bouncing plate has a surface coating for for giving toner particles bouncing on it a higher charge to mass ratio.
- A direct electrostatic printing device according to claim 1, wherein said stream of charged toner particles is provided proximate to said printhead structure from a charged toner conveyer whereon charged toner particles are deposited by an electrostatic spray gun.
- A direct electrostatic printing device according to claim 9, wherein proximate to said charged toner conveyer an electrode is present for attracting right-sign-toner particles towards said charged toner conveyer.
- A direct electrostatic printing device according to claim 9 or 10, wherein proximate to said charged toner conveyor a corona device is present for levelling the charge on the toner particles on said charged toner conveyor to a constant level.
- A direct electrostatic printing device according to any of the previous claims, wherein a spray gun having a high voltage charging electrode is used and operated at a voltage below 30,000 V.
- A direct electrostatic printing device according to any of the previous claims, wherein a spray gun is operated at an air pressure below 106 Pa.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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EP99201790A EP1058165A1 (en) | 1999-06-03 | 1999-06-03 | A direct electrostatic printing device wherein charged toner particles are brought proximate to a printhead structure using an electrostatic powder spray gun |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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EP99201790A EP1058165A1 (en) | 1999-06-03 | 1999-06-03 | A direct electrostatic printing device wherein charged toner particles are brought proximate to a printhead structure using an electrostatic powder spray gun |
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EP99201790A Withdrawn EP1058165A1 (en) | 1999-06-03 | 1999-06-03 | A direct electrostatic printing device wherein charged toner particles are brought proximate to a printhead structure using an electrostatic powder spray gun |
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EP0464741A2 (en) * | 1990-07-02 | 1992-01-08 | Xerox Corporation | Cyclonic toner charging donor |
US5159472A (en) * | 1989-06-06 | 1992-10-27 | Brother Kogyo Kabushiki Kaisha | Image forming apparatus using solid image-pickup element |
EP0763785A1 (en) * | 1995-09-14 | 1997-03-19 | Agfa-Gevaert N.V. | A DEP (Direct Electrostatic Printing) device using gas stream to provide a toner cloud |
-
1999
- 1999-06-03 EP EP99201790A patent/EP1058165A1/en not_active Withdrawn
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US5159472A (en) * | 1989-06-06 | 1992-10-27 | Brother Kogyo Kabushiki Kaisha | Image forming apparatus using solid image-pickup element |
EP0464741A2 (en) * | 1990-07-02 | 1992-01-08 | Xerox Corporation | Cyclonic toner charging donor |
EP0763785A1 (en) * | 1995-09-14 | 1997-03-19 | Agfa-Gevaert N.V. | A DEP (Direct Electrostatic Printing) device using gas stream to provide a toner cloud |
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