MXPA98000450A - Composition for an organic pigment removal roller coated with ceramic for use in a electrostatograf cleaning apparatus - Google Patents

Abstract

An organic pigment release roll, having a ceramic outer coating for removing residual organic pigment particles from a cleaning reproduction machine. The ceramic outer coating consists essentially of a suitable mixture of alumina and titanium oxide by weight giving the organic pigment release roller a desired resistivity between the range of 2.8 x 10-7 - 2.10 x 10-9 (ohm-cm), a discharge time current greater than 600 microseconds and a dielectric constant in a range of 12-24 to 100 M

Description

COMPOSITION FOR TN ROLLER OF DETACHMENT OF ORGANIC PIGMENT COATED WITH CERMICA TO USE IN DNOS ELECTROSTATIC CLEANING APPARATUS BACKGROUND OF THE INVENTION This invention relates in general to electrostatic reproduction machines and more particularly relates to a composition for an organic pigment release roll coated with ceramics, for use in a cleaning apparatus of said machines. Electrostatic reproduction machines such as xerographic and copier printers, conventionally each have a cleaning or cleaning apparatus that uses an organic aluminum release roll, with an anodized surface of about 50 microns. The electrical properties of an organic pigment stripping roll are ordinarily required to produce a dielectric constant sufficient to support an electric field bypass cleaning. It is usually intended that the anodized aluminum organic pigment release roll will have the service life or last as long as the machine. However, some cleaners have shown that the rollers wear out before the life of the machine, requiring replacement of the entire cleaner. Based on field data, it has been estimated that a cleaner will have to be replaced at least twice during the useful time of the machine, which can be very expensive. The following descriptions may be relevant to various aspects of the present invention and may be briefly summarized as follows. The U.S. Patent No. 5,384,627 issued to Behe et al., Discloses a developing unit adapted to reveal a latent image with organic pigment particles. The unit includes a housing defining a chamber for storing a supply of organic pigment particles in the chamber. The unit also includes a donor roller with a circumferential surface having a conductivity of less than 10"8 (ohm-cm) _1 having a central region and opposite marginal regions.The donor roller is separated from the latent image to form an area of The unit further includes an electrode member which is placed in the developing zone adjacent to opposite marginal regions and spaced from the central regions of the donor roller.The electrode member is electrically derived to loosen particles of organic pigment from donor roller, to form a cloud of organic pigment powder in the developing zone, with organic pigment particles from the organic pigment cloud that reveal the latent image US Patent No. 5,322,970 issued to Behe et al. describes a donor roller for the transport of organic pigment in a development system for an electrophotographic printer. Includes an exterior ceramic surface. The ceramic has a convenient conductivity to facilitate a constant discharge time of less than 600 microseconds. The donor roller is used in conjunction with an electrode structure as used in the development without cleaning. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an organic pigment release roll for use in a cleaning apparatus of an electrostatic reproduction machine for removing residual organic pigment particles from an image forming member. The organic pigment release roller includes a conductive core, and a ceramic outer coating on the conductive core. The ceramic coating consists essentially of a mixture of alumina and titanium oxide by weight, to give the organic pigment release roll, a desired resistivity within a range of 2.8 x 107 - 2.10 x 109 (ohm-cm), and a approximate discharge time constant of 600 microseconds. BRIEF DESCRIPTION OF THE DRAWINGS Other characteristics of the present invention will be apparent as the following description proceeds and with reference to the drawings in which: Figure 1 is a schematic elevational view of an electrostatic cleaning apparatus including the detachment roller of organic pigment of the present invention; Figure 2 is a plan view of an embodiment of the organic pigment release roller of the present invention; Figure 3 is a table of various combinations of a percentage of a batch of AT-87 and that of a batch of AT-60 commercial ceramic powder compositions and the resulting composition; Figure 4 is a plot or plot of measured time constant values measured for various percentage compositions that are obtained as in Figure 3; and Figure 5 is a schematic illustration of an electrostatic reproduction machine incorporating the cleaning apparatus and the organic pigment release roller of the present invention. DETAILED DESCRIPTION OF THE INVENTION While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the cont, it is intended to cover all alternatives, modifications and equivalents that may be included within the spirit and scope of the invention, as defined by the appended claims. Now with reference to the drawings, wherein the illustrations are for the purpose of describing a preferred embodiment of the invention and not to limit it, and wherein the various processing stations employed in a reproduction machine as illustrated in the Figure 5, will be described only briefly. Now with reference to Figure 5, the reproduction machine, wherein the present invention finds advantageous use, utilizes a load retentive image support member in the form of a photoconductive strip 10 consisting of a photoconductive surface 11 and a substrate. electrically conductive light transmitter, mounted for movement beyond an AA charging station, a BB display station, DC developer stations, DD transfer station, EE fusing station and FF cleaning station. The band 10 moves in the direction of the arrow 16 to advance successive portions thereof, sequentially through the various processing stations arranged with respect to the trajectory of their movement. The band 10 is trapped with respect to a plurality of rollers 18, 20, and 22, the latter of which can be used to provide convenient tensioning of the photoreceptor band 10. The roller 20 is coupled to the motor 23 by convenient means such as an impeller of band. The motor 23 rotates the roller 20 to advance the web 10 in the direction of the arrow 16. As can be seen by further reference to Figure 5, initially successive portions of the web 10 pass through the charging station AA. At the AA charging station, a corona discharge device such as a scorotron, corotron or dicorotron, indicated generally by the reference number 24, charges the band 10 to a uniformly high positive or negative potential. Any convenient control, well known in the art, can be used to control the corona discharge device 24. Then, the charged portions of the photoreceptor surface are advanced through the exposure station BB. In the display station BB, the uniformly charged photoreceptor or charge retentive surface 10 is exposed to an input and / or output laser-based scanning device 25, which causes the charge retentive surface to discharge according to the output from the scanning device. The scanning device is a three-level laser scan set (ROS = Raster Output Scanner). The resulting photoreceptor contains both charged area images and downloaded area images. In the DC developing station, a developing system, indicated generally by the reference number 30, advances revealing material in contact with the latent electrostatic images and reveals the image. The developing system 30 as illustrated, comprises first and second developer apparatuses 32 and 34. The developer apparatus 32 comprises a housing containing a pair of magnetic brush rollers 35 and 36. The rollers advance revealing material 40 in contact with the photoreceptor to reveal the images of unloaded area. The developer material 40, by way of example, contains negatively charged colored organic pigment. The electrical bypass is achieved by power supply 41, electrically connected to the developing apparatus 32. A DC bypass (DC) is applied to the rollers 35 and 36, by the power supply 41. The developing apparatus 34 comprises a housing containing a pair of magnetic brush rolls 37 and 38. The rollers advance the developer material 42 in contact with the photoreceptor to reveal images of charged area. The developer material 42, by way of example, contains positively charged black organic pigment to reveal the images of charged area. Appropriate electrical derivation is achieved by the power supply 43, electrically connected to the developing apparatus 34. A DC shunt is applied to the rollers 37 and 38 by the shunt energy supply 43. Because the composite image developed in the photoreceptor consists of both of positive and negative organic pigment, a pre-transfer corona discharge member 56 is provided to condition the organic pigment for effective transfer to a substrate using corona discharge of a desired plurality either "negative or positive".

