Patent Grant
7020420
The present application is related to copending application of Martin Berg et al Ser. No. 10/297,165, filed Apr. 21, 2003, entitled “Device And Method For Cleaning and For Regenerating An Imaging Carrier During Electrographic Printing Or Copying By Using Liquid Ink”; and also copending application of Martin Berg et al Ser. No. 10/297,227, filed Apr. 15, 2003, entitled “Applicator Element and Method for Electrographic Printing or Copying by Using Liquid Ink.
The invention relates to a device and a method for electrographic printing or copying by using liquid ink. Further, the invention relates to an applicator element, a cleaning station and a regeneration station, each of which is adapted to the use of liquid ink.
Known devices for electrographic printing or copying make use of a process in which dry toner is applied to the latent image of a latent image carrier, for example a photoconductor. Such dry toner results in relatively thick toner layers since the toner particles have a relatively large particle size and a plurality of toner particles have to be deposited on top of each other for achieving sufficient color coverage. The dry toner layer applied to the latent image has to be fixed, this requiring a relatively high energy. This high energy leads to a high stress on the final image carrier, preferably paper, as a result of the fixing by means of heat and/or pressure.
Liquid toners that have been used up to now contain a carrier liquid that is odorous and inflammable. Often, the final image carrier to which the liquid toner is applied is likewise odorous. When liquid toner is used, it is brought into contact with the latent image carrier.
U.S. Pat. No. 5,943,535 discloses the use of a water-based liquid toner that is brought into contact with the latent image carrier. Owing to the conductive liquid toner, a deposit corresponding to the electrostatic charge image is formed on the latent image carrier.
DE-A-30 00 019 which corresponds to U.S. Pat. No. 4,268,597 discloses a device for a liquid developer. A latent image, for example a potential pattern, is generated on the final image carrier. An applicator element carries a liquid layer. An air gap having a predetermined air gap width is set between the liquid layer and the final image carrier. Liquid elements of the liquid layer are transferred onto the surface of the final image carrier due to its electric potential.
U.S. Pat. No. 4,982,692 discloses a method for printing that uses a liquid developer. Under effect of an electrostatic force field, droplets of a liquid layer on an applicator element are transferred onto the surface of a latent image carrier.
Further, U.S. Pat. No. 5,622,805 discloses a method using a liquid developer in which method droplets on an applicator roller are transferred onto the surface of a latent image carrier under influence of an electrostatic field.
Furthermore, reference has to be made to conventional printing methods, such as offset printing, which use liquid ink. With these conventional printing methods, the print form is not variable so that economical printing of small numbers of copies is not possible.
An object of the invention is to specify a device and a method for electrographic printing or copying which allows the use of liquid ink.
This object is achieved by a method and device wherein for electrographic printing or copying, a latent image carrier is provided having a surface with a potential pattern corresponding to an image pattern to be printed. An applicator element is provided with a liquid layer of ink. An air gap is provided between the liquid layer and the surface of the latent image carrier opposed thereto. For inking the latent image on the latent image carrier, droplets are transferred from the liquid layer onto the surface of the latent image carrier by overcoming the air gap. An alternating force field is provided in the air gap so that the force field acts on the liquid layer.
A preferred embodiment of the invention is explained in the following with reference to the drawings.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and/or method, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.
Liquid ink is prepared in an inking station such that an amount of liquid that is constant per time and per area is present on an applicator element in the form of a liquid layer. On this applicator element, preferably a band or a roller, the liquid film is conveyed into the effective area of the potential pattern, the potential of which is distributed in accordance with an image pattern to be printed. Preferably, the potential pattern corresponds to an electrostatic charge image. The potential pattern was previously generated on the latent image carrier by suitable means, for example by means of electrostatic charging and exposing a photoconductor. An air gap exists between the surface of the liquid layer and the latent image carrier with the potential pattern. Between the surface of the applicator element and the image locations of the potential pattern on the latent image carrier, there results a potential contrast, for example supported by the application of a voltage to the applicator element. Sections of the liquid layer are then partially separated from the applicator element and jump in the form of small droplets or transfer by means of a deformation of droplets in accordance with the field lines onto the surface of the latent image carrier and ink the latent image so as to form the ink image. Afterwards, this ink image can directly be transferred onto the final image carrier, for example paper. Another possibility is to first transfer the ink image from the latent image carrier onto an intermediate carrier and from there onto the final image carrier.
