Patent Application
20050201781
The present invention is directed generally the field of electrophotographic printing, and more particularly to a toner regulating member with a metallic coating on a flexible substrate.
One step in the electrophotographic printing process typically involves providing a relatively uniform layer of toner on a toner carrier, such as a developer roller, that in turn supplies that toner to photoconductive element to develop a latent image thereon. Typically, it is advantageous if the toner layer has a uniform thickness and a uniform charge level. As is known in the art, one typical approach to regulating the toner on the toner carrier is to employ a doctor (or metering) blade. While there have been a number of doctor blade designs proposed in the art, there remains a need for alternative designs that address the special concerns of the electrophotographic development process.
The present invention, in one embodiment, provides a toner layer regulating system for an electrophotographic image forming apparatus. The toner regulating system may include a toner carrier; a toner regulating member (e.g., doctor blade) disposed proximate the toner carrier, with the toner regulating member having a first surface disposed toward the toner carrier and forming a nip with the toner carrier. The toner regulating member comprises a flexible metallic substrate and a metallic coating disposed to cover an area of the first surface forming the nip. The coating on the toner regulating member may advantageously comprise at least a material selected from the group consisting of molybdenum and tungsten; indeed, such a material may be the largest constituent component of the coating. The coating may advantageously be substantially homogeneous and/or uniform in composition, have a thickness of not more than 30 um, and/or be a thermally sprayed coating of a thickness of not more than 30 um. The toner regulating member may have a first portion mounted to a support and a second portion supported in cantilever fashion by the first portion, with the nip disposed in the second portion. The coating may be limited to the second portion of the toner regulating member. The substrate may be a first material and the coating a second material different from the first material. The substrate may have a thickness in the range of 0.02 mm to 2.0 mm. The coating may advantageously have a surface roughness of ≦2.0 um Ra, more advantageously 0.2 um to 1.5 um Ra, and still more advantageously a surface roughness of 0.7 um to 1.1 um Ra.
In other embodiments, the toner regulating system generally described above may be incorporated into a toner cartridge and/or an image forming device.
As the present invention relates to the regulation of toner in an electrophotographic image forming apparatus, an understanding of the basic elements of an electrophotographic image forming apparatus may aid in understanding the present invention. For purposes of illustration, a four cartridge color laser printer will be described; however one skilled in the art will understand that the present invention is applicable to other types of electrophotographic image forming apparatuses that use one or more toner colors for printing. Further, for simplicity, the discussion below may use the terms “sheet” and/or “paper” to refer to the recording media 5; this term is not limited to paper sheets, and any form of recording media is intended to be encompassed therein, including without limitation, envelopes, transparencies, postcards, and the like.
A four color laser printer, generally designated 10 in
The toner cartridge 20 typically includes a photoconductor 22 (or “photo-conductive drum” or simply “PC drum”), a charger 24, a developer section 26, a cleaning assembly 28, and a toner supply bin 30. The photoconductor 22 is generally cylindrically-shaped with a smooth surface for receiving an electrostatic charge over the surface as the photoconductor 22 rotates past charger 24. The photoconductor 22 rotates past a scanning laser 32 directed onto a selective portion of the photoconductor surface forming an electrostatically latent image representative of the image to be printed. Drive gears (not shown) may rotate the photoconductor 22 continuously so as to advance the photoconductor 22 some uniform amount, such as 1/120th or 1/1200th of an inch, between laser scans. This process continues as the entire image pattern is formed on the surface of the photoconductor 22.
After receiving the latent image, the photoconductor 22 rotates to the developer section 26 which has a toner bin 30 for housing the toner and a developer roller 27 for uniformly transferring toner to the photoconductor 22. The toner is typically transferred from the toner bin 30 to the photoconductor 22 through a doctor blade nip formed between the developer roller 27 and the doctor blade 29. The toner is typically a fine powder constructed of plastic granules that are attracted and cling to the areas of the photoconductor 22 that have been discharged by the scanning laser 32. To prevent toner escape around the ends of the developer roller 27, end seals may be employed, such as those described in U.S. Pat. No. 6,487,383, entitled “Dynamic End-Seal for Toner Development Unit,” which is incorporated herein by reference.
The photoconductor 22 next rotates past an adjacently-positioned intermediate transfer medium (“ITM”), such as belt 34, to which the toner is transferred from the photoconductor 22. The location of this transfer from the photoconductor 22 to the ITM belt 34 is called the first transfer point (denoted X in
As illustrated in
The paper 5 may be stored in paper supply tray 14 and supplied, via a suitable series of rollers, belts, and the like, to the location where the sheet 5 contacts the ITM belt 34. At this location, called the second transfer point (denoted Z in
The present invention relates to a toner regulating system 40 that may be employed in electrophotographic imaging devices, such as the printer 10 described above. The illustrative toner regulating system 40 includes the developer roller 27 and the doctor blade 29. Referring to
The doctor blade 29 has a generally rectangular form and may be conceptually divided into a mounting portion 60 and a nip portion 70. The mounting portion 60 of the doctor blade 29 mounts to the frame of the cartridge 20, either directly or via a suitable bracket 44. Such a bracket 44, if used, may have a simple bar-like shape and be secured to the frame of the cartridge 20 by suitable fasteners 46. Alternatively, the bracket 44 may have a curved or bowed shape, such as that shown in U.S. Pat. No. 5,489,974, or any other shape known in the art. Further, as shown in the figures, the mounting portion 60 may be advantageously mounted at an angle either toward or away from the center of the developer roller 27. For example, if a bracket 44 is used, the front face of the bracket 44 may be angled, such as a slight forward slant of 12.5° as shown in
The nip portion 70 of the doctor blade 29 is supported by the mounting portion 60 in a cantilever fashion. That is, the nip portion 70 is not affixed to another portion of the frame, but is instead supported from the frame by the mounting portion 60. The nip portion 70 includes a portion that forms the nip 42 with the developer roller 27 and an optional overhang portion 72 that extends beyond the nip 42. Due to the flexibility of the doctor blade 29, the nip portion 70 presses against the developer roller 27 due to its inherent spring force. This is represented in
As described above, the doctor blade 29 shown in the foregoing Figures is disposed in what is commonly referred to as a “counter” orientation in that the moveable tip 74 of the doctor blade 29 at or near the nip 42 is disposed upstream of the mounting portion 60 of the doctor blade 29, with respect to the direction of the rotation of the developer roller 27. For some embodiments of the present invention, the doctor blade 29 may instead be oriented in a following (or “trailing”) orientation, where the nip portion 70 is disposed downstream from the mounting portion 60. Further, the mounting method employed to mount the doctor blade 29 may advantageously allow for a bias voltage to be applied to the doctor blade 29 to assist in controlling toner charge for the residual toner on the developer roller 27. The particular characteristics of the applied bias voltage, if any, are not important to understanding the present invention, and any approach known in the art may be employed.