Sheets of support material or substrate 58 are advanced to the transfer station DD from a supply tray, not shown. Leaves are fed from the tray by a sheet feeder, also not shown, and advanced to the transfer station DD through a crown loading device 60. After transfer, the sheets continue to move in the direction of arrow 62 to the fusion station EE The fusing station EE includes a fusing assembly, generally indicated by reference numeral 64, which permanently fixes the organic pigment powder images transferred to the sheets. Preferably, the fusing structure 64 includes a heated fusing roll 66, adapted to press fit with a backup roll 68, with the images of organic pigment powder contacting the fusing roll 66. In this way, the powder image of Organic pigment is permanently fixed to the leaf. After merging, the copy sheets are directed to the receiving tray, not shown, or a finishing station for binding, stapling, collating, etc., and removing from the machine by the operator. Residual organic pigment and debris remaining in the photoreceptor band 10 after each copy is made, are removed in the cleaning station FF with a cleaning apparatus 70 including an organic pigment release roll coated with ceramic 80 of the present invention . Now with reference to Figure 1, the cleaning apparatus 70 of the present invention is illustrated in detail, and it is convenient to remove residual organic pigment particles 15 from the surface 11 of an image-containing member 10 of an electrostatic reproduction machine. . The cleaning apparatus 70 includes a housing 102 defining a cleaning chamber 104. A cleaning member 50, such as a brush, is mounted within the chamber and includes fibers 57 which are placed in cleaning contact with the supporting surface 11. The cleaning member or brush 50 is electrically derived by a cleaning field source VB and rotatably moved in the direction of the arrow 55 to remove residual organic pigment particles 15 from the image support surface 11 and to trap and move said particles 15 within the fibers 57. Importantly, the cleaning apparatus 70 includes a rotatable organic pigment release roll 80 of the present invention, which is connected to a bypass source VD. As illustrated, the organic pigment release roll 80 is rotatable in the direction of arrow 86 and is mounted within chamber 104 to form an organic pigment release fastening point 88, with fibers 57 of the brush or member 50 for removing organic pigment or receiving the organic pigment particles trapped 15 from the fibers 57. As further illustrated, the cleaning apparatus 50 includes a scraper blade 87, for removing the residual organic pigment particles 15 from the roller. organic peel 80. An extraction system including a borehole or screw 89, is provided to take the residual organic pigment particles from the housing 102. The scraper blade 87 may be made of a urethane or stainless steel material, depending on the surface finish of the organic pigment release roll 80. In accordance with the present invention, a blade of urethane 87 is preferred when the surface finish of the ceramic-coated roll 80 is substantially unfinished, that is, it basically remains in a "sprayed condition" at about 3 microns. The relatively high roughness of the unfinished ceramic surface works to reduce the current contact area in which the organic pigment release roller and a scraper blade cleaning edge, this reduces the drag of the blade during cleaning. For stainless steel blades 87, the ceramic coating as sprayed of about 3 microns, is diamond ground to a surface finish within 0.43 to 1.0 miera, in order to similarly reduce blade drag during cleaning. Now with reference to Figures 1 and 2, the organic ceramic pigment release roll 80 of the present invention includes a core 95, an electrically conductive substrate 90, and a ceramic outer coating 85 that is formed on the conductive substrate 90. and has a thickness 96 and a desired surface finish 97. As illustrated, the organic ceramic pigment release roll 80 has an elongated, generally cylindrical shape. The electrically conductive substrate 90 can be made from any suitable conductive material, such as aluminum and can be manufactured by any method such as by machining or extrusion. In accordance with the primary aspect of the present invention, the outer layer 85 is preferably made of a particular advantageous ceramic compound or composition (which will be described in detail below). The ceramic is ordinarily an inorganic, non-metallic compound which normally comprises a mixture of any of a number of materials including, for example, the following: alumina, zirconia, thoria, beryllia, magnesia, spinel, silica, titanium oxide and forsterite. Ceramics that include at least one of aluminum (Al), boron (B), carbon (C), germanium (Ge), silicon (Yes), titanium (Ti), zirconium (Zr), magnesium (Mg), beryllium (Be), and tungsten (W) are particularly hard, highly resistant to abrasion, have high resistivity and have high dielectric strength.

