JPH11202631A - Image pickup device and method using liquid developer layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the image separation of a liquid developer layer and developing efficiency accompanied therewith and to optimize output image quality by applying charge to the layer or removing it from the layer and further increasing the operation tolerance of a contact electrostatic printing process. SOLUTION: A latent image is obtained by forming electric field in an image direction in a processing unit 59 and the liquid developer layer is separated to an image area and a non-image area. A liquid developer supply device 50 is equipped with a supply roller 56 moving the liquid developer on the surface of a liquid developer layer coating machine 40. The liquid developer layer is formed on the surface of the machine 40 only by giving an appropriate proximity distance and/or contact pressure between the roller 56 and the roll surface of the layer coating member 40. An electric bias source 45 is coupled with the machine 40 and electric bias is applied to the machine 40, so that the electrostatic field is generated between the surface of the machine 40 and an image surface or a non-image surface on the surface of an image pickup member 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electrostatographic printing with a liquid developer, and more particularly, to a liquid developer by pressing a substantially uniform charged liquid developer layer against a latent image holding surface. An electrostatic latent image development system that causes selective image direction separation of layers to produce the required output image corresponding to the latent image.

[0002]

2. Description of the Related Art In general, processes relating to electrostatography and electrostatography printing involve selectively charging and / or charging a charge receiving imaging member in response to an input document or imaging signal.
Alternatively, the discharge is started to generate an electrostatic latent image on the imaging member. The electrostatic latent image is then developed into a visible image by a process that brings the charged toner particles closer to the latent image and causes the charged toner particles to migrate to the image surface of the latent image. Generally, the developer may contain carrier particles to which the marking particles, i.e., toner particles, are adhered by triboelectricity. In this case, the toner particles are electrostatically separated from the carrier particles and adhere to the latent image surface to form a powder toner image on the imaging member. In a variant, the developer may comprise a liquid developer containing a carrier liquid impregnated with charged colored marking particles (ie, so-called toner solids). In this case, the charge on the marking particles is formed by a soluble ionic surfactant, ie a so-called charge director agent dispersed and / or dissolved in the liquid carrier / marking particle composition, and formed by the marking particles and the charge director. An electrochemical reaction is caused to exchange ionic species with the micelles. While this electrochemical reaction causes a charge to form on the toner particles,
This reaction also produces mobile charges in the liquid developer in the form of co-ions, counter-ions and other similar mobile charge species.

Regardless of the type of developer used, the toner or marking particles of the developer are generally uniformly charged by either triboelectric or charge directors and are electrostatically attracted to the latent image via an electrostatic field. Then, a visible developed image corresponding to the latent image is formed on the imaging member. In the case of a conventional developing process using a liquid developer, the liquid developer generally adheres to the surface of the latent image holding member, causes the charged marking particles to be electrically precipitated from the liquid developer dispersion liquid, and migrates to the image surface of the latent image. Together with the latent image on the image surface,
Form a developer image. The developed image is then directly or indirectly transferred from the imaging member to a copy substrate, such as paper,
This produces an output document called a "hard copy". In a final step, the imaging member is cleaned and any residual developer and / or charge is removed from the imaging member in preparation for a subsequent imaging cycle.

As noted above, a typical electrostatographic printing process physically transports a developer containing toner particles or marking particles near a latent image bearing imaging member and transfers the toner particles or marking particles to their electrical charge. A developing step of causing the latent image to migrate to the image surface by the attractive force and selectively adhering to the imaging member in the image direction configuration. The development process is most effectively accomplished when the particles are oppositely charged in polarity and polarity of the latent image, and the amount of toner or marking particles attached to the latent image is proportional to the electric field associated with the image surface.

[0005] Many different variants of developing a latent image include:
Electrophotographic printing systems and electrophotographic copying systems have been described in the art. Of particular interest to the present invention is forming a thin layer of liquid developer containing a high concentration of charged marking particles on a surface, contacting this layer on another surface with an electrostatic latent image, The idea is to develop the latent image as a function of the electric field intensity generated by the latent image at the same time as the separation of the first surface from the second surface. In this process, the migration or electrophoresis of the toner particles is replaced by a direct surface-to-surface transfer of the toner layer induced by an electric field in the image direction. For the purpose of the present description, the concept of latent image development via direct surface-to-surface transfer of the toner layer via an image-directional electric field is commonly known as contact electrostatic printing (CEP). An example of a patent describing certain general aspects of CEP, along with its particular device, is found in Landa
It is found in U.S. Patent Nos. 5,436,706 and 5,596,396 issued to da) et al.

US Pat. No. 5,436,706 discloses an image pickup apparatus having a first member having a first surface on which an electrostatic latent image is formed. In this case, the electrostatic latent image includes an image area at the first voltage and a background area at the second voltage. A second member charged to a third voltage intermediate the first and second voltages while resiliently engaging the second surface with the first surface is also provided.