Liquid ink is used preferably having a solid matter content of 20% or more. This liquid ink contains a carrier liquid that is preferably non-odorous, nonflammable, environmentally friendly and nontoxic. Preferably, water is used as a carrier liquid.
The use of a liquid ink has the advantage that it can easily be stored in a reservoir, that no segregation and no phase separation take place in the reservoir and the associated transport lines, and that the ink does neither irreversibly dry onto the reservoir nor onto the associated transport lines. By means of the addition of a carrier liquid, the solid matter concentration or the ink concentration can easily be varied. The liquid ink can be supplied such that an ink concentrate and the carrier liquid can be stored and transported separately from one another.
Owing to the injection of a defined excess charge into the droplets to be transferred during detachment of these droplets from the applicator element, an unintended background inking is avoided.
An air gap is present between the surface of the applicator element and the surface of the latent image carrier, the air gap being overcome by the liquid ink. This inking of the potential pattern on the latent image carrier across an air gap has the advantage that no wear takes place on the latent image carrier, wear is at least minimized. When the droplets overcome the air gap, they are focused in accordance with the potential pattern, this resulting in a sharp line formation. The liquid ink image aligns itself automatically in accordance with the potential pattern, this particularly allowing a clear definition of the image edges.
The use of liquid ink further has the advantage that relatively thin ink layers can be generated on the final image carrier. In this way, the ink consumption is low and high printing speeds can be achieved. Advantages also result with regard to the fixing of the ink image on the final image carrier. The energy to be expended can be reduced and the processing speed can be increased.
The potential pattern on the latent image carrier is preferably formed as an electrostatic charge image. It is, however, also possible to generate a potential pattern in the form of magnetic field lines. In this case, the liquid ink should contain carrier particles that can be magnetically influenced and have the effect that ink is transferred onto the latent image carrier by overcoming the air gap and ink the latent image. The term “electrographic printing or copying” means that a plurality of electrically operating methods can be used with which a latent image can be generated on a latent image carrier.
An alternating force field is present in the air gap, the force field acting on the liquid layer. An alternating electric field and/or an alternating magnetic field and/or an alternating acoustic field, particularly an ultrasonic field, can be used as an alternating force field. In practice, it has shown that such an alternating field is advantageous in order to generate fine printing structures. The alternating force field supports the formation of droplets in the liquid layer or the formation of small channels between the liquid layer and the surface of the latent image carrier.
Advantageously, the respective alternating field has a frequency of greater than or equal to 200 Hz, in particular a frequency of 1 kHz to 20 kHz, and preferably a frequency of 1 kHz to 5 kHz. At the frequencies mentioned, a favorable printing result can be achieved.
According to one embodiment, the gap width of the air gap is set depending on the printing resolution. As a printing resolution, usually the measure dpi is used, i.e. “dots-per-inch”. Preferably, the gap width is set such that it is two times to twenty times the distance between the picture elements, given a predetermined print point resolution, in particular five times to ten times the distance. Given a print point resolution of dpi=600, the distance between two picture elements is 42 μm. A favorable gap width of the air gap is then about 200 μm.
The surface tension and the viscosity of the liquid layer are of particular importance for a good printing result. Two embodiments A and B with different emphasis of the parameters are presented. In the first embodiment A, a relatively low surface tension and a relatively low viscosity are selected. Typically, the surface tension lies in the range of 20 to 45 mN/m, in particular in the range of 25 to 35 mN/m. The corresponding viscosity is set in the range of 0.8 to 50 mPa·s, in particular in the range of 3 to 30 mPa·s. The values mentioned for the surface tension and for the viscosity minimize the energy required for the formation of liquid channels between the liquid layer on the applicator surface and the surface of the latent image carrier. At the same time, the surface energy that has been set prevents the liquid from permanently depositing on image locations of the latent image carrier that are not to be inked.