The testing and selection of combinations and particular compositions among the above materials to meet the cost, process and cleaning process requirements of an electrostatic process, would clearly seem impronosticable and time consuming. In general, the use of an organic pigment release roller coated with a ceramic compound is described, for example, in the co-pending US patent application. Serial No. 08 / 517,024 filed on 08/18/95 and commonly assigned to the assignee of this application. In addition, a roller coated with a similar, but different, ceramic composition (a developing donor roller) that requires and has a relatively faster time constant is described in US Pat. No. 5,473,418 commonly assigned, issued December 5, 1995. The contents and description of Patents Nos. 5,322,970; 5,473,418; and from the U.S. Patent Application. Serial No. 08 / 517,024, here they are fully incorporated in this application by reference. The ceramic surface layer or coating 85 of the organic pigment release roll 80 of the present invention is preferably sprayed with plasma onto the substrate 90. Initially, it should be sprayed with plasma to a desired thickness of about 3 microns to be sufficient to achieve required surface finishes as well as electrical properties of the cleaning apparatus. Plasma spraying as a process, generates a plasma passing an inert gas through a high-voltage electric arc. The ionized gas is forced through a nozzle, where the powder is introduced into the plasma stream. The powder melts and projects at high speeds on the substrate. Depending on the particular substrate used, it may be necessary to cool the samples with an air jet during the plasma spray process. Because in plasma spraying the ceramic coating 85 can be precisely controlled, in this way it can be controlled in order to ensure that surface anomalies such as craters or pitting are kept to a minimum. The use of a plasma spray method to apply ceramic coating also results in a much more uniform peripheral geometry than that obtained from other methods. In this way, grinding subsequent to plasma coating if not desired, can often be eliminated. An organic pigment release roll 80 having a ceramic coating surface 85, therefore, is unlikely to show any significant abrasion problems when used for a prolonged period of time in a cleaning apparatus, despite movement with the brushes of the cleaning brush 50. Unlike the ceramic coated donating rollers employed in the development without hybrid cleaning or debugging, the ceramic composition for the ceramic pigmented organic pigment release roller 80 of the present invention is disclosed to have a constant slower discharge time within a range of about 2,000 microseconds to 600 microseconds, with a preferred download constant close to 1,300 microseconds. According to the present invention specifically, it has been found that a particular combination of ceramic-producing materials consisting essentially of alumina and titania in specific proportions, is sufficient to produce a plasma-sprayed coating on an organic pigment release roller. with aluminum core that satisfies the requirements of resistivity, dielectric constant, and discharge time constant of the cleaning apparatus of the present invention. Commercially, however, alumina and titanium oxide compounds, which are suitable for plasma spray coating applications are available primarily as preformulated powder compounds such as At-87 and At-60 both available from a White Engineering Surfaces Corporation distributor. of Newton Pa. The rod test batches of this distributor showed a batch of 100% At-87 which is a powder consisting essentially of 87% alumina and 13% titanium oxide, by weight. A more accurate test of another batch of 100% At-87 showed that it consists of approximately 88% alumina, 11% titanium oxide and approximately 1% other oxides, by weight.

