Self biasing transfer member

Abstract: A self biasing transfer member (10) for transferring toner particles (17) from an image support surface (15) to a copy substrate (16), including a conformable layer (13) and a layer (14) of piezoelectric material thereover which generates an electric field when deformed. In one embodiment the transfer member is a roll (10) having an axial core (12) about which the conformable layer is cylindrically formed, and the piezoelectric material is a film circumferentially surrounding the conformable layer. The transfer member is urged against the imaging support surface to form a nip (22) which causes the conformable layer to conform thereagainst and deform the piezoelectric material. In another embodiment, a blade (50) is used to clean and deform the transfer member.

Description: The present invention relates generally to an apparatus for transfer of charged toner particles in an electrostatographic printing machine, and more particularly, concerns a transfer member for use in electrostatographic printers. Existing transfer and charging systems for electrophotographic printers require sources of high voltage at low current levels for maintaining the same pattern and intensity of electrostatic fields as on the original latent electrostatic image being reproduced to induce transfer. This requirement has been usually met by incorporating high voltage power supplies for feeding the coronas and bias rolls which perform such processes as precharge, development and transfer. These high voltage power supplies add to the overall cost and weight of electrophotographic printers. A simple, relatively inexpensive, and accurate approach to eliminate the expense and weight of traditional high voltage sources in such printing systems has been a goal in the design, manufacture and use of electrophotographic printers. The need to provide accurate and inexpensive transfer and charging systems has become more acute, as the demand for high quality, relatively inexpensive electrophotographic printers has increased. Various techniques for charging without incorporating high voltage power supplies have been devised. US-A-4106933 to Taylor teaches a method for printing using photoconductor with piezoelectric material having dipoles that are permanently poled to form a permanent pattern corresponding to a graphic representation. Subsequently, the permanently poled material can be used by straining the material to produce a charge pattern representative of the graphic representation, which can then be developed with toner powder, transferred to a sheet of paper, and fused to form a printed page. The straining, toning and fusing process may be repeated, thereby producing multiple copies. An object of the present invention is to strive to meet the above need. Accordingly, the present invention provides a self-biasing transfer member for use in electrostatographic printers, comprises: a layer of compressible material; and a layer comprising piezoelectric material positioned on said compressible layer, the piezoelectric material being the type which generates an electric field in response to being deformed to compress the compressible material. In one embodiment of the present invention, there is provided a roll member, comprising an interior layer of compressible material, and an exterior surface layer comprising piezoelectric material positioned about said exterior layer for generating an electric field in response to being deformed. In accordance with another embodiment of the present invention an electrostatographic printer includes a transfer member in accordance with the invention and an imaging support surface, wherein said transfer member is urged into contact with the imaging support surface to form a nip region therebetween; and wherein the compressible material is compressed by the support surface under said urging of the transfer member and said piezoelectric material is deformed thereby. The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view illustrating the geometry of a piezoelectric sheet; Figure 2 is an elevational view illustrating a (bimorph) Xeromorph sheet which is utilized by the present invention; Figure 3 is an elevational view illustrating a (unimorph) Xeromorph sheet which is utilized by the present invention; Figure 4 is an elevational view illustrating the novel self biasing roll of the present invention in a transfer mode, as may be found in a typical electrostatographic copying process; and Figure 5 illustrates the novel self biasing roll of the present invention employing a conductive blade. Referring to Figure 4, a conformable, self biasing roll member 10 in accordance with the present invention is shown in the configuration of a transfer system of a typical electrostatographic printing machine. A drum-type photoconductive insulating surface 15 is shown in operative engagement with the self biasing roll 10, forming a nip 22 therebetween. A powder toner image 17 previously formed and developed in accordance with conventional electrostatographic copying processes is present on the surface of the photoconductive insulating drum. A copy sheet 16 or other support substrate travels through the nip 22 formed in the area of contact between the self biasing roll 10 and the photoconductive insulating surface 15 for receiving the powder toner image 17 from drum 15. Thus, the powder toner image is transferred to the support sheet 16, appearing as a transferred image 18 thereon. The physics involved in using a conformable roll for the transferring process in such an electrostatographic printing apparatus is well known in the industry. The transferred image 18 on the support sheet 16 may be subsequently processed, for example, by fusing the image onto the support sheet. The conformable roll 10 comprises a layer of compressible material 13 coated onto core 12. The roll member 10 is normally cylindrical with the layer 13 uniformly surrounding the central core 12 in a coaxial manner. The layer 13 may be comprised of a polyurethane formulation or any other material capable of providing desirable compressibility characteristics. This formulation may be closed cell or open cell, i.e., a foam material, which is sufficiently compressible. In addition, a peripheral surface layer 14 comprises a piezoelectric polymer film, such as polyvinylidene fluoride (PVDF) film, preferably Kynar® piezo film manufactured by Pennwalt KTM. Piezoelectric materials are formed by stretching PVDF film in one direction, and applying a large electric field to electrically polarize it in a direction perpendicular to the film. As shown in figure 1, the stretch direction is denoted by "T" and the polarization direction is denoted by "P", or in the polar coordinates shown by "1" and "3" respectively. When a PVDF sheet is strained, it develops an internal electric field which is proportional to the deformation. The present invention utilizes either a bimorph or a unimorph structure referred to as a "Xeromorph". A bimorph Xeromorph consists of two PVDF sheets 6 laminated together with each sheet polarization direction opposed to each other having only a bottom electrode 7, as shown in Figure 2. An unimorph Xeromorph consists of a single PVDF sheet 6 laminated to a thick substrate 4 as shown in Figure 3. The substrate material may comprise materials which can be bent, and have no piezoelectric properties. In Figure 4, Xeromorph surface layer 14 is sufficiently elastic and resilient to yield to the compressible characteristics of the conformable underlying layer 13. The conformable roll 10 is subjected to a compressive force in the nip 22 formed in the area of contact between the roll 10 and the photoconductive drum 15. As roll 10 is brought into much closer proximity to the photoconductive surface 15, upon which the powder toner image is located, the compressive force causes deformation of the piezoelectric layer such that an electric potential is generated on the surface of roll 10 in the nip region in order to induce transfer of the powder toner image to copy sheet 16. Conformable roll 10 is maintained in tension by a pair of springs (not shown) resiliently urging conformable roll 10 against drum with the desired spring force to deform conformable roll 10 to generate the desired electric potential. It should be evident other means for urging conformable roll surface 10 against drum 15 could be employed. Also, as conformable roll 10 rotates, neutralization and cleaning brush 30 cleans the surface of conformable roll 10 and eliminates residue charges thereon by being connected to ground, so that there is no electric field in the pre-nip region prior to deformation in the nip 22. Deformation of the peripheral surface layer 14 in the transfer nip 22 can be increased such that higher transfer fields can be applied to achieve high transfer efficiencies, if necessary. Another embodiment of the present invention is illustrated in Figure 5. Conformable roll 10 is subjected to a compressive force applied by conductive blade 50. Blade 50 serves three functions: 1) deform Xeromorph surface layer to create a net charge and non-zero potential; 2) neutralize this non-zero surface potential by commutating this net charge to ground through the conductive blade; 3) clean debris from the surface of the Xeromorph surface layer. An advantageous feature of this specific embodiment is the independence from nip pressure to generate the desired electrical potential on the surface of the roll thereby eliminating the possibility of excess nip pressure which can result in hollow character images due to compaction of toner against the surface of the photoconductive member. It should be noted that sufficient nip pressure should be applied to minimize the transfer zone air gap. The roll member of the present invention is operated in a synchronous mode in which the roll rotates in the same direction as the photoconductive surface. Alternatively, it is contemplated that the conformable roll member of the present invention can be operated in an asynchronous mode, in which the roll rotates in the opposite direction as the image receiver and the photoconductive surface. It is apparent that a self-biasing transfer member which is in the form of a roll member fully provides the advantages of the invention as described above. It is also evident to those of the ordinary skill in the art that the self-biasing transfer member could be in the form of an endless belt entrained over a pair of rollers, wherein, for example, one of the rollers performs the function of an incompressible material against which the conformable material of the endless belt is depressed to enable the piezoelectric material thereover to deform.