In the second embodiment B, a relatively high surface tension and a viscosity adapted thereto are employed for the liquid. For this example, the surface tension lies in the range of 50 to 80 mN/m, preferably in the range of 55 to 70 mN/m. The viscosity has a value in the range of 0.8 to 300 mPa·s. With the values selected for the surface tension and the viscosity of the liquid, liquid droplets that can easily be separated form on the surface of the applicator. Owing to the high surface tension of the liquid, these droplets do not adhere to image locations on the latent image carrier that are not to be inked. By adapting the viscosity, the droplets obtain the property that upon collisions between droplets, a droplet and the surface of the latent image carrier or droplets and the applicator surface there mainly result elastic deformations of the droplets; as a result thereof, agglomeration of the droplets or wetting of the surface of the latent image carrier at image locations that are not to be inked, is avoided.
According to a further aspect, a method for electrographic printing or copying is specified.
According to another aspect, an applicator element is specified that can accept an ink-containing liquid layer.
A further aspect relates to a cleaning station that serves to clean the latent image carrier or an intermediate carrier of residual ink and to reestablish a defined initial condition after the transfer printing of the ink image.
Conventionally, a regeneration of the surface of the latent image carrier, for example a photoconductor, takes place by erasing exposure and by the effects of the electric field of a discharge corotron. Regeneration with respect to the surface energy does not take place. According to the mentioned aspect, the inventive regeneration station allows a regeneration of the surface of the latent image carrier with regard to maintenance of a defined surface energy.
With the aid of the before-mentioned cleaning station and the regeneration station, it is possible to realize a continuous cleaning in conjunction with the regeneration of the surface energy conditions of a surface bearing liquid ink. In addition, a regeneration of the charge carrier injection conditions of the surface of the latent image carrier takes place. The continuous cleaning in conjunction with the regeneration extends the working life of the image carrier, i.e. of a latent image carrier or an intermediate carrier. The regeneration of the latent image carrier and of a possibly following intermediate carrier can be coordinated such that there are always constant adhesion conditions at the point of contact. In this way, the transfer of the ink image is improved. Further, by means of the cleaning of the latent image carrier or of the intermediate carrier, ink can be recovered and can be reused for further printing processes.
A further aspect relates to a regeneration station that establishes the defined initial condition for a latent image carrier.
A further aspect relates to an arrangement and a method for the electrographic printing or copying, in which a band-shaped intermediate carrier is used on which a latent image forms.
As one preferred embodiment,
At the circumference of the photoconductor drum 12, there are arranged an exposure station 18, a corotron 20, a light source 22 for generating a latent image on the photoconductor drum 12, an inking station 24 with an applicator roller 26, a hot air generator 28, a cleaning station 30 and a regeneration station 32. The functions of these units 18 through 32 will be explained in more detail below.
At the circumference of the intermediate carrier drum 14, there are arranged a further cleaning station 34 and a hot air station 35. The further cleaning station 34 can have the same structure as the cleaning station 30.
A doctor blade 46 acts at the outer circumference of the scoop roller 40, the doctor blade 46 having the effect that only the volume of ink that is contained in the cups 42 is conveyed. The feed roller 36 is deformable. The cups 42 empty themselves on the surface of the feed roller so that the smooth liquid film 38 is formed thereon. This liquid film 38 is brought to the applicator roller 26.
The feed roller 36 can rotate in the same or in opposite direction with regard to the applicator roller 26. Preferably, the applicator roller 26 and the feed roller 36 rotate in the same direction, as shown in
For supporting the transfer of the droplets 50 from the surface of the applicator roller 26 onto the surface of the photoconductor 12, a bias potential UB in the form of a direct voltage is applied to the applicator roller 26. Due to this bias potential UB, there results a potential contrast between image locations on the photoconductor 12 and the bias potential UB. In addition, an alternating voltage having a frequency of preferably 5 kHz or more can be superimposed on the bias potential UB.
