Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-03-07
2001-06-05
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109500
Reexamination Certificate
active
06242145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to toners, a method of making the toners, developers containing the toners, a method of making coated carriers for the developers, and a method of forming images of offset-like print quality with the developers. More in particular, the invention relates to toners and developers having carefully controlled properties to that provide offset-like print quality when used in developing electrostatic images with a device containing a hybrid scavengeless development system.
2. Description of Related Art
Historically, xerography has not been required to deliver prints of the same caliber as offset lithography. The offset lithography customer demands a level of print quality much higher than is available from conventional xerographic machines.
U.S. Pat. No. 5,545,501 describes an electrostatographic developer composition comprising carrier particles and toner particles with a toner particle size distribution having a volume average particle size (T) such that 4 &mgr;m≦T≦12 &mgr;m and an average charge (absolute value) pro diameter in femtocoulomb/10 &mgr;m (C
T
) after triboelectric contact with said carrier particles such that 1 fC/10 &mgr;m≦C
T
≦10 fC/10 &mgr;m characterized in that (i) said carrier particles have a saturation magnetization value, M
sat
, expressed in Tesla (T) such that M
sat
≧0.30 T, (ii) said carrier particles have a volume average particle size (C
avg
) such that 30 &mgr;m ≦C
avg
≦60 &mgr;m, (iii) said volume based particle size distribution of said carrier particles has at least 90% of the particles having a particle diameter C such that 0.5 C
avg
≦C≦2 C
avg
, (iv) said volume based particles size distribution of said carrier particles comprises less than b % particles smaller than 25 &mgr;m wherein b=0.35 X (M
sat
)
2
X P with M
sat
; saturation magnetization value, M
sat
, expressed in T and P: the maximal field strength of the magnetic developing pole expressed in kA/m, and (v) said carrier particles comprise a core particle coated with a resin coating in an amount (RC) such that 0.2% w/w≦RC≦2% w/w. See the Abstract. This patent describes that such developer achieves images of offset-quality in systems in which a latent image is developed with a fine hair magnetic brush. See column 4, lines 7-17.
What is still desired is a set of developers comprised of toners and carriers that possess a combination of properties such that when used to develop a latent image on the surface of a photoreceptor, preferably in an image-on-image device, more preferably in a device utilizing a hybrid scavengeless development system, the color image produced in this xerographic manner exhibits a quality analogous to that achieved in offset lithography.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a set of color toners and developers each having a set of properties such that the developers containing such toners can achieve xerographically produced images having offset-like print quality. It is a further object of the invention to develop such set of color toners and developers capable of producing such images when used in a development device utilizing a hybrid scavengeless development system.
It is a still further object of the invention to provide a method for manufacturing the toners and developers to consistently achieve the required properties.
It is a still further object of the invention to develop suitable carriers for use in combination with the toners in order to obtain two component developers possessing the required properties. It is a still further object of the invention to develop a preferred method of manufacturing coated carriers for use in combination with the toners in order to obtain two component developers possessing the required properties.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from, for example, a scanning laser beam, an LED source, etc., or an original document being reproduced. This records an electrostatic latent image on the photoconductive surface of the photoreceptor. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed.
In the present invention, two-component developer materials are used in the first step of the development process. A typical two-component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. Toner particles are attracted to the latent image, forming a toner powder image on the photoconductive surface. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
The electrophotographic marking process given above can be modified to produce color images. One type of color electrophotographic marking process, called image-on-image (IOI) processing, superimposes toner powder images of different color toners onto the photoreceptor prior to the transfer of the composite toner powder image onto the substrate. While the IOI process provides certain benefits, such as a compact architecture, there are several challenges to its successful implementation. For instance, the viability of printing system concepts such as IOI processing requires development systems that do not interact with a previously toned image. Since several known development systems, such as conventional magnetic brush development and jumping single-component development, interact with the image on the receiver, a previously toned image will be scavenged by subsequent development if interacting development systems are used. Thus, for the IOI process, there is a need for scavengeless or noninteractive development systems.
Hybrid scavengeless development (HSD) technology develops toner via a conventional magnetic brush onto the surface of a donor roll. A plurality of electrode wires is closely spaced from the toned donor roll in the development zone. An AC voltage is applied to the wires to generate a toner cloud in the development zone. This donor roll generally consists of a conductive core covered with a thin, for example 50-200 &mgr;m, partially conductive layer. The magnetic brush roll is held at an electrical potential difference relative to the donor core to produce the field necessary for toner development. The toner layer on the donor roll is then disturbed by electric fields from a wire or set of wires to produce and sustain an agitated cloud of toner particles. Typical AC voltages of the wires relative to the donor are 700-900 Vpp at frequencies of 5-15 kHz. These AC signals are often square waves, rather than pure sinusoidal waves. Toner from the cloud is then developed onto the nearby photoreceptor by fields created by a latent image.
In the present invention, while any suitable electrostatic image development device may be used, it is most preferred to use a device employing the hybrid scavengeless development system. Such a system is described in, for example, U.S. Pat. No. 5,978,633, the entire disclosure of which is incorporated herein by reference.
Satisfaction of stringent offset-like print quality requirements in a xerographic engine has been enabled in the present invention by IOI xerography of which hybrid scavengeless development is a preferred subsystem component. Both the image quality and the unique subsystem requirements result in highly constrained toner designs. This invention describes the aspects of novel toners that operate in this restrictive atmosphere to produce prints of near offset quality.
In addition to achieving offset-like print quality, the digital imaging processes of the above-described device also enables customization of each print (such as an address, or special information for regional distribution), which is not pract
Galloway Merrilee A.
Hollenbaugh, Jr. William H.
Muller Richard J.
Silence Scott M.
Stamp Amy L.
Goodrow John
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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