Claims: A self-biasing transfer member (10) for use in electrostatographic printers, comprising: a layer of compressible material (13); and a layer comprising piezoelectric material (14) positioned on said compressible layer, the piezoelectric material being the type which generates an electric field in response to being deformed to compress the compressible material (13). A transfer member according to claim 1 wherein said transfer member comprises: a roll (10) with the compressible material cylindrically formed on an axially positioned core; and wherein the roll is rotatable about the axis of said core. A transfer member according to claim 1, wherein the layer of compressible material and the layer comprising piezoelectric material define an endless belt, the belt being entrained around a pair of rollers. A transfer member according to any one of the preceding claims wherein said piezoelectric material comprises a layer of piezoelectric polymer film. A transfer member according to any of the preceding claims, wherein said piezoelectric material (14) comprises: a first layer of piezoelectric polymer film having a first polarization direction; and a second layer of piezoelectric polymer film disposed on said first layer and having a second polarization direction opposed to the first direction. An electrostatographic printer including a transfer member (10) in accordance with any one of the preceding claims, and an imaging support surface (15), wherein said transfer member (10) is urged into contact with the imaging support surface (15) to form a nip region therebetween; and wherein the compressible material (13) is compressed by the support surface under said urging of the transfer member (10) and said piezoelectric material (14) is deformed thereby. An electrostatographic printer according to claim 6, wherein said transfer member (10) is urged into the imaging support surface (15) by springs. An electrostatographic printer including a transfer member (10) in accordance with any one of claims 1 to 5, and a blade (50), the transfer member (10) being deformed by the blade (50) which compresses the compressible material (13). An electrostatographic printer according to claim 6, 7 or 8, wherein the transfer member (10) is cleaned by a brush (30) which concurrently eliminates residual charges on the surface of the piezoelectric material (14).

Inventors: SNELLING CHRISTOPHER, SNELLING, CHRISTOPHER
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: G03G15
IPC codes: G03G15