Laser printing with rewritable media

Details Laser printing with rewritable media Laser printing with rewritable media

2001-10-30

2003-12-30

Pham, Hai (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

With record receiver or handling means therefor

C347S262000, C430S037000

Reexamination Certificate

active

06670981

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO AN APPENDIX
The present application includes a hard copy appendix comprising pertinent specification pages and drawings of partial co-inventors' U.S. patent application Ser. No. 09/844,862, filed Apr. 27, 2001 by ZHANG et al. for MOLECULAR MECHANICAL DEVICES WITH A BAND GAP CHANGE ACTIVATED BY AN ELECTRIC FIELD FOR OPTICAL SWITCHING APPLICATIONS as relates to subject matter claimed in accordance with the present invention.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to printing and, more particularly, to laser printing on rewritable media employing a molecular colorant.
2. Description of Related Art
The majority of printed paper is read once or twice then discarded. Not only is this wasteful of a valuable nature resource (trees), but paper constitutes a significant volume of waste disposal and recycling. There is much interest in providing a paperless office through electronic displays and the Internet. Users, however, find displays to be an inferior alternative to the printed page over a wide range of parameters, such as limited portability of large screen models, substantially fixed viewing location and posture even with portable computers, off-axis viewability issues inherent in some screen technologies, and eyestrain. Thus, there is a growing need and market for a paper or paper-like sheet that can be electronically printed, erased and re-used.
Electrostatically polarized, dichroic particles for displays are well known. Published works such as by Jacques Pankove of RCA date back to at least March 1962 (RCA Technical Notes No. 535). Dichroic spheres having black and white hemispheres are reported separately for magnetic polarization by Lawrence Lee and for electrostatic polarization by Nick Sheridon of Xerox, as early as 1977 (S.I.D. Vol. 18/3 and 4, p. 233 and 239, respectively).
The need for an electronic paper-like print means has recently prompted development of at least two electrochromic picture element (pixel) colorants: (1) a microencapsulated electrophoretic colorant (see e.g., U.S. Pat. No. 6,124,851 (Jacobson) for an ELECTRONIC BOOK WITH MULTIPLE PAGE DISPLAYS, E Ink Corp., assignee), and (2) a field rotatable bichromal colorant sphere (e.g., the Xerox® Gyricon™). Each of these electrochromic colorants is approximately hemispherically bichromal, where one hemisphere of each microcapsule is made the display background color (e.g., white) while the second hemisphere is made the print or image color (e.g., black or dark blue). The colorants are field translated or rotated so the desired hemisphere color faces the observer at each pixel.
Xerox Corporation has been most active in developing dichroic spheres for displays and printer applications. U.S. Pat. No. 4,126,854, issued Nov. 21, 1978 to Sheridon, describes a dichroic sphere having colored hemispheres of differing Zeta potentials that allow the spheres to rotate in a dielectric fluid under this influence of an addressable electric field. In this, and subsequent U.S. Pat. No. 4,143,103, issued Mar. 6, 1979, Sheridon describes a display system wherein the dichroic spheres are encapsulated in a transparent polymeric material. The material is soaked in a dielectric fluid plasticizer to swell the polymer such that cavities form around each dichroic sphere to allow sphere rotation. The same dichroic fluid establishes the Zeta potential electrostatic polarization of the dichroic sphere. In U.S. Pat. No. 5,389,945, issued Feb. 14, 1995, Sheridon describes a printer that images the polymeric sheet containing the dichroic spheres with a linear electrode array, one electrode for each pixel, and an opposing ground electrode plane. In U.S. Pat. No. 5,604,027, issued Feb. 18, 1997, Sheridon describes SOME USES OF MICROENCAPSULATION FOR ELECTRIC PAPER.
The dichroic sphere has seen little commercial exploitation in part because of its high manufacturing cost. The most common reported manufacturing technique involves vapor deposition of black hemispheres on the exposed surface of a monolayer of white microspheres, normally containing titanium dioxide colorants. Methods of producing the microspheres and hemisphere coating are variously described by Lee and Sheridon in the above-identified S.I.D. Proceedings. More recently, Xerox has developed techniques for jetting molten drops of black and white polymers together to form solid dichroic spheres when cooled. These methods include circumferentially spinning jets, U.S. Pat. No. 5,344,594, issued Sep. 6, 1994. Unfortunately, the colliding drops produce swirled colorant about the resultant sphere and it is difficult to prevent agglomeration of molten spheres when the concentration of droplets emitted approaches reasonable volumes. None of these techniques lend themselves to bulk, large-scale production because they lack a continuous, volume process.
Lee has described microencapsulated dichroic spheres within an outer spherical shell to provide free rotation of the colorants within a solid structure. A thin oil layer separates the dichroic sphere and outer shell. This allows the microspheres to be found in solid film layers and overcomes the need to swell the medium binder, as proposed by Sheridon. This technique, however, is generally described for magnetic dichroic spheres in the above-referenced S.I.D. Proceedings authored by Lee.
Sheridon describes an electrode array printer for printing rewritable paper in U.S. Pat. No. 5,389,945, issued Feb. 14, 1995. Such a printer relies on an array of independently addressable electrodes, each capable of providing a localized field to the rewritable media to rotate the dichroic spheres within a given pixel area. Although electrode arrays provide the advantage of a potentially compact printer, they are impractical for microcapsule dichroic sphere technologies from both cost and print speed standpoint. Each electrode must have its own high voltage driver to produce voltage swings of 500-600 volts across the relatively low dielectric rewritable paper thickness to rotate the dichroic spheres. Such drivers and their interconnects across an array of electrodes makes electrode arrays costly. The print speed achievable through electrode arrays is also significantly limited because of the short nip time the paper experiences within the writing field. The color rotation speed of dichroic spheres under practical field intensities is in the range of 20 msec or more. At this rate, a 300 dpi resolution printer employing an electrode array would be limited to under one page per minute print speed.
Thus, it can be seen that electrode array printing techniques using microcapsule-based electronic media impose resolution, cost and speed limits upon rewritable media printing, and hinder the exploitation for many commercial applications. Therefore, there is an unresolved need for a printing technique that can quickly and inexpensively print to rewritable media at high resolution. More specifically, there is a need for a media for use with a laser printer wherein the media colorant has superior characteristics and advantages over microcapsule-based types.
BRIEF SUMMARY OF THE INVENTION
In its basic aspect, the present invention provides a hard copy system including: a rewritable medium having a molecular colorant; and a laser printer for generating electric fields associated with said molecular colorant for writing and erasing a print image therewith.
In another aspect, the present invention provides a printer for a rewritable medium, the medium having at least one layer of a rewritable molecular colorant, the printer including: a photoconductor means for storing a voltage charge deposited thereon; writing means for writably erasing the charge deposited on the photoconductor means; and support means for holding the rewritable medium proximate to the photoconductor means in a nip contact area such that when the rewritable medium passes a charge written on the photo

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