The potential pattern on the photoconductor 12 is referenced UP. This potential pattern UP is generated as a charge image for example with the aid of a conventional electrographic process by means of charging with a corotron 20 (see
At the image locations of the surface of the photoconductor 12 that are defined by the potential pattern UP, there results a charge transfer within the liquid droplets in the droplet covering 48 due to the difference in potential and as a consequence thereof there results a detachment of droplets, for example of the droplet 50. Moreover, during the detachment an excess charge is injected into the droplet. As a result of the effect of the electric field and the kinetic impulse or kinetic momentum, the droplet 50 moves towards the photoconductor surface and, by means of the field lines, is focused onto the image locations that are to be developed.
Alternative embodiments of an inking station can comprise an anilox roller with a chamber doctor blade as scoop roller. Another alternative provides that a smooth liquid film is sprayed onto the feed roller. A further alternative embodiment provides that the applicator roller dips with one portion thereof into a bath with ink and that the dosage of the accepted amount of liquid is effected via an elastic roll doctor that acts on the surface of the applicator roller. Further alternative embodiments of the inking station will be explained further below.
In
In the following
The applicator roller 26 of
In the areas 80 left vacant from the first areas 78, the surface energy is increased so that there is the tendency to form droplets. The cover layer can, for example, be made of the material DLC (diamond like carbon). The doping of the first areas 78 can be selected such that an almost rectangular transition of the conductivity is present. Alternatively, a soft, continuous transition can likewise be selected. The type of the transition and also the size of the first areas 78 and the vacant areas 80 define the size of the droplets. In this way, droplets can be generated that have a diameter of up to 10 μm at a maximum and can easily be detached from the areas 80.
The advantage of the arrangement shown in
The combination of two materials allows for multiple alternatives. For example, ceramics can be provided as a first material and Teflon as a second material. Further, as a first material, DLC material, F-DLC material (fluor diamond like carbon material) or SICON material can be provided and Teflon as a second material. A further material combination results, when an Ni layer or a layer made of an Ni alloy, preferably CrNi, is provided as a first material and Teflon is provided as a second material, the Teflon material preferably being embedded in the Ni layer in the form of pellets.
The advantages of the arrangement according to
The next example shows the second areas 86 that have the form of cups and have a varied surface energy. The next example shows the surface structure with the third areas of a microscopic regular surface contour. The next example shows a stochastically distributed surface contour with third areas 88. The further example shows a surface structure with a combination of first areas 78 and second areas 86. The further example shows a combination of first areas 78 of varied conductivity and third areas 88 with a microscopic surface contour. The last but one example shows the combination of second areas 86 and third areas 88. The last example shows a surface structure with a combination of first areas 78, second areas 86 and third areas 88.
In the following, further units of the printer device shown in
Instead of the intermediate carrier drum 14, a band can alternatively be provided as an intermediate carrier, said band having a defined electrical resistance, preferably in the range of 105 to 1013 Ωcm and being advanced to the inked image on the latent image carrier, for example the photoconductor drum 12, by a highly electrically conductive element which is preferably made of a metal. This band, too, preferably carries an electric potential on the surface, which potential supports the transfer of the liquid image from the latent image carrier to the intermediate carrier. The electric potential of the surface of the intermediate carrier is set by an auxiliary voltage, which is directly applied to the intermediate carrier or to the highly electrically conductive element, which advances the intermediate carrier surface to the inked image on the latent image carrier. This auxiliary voltage can include direct voltage components and alternating voltage components.
