Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-01-29
2001-03-20
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S137170
Reexamination Certificate
active
06203957
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel toner for use in the development of an electrostatic latent image in an electrophotographic printer or copying machine. More particularly, the present invention relates to a novel toner which provides an excellent image quality and can be consumed in a drastically reduced amount per page of printing paper.
BACKGROUND OF THE INVENTION
In recent years, it has been important to further reduce the particle diameter of powder toners for electrostatic image development in order to improve image properties such as resolution. Thus, various technical developments have been made. Most of powder toners for development of electrostatic image commercially available at present have a volume-average particle diameter of from about 8 to 13 &mgr;m. Powder toners having the smallest particle diameter have a particle diameter of about 7 &mgr;m (as measured by means of Coulter Multisizer).
Images outputted from the current electrophotographic copying machines or printers have far poorer quality than lithographic print or silver salt system photograph. For the part of toner, it is effective to develop a toner having an even smaller particle diameter and an excellent triboelectricity in order to improve these image properties. Such a toner has thus been keenly desired.
The processes for the preparation of toners can be roughly divided into two groups, i.e., dry process and wet process. Examples of the dry process for the preparation of toners include pulverization process. Examples of the wet process for the preparation of toners include polymerization process, and so-called phase inversion emulsification process as disclosed in JP-A-5-66600 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) It is said that the minimum allowable particle diameter of toners obtained on an industrial basis by pulverization process using the current crushing machine is about 7 &mgr;m. Of course, toners having a particle diameter as small as about 5 &mgr;m can be produced. However, the production of such a small particle diameter toner is not practical because it adds to production cost and is liable to deterioration of triboelectricity or powder fluidity accompanying the reduction of the particle diameter of toner particles.
It is said that a wet process such as polymerization process and emulsion process essentially finds no difficulty in the reduction of the particle diameter of toner particles. However, the development or production of the prior art wet process toners is mainly intended to replace crushed toners having a particle diameter of from about 7 to 13 &mgr;m. Small particle diameter toners having a volume-average particle diameter of not more than about 6 &mgr;m have been so far known only in fragments. No practical formulations have been known.
U.S. Pat. No. 5,691,095 discloses inventions of spherically particulate toner and process for the preparation thereof. However, no studies were made of the range of concentration of colorant. The values of concentration of colorant described in the examples in the above cited US patent are all lower than that of the present invention. Thus, the toner according to the above cited US patent doesn't exert the effect of the, present invention.
An object of the present invention is to provide a novel toner for use in the development of an electrostatic latent image in an electrophotographic printer or copying machine which provides an excellent image quality and can be consumed in a drastically reduced amount per page of printing paper.
SUMMARY OF THE INVENTION
The inventors made extensive studies of powder toner excellent in density, resolution and tone reproduction in printed image. As a result, it was found that a spherically particulate toner having a small particle diameter and a high pigment concentration provides an excellent image quality and can be consumed in a drastically reduced amount per gage of printing paper. It was also found that such a spherically particulate toner produced by emulsification method or polymerization method is suitable for the present invention. It was further found that such a spherically particulate toner can be preferably used as a toner for non-magnetic one-component development process and two-component development process. The present invention has thus been worked out.
The present invention provides the following inventions:
1. A spherically particulate toner comprising a colorant and a binder resin, wherein said toner has a volume-average particle diameter of from 1 to 6 &mgr;m, the content of the colorant is not less than 9.1% by weight based on the total weight of the binder resin and the colorant, and said toner has an average circularity (average of circularity defined by (perimeter of circle having the same area as the projected area of particle)/(perimeter of the projected image of particle)) of not less than 0.98.
2. The spherically particulate toner according to Clause 1, having a particle size distribution such that the ratio of 50%-volume particle diameter/50%-number particle diameter is not more than 1.25 and the square root of the ratio of 84%-volume particle diameter/16%-volume particle diameter is not more than 1.25 and comprising the colorant encapsulated in the binder resin.
3. The spherically particulate toner according to Clause 1, comprising inorganic oxide fine particles externally added to the surface thereof in an amount represented by the following general formula:
3.5714X
−0.9942
≦Y≦31.399X
−0.9477
wherein X represents a volume-average particle diameter (&mgr;m) of toner particles; and Y represents an added amount (wt-%) of the inorganic oxide fine particles based on the weight of toner particles.
4. The spherically particulate toner according to any one of Clauses 1 to 3, wherein said particulate toner is obtained by mixing an organic solvent solution comprising a colorant and a water-insoluble binder resin as essential components and an aqueous medium, emulsifying the mixture to form spherical colored particles, and then withdrawing the said particles dispersed in the liquid medium in the form of dried powder.
5. The spherically particulate toner according to any one of Clauses 1 to 3, wherein said particulate toner is obtained by a process which comprises allowing a polymerizable monomer having a colorant dispersed therein to undergo polymerization in a liquid medium to form spherical colored particles, and then withdrawing the said particles dispersed in the liquid medium in the form of dried powder.
6. A spherically particulate color toner comprising a colorant and a binder resin, wherein said toner has a volume-average particle diameter of from 1 to 6 &mgr;m and an average circularity (average of circularity defined by (perimeter of circle having the same area as the projected area of particle)/(perimeter of the projected image of particle)) of not less than 0.98 and said colorant is an organic chromatic pigment and the content thereof is not less than 5% by weight based on the total weight of the binder resin and the colorant.
7. The spherically particulate color toner according to Clause 6, having a particle size distribution such that the ratio of 50%-volume particle diameter/50%-number particle diameter is not more than 1.25 and the square root of the ratio of 84%-volume particle diameter/16%-volume particle diameter is not more than 1.25 and comprising the colorant encapsulated in the binder resin.
8. The spherically particulate color toner according to Clause 7, comprising inorganic oxide fine particles externally added to the surface thereof in an amount represented by the following general formula:
3.5714X
−0.9942
≦Y≦31.399X
−0.9477
wherein X represents a volume-average particle diameter (&mgr;m) of toner particles; and Y represents an added amount (wt-%) of inorganic oxide fine particles based on the weight of toner particles.
9. The spherically particulate color toner according to any one of Clauses 6 to 8, wherein said colorant is an organic
Hirabayashi Kenichi
Ito Takashi
Itoya Kazuo
Nomura Minoru
Takayanagi Hitoshi
Armstrong, Westerman Hattori, McLeland & Naughton, L.L.P.
Chapman Mark
Dianippon Ink and Chemicals, Inc.
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