Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-02-05
2002-09-10
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S138000
Reexamination Certificate
active
06447971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner used in an electrophotographic apparatus, such as an electrophotographic copying machine, an electrophotographic printer, or an electrostatic recording apparatus. The present invention also relates to a method of producing such a toner.
2. Description of the Related Art
FIG. 1
is a schematic view of the structure of an electrophotographic image forming apparatus. In this apparatus, electrostatic charges are uniformly induced on the photoconductive insulating member such as a photosensitive drum
10
by an electrostatic-charging device
20
, and a light image
30
is emitted onto the photoconductive insulating member by a given manner, thereby forming an electrostatic latent image. Using colored fine particles called toner, the latent image is then developed into a toner image that is visible to the eye. The toner image is transferred onto a recording medium PA, such as paper, by a transfer unit
50
, and fixed by a fixing unit
80
, thereby obtaining a desired printed material. In the toner fixing process, the paper having the toner image fixed thereon passes through heating rollers
81
, where the toner is melted and solidified. This is a so-called heat fixing method, which is the most widely used. The heat fixing method excels in simplification and cost performance, compared with other fixing methods.
In the heat fixing method, release agent (also referred to as “wax”) is applied onto each toner particle so as to prevent the toner from adhering to the fixing members such as the heating rollers
81
. Also, release agent such as silicone oil may be applied to the heating rollers
81
in the fixing unit
80
or some other members in the image forming apparatus. However, the release oil used for the apparatus gives glare to a fixed image formed on paper, and the mechanism for supplying the release oil complicates the structure of the fixing unit. In view of those problems, studies on techniques that involve no oil (oilless techniques) have been made. One of such oilless techniques involves an oilless toner that includes a large quantity of wax so that no fixing oil is necessary in the apparatus.
However, a toner is generally produced by melting and mixing resin, wax, and colorant, and then pulverizing the resultant material. If a toner containing a large quantity of wax is produced by a normal production method, the wax is liable to be exposed through the surfaces of the toner particles. As a result, the wax contained in the toner forms film and adheres to the photosensitive drum or the developing unit. This causes contamination on the photosensitive drum or the developing unit, and results in poor printing quality.
In view of the above problems, Japanese Laid-Open Patent Application No. 9-319143 discloses a technique for producing a toner having less exposed wax. In this technique, resin, colorant, and wax are melted and dispersed in an oily medium, and the oily mixture is dispersed in a water solvent so as to form oil droplets. After that, the oily medium is removed, thereby obtaining the toner having less exposed wax. However, in this technique, it is difficult to disperse the wax in the oily medium. Also, the use of the oily medium does not ensure safety in the toner production process.
Japanese Laid-Open Patent Application Nos. 63-113560 and 4-63358 both disclose a technique of producing a suspension polymerization toner that is obtained in the following manner. First, a monomer containing wax is heated to a temperature higher than the melting point of the wax, so that the wax is uniformly dispersed in the monomer. The monomer compound is dispersed in water and polymerized to obtain the suspension polymerization toner. However, the wax cannot completely be prevented from being exposed through the surfaces of toner particles. Further, Japanese Laid-Open Patent Application No. 5-197193 discloses a technique of producing a toner containing wax by a suspension polymerization method. However, in order to disperse the wax, the monomer provided with the wax is heated to a temperature higher than the melting point of the wax, which involves the danger of heating inflammable monomer in a bulk state. In this technique, the polymerization is carried out in the existence of pigments. As a result, polymerization trouble is easily impeded due to the existence of pigment, and there is also a problem with the rheology control. Furthermore, since the pigment is exposed through the surfaces of the toner particles produced by the above technique, the charge amount, which is an essential characteristic value of the toner, easily varies due to the pigment exposed through the surfaces.
Meanwhile, Japanese Laid-Open Patent Application No. 7-64335 discloses a toner that is colored resin particles containing wax. This toner is obtained in the following manner. Wax emulsion is mixed with an emulsion polymerization liquid obtained by emulsion-polymerizing a polymerization monomer. A salting-out process is then performed on the resultant. However, since the technique requires emulsion agent and salting-out agent both having hygroscopicity, the resultant toner also exhibits hygroscopicity and lacks environmental stability. Also, since the pigment is exposed through the surfaces of toner particles also in this technique, there will be a problem of charge instability.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide toners containing release agent and method of producing the toners in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a toner that contains enough release agent for realizing oilless fixing of images, does not cause contamination in an electrophotographic apparatus, excels in production workability, and maintains environmental stability and charge stability. Another specific object of the present invention is to provide a method of producing the above toner.
The above objects of the present invention are achieved by a release agent-containing toner that comprises: a center portion that contains release agent and pigment; and a surface layer portion that is formed by a resin phase that covers the center portion.
With this release agent-containing toner, the problem of contamination in an electrophotographic apparatus can be prevented, because the release agent is not exposed through the surface of the toner particles. Thus, excellent printing quality can be expected. Also, since the pigment and the release agent are contained by the resin phase of the surface layer, excellent charge stability can be obtained. Furthermore, the release agent-containing toner excels in environmental stability, because no emulsifier having absorption properties was contained in the toner.
The above objects of the present invention are also achieved by a release agent-containing toner that comprises: a center portion that contains release agent; and a surface layer portion that is formed by a resin phase containing dye that covers the center portion.
The above objects of the present invention are also achieved by a method of producing a release agent-containing toner, comprising the steps of:
dispersing release agent in a water-based medium, the release agent being insoluble in a polymerization monomer compound;
mixing the dispersed release agent with the polymerization monomer compound;
covering the polymerization monomer compound with dispersion particles of the release agent as a seed; and
forming a surface layer of a resin phase by polymerizing the polymerization monomer compound.
Generally, compounds having polarities exhibit affinities to one another. For instance, a styrene- or acrylic-based polymerization monomer that is generally used is a material having relatively high polarity. In a water-based medium in which the emulsion of a polymerization monomer and low-polarity resin coexist, a small amount of polymerization monomer dissolved the water-based re-precipitates through the surface, with the dispersed particles of th
Takezawa Satoshi
Tanaka Tomoaki
Armstrong Westerman & Hattori, LLP
Goodrow John
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