At the point of transfer from the latent image carrier to the intermediate carrier, for example the intermediate carrier drum 14, there results the following relationship with respect to the adhesive forces: the cohesion of the ink image is greater than the adhesion between the intermediate carrier and the ink image; the adhesion between the intermediate carrier and the ink image is in turn greater than the adhesion between the surface of the latent image carrier and the ink image. Due to these relations of adhesive forces, the ink image is transferred from the latent image carrier onto the intermediate carrier.
At the intermediate carrier, the viscosity of the transferred ink image can be further increased by suitable means, preferably by a dry hot air stream. In this way, it is guaranteed that the cohesion of the ink image is sufficiently high to ensure a complete transfer onto the final image carrier 10. Further, it is ensured that in the operating mode “collecting mode”, which will be explained in more detail further below, each ink image that has been generated last has a lower cohesion than the respective previously collected ink images. In this way, a back transfer of ink onto the surface of the photoconductor is avoided.
According to
A cleaning station 30 or a cleaning station 34 is arranged at the circumference of the photoconductor drum 12 or of the intermediate carrier drum 14. These cleaning stations 30, 34 serve to remove the remainders of the ink image that is still left after transfer printing. The structure of the cleaning station 30 or 34 will be explained in more detail further below. Further, following the cleaning station 30, a regeneration station 32 is arranged at the circumference of the photoconductor drum 12, the regeneration station generating defined surface properties and charge injection conditions on the surface of the photoconductor drum 12.
For the realization of a multicolor print on the final image carrier 10, various operating modes can be provided. In a first operating mode, various color image separations are generated successively on the latent image carrier, i.e. the photoconductor drum 12, and are successively transferred directly onto the final image carrier 10.
In a second operating mode, several color image separations are superimposed on the photoconductor 12. The superimposed color image separations are then transferred jointly onto the final image carrier 10.
A third operating mode provides that for the realization of a multicolor print, several color image separations are generated successively on the latent image carrier and are superimposed on the intermediate carrier. The superimposed color image separations are jointly transferred from the intermediate carrier onto the final image carrier 10.
In a fourth operating mode, a printing unit comprising a latent image carrier and an applicator element is provided for each color image separation, the printing units each generating a color separation. The various color separations are successively transferred with register accuracy directly onto the final image carrier 10 or first onto an intermediate carrier, e.g. the intermediate carrier drum 14, and are transferred from there onto the final image carrier 10. This operating mode is also referred to as single pass method.
A fifth operating mode is characterized in that for the realization of a multicolor print, a single latent image carrier is provided to which a plurality of applicator elements, for example of the type of the applicator roller 26, is allocated. Each applicator element generates a color image separation that is transferred directly onto the final image carrier 10 or first onto an intermediate carrier and from there onto the final image carrier 10. This operating mode is also referred to as multi-pass method.
An embodiment of the single pass method presents up to five complete printing units, each having a character generator, a latent image carrier and at least one inking station, and has one joint intermediate carrier. The multicolored image is generated in a single pass. For this purpose, the individual partial color images are generated on the latent image carriers allocated to them with such a temporal distance that they hit the same surface area of the intermediate carrier with register accuracy, the intermediate carrier being successively moved past the individual inked latent image carriers and, in contact with those, accepts the partial color images. As a result of the superposition on the intermediate carrier, the partial color images jointly form the mixed color image. The cohesion of the individual ink images is set on the respective latent image carrier such that the cohesion of the ink image that has first been transferred onto the intermediate carrier is higher than that of each following ink image. This can, for example, be achieved by a respectively differently progressed dried state of the ink images.
The cleaning station 30 shown in
Numerous modifications of the cleaning station are possible. For example, the cleaning station can include a removal roller that is pressed against the surface of the image carrier. A doctor blade, which is arranged following the point of contact as viewed in the direction of rotation of the removal roller, serves to strip off the ink accepted by the removal roller. Preferably, the removal roller dips into a bath with carrier liquid. After passing through the bath, a further doctor blade can be arranged at the circumference of the removal roller in order to strip off the liquid at the surface of the removal roller. The surface energy of the surface of the removal roller should be set such that between the residual ink and the surface of the removal roller an adhesion is present that is higher than the cohesion within the residual ink. The cohesion within the residual ink should be greater than the adhesion between the residual ink and the surface of the image carrier.
