Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-11-04
2004-09-07
Goodrow, John L (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108600, C430S108700, C430S120400, C430S137150
Reexamination Certificate
active
06787280
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a toner for use in a developer for developing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing and so on, a method for producing the toner, and a developing method using the toner. More particularly, the present invention relates to an electrophotographic toner for use in an apparatus, such as a copying machine, a laser printer or a plain paper facsimile machine, employing a direct or indirect electrophotographic developing system, and in an apparatus, such as a full-color copying machine, a full-color laser printer and a full-color plain paper facsimile machine, employing an electrophotographic multi-color developing system, a method for producing the toner and a developing method using the toner.
A developer for use in electrophotography, electrostatic recording, electrostatic printing and so on is attached to an image carrier such as a photoconductor on which an electrostatic image has been formed in a developing process, then transferred from the photoconductor to a transfer medium such as a transfer paper in a transfer process, and fixed on the paper in a fixing process. As the developer for developing the electrostatic image formed on a latent image holding surface of the image carrier, a two-component developer comprising a carrier and a toner and a one-component developer requiring no carrier (magnetic or nonmagnetic toner) are known.
As a dry toner for use in electrophotography, electrostatic recording, electrostatic printing and so on, a toner obtained by melt-kneading a toner binder such as a styrene resin or polyester together with a colorant and so on and finely pulverizing the kneaded mixture is conventionally used.
For the purpose of producing an image with high fineness and high quality, improved toners having a small particle size have been proposed. However, particles of a toner produced by a normal kneading-pulverizing method have irregular shapes. Thus, the toner particles may be further pulverized into superfine particles or a fluidizing agent is buried in the surfaces of the toner particles when the toner is agitated with a carrier in a developing unit or when, in the case of being used as a one-component developer, the toner particles receive a contact stress from a developing roller, a toner supply roller, a layer thickness regulating blade, a frictional electrification blade and so on, resulting in deterioration of image quality. Also, the toner is poor in fluidity as a powder because of the irregular shapes of the particles thereof, and thus requires a large amount of fluidizing agent or cannot be filled in a toner bottle with a high filling rate, which makes it difficult to downsize the apparatus. Thus, the advantage of small-seized particles is not fully utilized. Also, a kneading-pulverizing method has a limit on the particle size that it can produce and cannot meet the requirement for smaller sized toner particles.
Additionally, the process of transferring an image formed of color toners from a photoconductor to a transfer medium or a paper to produce a full-color image is becoming more complicated, so that low transferability of a pulverized toner due to the irregular shapes of the particles thereof causes a void in a transferred image or an increase in consumption of toners to prevent it.
Thus, there is an increasing demand for producing a high quality image without a void while reducing consumption of toners and decreasing running cost by improving transfer efficiency. When transfer efficiency is significantly high, there is no need for a cleaning unit for removing untransferred toner from a photoconductor and a transfer medium, which leads to downsizing of the apparatus and cost reduction. This has also a merit of generating no waste toner. For the purpose of overcoming the drawbacks of the toner of irregular particle shape, there have been proposed various methods for producing a toner of spherical particles. However, a spherical toner has the following problems.
Spherical toner particles can be produced by suspension polymerization or emulsion polymerization. However, there is a limitation on the type of the resin that can be used in these methods, so that the toner particles are not suitable for a full-color process. Especially, a toner for use in a full-color copying machine or a full-color printer must have a low melt viscosity to provide gloss and color mixability in a printed image and thus contains a polyester type toner binder having a sharp melt property. It is difficult for a toner obtained by suspension polymerization or emulsion polymerization of a vinyl polymer to produce such properties.
Since a toner containing a polyester type toner binder having a sharp melt property is likely to cause hot offset, a silicone oil or the like is conventionally applied to a heat roll in full-color machines. However, in order to apply a silicone oil to a heat roll, an oil tank and an oil applying unit are necessary, which makes the apparatus unavoidably complicated and large. Also, application of oil causes deterioration of the heat roll, so that the heat roll needs regular maintenance. Additionally, it is unavoidable for the oil to adhere a copying paper and an OHP (overhead projector) film. Especially, the oil adhered to OHP films impairs color tone of printed images.
As a method to overcome the problems, Japanese Laid-Open Patent Publications No. H07-152202, H09-015903, H11-133665 and H11-149179 disclose a method involving volume shrinkage, called polymer solution suspension method. The method comprises the steps of dispersing and dissolving toner ingredients in a volatile solvent such as a low-melting point organic solvent, emulsifying and granulating the composition in an aqueous medium containing a dispersing agent, and removing the volatile solvent. This method can use a wide variety of resin materials and can be applied to production of a full-color toner as well as a monochrome toner. Also, this method can produce a various shapes of particles with the use of, for example, a water-insoluble solid fine powder dispersing agent although it involves a volume shrinkage of the granules during the production process. However, in producing particles in an aqueous medium by a polymer suspension method, as in the case with suspension polymerization or emulsion polymerization, a polar material such as a suspension stabilizer, emulsion stabilizer or surfactant must be used to stably produce particles in the aqueous medium. Such a polar material, which cannot be easily removed by a simple washing method and remains on the surfaces of the resulting toner particles, adversely affects the charging properties of the toner, especially under high temperature and high humidity. Also, the polar material remaining on the surfaces of the toner particles adheres to a surface of a photoconductor in developing or cleaning and causes a blur of a latent image formed thereon (at worse, the image flows and becomes indistinguishable). Especially, when an image is formed by dots in a digital machine, this tendency is strong when the diffusion rate of the latent image is low.
Thus, in order to obtain a consistent image quality in any environment, the photoconductor must be heated to prevent effects of humidity and adhesion of the polar material thereto, especially in a machine for producing high-quality images.
SUMMARY OF THE INVENTION
The objects of the present invention are as follows:
(1) To provide a toner which is produced, in an aqueous medium, from a toner composition dispersed and dissolved in an organic solvent, which can be charged stably in any environment, and which can consistently produce high-quality images.
(2) To provide a method for producing the above toner.
(3) To provide a developing method and a multi-color developing method using the above toner, which cause less contamination of a photoconductor even when the photoconductor is not heated and which can consistently produce high-quality images.
Particles prepared by a solution suspension metho
Emoto Shigeru
Nanya Toshiki
Sugiyama Tsunemi
Takigawa Tadao
Tomita Masami
Goodrow John L
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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