The present invention relates to a process for producing a charging member, such as a donor member, or other like member, used in electrostatographic, including digital, apparatuses. The invention further relates to a process comprising grit blasting a charging member substrate or core, and plasma spraying a single component outer coating. The coating, in embodiments, consists essentially of titanium dioxide powder applied directly to said grit blasted stainless steel substrate or core. In further embodiments, the outer coating has a resistivity of from about 10−10 to about 10−3 ohms-cm. In embodiments, the titanium dioxide is “pure,” and comprises from about 99 percent to about 100 percent by might titanium dioxide.
In the well-known process of electrophotographic printing, a charge retentive surface, typically known as a photoreceptor or photoconductor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface.
Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member, such as paper, and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface.
The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
In the process of electrophotographic printing, the step of conveying toner to the latent image on the photoreceptor, is known as development. The object of effective development of a latent image on the photoreceptor is to convey toner particles to the latent image at a controlled rate so that the toner particles effectively adhere electrostatically to the charged areas on the latent image. A commonly used technique for development is the use of a two-component developer material, which comprises, in addition to the toner particles which are intended to adhere to the photoreceptor, a quantity of magnetic carrier beads. The toner particles adhere triboelectrically to the relatively large carrier beads, which are typically made of steel.
Specifically, when the developer material is placed in a magnetic field, the carrier beads with the toner particles thereon form what is known as a magnetic brush, wherein the carrier beads form relatively long chains, which resemble the fibers of a brush. This magnetic brush is typically created by means of a developer roll. The developer roll is typically in the form of a cylindrical sleeve rotating around a fixed assembly of permanent magnets. The carrier beads form chains extending from the surface of the developer roll. The toner particles are electrostatically attracted to the chains of carrier beads. When the magnetic brush is introduced into a development zone adjacent the electrostatic latent image on a photoreceptor, the electrostatic charge on the photoreceptor will cause the toner particles to be pulled off the carrier beads and onto the photoreceptor.
Another known development technique involves a single-component developer, that is, a developer consisting entirely of toner. In a common type of single-component system, each toner particle has both an electrostatic charge to enable the particles to adhere to the photoreceptor, and magnetic properties to allow the particles to be magnetically conveyed to the photoreceptor. Instead of using magnetic carrier beads to form a magnetic brush, the magnetized toner particles are caused to adhere directly to a developer roll. In the development zone adjacent the electrostatic latent image on a photoreceptor, the electrostatic charge on the photoreceptor will cause the toner particles to be attracted from the developer roll to the photoreceptor.
An important variation to the general principle of development is the concept of “scavengeless” development. The purpose and function of scavengeless development are described more fully in, for example, U.S. Pat. No. 4,868,600 to Hays et al.; U.S. Pat. No. 4,984,019 to Folkins; U.S. Pat. No. 5,010,367 to Hays; or U.S. Pat. No. 5,063,875 to Folkins et al. In a scavengeless development system, toner is detached from the donor roll by applying AC electric field to self-spaced electrode structures, commonly in the form of wires positioned in the nip between a donor roll and photoreceptor. This forms a toner powder cloud in the nip and the latent image attracts toner from the powder cloud thereto. Because there is no physical contact between the development apparatus and the photoreceptor, scavengeless development is useful for devices in which different types of toner are supplied onto the same photoreceptor such as in “tri-level”; “recharge, expose and develop”; “highlight”; or “image-on-image” color xerography.
A typical “hybrid” scavengeless development apparatus includes, within the developer housing, a transport roll, a donor roll, and an electrode structure. The transport roll advances carrier and toner to a loading zone adjacent the donor roll. The transport roll is electrically biased relative to the donor roll, so that the toner is attracted from the carrier to the donor roll. The donor roll advances toner from the loading zone to the development zone adjacent the photoreceptor. In the development zone, that is the nip between the donor roll and the photoreceptor, are the wires forming the electrode structure. During development of the latent image on the photoreceptor, the electrode wires are AC-biased relative to the donor roll to detach toner therefrom so as to form a toner powder cloud in the gap between the donor roll and the photoreceptor. The latent image on the photoreceptor attracts toner particles from the powder cloud forming a toner powder image thereon.
Another variation on scavengeless development uses a single-component developer material. In a single component scavengeless development, the donor roll and the electrode structure create a toner powder cloud in the same manner as the above-described scavengeless development, but instead of using carrier and toner, only toner is used.
In any type of scavengeless development apparatus, the donor member is used to convey toner particles to the wires forming the electrode structure in the nip between the donor roll and the photoreceptor. Broadly speaking, a donor member can be defined as any member having only toner particles adhering to the surface thereof.
To function commercially in scavengeless development, a donor member should meet certain requirements. In general, a donor member should include a conductive substrate and define a partially conductive surface, so that the toner particles may adhere electrostatically to the surface in a reasonably controllable fashion. In hybrid scavengeless development, the donor member provides an electrostatic intermediate between the photoreceptor and the transport member. The provision of this intermediate and the scavengeless nip minimizes unwanted interactions between the development system and the photoreceptor, in particular with a pre-developed latent image already on the photoreceptor, before the latent image in question is developed. Minimized interactions make scavengeless development preferable when a single photoreceptor is developed several times in a single process, as in color or highlight color xerography.