Similarly, the test of a batch of 100% At-60 showed is a powder that essentially consists of approximately 60% alumina and approximately 40% titanium oxide, by weight and more accurate testing of another batch AT-60 showed that it consists of about 52% alumina, about 46% titanium oxide and about 2% other oxides. These types of ceramic powders were also chosen because they are relatively thinner than other possible powders. By using these finer powders a final coating having a theoretical density higher than and thus no pitting and voids is produced in order to provide the disruptive voltage protection greater than 2000 volts, even for a thin coating. Alumina is an excellent insulator with resistivity values of 10"6 ohm-cm at room temperature, pure stoichiometric titanium oxide is also used as an insulator with values of 10" 13 ohm-cm at room temperature. The dielectric constants of alumina and titanium oxide are reported at 1 MHz and are approximately 9 and 100, respectively. An important feature of titanium oxide is the extent to which it can be reduced chemically when exposed to temperatures exceeding 900 ° C. The reduction of titanium oxide leads to significant changes in electrical conductivity. As oxygen is lost during the plasma spray process, the Ti ions move over the interstitial sites and the resistivity decreases. The particular ceramic composition of the present invention is found by combining an understanding of the temperatures that are generated in the plasma spray process and the knowledge of the ability to reduce titanium oxide at high temperatures as before, thereby controlling the electrical conductivity of the resulting coating within the desired range. It has also been found that organic pigment coating rolls coated with a batch of At-87 ceramic compound have time-of-discharge constants that were slow (ie, time constants barely greater than 600 microseconds (see Figure 5)) for applications of organic pigment release roller coating. The particular batch of At-87 was therefore not quite acceptable only for purposes of the present invention. On the other hand, the organic pigment release rollers coated with a batch of At-60 ceramic compound, although fulfilling other requirements, generally had a too high conductivity, and the constant discharge times were relatively too fast for the purposes of the present invention. Although the formulation and testing of various ratios of At-87 and At-60 (Figure 3), in order to achieve various non-commercially available ratios of alumina and titanium oxide, it has been found in accordance with the present invention, that the organic pigment-release rollers coated with a ceramic compound made from 94% AT-87 and 6% AT-60 (indicated by *) and consisting of approximately 86 alumina (A1203) and approximately 14 titanium dioxide (Ti02) , in weight, effectively additionally meet the resistivity and discharge time constant requirements for the cleaning apparatus of the present invention. As illustrated in Figures 3 and 4 for example only, the ceramic compound of the present invention should preferably be made from approximately 94% AT-87 and 6% AT-60 to have the desired discharge time constant greater than 600 microseconds, and may consist of 84% -88% alumina and approximately 12% -lβ% titanium oxide by weight, depending on the method and application equipment. This preferred choice of powders for coating is found by empirical methods. By using fused and broken or ground inventory powders it was possible to mix appropriate quantities of two different prepared batches to achieve the present coating. As illustrated in Figure 3, this particular relationship is achieved for example by using 94% of a typical batch of At-87, and about 6% of a typical batch of At-60 powders from the aforementioned distributor, to exhibit a dielectric strength of 300-600 volts per .0254 mm (1 mil) of coating thickness. Other percentages around 94% and 6% as combinations can of course be employed, since both powders include alumina and titanium oxide. However, in the final composition, it is considered that the percentage of titanium oxide of 12% -16% is more critical or more sensitive with respect to the desired resistivity and the desired resistivity and time constant requirements. According to this, the approach will be to seek to achieve this and then replenish the rest with alum and about 1 or 2% of other oxides. Figure 5 shows a trace of several of these ceramic formulations against discharge time constants measured in oscilloscope for each one of them. The preferred range of discharge time constants for the organic pigment release roll 80 of the cleaning apparatus 70 according to the present invention is between 200 and 2000 microseconds, as a preferred value around 1300 microseconds. It should be noted that the discharge time constant for the sample of 94% AT-87 and 6% AT-60 illustrated as 106 is greater than 600 microseconds, and is approximately 1300 microseconds. This discharge time constant value is obtained for coated rollers with a composition having a dielectric connector within a range of 12-24 at 100 KHz and a resistances of 2.8 x 107 - 4.2 x 108 (ohm-cm) at temperature ambient. The above time is obtained by verifying a deterioration of a 100-volt pulse imparted on the coated roller using an oscilloscope. The particular preferred ratio of powders of 94% AT-87 and 6% AT-60 is prepared for plasma spraying by a method that mixes appropriate amounts of the required powders, and melts and fuses them together. The powders are then broken, milled and sieved before being sprayed with plasma. Therefore, it is apparent that there has been provided in accordance with the present invention, a ceramic pigmented organic pigment release roll, having a ceramic composition and surface finish that fully satisfies the previously established objects and advantages. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to cover all these alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, the content of the following is claimed as property:

Claims (9)

1. CLAIMS 1. - A roller for detaching organic pigment, for use in a cleaning apparatus of an electrostatic reproduction machine, for removing residual organic pigment particles from an image forming member, the organic pigment release roller is characterized in that comprises: (a) a conductive core; and (b) a ceramic outer coating formed on the conductive core, the ceramic outer coating consists essentially of a mixture of alumina and titanium oxide by weight, to give the organic release roll, a desired resilience in the range of 2.8 × 10 7. - 2.10 x 109 (ohm-cm), and a discharge time constant greater than 600 microseconds.
2. 2. - A release roller according to claim 1, characterized in that the mixture of alumina and titanium oxide by weight gives the organic release roller a dielectric constant within a range of 12-24 to 100 KHz and a constant of approximate download time of 1300 microseconds.
3. 3. - A release roller according to claim 1, characterized in that the ceramic outer coating essentially comprises about 84-87 of alumina and about 12-16% of titanium oxide by weight.
4. 4. - A release roll according to claim 3, characterized in that the ceramic outer coating exhibits a dielectric strength within a range of 300-600 volts per .0254 mm (thousandth of an inch) of coating thickness.
5. 5. - A release roller according to claim 4, characterized in that the ceramic outer coating has a disruptive voltage of less than 2000 volts.
6. 6. A cleaning apparatus for removing residual organic pigment particles from a surface containing an image of an electrostatic reproduction machine, the cleaning apparatus is characterized in that it comprises: (a) a housing defining a cleaning chamber; (b) a cleaning member mounted within the chamber, in cleaning contact with the image support surface for removing and trapping residual organic pigment particles from the surface containing the image; and (c) a pivotable peel roll, mounted within the chamber forming an organic pigment peel holding point with the cleaning member for receiving trapped organic pigment particles from the cleaning member, the peel roll includes: (i) a driver core; and (ii) a ceramic outer coating consisting of approximately 85% alumina (A1203) and approximately titanium oxide (Ti02), by weight.
7. 7. The cleaning apparatus according to claim 6, characterized in that it includes electric bypass sources connected to the cleaning member and the organic pigment release roller, to create organic pigment extraction and reception fields.
8. 8. - The cleaning apparatus according to claim 7, wherein the cleaning member is a rotatable brush that has fibers to remove and trap particles of organic pigment.
9. 9. An electrostatic reproduction machine, characterized in that it comprises: (a) an image-forming member having a surface that contains an image; (b) means for electrostatically forming a latent image on the surface containing the image; and (c) a developing apparatus for the latent image with organic pigment particles, to form an organic pigment image; (d) means for transferring the organic pigment image from the surface containing the image to a receiving sheet; and (e) a cleaning apparatus for removing residual organic pigment particles from the image-containing surface, the cleaning apparatus includes: (i) a housing defining a cleaning chamber, - (ii) a cleaning member mounted within of the chamber and in cleaning contact with the image-containing surface, to remove and trap residual organic pigment particles from the surface containing the image; and (iii) a rotatable organic pigment release roller mounted within the chamber and forming an organic pigment release fastening point with the cleaning member, to receive entrained organic pigment particles from the cleaning member, the roller of organic pigment release has a conductive core and a ceramic outer coating consisting of 84% -87% alumina (A1203) and 12% -16% titanium oxide (Ti02), by weight.