US Pat. No. 5,596,396 discloses that an electrostatic latent image includes an image area at a first voltage and a background area at a second voltage, the first surface having the electrostatic latent image formed thereon. A first member having a second surface charged to a third voltage intermediate the first and second voltages and having a second surface resiliently engaged with the first surface; And an imaging device comprising a third member resiliently contacting the second surface in the transfer area. The imaging device also includes a device for supplying liquid toner to the transfer area to form a thin layer of toner liquid containing a relatively high concentration of charged toner particles on the second surface and a layer of toner liquid. An apparatus is also provided for developing the latent image by selectively transferring portions from the second surface to the first surface.

[0008]

The image quality in electrostatographic printing applications, including CEP, is of course not limited to the charge levels and densities in both the latent image and the developer itself, but can be used to develop images that include them. It can vary considerably due to many conditions that affect it. In the case of toner migration, electrophoretic sedimentation, or CEP, it is these charges that generate the necessary electrical force to cause selective separation of the toner layer in the image direction and produce the required output image. It is. Further, in the case of a specific CEP in which the concentrated layer of the liquid developer receives a contact pressure in addition to the electric field to cause selective separation of the liquid developer layer in the image direction, the magnitude of the charge in the liquid developer layer and It has been found advantageous to selectively modify the charge density. Accordingly, the present invention improves the image separation and associated development efficiency of an imagewise separated liquid developer layer by adding or removing charge from a layer, as well as a contact electrostatic printing process. CEP with charge correction device to increase the operating tolerance of the device and optimize the output image quality
The aim is to get the system.

[0009]

According to one aspect of the present invention, an image surface formed by a first voltage potential and a non-image surface formed by a second voltage potential are provided. A first movable member forming an electrostatic latent image, a second movable member operably engaged with the first movable member to form a process nip between the first movable member and the first movable member, A liquid developer supply device for forming a liquid developer layer on a surface associated with one of the first or second possible members and transferring the liquid developer layer to a process nip; and transferring the liquid developer layer to the process nip An image pickup device is provided with a charge correction device that adjusts the charge in the liquid developer layer before performing the operation.

According to another aspect of the present invention, a first electrostatic latent image is formed that includes an image surface formed by a first voltage potential and a non-image surface formed by a second voltage potential. Providing a process nip between the first movable member and the first movable member, wherein the second movable member is operably engaged with the first movable member; Supplying a liquid developer layer to a surface associated with one of the possible members, and charging the liquid developer layer with a net via an external charge application source,
Transferring the liquid developer layer to the process nip. In this case, the electrostatic latent image on the first member generates an image direction electric field across the liquid developer layer in the process nip. The charge modifying device may operate to remove or partially remove mobile charge species from the liquid developer layer.

According to another aspect of the present invention, a first electrostatic latent image forming apparatus includes an image surface formed by a first voltage potential and a non-image surface formed by a second voltage potential. Associated with one of the second movable member, the first or second possible member operatively engaged with the first movable member to form a process nip with the first movable member. A liquid developer supply device for forming a liquid developer layer on the surface thus formed, and transferring the liquid developer layer to a process nip;
Also, an image pickup device provided with a charge correcting device for charging the liquid developer layer before transferring the liquid developer layer to the process nip is provided.

According to another aspect of the present invention, a first electrostatic latent image forming method includes an image surface formed by a first voltage potential and a non-image surface formed by a second voltage potential. Providing a movable member, the second movable portion is operably engaged with the first movable member, forming a process nip between the first movable member,
Electrostatographic imaging including forming a liquid developer layer having a substantial net charge on a surface associated with one of the first or second movable members, and transferring the liquid developer layer to a process nip. The process is disclosed. In this case, the electrostatic latent image on the first member generates an image direction electric field across the liquid developer layer in the process nip. The charge modifying device may operate to remove or partially remove mobile charge species from the liquid developer layer.

According to still another aspect of the present invention, there is provided a liquid developer delivery system for transferring a liquid developer layer containing charged toner particles immersed in a liquid carrier medium and bringing the liquid developer layer into contact with a latent image holding surface. An electrostatographic printing system is provided. In this case, a means is also provided for generating a net electrical charge in the liquid developer before contacting the latent image holding surface. The means for generating net charge in the electrostatographic printing system may act to remove mobile charged species from the liquid developer layer or may be substantially equal to the charge level associated with the charged toner particles. The agent may act to charge the net.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to FIG. 1, which illustrates an imaging device constructed and operative in accordance with one possible embodiment of the present invention. The apparatus of FIG. 1 includes a first movable member in the form of an imaging member 10 having any type of imaging surface capable of forming an electrostatic latent image. The copy substrate 70, for example, paper
It is pinched and moved between the roller 80 and the imaging member 10. The example imaging member 10 may comprise a typical photoconductor or other photosensitive element of a type known to those skilled in the art of electrostatography, in which case the surface layer 14 having photoconductive properties is provided. Are supported on the conductive support substrate 16. The following description, for example, describes a system and process according to the present invention that incorporates a photosensitive imaging member, but the present invention is not limited to such non-photosensitive members, such as dielectric charge holding members of the type used in ionographic printing machines. It goes without saying that the use of various variants of imaging members known in the field of electrostatographic printing, including but not limited to imaging members or electroded sub-structures capable of producing charged latent images, is of course considered. Would be.