The donor member must further have desirable wear properties so the surface thereof will not be readily abraded by adjacent surfaces within the apparatus, such as the magnetic brush of a transport roll. Further, the surface of the donor member should be without anomalies such as pin holes, which holes may be created in the course of the manufacturing process for the donor roll. The reason that such small surface imperfections must be avoided is that any such imperfections, whether pinholes created in the manufacturing process or abrasions made in the course of use, can result in electrostatic “hot spots” caused by arcing in the vicinity of such structural imperfections.
Another desired property of the donor member is summarized by the phrase “uniform conductivity;” the surface of the donor roll must be partially conductive relative to a more conductive substrate, and this partial conductivity on the surface should be uniform through the entire circumferential surface area.
Other physical properties of the donor member, such as the mechanical adhesion of toner particles, are also desired, but are generally not as quantifiable in designing a development apparatus. In addition, the range of conductivity for the service of a donor member should be well chosen to maximize the efficiency of a donor member in view of any number of designed parameters, such as energy consumption, mechanical control and the discharge time-constant of the surface.
U.S. Pat. No. 6,226,483 B1 discloses an article including a cylindrical roller core, and a titanium dioxide ceramic layer bonded to the exterior of the cylindrical core, wherein the resistivity of the coated roller article can be from about 10−3 to about 1010 ohm-cm.
U.S. Pat. No. 5,869,808 discloses a thermal conductive roller for use in copying machines, steam-heated and induction-heated applications including a ceramic heating layer formed by plasma spraying a ceramic material to form an electrically conductive heating layer of preselected and controlled resistance.
U.S. Pat. No. 5,707,326 discloses a charging roller for use in xerographic copying machines including a cylindrical roller core, and a ceramic layer formed by plasma spraying of a blend of an insulating ceramic material and a semiconductive ceramic material in a ratio which is selected to control an RC circuit time constant of the ceramic layer in response to an applied voltage differential.
U.S. Pat. No. 5,701,572 discloses an apparatus including a cleaning brush or other cleaning device and a ceramic coated detoning roll resistive to wear.
U.S. Pat. No. 5,609,553 discloses an electrostatic assist roller for use in a coating, printing or copying machine, which includes a cylindrical roller core, and a ceramic layer formed by plasma spraying a blend of an insulating ceramic material and a semiconductive ceramic material in a ratio which is selected to control the resistance and thickness of the ceramic layer in response to an applied voltage differential.
U.S. Pat. No. 5,600,414 discloses a charging roller for use in a xerographic copying machine that includes a cylindrical roller core, and a ceramic layer formed by plasma spraying a blend of an insulating ceramic material and a semiconductive ceramic material in a ratio, which is selected to control an RC circuit time constant of the ceramic layer in response to an applied voltage differential.
U.S. Pat. No. 5,322,970 discloses a donor roll for the conveyance of toner in a development system for an electrophotographic printer including an outer surface of ceramic having a suitable conductivity to facilitate a discharge time constant thereof of less than 600 microseconds.
U.S. Pat. No. 5,043,768 discloses a rotating release liquid applying device for a fuser including an outer porous ceramic material.
U.S. Pat. No. 4,893,151 discloses a single component image developing apparatus including a developing roller coated with a Chemical Vapor Deposition ceramic and an elastic blade coated with a ceramic.
U.S. Pat. No. 4,544,828 discloses a heating device using ceramic particles as a heat source and adapted for use as a fixing apparatus.
The aforementioned patents are incorporated by reference herein in their entirety.
Recently, use of emulsion aggregation (EA) toner has become of interest. The EA toner is superior in many ways, including the fact that the toner can be processed easier and that the toner formed is spherical. The spherical shape of the toner allows for a more uniform and superior image. The EA toner also has superior print quality when printed on various substrates, such as rough substrates.
Most known developer members use a stainless steel coating that is plasma sprayed onto a stainless steel sleeve, and/or an aluminum or stainless steel sleeve that has been grit blasted by some method to roughen the surface. Although the stainless steel coating meets the wear resistance and electrical conductivity requirements of the coating, plasma spraying creates hazardous and possibly explosive products. The grit blasted surface has limitations on the degree of roughness (Rz) that can be achieved without distortion of the substrate itself.
Therefore, it is desired to provide a developer member coating that has the desired surface texture, wear resistance and electrical conductivity to work with EA toner. It is also desired to provide a developer member coating that is inert and remains inert during the plasma spray process. It is further desired to provide a developer member coating useful for semi-conductive magnetic brush development (SCMB). Moreover, it is desired to provide a coating for a development member that does not require blending of two materials. Further, it is desired that the coating not require an over-firing step to meet the desired electrical properties. Another desired property of the coating, is that the process for producing the coating not be hazardous or explosive.