Referring to
The coating 90 of the doctor blade 29 is disposed on at least the front side 52 of the substrate 80 in the area of the nip 42. For instance, the coating 90 may be disposed over an area extending from a point near the tip 74 of the substrate 80 to a point on the other side of the nip 42 (towards the mounting portion 60). The length Lc of coating 90 may be, for example, approximately 4 mm. The thickness Tc of the coating 90 may be in the range of 3 um to 30 um, and more advantageously be in the range of 5 um to 15 um. The coating 90 is advantageously metallic. Further, the coating may advantageously substantially homogeneous and/or substantially uniform in composition. In addition, the coating 90 may advantageously have an “as applied” (without further processing) surface roughness in the range of ≦2.0 um Ra measured using a contact profilometer, advantageously in the range of 0.2 to 1.5 um Ra, and more advantageously in the range of 0.7 to 1.1 um Ra. It should be noted that the material of the coating 90 should have suitable abrasion properties so as be able have a sufficient operating life, such as twelve thousand pages or more, depending on the application.
As noted above, the coating 90 is of a metallic type. Suitable known metallic materials for the coating 90 include molybdenum, tungsten carbide, and alloys of those materials. More broadly stated, the coating, in some embodiments, is composed of one or more materials, where at least one material is selected from the group consisting of molybdenum and tungsten. Necessarily included under such a description are pure molybdenum, tungsten carbide, etc. and alloys or mixtures of any of the aforesaid materials. When applied using the plasma deposition type of thermal spray deposition process (discussed further below), it is believed that molybdenum and tungsten carbide (typically in a cobalt matrix) will provide good performance at a reasonable manufacturing cost.
As indicated below, the coating 90 may be applied to the substrate 80 using a thermal spray process, such as the plasma deposition process that is sometimes referred to as “air plasma spraying,” High Velocity Oxy-Fuel Spray (HVOF), electric arc wire spray, or other thermal spray techniques known in the art. By way of non-limiting example, the plasma deposition process for a molybdenum coating 90 may use a type 9 MB plasma spray gun; a type 4 MP feeder with vibrating air; a type 7 M plasma spray control unit; all from Sulzer Metco of Westbury, N.Y.; a Jet Kote Surfacing Systems feeder control unit Deloro Stellite Co. of Goshen, Ind., and a GE 728 five port nozzle from A-Flame Corp. of Cincinnati, Ohio placed three and one-half to six inches (more advantageously four to five inches, such as four and one-half inches) from the substrate. The gas mixture may be argon/helium, with the argon primary gas supplied at 65-75 psi and 150 liters/minute and the helium secondary gas supplied at 65-75 psi and 65 liters/minute. A molybdenum powder of type 118FNS molybdenum from Powder Alloy Corp. of Cincinnati, Ohio may be used with a feed pressure of 92 psi. The cooling air may be at 55 psi. The plasma discharge may have an arc pressure of 60 volts and a current of 800 amps. Alternative powders include type AE8245 (Sulzer Metco), type AE8175 tungsten carbide-cobalt (Sulzer Metco), and blends thereof.
The doctor blade 29 described above may be used in a toner regulating system 40 to help regulate the amount of toner on the developer roller 27. In the illustrative toner regulating system 40, a doctor blade 29 as described above is mounted to a frame of the cartridge 20 along its mounting portion 60, and presses against the developer roller 27 at its nip portion 70 to form a nip 42. The formed nip 42 helps regulate the thickness of the residual toner left on the developer roller 27, and also advantageously applies a triboelectric and/or induced charge on the residual toner. Thus, as suitably thick and charged layer of toner may be formed on the developer roller 27 and carried to the developing location. Just by way of non-limiting example, the residual toner may have a thickness in the range of 4 um to 20 um, for a density of 0.3 to 1.2 mg/cm2, and a charge of −12 uC/gm to −35 uC/gm.
Such a toner regulating system 40 may be used with toner that is mono-component or multi-component, magnetic or non-magnetic, color or black, or any other toner used in electrophotographic systems.
The discussion above has been in the context of a conventional multi-color laser printer 10 for illustrative purposes; however, it should be noted that the present invention is not so limited and may be used in any electrophotographic system, including laser printers, copiers, and the like. Further, the illustrative discussion above has been used a developer roller 27 and the relevant toner carrier, but the present is invention is not limited to use with developer rollers 27, and may be used to regulate the thickness and/or charge on developer belts or any other developer carrier.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