The imaging member 10 rotates as indicated by arrow 12 to move its surface in the process direction and performs a series of image forming steps in a manner similar to a typical electrostatographic printing process. Although the imaging member 10 is shown and described herein in the form of a drum, in a variant, the imaging member is carried around a series of rollers and in the form of a continuous flexible belt movable in the same direction as shown. It goes without saying that it may be formed.

In the exemplary embodiment of FIG. 1, initially the photoconductive surface 14 of the imaging member 10 is
0 through a charging station that charges the surface of the imaging member 10 with a substantially uniform static charge. Corona generator 20 is provided to charge photoconductive surface 14 of imaging member 10 to a relatively high and substantially uniform charge potential. Among various charging devices, such as charge rollers and charge brushes, and others known in the art, inductive charging devices and semiconductor charging devices are utilized at the charging station to provide the photoconductive surface 14 of the imaging member 10 with a photoconductive surface. It goes without saying that it may be charged to a substantially uniform potential.

After the imaging member 10 has reached a substantially uniform charge potential, the charged surface advances to an image exposure station generally identified by the reference numeral 30. The image exposure station projects a light image corresponding to the input image on the charged photoconductive surface. In this case, the light image selectively dissipates the charge on the photoconductive surface 14 and records an electrostatic latent image on the imaging member 10. An electrostatic latent image generally includes an image surface formed by a first charge voltage potential and a non-image surface formed by a second charge voltage potential in an image configuration corresponding to input image information. The image exposure station may incorporate various optical image projection and imaging elements known in the art, and may include an imaging member 10.
It will be appreciated that various known optical lenses or digital scanning systems for forming or projecting an image from the input document may be provided thereon. In a variation, various other electronic devices available in the art may be used to generate electrical information to form an electrostatic latent image on the imaging member 10. It will be appreciated that the electrostatic latent image may include image and non-image surfaces formed by regions having opposite charge polarities or by regions having distinguishable first and second voltage potentials of the same charge polarity. Would be.

As described above, in a typical electrostatographic printing process, an electrostatic latent image is generated on the surface of an imaging member, and then the developer is transported to the vicinity of the latent image-bearing imaging member, thereby forming a latent image. Develop the image into a visible image. In this case, the voltage potential difference associated with the image and non-image surfaces of the latent image induces selective attraction of the individual toner particles depending on the required image to be generated. In many systems using liquid developer, the developer deposited on the latent image is generally
It is a liquid composition having a low solids content having a relatively low concentration of charged toner particles dispersed in a liquid carrier agent. In this case, the image is developed by electrophoretic sedimentation of charged toner particles from the dispersion. In contrast, according to the so-called contact electrostatic printing process according to the invention,
A thin layer of a liquid developer having a high toner solid content having a relatively high concentration of charged toner particles dispersed in a liquid carrier is pressed against the entire surface of the latent image holding and imaging member 10. Thus, the developed image is formed by separating and selectively transferring the liquid developer layer according to the image area and the non-image area of the latent image.

Therefore, according to the known CEP process,
After the liquid developer layer or toner cake 58 is formed on the surface of the liquid developer layer applicator, the toner cake 58 is applied to the process nip 59 formed by operable engagement of the layer applicator 40 with the imaging member 10. Transfer directly to At the process nip, the latent image forms an image-wise electric field within the process nip 59, separating the liquid developer layer into image and non-image areas and separating the layer in the image direction. Imaging member 1
It will be appreciated that the presence of a latent image on zero may create some fringe fields at the interface between the image and non-image surfaces of the latent image. But,
Image direction separation and development constitute a specific fragment of the toner cake associated with the image or non-image side of the latent image, quite unlike electrostatic attraction or sedimentation of individual toner particles dispersed in a carrier liquid. It occurs as a function of surface-to-surface transport of the aggregate or assemblage of particles.

The liquid developer layer with a high solids content used in CEP is generally characterized as having a solids content on the order of about 20% or more. In this case, the solid content of the liquid developer consists of charged marking particles, that is, charged toner particles. Accordingly, the liquid developer delivery system includes a liquid developer 58 having a high solids content,
That is, it is provided for transferring a so-called “toner cake” layer and pressing it against the latent image in the process nip 59. It will be appreciated that the toner cake may be formed either on the surface of the layer applicator 40 or on the surface of the imaging member 10 and transferred to the process nip.

[0021] Toner cakes having a solids content on the order of about 20% or more can be formed in a variety of ways.
According to the exemplary embodiment of FIG. 1, the movable member in the form of a liquid developer layer applicator 40 generally includes a fixed supply of a low concentration level of toner particles immersed in a liquid carrier material. Reservoir 52 containing liquid developer 54
Are provided in combination with the liquid developer supply device 50. This supply of liquid developer 54 also generally includes a charge director that provides a mechanism to cause an electrochemical reaction within the liquid developer composition that generates the required charge on the toner particles. While the charge director generates charge on the toner particles, the charge director also creates mobile charge species within the entire liquid developer, so that the overall liquid developer layer is substantially neutral Has a net charge. The present invention allows the use of such charge directors to be avoided, if desired, and also allows for the correction of the overall charge in the liquid developer layer to generate net charge in the liquid developer layer. This will be discussed later.

