Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – To produce color reproduction
Reexamination Certificate
2000-09-12
2003-09-16
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
To produce color reproduction
C430S107100, C399S223000, C399S299000
Reexamination Certificate
active
06620566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus such as a color electrophotographic apparatus and a color image forming method using this apparatus.
Digital full-color electrophotography uses the following method. First, R (red), G (green), and B (blue) image signals of an original read from a scanner or R, G, and B image signals obtained through an external interface are color-converted into Y (yellow), M (magenta), and C (cyan). Black generation and color correction are performed to produce signals of four colors Y, M, C, and K (black).
After that, magnification change such as enlargement or reduction is performed, and image area separation is performed to separate a character-line region and a halftone region from each other. Furthermore, spatial filter processing for performing edge emphasis-MTF correction, smoothing-moiré removal, and the like is performed, and &ggr; conversion is performed to obtain a linear relationship between the recording signal intensity and the reproduced image density. Finally, to output the data to a laser or a liquid crystal filter, halftoning is performed by assembling a dot pattern or a line pattern by dithering or error diffusion.
Depending on the type of output device, this method expresses not only binary signals but also multilevel signals by varying the intensity of a laser or varying the pulse width, and can thereby more smoothly express halftone with high resolution. Hence, this method is essential for clear image expression.
A photoreceptor having a charged surface is irradiated with the Y, M, C, and K optical signals generated by a laser or a liquid crystal filter through the image processing as described above. This produces a potential drop and forms an electrostatic latent image. The latent image is visualized by bringing charged toner into contact with the image. Other image visualizing schemes are a method (tandem scheme) which uses separate photoreceptors for four colors Y, M, C, and K and separately develops images of these four colors, and a scheme by which latent images of Y, M, C, and K are sequentially formed and developed by a single photoreceptor and transferred onto an intermediate transfer medium or a paper sheet. After being transferred onto a paper sheet, toner components of the four colors are melted to mix these colors by a fixing device such as a heat roller. A final image is obtained through a series of electrophotographic processes as described above.
Both the digital image processing and analog electrophotographic process described above are factors that determine the final image. In particular, the stability of the electrophotographic process is important for the stability of an image. Throughout life, during continuous copying, and against environmental changes, the same image must be output for the same input optical image for each of the four colors. For this purpose, the apparatus includes, as an image quality maintaining mechanism, a mechanism which varies the surface potential or development bias of a photoreceptor or varies the toner specific density, in accordance with the life counter or with temperature and humidity fluctuations. It is also possible to use a mechanism which actually develops a test pattern on a transfer belt or the like and feeds the result back to the process conditions so that the same image density is maintained.
In this manner, the &ggr; values of the four colors must be adjusted to be constant at any time. Otherwise, the image density changes, or a color shift occurs if the four colors change separately. For example, a bluish image or a yellowish image forms. However, the process conditions such as the surface potential and bias of a photoreceptor and the toner specific density cannot be unlimitedly changed from a physical or image-quality viewpoint. Finally, the physical properties of a developing agent, particularly the stability of the charging characteristics is important. For example, if the charge amount becomes too large, the adhesive force to a carrier abruptly increases, so no sufficient ID can be obtained even when the development contrast potential is raised. On the other hand, if the charge amount becomes too small or if 0 charge or reverse charge increases in a charge amount distribution, fog or toner scattering increases even when the white contrast potential is raised.
Also, when multilevel exposure is performed to improve tone reproduction, the potential on the photoreceptor eventually becomes multilevel and is readily influenced by the &ggr; characteristic of development. Hence, the stability of the characteristics of a developing agent is more and more required.
Color toner generally contains a binder, wax, colorant, charge control agent, and additive. It is basically necessary to use colorless materials except for pigments. As a charge control agent (CCA), not colored azo-based CCAs used in monochromatic toner but colorless CCAs such as a complex of salicylic acid-based zinc, boron complex, quaternary ammonium salt, and resin are extensively used. However, no CCA stable throughout its life and against environmental changes is obtained.
As a colorant, an organic pigment is generally used except for carbon black used as black. Examples of magenta pigments are an azolake pigment, &bgr; naphthol insoluble azo pigment, naphthol AS insoluble azo pigment, pyrazolone pigment, quinacridone pigment, carbazole violet pigment, perillene pigment, and thioindigo pigment. Examples of yellow pigments are a monoazo yellow pigment, benzidine yellow pigment, monoazo yellow lake pigment, benzimidazolone pigment, and condensed azo pigment. Examples of cyan pigments are a phthalocyanine pigment and indanthrene blue pigment.
To improve the color generation and transparency, these pigments and a binder resin are generally subjected to preliminary dispersion called masterbatch. Dispersibility is improved by enhancing dispersion by a kneader such as a three-roll mill which applies a shearing force, by dispersing crude pigments before drying, or by adding a dispersing agent. Dispersion is basically dominated by the chemical affinity between pigments and a binder resin.
The dispersibility of a pigment has influence not only on the transparency but also on the chargeability of toner, since the pigment itself has high chargeability. Generally, if the dispersibility is low, the charge amount distribution widens, and this increases fog and toner scattering. Also, the structure of a pigment has influence on the chargeability and the environmental resistance. To improve the dispersibility of a pigment, a large amount of a polar group such as a carboxyl group can be added to the binder resin. This method is readily achievable when a polyester resin commonly used in color toner is used. However, the charge amount easily decreases in a high-humidity environment or by developing agent stirring throughout life.
As described above, pigments are selected in accordance with the dispersibility to resin, the chargeability, and the tone of color transparency. In particular, the color tone is preferably so selected as to be close to Japan colors as standard colors of three primary colors Y, M, and C. In addition, in accordance with recent regulations for the sake of safety, the use of, e.g., a benzidine yellow pigment is often avoided.
Also, to obtain a color tone having high saturation, the transparency of each toner must be high, and it is necessary to obtain a uniform fixing surface with little graininess in order to suppress diffused reflection on the surface or in the grain boundary. To this end, a low-molecular-weight polyester resin which-readily sharply melts is generally used as a binder. However, the mechanical strength of this low-molecular-weight polyester resin is low, so sufficient life is difficult to ensure.
Toner which easily sharply melts often produces offset because the elasticity during melting lowers. Therefore, the general conventional approach is to use a mechanism which prevents offset by steadily coating a fixing roller with silicone o
Dote Janis L.
Foley & Lardner
Kabushiki Kaisha Toshiba
LandOfFree
Image forming apparatus and image forming method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus and image forming method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus and image forming method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3022234