Another embodiment of the cleaning station comprises a cleaning fleece that is pressed against the image carrier. Preferably, the cleaning fleece is moved at a speed that is considerably lower than the circumferential speed of the image carrier. The cleaning fleece can be designed as a continuous band that, after contact with the surface of the image carrier is passed through a bath filled with carrier liquid. Thus, the ink is dissolved and removed from the cleaning fleece. A doctor blade and preferably ultrasound are applied to the continuous band. After leaving the bath, excess carrier liquid is removed from the continuous band, preferably with the aid of a pair of press rollers.
Alternatively, the cleaning fleece can be rolled onto a supply roll and is brought into contact with the surface of the image carrier with the aid of a roller and a saddle. Subsequently, the cleaning fleece is wound up onto a take-up roll. The cleaning fleece is moved stepwise from the supply roll to the take-up roll. Between two steps, up to several thousands of sheets can be printed.
In a further alternative of the cleaning station, the station comprises a doctor blade that is pressed against the image carrier. If the image carrier is present in the form of a band, a roller or a rod can be provided as a counter-bearing for the doctor blade.
In another embodiment of the cleaning station, the station includes a splash bath device that directs a jet of cleaning liquid onto the surface of the image carrier. The carrier liquid of the ink is preferably used as a cleaning liquid.
Another alternative of the cleaning station includes a roller bath device that supplies cleaning liquid to the surface of the image carrier with the aid of a roller. This cleaning liquid, preferably the carrier liquid of the ink, dissolves the residual ink that is transported away upon rotation of the roller. A doctor blade, which strips off the dissolved liquid ink, then acts on the roller.
Another alternative of the cleaning station includes an air knife. It displaces the liquid ink from the image carrier to be cleaned. The displaced residual ink can be collected, treated and reused for the printing process.
Another embodiment of a cleaning station includes a suction device, which sucks the residual liquid ink from the surface of the image carrier. The sucked-off discharge air can be filtered and the liquid ink can be separated and is preferably reused in the further printing process.
As viewed in the direction of motion of the image carrier, a dissolving station (not shown) can optionally be arranged before the cleaning station 30, said dissolving station applying a cleaning liquid onto the surface of the image carrier. A scoop roller can be provided for the application; alternatively, a section of the image carrier can pass through a bath with cleaning liquid. It is advantageous when the carrier liquid of the ink is used as the cleaning liquid. It is advantageous when an ultrasonic energy is applied to the point of contact between cleaning liquid and image carrier.
In the embodiment shown in
Further, the regeneration station can include a corona device that has a corona with an alternating voltage in the range of 1 to 20 kVpp (measured from peak to peak) at a frequency in the range of 1 to 10 kHz. This corona device can be used as an alternative with respect to the application of the substance or in combination together with the substance.
In a further alternative, the cleaning and the regeneration take place in a combined manner in one single operation. For example, the splash bath cleaning or a roller bath cleaning is used. For this purpose, a substance that controls the surface energy, preferably a tenside solution, is added to the cleaning liquid. This substance is then transferred onto the image carrier together with the cleaning liquid. Excess cleaning liquid can again be removed, with the possibility that such remainders are supplied to a recycling process.
Optionally, if cleaning is performed with a cleaning liquid and an added substance that controls the surface energy and after a regeneration has taken place, a drying of the surface of the image carrier by suitable means can take place, for example by means of a warm and dry air stream that is directed onto the surface. This drying serves to increase the surface-active components and as a result thereof to increase their effect. Moreover, a possibly disturbing effect of excess cleaning liquid is avoided.