Generally, the liquid carrier medium is a developer 54
The quantity present in the initial supply of is high. Initially, the liquid carrier medium is present in an amount of about 85 to 99.5% by weight. However, percentage amounts may vary from this range as long as the objects of the present invention are achieved. By way of example, the liquid carrier medium is Exxon Corporation
and hydrocarbons such as high purity alkane having about 6 to about 14 carbon atoms, such as Norparl® 12, Norpar® 13 and Norpar® 15 available from the company. Although not limited to any of the several hydrocarbon liquids conventionally used for liquid development processes, including isoparaffinic hydrocarbons such as Isopearl RG, H, L and N, it is possible to select from a variety of materials including them. Good. Other examples of materials suitable for use as liquid carriers include American Mineral Spirit Company (American)
Amsco® 460 Solvent, available from Mineral Spirits Company)
Amsco® OMS, Phillips Petroleum Campani
(trademark) available from Mobil Oil Corporation, Pagasol (registered trademark) available from Mobil Oil Corporation, Shellsol (registered trademark) available from Shell Oil Company. And the like. Isoparaffin hydrocarbons are a preferred liquid medium because they are colorless and environmentally safe. These particular hydrocarbons may have a vapor pressure high enough for a thin film of liquid to evaporate from the contact surface within seconds at room temperature.

[0023] Toner particles, so-called marking particles, are notably described, for example, in US Pat. No. 3,729,419.
No. 3,841,893, No. 3,968,044
No. 4,476,210, No. 4,707,429
No. 4,762,764, No. 4,794,651
And any particulate matter that is compatible with the liquid carrier medium, such as those contained in the liquid developer disclosed in U.S. Pat. No. 5,451,483. Preferably, the toner particles have an average particle diameter ranging from about 0.2 to about 10 μm, and most preferably, from about 0.5 to about 2 μm. The toner particles may be present in an amount from about 5 to about 20% by weight of the developer composition. The toner particles
It may contain only pigment particles, or may contain resin and pigment, resin and dye, or may contain resin, pigment and dye, or may contain only resin.

Suitable resins include, for example, EI DuPont de Nem and Co., Wilmington, Delaware.
OURS & CO. ), Including poly (ethyl acrylate-co-vinyl pyrrolidone) and poly (N-vinyl-2-pyrrolidone), including Elvacs and / or Nukulère, available from Co. Suitable dyes include Orasol Blue 2GLN, Red G, Yellow 2GLN, Blue GN, Blue BLN, Black C, all available from Ciba-Geigy, Inc., Mississauga, Ontario.
Morton Chemical Company, Ajax, Ontario, USA
Chemical Company) Morphofast Blue 100, Red 101, Red 104, Yellow 102, Black 101, Black 1
08; Bismarck Brown R (Aldrich Ald
Rich), Neoran Blue (Sibaigagi), Sandos Campani (Sa), Mississauga, Ontario
subvinyl yellow RLS, black RLS, red 3GL, all available from ndoz Company)
S and Pink GBLS, etc., and US Pat.
No. 23,368, No. 5,484,670,
Many of the pigments described are mentioned, and these patents are incorporated herein by reference. The dye is generally present in an amount from about 5 to about 30% by weight of the toner particles. However, other amounts may be present as long as the object of the present invention is achieved.

Suitable pigmentary materials include Microrich® RCT, Degussa, available from BASF.
gussa), PRINTEX® 140V, Columbia Chemical Company (Co)
carbon blacks, such as Raven® 5250 and Raven® 5720, available from Lumbian Chemical Company. The pigment material may be colored, and the pigment material may be a magenta pigment such as Hostapan Pink E (American Hoechst Corporation) or Litol Scarlet (BASF), or a yellow pigment such as Diarylide Yellow (Dominion Color Company). And cyan pigments, such as Sudan Blue OS (BASF), and many of the pigments described and described in U.S. Patent Nos. 5,223,368 and 5,484,670, the disclosures of which are incorporated herein by reference. And incorporated herein by reference. In general, any pigmentary material is suitable so long as it contains small particles that are suitably co-existing with any polymeric material also included in the developer composition. The pigment material generally comprises from about 5 to about 60%, preferably from about 10 to about 30%, by weight of the toner particles.
Present in the amount.

As explained previously, the liquid carrier vehicle (l
In addition to the liquid carrier and the toner particles, typical liquid developers also aggregate into micelles or reverse micelles to promote and maintain a uniform charge on the marking particles in an effective solution of the liquid developer. It contains a charge director (sometimes called a charge control agent) in the form of a soluble ionic surfactant. It is believed that the toner or marking particles acquire charge by deprotonating micelles that form loosely bound counterions and co-ions in the presence of the charge director. Second, the micelles readily provide a reaction field for the generation of toner charge, thus imparting a selected polarity (positive or negative) charge to the marking particles, while providing a mobile charge in the overall liquid developer. It also gives rise to seeds. However, the entire liquid developer is neutral in the absence of an electric field, even if the toner particles are charged by the effect of mobile charged species. Examples of suitable charge director compounds include Fisher
Inc. ), A lecithin available from Chevron Chemical C.
OLOA1200, polyisobutylene succinimide, available from Witco Inc.
Inc. ), Zirconium octoate available from Nuodes, aluminum stearate in various forms; salts of calcium, manganese, magnesium and zinc; heptanoic acid; barium, aluminum,
Cobalt, magnesium, zinc, cerium and zirconium octoate salts and the like. The charge control agent is
It may be present in an amount of about 0.01 to about 3% by weight of the solids, preferably about 0.02 to about 0.05% by weight of the solids of the developer composition.

Returning now to the description of the liquid developer supply device 50, the device of the embodiment shown in FIG. 1 rotates in the direction indicated by the arrow 57 to rotate the liquid developer layer coating machine (layer coating member). Supply roller 5 for transporting the liquid developer onto the surface of 40
6 is provided. The liquid developer is preferably formed in the form of a relatively thin and substantially uniform layer 58 of toner particles tightly packed in a liquid carrier. Depending on the materials utilized in the liquid developer composition 54 and other process parameters relating to the printing system such as process speed, etc., preferably between 2 and 15 μm and more than 15% solids, more preferably 5 μm or less A liquid developer layer having a sufficient thickness and solids content on the order of 3 mm is obtained by simply providing an appropriate close distance and / or contact pressure between the supply roller 56 and the roll surface of the layer coating member 40. It can be formed on the surface of the agent layer coater 40. Alternatively, or additionally, when the liquid developer includes charged toner particles, an electrical bias source 55 may be coupled to the supply roller 56 as if the supply of the liquid developer 54 included a charge director compound. It may assist in electrostatically transferring toner particles onto the surface of layer coater 40. Thus, in one exemplary embodiment, the supply roller 56 can be combined with an electrical bias source 55 to perform a so-called forward bias scheme. In this case, the toner coating machine 56
Is provided with an electrical bias of sufficient magnitude and polarity to create an electric field extending from the supply roller 56 to the surface of the layer application member 40. These electric fields cause the toner particles to be transported substantially uniformly to the surface of the liquid developer layer applicator 40 to form a liquid developer layer 58 having concentrated and substantially uniform distribution of toner particles in the layer. Let it.

Although not limited to various known systems for the transfer of liquid developers having toner particles immersed in a carrier liquid, they are used in conventional lithographic printing and conventional liquid electrostatographic coatings, including them. It should be understood that toner layer 58 may be applied to the surface of layer applicator 40 using a number of other devices or devices, including various known devices. For example, the liquid transfer system includes a fountain-type device generally disclosed in U.S. Patent No. 5,519,473 (incorporated herein by reference) as generally illustrated in the alternative embodiment of FIG. No. In an embodiment of this variation, the housing forms a long opening to transport the liquid developer and contact the surface of the layer coater 40 with the liquid developer coater 152.
Is provided. Preferably, the housing also includes a flat surface adjacent the long opening so that the liquid developer can be applied to the layer coater 40.
To form a liquid developer adhering area which can flow freely in contact with the liquid developer. A reverse roll member 154 that is arranged adjacent to the liquid developer coating machine 152 and downstream from the liquid developer coating machine 152 is also provided. The roll member 154 can have two functions. That is, while the liquid developer is being adhered to the surface of the layer coating machine 40, the portion of the liquid carrier that is released from the liquid developer is adjusted to increase the toner solid concentration in the liquid developer, and / or the layer coating is performed. It serves two functions: electrostatically pressing the liquid developer against the surface of the machine 40 (via the combined bias source 155).

According to the exemplary apparatus of FIG. 1, the electrical bias source 45 is coupled to the liquid developer layer coater 40 and applies an electrical bias to the liquid developer layer coater 40 to cause the layer coater 40 to be electrically biased. An electrostatic field is generated between the surface of the imaging member 10 and the image surface or the non-image surface on the surface of the imaging member 10. These electrostatic fields are generated in opposite directions. That is, the direction is either the surface direction of the imaging member 10 or the surface direction of the layer coating machine 40 according to the image portion and the non-image portion of the latent image. In addition, these electrostatic fields are applied to the imaging member 10 and the layer coater 4 at the nip exit.
Toner layer (liquid developer layer) 5
8 is separated from the non-image surface and the liquid developer layer 58
Are simultaneously separated into an image portion and a non-image portion on the facing surfaces of the imaging member 10 and the layer coating machine 40 and developed. Biasing the liquid developer layer applicator 40 to repel the toner segments in the image plane, producing a developed image on the surface of the imaging member 10 consisting of selectively separated and developed portions of the toner cake 58; On the other hand, the background image by-product remains on the surface of the toner layer coater 40. The resulting image / background separation was illustrated in the system of FIG. In a modification, the layer developer 40 is repelled from the non-image surface toward the imaging member 10 while applying an electrical bias corresponding to the attraction of the toner segment to the image surface. The portion of the toner cake corresponding to the image surface is maintained on the surface of 40, and a developed image is generated on the image surface. The image / background separation that occurred in this variant was illustrated in the system of FIG.