In the following, photodielectric image generation processes are explained with the aid of which latent images can be generated on a photoconductor, which latent images can be inked by the liquid ink by overcoming the air gap. For this purpose, an image-wise distributed electric field is generated with the aid of the layer system of the photoconductor, the components of which electric field, in the space above the surface, exert a force effect on charged particles, and polarizable and conductive objects, i.e. for example on polarizable components of the ink liquid. The electric field distribution on the surface of the photoconductor is made visible during the development with the aid of the transferring liquid ink. The cleaning of the upper-most layer of the photoconductor that comes into contact with the ink has to be adapted to the particularities of the liquid ink. In addition to a cleaning of this surface and the establishment of a defined charge condition of the upper insulating cover layer of the photoconductor, the surface energy condition of this cover layer also has to be re-established or, respectively, maintained after each ink transfer change. Accordingly, the material of the upper insulating cover layer of the photoconductor has to be adapted to the use of aqueous ink. For inking the surface of the photoconductor, the surface energy conditions have to be such that in the latent image areas that are to be inked, the carrier liquid with the ink adheres to the surface. This adhesion requirement must at least be valid for the solid matter content of the ink. In the areas of the surface of the photoconductor that are not to be inked, the electrical repulsive effect has to predominate such that no liquid comes into contact with the insulating surface of the photoconductor.
An alternative is provided in the fact that due to the stability of the electric field above the insulating cover layer of the photoconductor a permanent supply of the ink-containing liquid to this insulating layer can also take place, the polarity of the solid ink particles in the liquid having to be such that these particles are attracted by the electric field in the areas to be inked. In the areas that are not to be inked, the electric field direction is reversed so that charged solid ink particles are repelled.
An image-wise inking of the cover layer of the photoconductor can also be achieved in that the areas to be inked are wetted relatively well by the combined effect of the surface energy relationship between the insulating cover layer and the liquid and the electric field, and the areas that are not to be inked are wetted relatively poorly as a result of the reversed field direction. This type of inking or the combination with the deposition of the charged solid ink particles is particularly suitable for the development process at high speed. In order to realize a high speed process with a pure particle deposition without substantial wetting differences between the areas that are to be inked and those that are not to be inked, the liquid layer has to be very thin and the concentration of the solid ink particles has to be relatively high. A particle charge as large as possible is advantageous for the high-speed development.
According to one embodiment, for a conventional photoconductor with an externally positioned photoconductive layer, this photoconductive layer can be provided with a thin insulating cover layer. This cover layer is selected such that it meets the requirements made to the wettability and to further surface properties, such as the charge injection property, for the acceptance and the release of liquid ink.
In
With reference to
In the image generation process according to
In
The band-shaped intermediate carrier is arranged between the respective applicator element A1 trough A5 and the associated latent image carrier LT1 through LT5. Due to the electrical properties of the intermediate carrier 116, a corresponding potential image or latent image as also presented by the surface of the respective latent image carrier LT1 through LT5 forms on the surface that faces the respective applicator element A1 through A5. In this respect, the intermediate carrier band can also be referred to as latent image carrier. The latent image of the band-shaped intermediate carrier 116 is inked by the applicator elements A1 through A5, droplets of the liquid layer of the respective applicator roller being transferred onto the surface of the band-shaped intermediate carrier 116 by overcoming an air gap. Thus, the printing units DE1 through DE5 each generate one color separation. The various color separations are superimposed on one another with register accuracy upon circulation of the intermediate carrier band 116. At the transfer printing location 118, the superimposed color separations are transferred onto the final image carrier 10, for example a paper web. The intermediate carrier 116 and the final image carrier move in the direction of the arrows 120 or 122. As viewed in the running direction of the intermediate carrier 116, a station 124 is arranged before the first printing unit DE1, said station taking over the function of a cleaning and/or a regeneration for the band-shaped intermediate carrier 116, as described further above in connection with the cleaning station 30 and the regeneration station 31.
The arrangement according to
Instead of the intermediate carrier 116 in
While a preferred embodiment has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 100 27 173 | May 2000 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP01/06199 | 5/31/2001 | WO | 00 | 4/15/2003 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO01/92959 | 12/6/2001 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20030175048 A1 | Sep 2003 | US |