As explained earlier, the development of the image in the process of the present invention occurs as a function of the surface-to-surface transport of the aggregates or aggregates of the particles that make up a particular piece of the toner cake. In this case, the toner cake is separated into image segments and non-image segments against the electrostatic attraction of individual toner particles dispersed in the carrier liquid.
Thus, contrary to normal electrophoretic development, the transfer of the concentrated layer of toner particles from the first surface to the second surface does not depend on the mobility of the toner particles in the liquid developer.
Rather, image quality is determined when the liquid developer layer flows into the nip by maintaining the integrity of the toner cake or liquid developer layer 58, and especially the toner particles therein as an aggregate of toner particles. It depends on whether the toner particles in the toner cake maintain their original distribution and density level and whether the toner particles can sustain the image pattern as the liquid developer layer passes through the nip. Similarly, at the nip exit, depending on the electric field in the image direction within the nip, the segment of the liquid developer layer associated with the image surface is maintained on one surface while the background or non-image surface is associated with the non-image surface. The segments of the liquid developer layer are maintained on the other surface. Image quality depends on whether toner particles in the liquid developer layer 58 can be sharply separated under the influence of an electric field along the image / background boundary where the electrostatic force is substantially zero.

The image quality and process tolerance of the CEP development process are critically dependent on the electric field contrast in the development nip, limited by the latent image in use. For example, there are certain known photosensitive materials and photosensitive members that can achieve higher charge contrast. It is also known that the conductive surface opposite the latent image in the development nip maximizes the electric field contrast at a given latent image.

In addition to the latent image contrast, the charge characteristics of the toner layer play an important role in the development process.
Conventional liquid development processes use chemically charged toner, which, in addition to producing charged marking particles, also generates a substantial amount of other mobile charged species (eg, co-ions, counter-ions). . When subjected to an external electric field, these mobile charge species move under the influence of the electric field, which in turn causes a shift in the charge distribution that reduces the electric field, ultimately causing the electric field to drop with sufficient charge supply and time. May be destroyed. CE
In P development, the presence of mobile charged species certainly reduces the effective contrast of the developer field on the toner particles, and thus affects image quality and process tolerances. It has been found that too much charge in the liquid developer layer causes the collapse of the development field and serious image degradation. The ratio between the total charge per unit area in the liquid developer layer and the charge contrast of the latent image is generally substantially less than 1,
Preferably, it is less than 1/2.

In the contact electrostatic printing process, the liquid developer layer in the form of a thin layer supported on the first surface is maintained under pressure in the process nip 59, so that the layer coating member 40 or the imaging By providing any of the members 10 in the form of a corresponding member, it is desirable that the surface of one member can conform in shape or characteristics to the other surface in the nip region. When the surface of the layer application member 40 having the toner cake is engaged with the latent image holding surface of the imaging member 10, the toner cake layer 58 is substantially uniformly distributed in the nip formed between the two surfaces. The movement of the toner particles and / or the flow of the liquid is negligible, and no distortion occurs or occurs between the toner particles in the toner cake 58.

After the developed image has been formed at the exit of the nip,
Either on the surface of the imaging member 10 or on the surface of the toner layer applicator 40, any known in the art including an electrostatic transfer device including a corona generator or bias transfer roll of the type described above. The developed image may subsequently be transferred to the copy substrate 70 via the means. Alternatively, a pressure transfer system may be used that includes a heating and / or chemical fusing device to assist in pressure transfer and to fix the developed image on the output copy substrate 70. In yet another variation, image transfer can be achieved using surface energy differences. In this case, the surface energy between the image and the member supporting the image before transfer is smaller than the surface energy between the image and the substrate 70 onto which the image is transferred. In one embodiment, shown in FIG. 1, the image is transferred to the copy substrate via a heated pressure roll, whereby pressure and heat are simultaneously applied to the image and transferred and fixed to the copy substrate 70 simultaneously. It will be appreciated that separate transfer and fusing systems may be provided. In this case, the fusing system, or so-called fixing system, may be operated using heat (by any means such as radiation, convection, conduction, induction, etc.) or other methods involving the introduction of a chemical fixing agent. May be operated using the known fixing process. Since the art of electrostatographic printing is known, it is pointed out that some ideas regarding transfer and / or fusing that can be advantageously used in combination with the system of the present invention are disclosed in the related patent literature.

In the last step in the process,
Background image byproducts remaining on either the imaging member 10 or the toner layer applicator 40 are removed from the surface and the surface is cleaned for subsequent imaging cycles.
FIG. 1 shows a simple blade-type cleaning device 90 that scrapes the surface of an imaging member as is known in the art. As a modified embodiment, a brush member or a roller member may be provided to remove the toner from the surface where the toner exists. In a preferred embodiment, the removed toner associated with the background image can be transferred to a toner reservoir or other recycle bin, and the waste toner can be recycled and reused to generate a toner cake in a subsequent imaging cycle. Once again, it is pointed out that some ideas regarding cleaning and toner regeneration that can be advantageously used in combination with the image direction development system of the present invention are disclosed in the related patent literature.

As described above, the conventional liquid developer system including the known CEP process uses the liquid developer 5.
The liquid developer layer 58 is formed by using the charged toner particles in 4. The charging of the toner particles in the system by the liquid developer generally generates a charge on the toner particles while also generating a mobile charge species in most liquid developers via a charge director or charge control agent. Achieved. These mobile charge species cause most liquid developers to have a net neutralizing charge. Accordingly, the liquid developer layer 58 formed on the surface of the liquid developer layer coater 40 has a neutralizing charge of the net formed by the charged toner particles and the mobile charge species. In prior art systems, the neutralized charge layer of this net of liquid developer is transferred directly to a process nip 59 formed by the operable engagement of the layer application member 40 and the imaging member 10 to form a toner layer. Is divided into an image area and a non-image area. Thus, conventional liquid development systems provide a liquid developer having a substantially zero net charge and a substantial amount of charge of opposite polarity present therein to the development zone. Even though the toner particles in the developer are strongly charged (as opposed to chemically active charge directors and micelles, etc.), the liquid developer remains neutral due to the balance of the charge around the charged marking particles. It appears to be. Liquid developers acquire a net charge when charge injection or withdrawal occurs to the system. Especially,
The toner particles acquire a net charge when the counter ion is removed from near the toner particles. One finding that led to the present invention was that the removal of any mobile charged species (co-ions, counter-ions, etc.) other than marking particles could significantly improve the development process. Thus, according to the present invention, a liquid developer layer having a substantial net charge is utilized in the development area to enhance performance. Preferably, the net charge of the liquid developer layer is formed substantially from the charge of the toner particles in the liquid developer.

The present invention is particularly focused on correcting the charge in the entire liquid developer layer 58. More specifically, the relatively high toner solids concentration of the toner cake 58 optimizes the toner charge level (measured in microcoulombs per gram) in the toner cake 58 so that the toner layer exits the process nip 59 In the image direction of the liquid developer layer 58 in the process nip 59 and the division of the subsequent layer 58 into an image surface and a non-image surface on the opposing surfaces of the imaging member 10 and the liquid developer layer coater 40 It has been found according to the invention that it is important to optimize Further, the present invention provides a comparison of a layer 58 which permits extremely inefficient charging from an external ion source when used in a low concentration liquid developer layer of the type used in liquid development processes that rely on electrophoretic development. Attempts to exploit the properties of highly solid toners. The present invention also focuses on introducing toner charge into the liquid developer layer.

Thus, according to the present invention, the ion source is shown in FIG.
And in the form of a corona generator 48 (or an electrical bias roll member 49 shown in FIG. 2),
A predetermined charge or a selective charge is provided on the surface of the toner cake 58 by being disposed close to the liquid developer layer coater 40. The finding that led to the present invention is that mobile charge species in the neutral charge layer of the net reduced the useful electric field required for image separation. It is desirable to form the liquid developer layer using uncharged or neutrally charged toner particles. in this case,
Charge is induced on the toner particles after formation of the liquid developer layer. In a variation, it is desirable to selectively alter or modify the charge on the liquid developer layer formed of improperly charged toner particles before transferring the liquid developer layer to the process nip 59. In the absence of a charge director, a charged liquid developer layer can be generated with an ion source to prevent noticeable counterions and co-ions from being present in the liquid developer. Thus, according to the present invention, an ion source is provided and disposed adjacent to the liquid developer layer applicator 40 before the layer 58 flows into the process nip 59.
An apparatus is provided for selectively changing the charge level of toner particles in the liquid developer layer 58.

The ion source of the present invention also comprises a toner cake 5
8 to enhance or reverse the charge (similar to that previously provided via a charge director in the liquid developer) or to create a charge in the neutrally charged toner cake 58. May be provided. The present invention does not require a charge director and allows the use of a liquid developer in which no conductive species are present in the toner cake other than the toner particles themselves. In a variant, the inventive concept can be incorporated into a system that does use charge director agents. In this case, it is possible to minimize or eliminate the counter ion that is inherently generated in the micelle generated by the electrochemical reaction by the charge director. Then, by eliminating unnecessary conductive species such as counter ions in the toner cake, it is possible to reduce the potential difference to form the image area and the background area of the electrostatic latent image, and as a whole The operating speed range for the printing system is widened. Elimination of unnecessary conductive species also has the advantage of allowing the use of simple developer compositions and simple liquid developer management systems. By driving a relatively simple process to control the charge density of the toner cake, it has been found that the present invention extends the operating latitude in the CEP process.

FIGS. 1 and 2 show a CEP system with a liquid developer layer toner charging device, generally identified by the reference numerals 48 and 49, for implanting ions into the toner cake 58. FIG. In the embodiment of FIG. 1, ions are sprayed toward the liquid developer layer 58 using a known corona generator 48. In this case, the ions move through the liquid developer layer 58 and generate charges on the toner particles in the liquid developer layer or exist in micelles generated by the charge director in the liquid developer composition. Or neutralize certain counter ions. Similarly, in the embodiment of FIG. 2, a net charge is generated on the toner particles by removing the counter ions from the toner particles in the liquid developer using a known electric bias roll member 49. Examples of devices that may be used for roll member 49 include, among many other patents and technical documents known in the art and available to those of skill in the art, for example, US Pat. No. 2,912,586. No. 5,144,36
No. 8 describes a biased charge roll. In variations, examples of devices are known in the art and include, among other patents and technical literature,
For example, US Pat. Nos. 4,286,039 and 5,
Bias squeegee rolls of the type described in U.S. Pat. The aforementioned patents are incorporated herein by reference for the purpose of describing the invention in detail.

It will be appreciated that the above-described devices and processes represent just a few of the many variations of systems that can be implemented in the practice of the present invention. One particular variant printing system that includes the teachings of the present invention is shown in FIG. In this case, the toner supply device 150 is provided with a fountain type coating machine 152 having a measuring roll 154.
Is provided. The metering roll 154 is disposed close to the surface of the layer applying member 40, and preferably rotates in a direction opposite to the moving direction of the layer applying member 40, and moves the toner layer adhered on the surface of the layer applying member 40. It has a peripheral surface that applies a shearing force to control the thickness of the toner layer on the layer application member 40. Therefore, the metering roll 154 contains a predetermined amount of developer (which may contain toner particles immersed in a liquid carrier).
Weigh Excess material eventually falls off the metering rolls and is transferred to a reservoir (not shown) for reuse in the toner applicator 152.

The embodiment of FIG. 2 also shows that the image background can be removed from the liquid developer layer 58 using the imaging member (image holding member) 10. Accordingly, by biasing the liquid developer layer applicator 40, the imaging member 10 can attract the background surface, thus maintaining the toner segment corresponding to the image surface on the surface of the liquid developer layer applicator 40. Let it. Accordingly, while the liquid developer segment on the imaging member 10 is transferred to the cleaning device 90 realized as a roll member, the image surface remaining on the surface of the liquid developer layer coating machine 40 is the same as described above and Is transferred to a transfer station in a manner similar to that found on other electrostatographic printing machines. The liquid developer layer segments that make up the image are transferred to the copy substrate by any method that may be known in the art. The transferred image is then fixed, if necessary, to a copy substrate at a fixing station and transported to an output device for retrieval by a machine operator.

[Brief description of the drawings]

FIG. 1 includes a charge modifying device that selectively changes charge within a liquid developer layer prior to being maintained in contact with a latent image bearing surface, and a concentrated liquid developer layer in contact with the latent image bearing surface. 1 is a schematic elevational view showing a contact electrostatic printing (CEP) device according to the invention of the kind used for the development of an electrostatic latent image by maintaining

FIG. 2 is another elevational view showing a modified embodiment of the CEP device according to the present invention, including a modified embodiment relating to various subsystems in the CEP device with respect to the embodiment of FIG. 1; is there.

[Explanation of symbols]

10 imaging member, 12 rotation direction (arrow) of imaging member,
14 photoconductive surface (surface layer), 16 conductive support substrate, 20
Corona generator, 30 exposure station, 40 liquid developer layer coating machine (layer coating member), 45 electric bias source, 47 rotation direction of liquid developer coating machine, 48 corona generator, 49 electric bias roll member, 50
Supply device, 52 reservoir, 54 liquid developer, 55
Electrical bias source, 56 supply roller, 57 rotation direction of supply roller, 58 liquid developer layer (toner cake),
59 process nip (nip), 70 copy board, 9
0 cleaning device, 150 toner supply device, 152
Liquid developer coating machine, 154 measuring roll, 155 bias source.

Claims (3)

[Claims] A first movable member for forming an electrostatic latent image including an image surface formed by a first voltage potential and a non-image surface formed by a second voltage potential; A second movable member operably engaged with the first movable member to form a process nip with the first movable member; and a surface associated with one of the first or second movable members. A liquid developer supply device for forming a liquid developer layer and transferring the liquid developer layer to the process nip; and a charge correcting device for charging the liquid developer layer before transferring the liquid developer layer to the process nip An imaging device having: 2. The imaging device of claim 1, wherein the liquid developer supply deposits a liquid developer layer of at least about 20% solids weight percent. Providing a first movable member for forming an electrostatic latent image including an image surface formed by the first voltage potential and a non-image surface formed by the second voltage potential; A second movable member operably engaged with the first movable member to form a process nip with the first movable member; one of the first or second movable member; Forming a liquid developer layer on a surface associated with, charging the liquid developer layer via an external charge application source, and transferring the liquid developer layer to the process nip. Generating an imagewise electric field across the liquid developer layer within the process nip with the electrostatic latent image on one member.